Publications Report

  • Room temperature capacitance-voltage profile and photoluminescence for delta doped InGaAs single quantum well

    Type Conference Paper
    Author K.-Y. Ban
    Author S. N. Dahal
    Author S. P. Bremner
    Author C. B. Honsberg
    Place Princeton, NJ, USA
    Date 2009
    Conference Name NAMBE Conference
  • High open circuit voltages on 50 micron silicon substrates by amorphous-silicon (a-Si) and quinhydrone-methanol (QHY-ME) passivation

    Type Conference Paper
    Author B. Chhabra
    Author C.B. Honsberg
    Author R.L. Opila
    URL http://dx.doi.org/10.1109/PVSC.2009.5411398
    Series Proceedings of the 2009 34th IEEE Photovoltaic Specialists Conference (PVSC 2009)
    Place Piscataway, NJ, USA
    Publisher IEEE
    Pages 4 pp.
    Date 2009
    DOI 10.1109/PVSC.2009.5411398
    Accessed Tuesday, January 31, 2012 4:25:36 PM
    Library Catalog Engineering Village
    Abstract Thin silicon solar cells offer the well-known advantages of cost reduction and higher efficiencies. A thinner solar cell may have a higher open circuit voltage than a thicker one assuming the surfaces are well passivated and the light trapping is included thus resulting in improved efficiencies. High open circuit voltage, Voc, of 720 mV or above has been achieved from several technologies on conventional thickness wafers and has approached 740 mV on thinner wafers. However, the theoretical limit from detailed balance calculations is between 830 mV and 850 mV (depending on spectrum). In order to achieve silicon solar cells which approach the detailed balance voltage limits, controlling the broad mechanisms that limit the open circuit voltage becomes very important and these are: (1) Auger recombination (e.g., by controlling dopant concentration); (2) the thickness of the material; and (3) the surface passivation. While high open circuit voltages have been demonstrated on thicker silicon solar cells, achieving the necessary surface passivation for "thin" solar cells (i.e., less than 50 micron thick wafers) to show increase in Voc has remained a challenge. The present research demonstrates via Implied-Voc measurements that amorphous-Si passivation as well as organic passivation based on quinhydrone-methanol has sufficient surface passivation such that open circuit voltage increases even at thickness of 35 microns. These results are also significant in demonstrating that non-ideal effects, such as high injection, play a significant role in determining Voc, but nevertheless experimentally still allow high open circuit voltages as the device is thinned.
    Proceedings Title 2009 34th IEEE Photovoltaic Specialists Conference (PVSC 2009), 7-12 June 2009
  • Correlation between crystalline perfection of InGaN epi-layers and wide-band gap InGaN solar cell performance

    Type Conference Paper
    Author B. Jampana
    Author A. Melton
    Author N. Faleev
    Author O. Jani
    Author M. Jamil
    Author I. Ferguson
    Author R. Opila
    Author C. B. Honsberg
    Place Philadelphia, PA, USA
    Publisher IEEE
    Date 2009
    Conference Name Proceedings of the 34th IEEE Photovoltaic Specialists Conference
    Abstract We report the influence of crystalline quality of InGaN epitaxial layers grown by MOCVD on wide-band gap InGaN solar cell performance. The collection of photo-generated carriers is the primary challenge in InGaN solar cell design. This carrier collection is affected by the defects in the material, in particular the extended crystalline defects in III-nitrides epi-layers. The lattice-mismatch between InGaN and GaN results in creation of extended crystalline defects at the InGaN-GaN interface. The creation of these defects depends on the InGaN composition and thickness. An optimum thickness based on optical absorption properties and creation of extended crystalline defects needs to be established to successfully realize InGaN solar cells. This paper presents the spatial distribution of extended crystalline defects in InGaN and GaN epi-layers grown by MOCVD. The influence of these crystalline defects on homo-junction solar cells performance is presented. A critical thickness less than 100 nm for 15% InGaN epi-layers is observed, beyond which there is noticeable performance degradation in homo-junction solar cells. Extended design rules for InGaN solar cells based on optical absorption properties and crystalline quality are presented to be incorporated in future designs.
    Proceedings Title Proceedings of the 34th IEEE Photovoltaic Specialists Conference
  • Crystalline Perfection of Epitaxial Structure: Correlation With Composition, Thickness, and Elastic Strain of Epitaxial Layers

    Type Conference Paper
    Author B.R. Jampana
    Author N.N. Faleev
    Author I.T. Ferguson
    Author R.L. Opila
    Author C.B. Honsberg
    Series Materials Research Society Symposium Proceedings. Compound Semiconductors for Energy Applications and Environmental Sustainability
    Place Warrendale, PA, USA
    Publisher Materials Research Society
    Pages 71-6
    Date 2009
    Library Catalog Engineering Village
    Abstract Crystalline perfection of InGaN epi-layers is the missing design parameter for InGaN solar cells. Structural deterioration of InGaN epi-layers depends on the thickness, composition and growth conditions as well. Increasing the InGaN epi-layer thickness beyond a critical point introduces extended crystalline defects that hinder the optical absorption and electrical properties. Increasing the InGaN composition further reduces this critical layer thickness. The optical absorption band edge is sharp for Ill-nitride direct band gap materials. The band edge profile is deteriorated by creation of extended crystalline defects in the InGaN epitaxial material. The design of InGaN solar cells requires the growth of epi-layers where a trade off between crystalline perfection and optical absorption properties is reached.
    Proceedings Title Materials Research Society Symposium. Compound Semiconductors for Energy Applications and Environmental Sustainability, 14-16 April 2009
    Short Title Crystalline Perfection of Epitaxial Structure
  • Utilizing Polarization Induced Band Bending for InGaN Solar Cell Design

    Type Conference Paper
    Author B.R. Jampana
    Author I.T. Ferguson
    Author R.L. Opila
    Author C.B. Honsberg
    Series Materials Research Society Symposium Proceedings. Compound Semiconductors for Energy Applications and Environmental Sustainability
    Place Warrendale, PA, USA
    Publisher Materials Research Society
    Pages 3-8
    Date 2009
    Library Catalog Engineering Village
    Abstract Strong polarization effects observed in Ill-nitride materials can invert the surface carrier type. The corresponding band bending can be used to design InGaN solar cells. Similar surface inversion was observed in the past with silicon-based Schottky-barrier solar cells, but was limited by Fermi level pinning. The formation of two-dimensional electron gas by polarization fields in Ill-nitrides has been reported. Using a similar idea, the growth of a thin AlN capping layer on p-InGaN has resulted in band bending, hence depletion region, under the surface that can be used to separate any generated photo-carriers. Hall measurements at different depths on these structures confirm the inversion of surface carrier type. Solar cells based on this concept have resulted in an open circuit voltage of 2.15 V and short circuit current of 21.8 A.
    Proceedings Title Materials Research Society Symposium. Compound Semiconductors for Energy Applications and Environmental Sustainability, 14-16 April 2009
  • High indium composition (20%) InGaN epi-layers on ZnO substrates for very high efficiency solar cells

    Type Conference Paper
    Author A. Melton
    Author B. Jampana
    Author N. Li
    Author M. Jamil
    Author T. Zaidi
    Author W. Fenwick
    Author R. Opila
    Author C. Honsberg
    Author I. Ferguson
    URL http://dx.doi.org/10.1109/PVSC.2009.5411216
    Series Proceedings of the 2009 34th IEEE Photovoltaic Specialists Conference (PVSC 2009)
    Place Piscataway, NJ, USA
    Publisher IEEE
    Pages 4 pp.
    Date 2009
    DOI 10.1109/PVSC.2009.5411216
    Accessed Tuesday, January 31, 2012 4:26:54 PM
    Library Catalog Engineering Village
    Abstract In this report we present recent results for MOCVD growth of high indium content InGaN films on ZnO substrates. Growth was attempted on both bulk ZnO as well as ZnO epilayers grown on sapphire by MOCVD. ZnO is an attractive alternative substrate for III-Nitrides because of its superior lattice match: specifically ZnO is perfectly matched with In0.18Ga0.82N and low cost of substrates. Stable InGaN films with 18% indium were achieved on the bulk substrates and were characterized by HRXRD, PL, and optical transmission. Varying the growth parameters - primarily growth temperature and In/(In + Ga) flow ratio - was found to affect the optical and structural properties of the films. By growing on a better matched substrate the high indium composition InGaN epitaxial films experience less strain and can therefore be grown thicker without creating relaxation-induced extended crystal defects. This is important, as high indium content InGaN films cannot be grown on GaN thick enough for full above-bandgap absorption without introducing detrimental extended crystal defects. This limitation is thought to be a limiting factor in the achievable ISC in InGaN solar cells.
    Proceedings Title 2009 34th IEEE Photovoltaic Specialists Conference (PVSC 2009), 7-12 June 2009
  • High performance thin crystalline silicon solar cell grown on silicon-on-insulator

    Type Conference Paper
    Author C.P. Murcia
    Author Ruiying Hao
    Author T. Biegala
    Author C. Honsberg
    Author A. Barnett
    URL http://dx.doi.org/10.1109/PVSC.2009.5411219
    Series Proceedings of the 2009 34th IEEE Photovoltaic Specialists Conference (PVSC 2009)
    Place Piscataway, NJ, USA
    Publisher IEEE
    Pages 4 pp.
    Date 2009
    DOI 10.1109/PVSC.2009.5411219
    Accessed Tuesday, January 31, 2012 4:23:07 PM
    Library Catalog Engineering Village
    Abstract High open circuit voltage (VOC) is a potential benefit of thin silicon solar cells. A new thin silicon solar cell structure is proposed using silicon-on-insulator (SOI) technology that investigates the properties of high voltage in thin silicon designs with an epitaxial emitter. Key design parameters are low rear and front surface recombination, low dark current and efficient light trapping. We propose a patterned emitter area on a SOI substrate. The advantages of this design are the passivation properties embedded in the buried oxide and the reduced junction area. With a uniform epitaxial emitter, the top contact shadowing can be designed to be 0%. Preliminary results show Voc 525 mV and JSc 20 mA/cm2 with_anti-reflection coating. This represents a substantial increase from previous work by Danos et al. which reported Voc 500 mV and Jsc ~ 0.45 mA/cm2. This present design also demonstrates the effect of a smaller emitter area and reports higher performance parameters for reported silicon cells fabricated on SOI substrates.
    Proceedings Title 2009 34th IEEE Photovoltaic Specialists Conference (PVSC 2009), 7-12 June 2009
  • Very High Efficiency Solar Cell Modules

    Type Journal Article
    Author Allen Barnett
    Author Douglas Kirkpatrick
    Author Christiana Honsberg
    Author Duncan Moore
    Author Mark Wanlass
    Author Keith Emery
    Author Richard Schwartz
    Author Dave Carlson
    Author Stuart Bowden
    Author Dan Aiken
    Author Allen Gray
    Author Sarah Kurtz
    Author Larry Kazmerski
    Author Myles Steiner
    Author Jeffery Gray
    Author Tom Davenport
    Author Roger Buelow
    Author Laszlo Takacs
    Author Narkis Shatz
    Author John Bortz
    Author Omkar Jani
    Author Keith Goossen
    Author Fouad Kiamilev
    Author Alan Doolittle
    Author Ian Ferguson
    Author Blair Unger
    Author Greg Schmidt
    Author Eric Christensen
    Author David Salzman
    Volume 17
    Issue 1
    Pages 75-83
    Publication Progress in Photovoltaics
    ISSN 1062-7995
    Date 2009-1
    Extra WOS:000262575900007
    Journal Abbr Prog. Photovoltaics
    DOI 10.1002/pip.852
    Library Catalog ISI Web of Knowledge
    Language English
    Abstract The Very High Efficiency Solar Cell (VHESC) program is developing integrated optical system-PV modules for portable applications that operate at greater than 50% efficiency. We are integrating the optical design with the solar cell design, and have entered previously unoccupied design space. Our approach is driven by proven quantitative models for the solar cell design, the optical design, and the integration of these designs. Optical systems efficiency with an optical efficiency of 93% and solar cell device results under ideal dichroic splitting optics summing to 42.7 +/- 2.5% are described. Copyright (c) 2008 John Wiley & Sons, Ltd.
  • Optical properties of delta doped InAs/GaAs0.88Sb0.12 structure for novel concept solar cells

    Type Conference Paper
    Author K. -Y Ban
    Author S. N Dahal
    Author C. B Honsberg
    Publisher IEEE
    Pages 001264-001267
    ISBN 978-1-4244-2949-3
    Date 2009-06
    DOI 10.1109/PVSC.2009.5411245
    Library Catalog IEEE Xplore
    Conference Name 2009 34th IEEE Photovoltaic Specialists Conference (PVSC)
    Language English
    Abstract We have investigated optical properties of InAs quantum dots (QDs) on GaAsSb barrier layer with different doping levels. In order to precisely control occupancy of subband levels in conduction band offset (CBO) in the material system, delta doping layer in the barrier was incorporated as an efficient carrier supply. Interband transitions between ground states or excited states were detected by implementing time-integrated photoluminescence (PL) whereas intersubband transitions have shown via Fourier transform-infrared spectroscopy (FT-IR) at room temperature. The results are compared and discussed with theoretical calculation based on k.p. method.
    Proceedings Title 2009 34th IEEE Photovoltaic Specialists Conference (PVSC)
  • Passivation of InAs quantum dots for novel photovoltaics

    Type Conference Paper
    Author S. Bremner
    Author N. Faleev
    Author L. Nataraj
    Author S. Cloutier
    Author S. Dahal
    Author C. Honsberg
    Publisher IEEE
    Pages 001306-001311
    ISBN 978-1-4244-2949-3
    Date 2009-06
    DOI 10.1109/PVSC.2009.5411253
    Library Catalog IEEE Xplore
    Conference Name 2009 34th IEEE Photovoltaic Specialists Conference (PVSC)
    Language English
    Abstract Novel photovoltaic device designs offer the possibility of limiting efficiencies well in excess of conventional limits [1,2]. Many of the suggested devices rely on the inclusion of nanostructures in order to improve conventional energy conversion mechanisms or allow new mechanisms to be exploited. Because nanostructures rely on quantum confinement realized by heterojunctions, strain induced defects at hetero-interfaces, and the non-ideal recombination pathways they bring, need to be passivated, in order for the novel devices to operate as intended. We report attempts to passivate quantum dots in the much studied InAs/GaAs system using a Sb flux treatment immediately prior to capping of the quantum dots with GaAs. The photoluminescence results suggest an optimum exposure time to the Sb flux after which the performance degrades substantially. Temperature dependent photoluminescence results as well as X-ray diffraction results are also presented in order to explain the structure at the quantum dot - cap interface. The impact of these results in terms of the design of two novel photovoltaic devices, the intermediate band solar cell and the hot carrier solar cell is also discussed.
    Proceedings Title 2009 34th IEEE Photovoltaic Specialists Conference (PVSC)
  • InGaN solar cell design by surface inversion caused by piezoelectric polarization

    Type Conference Paper
    Author Balakrishnam Jampana
    Author Andrew Melton
    Author Muhammad Jamil
    Author Ian Ferguson
    Author Robert Opila
    Author Christiana Honsberg
    Publisher IEEE
    Pages 002175-002178
    ISBN 978-1-4244-2949-3
    Date 2009-06
    DOI 10.1109/PVSC.2009.5411401
    Library Catalog IEEE Xplore
    Conference Name 2009 34th IEEE Photovoltaic Specialists Conference (PVSC)
    Language English
    Abstract The III-nitride material system offers substantial potential to develop high-efficiency solar cells. The solar cell operation requires the formation of a depletion region. Conventionally, this is achieved by a p-n junction. The piezoelectric polarization introduces a strong band bending at the hetero-junction interface and hence creating a depletion region. The growth of a thin AlN or GaN epi-layer on InGaN introduces the required piezoelectric polarization to create a depletion region. This paper presents the polarization-incorporated simulations in モSilenseヤ showing the depletion region formation by GaN or AlN epilayers on p-InGaN. Three structures are then MOCVD grown and characterized for crystal quality and electrical properties. The fabricated devices demonstrated the diode characteristics with an open-circuit voltages ? 2.0 V.
    Proceedings Title 2009 34th IEEE Photovoltaic Specialists Conference (PVSC)
  • Light trapping designs for thin silicon solar cells based on photonic crystal and metallic diffractive grating structures

    Type Conference Paper
    Author J. G Mutitu
    Author Shouyuan Shi
    Author A. Barnett
    Author C. Honsberg
    Author D. W Prather
    Publisher IEEE
    Pages 000579-000583
    ISBN 978-1-4244-2949-3
    Date 2009-06
    DOI 10.1109/PVSC.2009.5411616
    Library Catalog IEEE Xplore
    Conference Name 2009 34th IEEE Photovoltaic Specialists Conference (PVSC)
    Language English
    Abstract We present novel light trapping designs applied to thin (5 micron) silicon solar cells. The design structures incorporate diffractive gratings to increase the optical path length of light within the solar cells. We incorporate a combination of dielectric and metallic materials to create the gratings. We form a one dimensional photonic crystal stack with the dielectric materials to which we then add the metallic layers. The combination of the two materials enhances the reflective properties of the gratings and thus increasing their effectiveness in light trapping. We use the particle swarm optimization and scattering matrix methods to realize the design structures.
    Proceedings Title 2009 34th IEEE Photovoltaic Specialists Conference (PVSC)
  • Thin silicon solar cells using epitaxial lateral overgrowth structure

    Type Conference Paper
    Author Ruiying Hao
    Author C. P Murcia
    Author T. Creazzo
    Author T. Biegala
    Author A. Lochtefeld
    Author Ji-Soo Park
    Author C. Honsberg
    Author A. Barnett
    Publisher IEEE
    Pages 000949-000953
    ISBN 978-1-4244-2949-3
    Date 2009-06
    DOI 10.1109/PVSC.2009.5411132
    Library Catalog IEEE Xplore
    Conference Name 2009 34th IEEE Photovoltaic Specialists Conference (PVSC)
    Language English
    Abstract Thin Si solar cell with epitaxial lateral overgrowth (ELO) structure described in this paper should demonstrate higher voltage. PC-1D program has been used to study the open circuit voltage and efficiency as a function of the thin Si thickness and light trapping. According to the simulation results, high voltage can be obtained even without light trapping on the backside of the thin Si layer. Thin n type silicon layer has been grown on p+ Si substrate using the method of epitaxial lateral overgrowth by CVD. The scanning electron microscopy (SEM) has been used to show the dimension of the pn junction region and light generation region after the n type Si growth.
    Proceedings Title 2009 34th IEEE Photovoltaic Specialists Conference (PVSC)
  • Improved outdoor measurements for Very High Efficiency Solar Cell sub-modules

    Type Conference Paper
    Author Xiaoting Wang
    Author N. Waite
    Author P. Murcia
    Author K. Emery
    Author M. Steiner
    Author F. Kiamilev
    Author K. Goossen
    Author C. Honsberg
    Author A. Barnett
    Publisher IEEE
    Pages 000409-000414
    ISBN 978-1-4244-2949-3
    Date 2009-06
    DOI 10.1109/PVSC.2009.5411652
    Library Catalog IEEE Xplore
    Conference Name 2009 34th IEEE Photovoltaic Specialists Conference (PVSC)
    Language English
    Abstract Very High Efficiency Solar Cell (VHESC) program is developing integrated optical/photovoltaic modules for portable applications that operate at 50 percent efficiency. Test sub-modules incorporating four p-n junctions and corresponding optics have been realized and are predicted to realize efficiency greater than 40%. Phased implementation requires corresponding measurement to inspect accomplished work and provide improvement direction for the next step. The comparison between the real performance of the four-junction test sub-module and the theoretical prediction of its efficiency is a significant indication of the realizability of the final VHESC module including six junctions which is designed to achieve 50% efficiency. For the sub-module measurement, a test bed was set up for outdoor test. Previous outdoor measurements of the VHESC test sub-modules resulted in a preliminary sub-module efficiency of 36.2%. As solar cells with better performance were fabricated, the measurement methodology was refined and corresponding improvements were made to the initial test bed. Three test sub-modules containing new solar cells were measured with the new test setup for three different concentration levels at University of Delaware (UD). One test sub-module demonstrated efficiency as high as 39.5%, coupled with 44.3% efficient solar cells and 89.1% efficient optics, at 30.48 X concentration. The measurements were taken when the direct light intensity was over 860 W/m2 and the Isc was not calibrated to 1000 W/m2. Another two test sub-modules including solar cells in the same batch as the ones tested at UD were taken to National Renewable Energy Laboratory (NREL). The Isc data of the two test sub-modules were recorded outdoors at NREL when the direct light intensity was over 970 W/m2. In addition, the Isc was calibrated to the standard spectrum condition using ASTM G173 direct data. Comparison of the results shows t- he difference between the test sub-module efficiency measured at UD and NREL is less than 4%.
    Proceedings Title 2009 34th IEEE Photovoltaic Specialists Conference (PVSC)
  • Optimization of interdigitated back contact silicon heterojunction solar cells by two-dimensional numerical simulation

    Type Conference Paper
    Author Meijun Lu
    Author U. Das
    Author S. Bowden
    Author S. Hegedus
    Author R. Birkmire
    Publisher IEEE
    Pages 001475-001480
    ISBN 978-1-4244-2949-3
    Date 7-12 June 2009
    DOI 10.1109/PVSC.2009.5411332
    Library Catalog IEEE Xplore
    Conference Name 2009 34th IEEE Photovoltaic Specialists Conference (PVSC)
    Language English
    Abstract In this paper, two-dimensional (2D) simulation of interdigitated back contact silicon heterojunction (IBC-SHJ) solar cells is presented using Sentaurus Device, a software package of Synopsys TCAD. A model is established incorporating a distribution of trap states of amorphous-silicon material and thermionic emission across the amorphous-silicon / crystalline-silicon hetero-interface. The 2D nature of IBC-SHJ device is evaluated and current density-voltage (J-V) curves are generated. Optimization of IBC-SHJ solar cells is then discussed through simulation. It is shown that the open circuit voltage (VOC) and short circuit current density (JSC) of IBC-SHJ solar cells increase with decreasing front surface recombination velocity. The JSC improves further with the increase of relative coverage of p-type emitter contacts, which is explained by the simulated and measured position dependent laser beam induced current (LBIC) line scan. The S-shaped J-V curves with low fill factor (FF) observed in experiments are also simulated, and three methods to improve FF by modifying the intrinsic a-Si buffer layer are suggested: (i) decreased thickness, (ii) increased conductivity, and (iii) reduced band gap. With all these optimizations, an efficiency of 26% for IBC-SHJ solar cells is potentially achievable.
    Proceedings Title 2009 34th IEEE Photovoltaic Specialists Conference (PVSC)
  • Correlation of crystalline defects with photoluminescence of InGaN layers

    Type Journal Article
    Author Nikolai Faleev
    Author Balakrishnam Jampana
    Author Omkar Jani
    Author Hongbo Yu
    Author Robert Opila
    Author Ian Ferguson
    Author Christiana Honsberg
    URL http://apl.aip.org/resource/1/applab/v95/i5/p051915_s1
    Volume 95
    Issue 5
    Pages 051915-051915-3
    Publication Applied Physics Letters
    ISSN 00036951
    Date 2009-08-06
    DOI doi:10.1063/1.3202409
    Accessed Tuesday, March 6, 2012 12:05:02 PM
    Library Catalog SPIE/AIP
    Abstract We report structural studies of InGaN epilayers of various thicknesses by x-ray diffraction, showing a strong dependence of the type and spatial distribution of extended crystalline defects on layer thickness. The photoluminescence intensity for the samples was observed to increase with thickness up to 200 nm and decrease for higher thicknesses, a result attributed to creation of dislocation loops within the epilayer. Correlation of physical properties with crystalline perfection open the way for optimized designs of InGaN solar cells, with controlled types and dislocation densities in the InGaN epilayers, a key requirement for realizing high photocurrent generation in InGaN.
  • From the Valley of Death to the Golden Decade: Crystalline Silicon Solar Cells from 10 to 100 microns

    Type Conference Paper
    Author Stuart Bowden
    Place Vail, Colorado
    Pages 192-195
    Date August 9, 2009
    Proceedings Title 19th Workshop on Crystalline Silicon Solar Cells and Modules
  • Minimizing shadow losses in III-nitride solar cells

    Type Conference Paper
    Author Andrew Melton
    Author Balakrishnam Jampana
    Author Robert Opila
    Author Christiana Honsberg
    Author Muhammad Jamil
    Author Ian Ferguson
    URL http://spiedigitallibrary.org.ezproxy1.lib.asu.edu/proceedings/resource/2/psisdg/7409/1/740916_1
    Volume 7409
    Pages 740916-740916-7
    Date 2009-08-20
    DOI doi:10.1117/12.829264
    Accessed Thursday, February 16, 2012 3:57:14 PM
    Library Catalog SPIE/AIP
    Abstract In this work InGa0.85N p-n homojunction solar cells were grown by MOCVD on GaN/sapphire substrates and fabricated using standard techniques. When illuminated from the backside, these devices showed 65.9% improvement in JSC and 4.4% improvement in VOC as compared to identical illumination from the front. These improvements arise from removal of the losses from electrical contact shading on the front of the devices (11.7% of active area), as well as significant optical absorption by the top current spreading layer. These improvements can likely be further enhanced by utilizing double-side polished wafers, which would eliminate scattering losses on the back surface. In addition to improving electrical characteristics of single cells, backside illumination is necessary for the realization of monolithic tandem InGaN solar cells.
    Proceedings Title Proceedings of SPIE
  • Absorption coefficients of intermediate-band media

    Type Journal Article
    Author M.Y. Levy
    Author C. Honsberg
    URL http://dx.doi.org/10.1063/1.3213337
    Series J. Appl. Phys. (USA)
    Volume 106
    Issue 7
    Pages 073103 (12 pp.)
    Publication Journal of Applied Physics
    ISSN 0021-8979
    Date 2009-10
    DOI 10.1063/1.3213337
    Accessed Tuesday, January 31, 2012 4:23:15 PM
    Library Catalog Engineering Village
    Abstract This paper models the absorption coefficients of an intermediate-band (IB) absorbing medium. Equilibrium absorption coefficients are presented for several IB absorbers, each distinguished by their energy-wavevector dispersion and equilibrium temperature. Nonequilibrium absorption coefficients are also presented for solar cells implemented with IB absorbers. Several simplifying assumptions are made including that the energy-wavevector dispersions are parabolic. The model requires the absolute locations of three quasi-Fermi levels. This is made possible by using two balance equations. One of these, a charge-neutrality condition, necessitates the numerical computation of the carrier statistics in each band of the IB absorber. The use of the incomplete Fermi-Dirac functions makes this possible. The authors conclude that (i) if the concentration of intermediate states is greater than the concentration of carriers in the conduction band and greater than the concentration of carriers in the valence band, then the IB will be partially filled; (ii) an IB absorber may or may not absorb all photons with energies greater than the smallest bandgap in the system; (iii) an IB absorber may permit absorption overlap so that an absorbed photon would likely generate an electron-hole pair across a bandgap other than the largest bandgap less than the energy of the absorbed photon; (iv) as the temperature of the IB absorber approaches absolute zero, the absorption edges resulting from transitions at intermediate levels may blueshift.
  • Room temperature capacitance-voltage profile and photoluminescence for delta doped InGaAs single quantum well

    Type Journal Article
    Author K.-Y. Ban
    Author S.N. Dahal
    Author C.B. Honsberg
    Author L. Nataraj
    Author S.P. Bremner
    Author S.G. Cloutier
    URL http://dx.doi.org/10.1116/1.3268614
    Volume 28
    Pages C3I6-C3I9
    Publication Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures
    Date 2010
    DOI 10.1116/1.3268614
    Accessed Tuesday, January 31, 2012 4:27:14 PM
    Library Catalog Engineering Village
    Abstract Room temperature capacitance-voltage (C-V) profile and photoluminescence (PL) studies of -doped single InGaAs quantum well samples are reported. The purpose was to obtain the confined carrier occupancy in the conduction band offset and observe any relevant phenomena. The results show that the peak intensity of the C-V profiles was almost linearly proportional to sheet carrier concentration and the full width at half maximum of the C-V profiles became narrower with increasing doping level in the barrier layer. This is interpreted as being due to improved confinement of electrons as a result of band bending induced by the -doping layer. This explanation was further supported by PL data that show the transition corresponding to the dominant peak changed with different -doping levels and that all of the transitions were redshifted. Finally, theoretical calculations of the band structure based on a four band kp method are presented to explain the observed results. 2010 American Vacuum Society.

    Notes:

    • Compilation and indexing terms, Copyright 2011 Elsevier Inc.

  • Photoluminescence study of InAs quantum dots on a ?-doped GaAsSb barrier

    Type Conference Paper
    Author K.-Y. Ban
    Author W.-K. Hong
    Author C. B. Honsberg
    Place San Francisco, CA, USA
    Date 2010
    Conference Name MRS Spring Meeting
  • Controllability of the occupation of quantum dot electronic states and determination of minimum valence band offset in InAs/GaAsSb

    Type Conference Paper
    Author K.-Y. Ban
    Author D. Kuciauskas
    Author S. P. Bremner
    Author S. N. Dahal
    Author N. J. Ekins-Daukes
    Author C. B. Honsberg
    Place Valencia, Spain
    Date 2010
    Conference Name 25th EU PVSEC & WCPEC-5
  • Determination of a Sb composition in InAs/GaAsSb for negligible valence band offset

    Type Conference Paper
    Author K.-Y. Ban
    Author D. Kuciauskas
    Author S.P. Bremner
    Author C.B. Honsberg
    URL http://dx.doi.org/10.1109/PVSC.2010.5617048
    Series 2010 35th IEEE Photovoltaic Specialists Conference (PVSC)
    Place Piscataway, NJ, USA
    Publisher IEEE
    Pages 003306-9
    Date 2010
    DOI 10.1109/PVSC.2010.5617048
    Accessed Tuesday, January 31, 2012 4:24:22 PM
    Library Catalog Engineering Village
    Abstract InAs quantum dots (QDs) embedded in GaAsSb barriers with various Sb compositions was investigated by photoluminescence (PL). The peak position of 8% and 13% Sb sample does not shift while that of 15% Sb sample was blue-shifted with increasing the excitation power. In addition, time-resolved PL (TRPL) data also show that 15% Sb sample has a much longer PL decay time compared to that of 8% and 13% Sb sample, implying that the transformation from type I to II occurs between 13% and 15% Sb composition. It is noted that the improvement of QD uniformity was achieved by an increase of a Sb composition in the GaAsSb barrier due to a Sb surfactant effect.
    Proceedings Title 2010 35th IEEE Photovoltaic Specialists Conference (PVSC), 20-25 June 2010
  • Moore's Law of Photovoltaics

    Type Journal Article
    Author Stuart Bowden
    Author Christiana Honsberg
    Author Dieter Schroder
    Issue 1
    Publication Future Photovoltaics
    Date 2010
  • High effective minority carrier lifetime on silicon substrates using quinhydrone-methanol passivation

    Type Journal Article
    Author Bhumika Chhabra
    Author Stuart Bowden
    Author Robert L. Opila
    Author Christiana B. Honsberg
    URL http://link.aip.org/link/APPLAB/v96/i6/p063502/s1&Agg=doi
    Volume 96
    Issue 6
    Pages 063502
    Publication Applied Physics Letters
    ISSN 00036951
    Date 2010
    Journal Abbr Appl. Phys. Lett.
    DOI 10.1063/1.3309595
    Accessed Tuesday, April 20, 2010 4:57:36 PM
    Library Catalog Engineering Village
  • Design and Realization of Wide-Band-Gap (similar to 2.67 eV) InGaN p-n Junction Solar Cell

    Type Journal Article
    Author Balakrishnam R. Jampana
    Author Andrew G. Melton
    Author Muhammad Jamil
    Author Nikolai N. Faleev
    Author Robert L. Opila
    Author Ian T. Ferguson
    Author Christiana B. Honsberg
    Volume 31
    Issue 1
    Pages 32-34
    Publication Ieee Electron Device Letters
    ISSN 0741-3106
    Date 2010-01
    Extra WOS:000273090800012
    Journal Abbr IEEE Electron Device Lett.
    DOI 10.1109/LED.2009.2034280
    Library Catalog ISI Web of Knowledge
    Language English
    Abstract The design of coherently strained InGaN epilayers for use in InGaN p-n junction solar cells is presented in this letter. The X-ray diffraction of the epitaxially grown device structure indicates two InGaN epilayers with indium compositions of 14.8% and 16.8%, which are confirmed by photoluminescence peaks observed at 2.72 and 2.67 eV, respectively. An open-circuit voltage of 1.73 V and a short-circuit current density of 0.91 mA/cm(2) are observed under concentrated AM 0 illumination from the fabricated solar cell. The photovoltaic response from the InGaN p-n junction is confirmed by using an ultraviolet filter. The solar cell performance is shown to be related to the crystalline defects in the device structure.
  • Room temperature capacitance-voltage profile and photoluminescence for delta doped InGaAs single quantum well

    Type Journal Article
    Author K.-Y. Ban
    Author S.N. Dahal
    Author C.B. Honsberg
    Author L. Nataraj
    Author S.P. Bremner
    Author S.G. Cloutier
    URL http://dx.doi.org/10.1116/1.3268614
    Series J. Vac. Sci. Technol. B, Microelectron. Nanometer Struct. (USA)
    Volume 28
    Issue 3
    Pages 3-6
    Publication Journal of Vacuum Science & Technology B (Microelectronics and Nanometer Structures)
    ISSN 1071-1023
    Date 2010-05
    DOI 10.1116/1.3268614
    Accessed Tuesday, January 31, 2012 4:31:26 PM
    Library Catalog Engineering Village
    Abstract Room temperature capacitance-voltage (C-V) profile and photoluminescence (PL) studies of -doped single InGaAs quantum well samples are reported. The purpose was to obtain the confined carrier occupancy in the conduction band offset and observe any relevant phenomena. The results show that the peak intensity of the C-V profiles was almost linearly proportional to sheet carrier concentration and the full width at half maximum of the C-V profiles became narrower with increasing doping level in the barrier layer. This is interpreted as being due to improved confinement of electrons as a result of band bending induced by the -doping layer. This explanation was further supported by PL data that show the transition corresponding to the dominant peak changed with different -doping levels and that all of the transitions were redshifted. Finally, theoretical calculations of the band structure based on a four band kp method are presented to explain the observed results.
  • Use of a GaAsSb buffer layer for the formation of small, uniform, and dense InAs quantum dots

    Type Journal Article
    Author Keun-Yong Ban
    Author S.P. Bremner
    Author Guangming Liu
    Author S.N. Dahal
    Author P.C. Dippo
    Author A.G. Norman
    Author C.B. Honsberg
    URL http://dx.doi.org/10.1063/1.3409691
    Series Appl. Phys. Lett. (USA)
    Volume 96
    Issue 18
    Pages 183101 (3 pp.)
    Publication Applied Physics Letters
    ISSN 0003-6951
    Date 2010-05
    DOI 10.1063/1.3409691
    Accessed Tuesday, January 31, 2012 4:31:18 PM
    Library Catalog Engineering Village
    Abstract InAs quantum dots grown on GaAsSb buffer layers with varying Sb content have been studied. Atomic force microscopy results show that the dot size is reduced as the Sb content increases with a concomitant increase in number density. Analysis of the size distribution indicates that the spread of dot sizes narrows with increasing Sb content. This is confirmed by photoluminescence measurements showing a significant narrowing of the dot emission peak for a GaAs0.77Sb0.23 buffer compared to a GaAs buffer. The results are attributed to the strained buffer reducing interactions between dots and the Sb acting as a surfactant.
  • Influence of Sb/As soak times on the structural and optical properties of GaAsSb/GaAs interfaces

    Type Journal Article
    Author S.P. Bremner
    Author K. Ghosh
    Author L. Nataraj
    Author S.G. Cloutier
    Author C.B. Honsberg
    URL http://dx.doi.org/10.1016/j.tsf.2010.07.060
    Series Thin Solid Films (Switzerland)
    Volume 519
    Issue 1
    Pages 64-8
    Publication Thin Solid Films
    ISSN 0040-6090
    Date 2010-06
    DOI 10.1016/j.tsf.2010.07.060
    Accessed Tuesday, January 31, 2012 4:24:35 PM
    Library Catalog Engineering Village
    Abstract The effects of Sb/As soak times, prior to growth of GaAsSb on GaAs were investigated by High Resolution X-Ray Diffraction (HRXRD) and photoluminescence (PL). Multiple quantum well samples with soak times of 0s, 30s and 60s were grown at 500C with nominally identical Sb and As fluxes. HRXRD results show that a 30s soak minimizes diffuse scattering seen around superlattice peaks in the reciprocal space maps, an effect attributed to corrugations in the GaAs-GaAsSb interface. An inferred band diagram calculated using a four band k.p model and modified taking into account the HRXRD results was used to explain PL spectra taken for each sample at 80K. It is concluded that an optimum soak time exists for GaASb growth on GaAs, determined by the growth conditions. [All rights reserved Elsevier].

    Notes:

    • Compilation and indexing terms, Copyright 2011 Elsevier Inc.

  • Effect of small continuous loads on system efficiency

    Type Conference Paper
    Author B. Chhabra
    Author R. Kamada
    Author R. L Opila
    Author C. B Honsberg
    Publisher IEEE
    Pages 002327-002331
    ISBN 978-1-4244-5890-5
    Date 2010-06
    DOI 10.1109/PVSC.2010.5614448
    Library Catalog IEEE Xplore
    Conference Name 2010 35th IEEE Photovoltaic Specialists Conference (PVSC)
    Language English
    Abstract The paper focuses on constructing software program to investigate lighting systems followed by system implementation and measurement of inverter efficiency at part-load condition with the small continuous load. The idea here is to observe the behavior of inverter efficiency and to see its effect on system performance and cost. The stand-alone systems are badly affected as compared to grid connected systems in terms of system performance and cost.
    Proceedings Title 2010 35th IEEE Photovoltaic Specialists Conference (PVSC)
  • 12.4% efficient freestanding 30ᄉm ultra-thin silicon solar cell using a-Si/c-Si heterostructure

    Type Conference Paper
    Author B. Chhabra
    Author R. L Opila
    Author C. B Honsberg
    Publisher IEEE
    Pages 001325-001329
    ISBN 978-1-4244-5890-5
    Date 2010-06
    DOI 10.1109/PVSC.2010.5614352
    Library Catalog IEEE Xplore
    Conference Name 2010 35th IEEE Photovoltaic Specialists Conference (PVSC)
    Language English
    Abstract The goal of this work is to demonstrate and analyze heterojunction devices on ultra-thin silicon wafers with imperfect surfaces and lower minority carrier lifetimes. Our previous results show intrinsic amorphous-Si passivation (i-a-Si) gives surface recombination velocity, S ~ 20 cm/sec on freestanding 35 ?m Si wafers (Chhabra et al., 2008), and the work presented in this paper shows S ~ 84 cm/sec on chemically etched wafers. The degradation in the S values is assumed mainly due to the contamination in the PECVD deposition system. The simulated results for this work show that the dominant loss mechanism is the low absorption in the a-Si layer thickness. The device results show that even without light trapping, texturing, optimizations, and with minority carrier lifetimes ~ 18 ?s, the structure can have realistic voltages ~ 613 mV and efficiencies ~ 12.4%.
    Proceedings Title 2010 35th IEEE Photovoltaic Specialists Conference (PVSC)
  • Absorption coefficients of quantum dot intermediate band material with negligible valence band offsets

    Type Conference Paper
    Author S. N Dahal
    Author Keun-Yong Ban
    Author C. Honsberg
    Publisher IEEE
    Pages 001797-001799
    ISBN 978-1-4244-5890-5
    Date 2010-06
    DOI 10.1109/PVSC.2010.5615908
    Library Catalog IEEE Xplore
    Conference Name 2010 35th IEEE Photovoltaic Specialists Conference (PVSC)
    Language English
    Abstract Solar cells with quantum dot nanostructure absorbing medium have a potential to overcome single junction limit and achieve the solar energy conversion efficiency as high as 63%. The confined energy states in quantum dots can mediate the absorption of photons with energy lower than the band gap of the barrier material. Closely spaced array of quantum dots (QDs) can form a mini band due to electronic coupling of the confined states among the neighboring dots. Absorption properties of the quantum dot nanostructures are different from that of a bulk material. For the detailed balance efficiency calculations, the absorption coefficients of the QD nanostructures are required for realistic QD structures. After finding out material combinations with negligible valence band offset for quantum dot intermediate band solar cells(QDIBSCs), present work is focused on the calculation of absorption coefficients of QD arrays. The confined electronic states are calculated with the effective mass theory for single and coupled quantum dots. The electronic coupling of the ground states of an array of quantum dots is calculated for negligible valence band offset material combinations (especially InAs dots in GaAs(0.84)Sb(0.16) matrix grown on [001] GaAs substrate). The intermediate bandwidth vs the vertical interdot separation is presented. For some suitable interedot separation, the absorption coefficients are calculated for valence band to intermediate band, Intermediate band to conduction band transitions.
    Proceedings Title 2010 35th IEEE Photovoltaic Specialists Conference (PVSC)
  • Identification of candidate material systems for quantum dot solar cells including the effect of strain

    Type Journal Article
    Author Som N. Dahal
    Author Stephen P. Bremner
    Author Christiana B. Honsberg
    Volume 18
    Issue 4
    Pages 233-239
    Publication Progress in Photovoltaics
    ISSN 1062-7995
    Date 2010-06
    Extra WOS:000277905100001
    Journal Abbr Prog. Photovoltaics
    DOI 10.1002/pip.937
    Library Catalog ISI Web of Knowledge
    Language English
    Abstract Heterostructures that include self-assembled quantum dots (SAQDs) have been suggested as model systems for the realization of novel high efficiency solar cells such as those based on intermediate bands (IBs). The lattice mismatch in the epitaxial growth of these structures, necessary for the formation of SAQDs, introduces strain throughout the structure, making the selection of materials systems with appropriate physical parameters problematic. The model solid theory is used to calculate the energy band edge alignment at Gamma point of such quantum dot (QD) heterostructures including the effects of strain. With the modified band gaps due to strain, a materials search was performed for high efficiency QD solar cells among III-V binaries and ternaries with negligible valence band offsets. This requirement of the valence band offset along with the limited band gap ranges for optimum efficiency results in only a few feasible materials systems being identified. The optimum barrier/dot material system found was Al(0.57)In(0.43)As/InP(0.87)Sb(0.13) grown on lattice matched metamorphic buffer layer, but due to miscibility gap concerns it is suggested that the Al(0.50)In(0.50)As/InAs(0.41)P(0.59) fully strained system may be preferred. Copyright (C) 2010 John Wiley & Sons, Ltd.
  • Determination of charged state density at the interface between amorphous silicon and crystalline silicon by lateral conductance

    Type Conference Paper
    Author K. Ghosh
    Author C. J Tracy
    Author B. Dauksher
    Author S. Herasimenka
    Author C. Honsberg
    Author S. Bowden
    Publisher IEEE
    Pages 002680-002683
    ISBN 978-1-4244-5890-5
    Date 2010-06
    DOI 10.1109/PVSC.2010.5617086
    Library Catalog IEEE Xplore
    Conference Name 2010 35th IEEE Photovoltaic Specialists Conference (PVSC)
    Language English
    Abstract The charged state density at the a-Si/c-Si interface is an important parameter in a heterojunction a cell. The extraction of the charged state density at the interface from measurements of lateral conductance is demonstrated by simulations. In a-Si/c-Si heterojunction an inversion layer is formed at the interface between a and c-Si (heterointerface). The lateral conductance of the inversion layer is much higher than the doped or intrinsic a-Si layer conductance and the current primarily flows through this path. The increase of the charged state density at the heterointerface weakens the invers hence lowers the lateral conductance of these devices This effect is studied in this work by applying a theoretical model developed in the commercial simulator Sentaurus. The simulation results based on this model have shown that in an optimized device structure the sensitivity of the measurement technique in determining the charged state density can be on the order of 1 ᅲ 1010/cm2.
    Proceedings Title 2010 35th IEEE Photovoltaic Specialists Conference (PVSC)
  • Explanation of the device operation principle of amorphous silicon/ crystalline silicon heterojunction solar cell and role of the inversion of crystalline silicon surface

    Type Conference Paper
    Author K. Ghosh
    Author C. J Tracy
    Author S. Herasimenka
    Author C. Honsberg
    Author S. Bowden
    Publisher IEEE
    Pages 001383-001386
    ISBN 978-1-4244-5890-5
    Date 2010-06
    DOI 10.1109/PVSC.2010.5614387
    Library Catalog IEEE Xplore
    Conference Name 2010 35th IEEE Photovoltaic Specialists Conference (PVSC)
    Language English
    Abstract The device operation principle of amorphous silicon/crystalline silicon heterojunction solar cell is discussed. The band diagram obtained by the computer model developed in the commercial simulator Sentaurus shows that the c-Si surface is inverted at the interface between a-Si and c-Si (heterointerface). A strong inversion gives a strong electric field at the c-Si surface, which in turn facilitates the transport of minority carriers across the heterointerface. A high performance device requires a strongly inverted c-Si surface. Calculations are performed to show that the doping of the doped a-Si layer, the thickness of the intrinsic layer, and the defect state density at the heterointerface all affect the inversion of the crystalline silicon surface. Unlike homojunction devices, the defects in heterojunction devices have a greater role in transport mechanism than in recombination mechanism. The results show that in devices with a large number of defects at the interface, the fill factor degrades with little change in open circuit voltage. This explains why it is relatively easy to obtain VOC's approaching 700 mV with heterojunctions but often with low fill factors.
    Proceedings Title 2010 35th IEEE Photovoltaic Specialists Conference (PVSC)
  • 2D modeling of Silicon Heterojunction Interdigitated Back Contact solar cells

    Type Conference Paper
    Author S. Herasimenka
    Author K. Ghosh
    Author S. Bowden
    Author C. Honsberg
    Publisher IEEE
    Pages 001390-001394
    ISBN 978-1-4244-5890-5
    Date 2010-06
    DOI 10.1109/PVSC.2010.5614394
    Library Catalog IEEE Xplore
    Conference Name 2010 35th IEEE Photovoltaic Specialists Conference (PVSC)
    Language English
    Abstract Silicon Heterojunction Interdigitated Back Contact (SHJ-IBC) solar cells were studied by two dimensional modeling using Sentaurus TCAD tools. It was shown that low fill factor caused by the S-shape behavior of experimental J-V curves of standard interdigitated back contact cells can be recovered by making small openings in the intrinsic buffer layer. The small openings in the buffer layer also substantially reduce the influence of the relative dimensions of the silicon strips as when compared to cells with a continuous buffer layer.
    Proceedings Title 2010 35th IEEE Photovoltaic Specialists Conference (PVSC)
  • Realization of InGaN solar cells on (111) silicon substrate

    Type Conference Paper
    Author B. Jampana
    Author Tianming Xu
    Author A. Melton
    Author M. Jamil
    Author R. Opila
    Author C. Honsberg
    Author I. Ferguson
    Publisher IEEE
    Pages 000457-000460
    ISBN 978-1-4244-5890-5
    Date 2010-06
    DOI 10.1109/PVSC.2010.5616748
    Library Catalog IEEE Xplore
    Conference Name 2010 35th IEEE Photovoltaic Specialists Conference (PVSC)
    Language English
    Abstract The III-nitride material system offers substantial potential to develop high-efficiency solar cells. Currently InGaN based solar cells have been demonstrated on sapphire substrate. This substrate expense adds up significantly to the cost of solar cells realization and further issues like sapphire substrate removal are of concern. Alternatively, InGaN epitaxial layers have been successfully grown on silicon substrate. An InGaN based quantum well solar cell structure is grown simultaneously by MOCVD on both GaN/sapphire and GaN/silicon substrates. The fabricated solar cells have comparable photo-response. The Voc of InGaN solar cell on sapphire is higher while the FF of InGaN solar cell on silicon is higher.
    Proceedings Title 2010 35th IEEE Photovoltaic Specialists Conference (PVSC)
  • Detailed balance calculations of multiple exciton generation and Tandem Hybrid solar cells

    Type Conference Paper
    Author Jongwon Lee
    Author C. Honsberg
    Publisher IEEE
    Pages 002932-002937
    ISBN 978-1-4244-5890-5
    Date 2010-06
    DOI 10.1109/PVSC.2010.5615913
    Library Catalog IEEE Xplore
    Conference Name 2010 35th IEEE Photovoltaic Specialists Conference (PVSC)
    Language English
    Abstract The detailed balance of multiple exciton generation and tandem hybrid photovoltaic devices are calculated for standard AM1.5G spectrum with one sun. We also obtain the efficiencies both unconstrained and constrained connection. The quantum yield is set to 2 to maximize the multiple exciton generation. The maximum efficiencies of two stacks unconstrained and constrained connection are 48.77% and 47.88% in AM1.5G. Its optimum bandgaps for unconstrained connection are Eg1: 0.7 eV and Eg2: 1.82eV as well as optimum bandgaps for constrained connection are Eg1: 0.57eV and Eg2: 1.38eV. For three stacks of unconstrained and constrained connection, the maximum efficiency is 52.78% and 51.78% respectively. The optimum bandgaps of unconstrained connection are Eg1: 0.69eV, Eg2: 1.64 eV and Eg3 2.25eV. The optimum bandgaps of constrained connection are Eg1: 0.7eV, Eg2: 1.2 eV and Eg3 1.8 eV.
    Proceedings Title 2010 35th IEEE Photovoltaic Specialists Conference (PVSC)
  • Variability of heterostructure type with thickness of barriers and temperature in the InAs/GaAsSb quantum dot system RID G-1695-2011

    Type Journal Article
    Author A. Pancholi
    Author S. P. Bremner
    Author J. Boyle
    Author V. G. Stoleru
    Author C. B. Honsberg
    Volume 94
    Issue 6
    Pages 1025-1030
    Publication Solar Energy Materials and Solar Cells
    ISSN 0927-0248
    Date 2010-06
    Extra WOS:000278206300015
    Journal Abbr Sol. Energy Mater. Sol. Cells
    DOI 10.1016/j.solmat.2010.02.002
    Library Catalog ISI Web of Knowledge
    Language English
    Abstract We report photoluminescence studies of InAs quantum dots embedded in GaAsSb barrier layers of various thicknesses. Time resolved photoluminescence results suggest that the thicknesses of the GaAsSb barrier layers determines whether the quantum dot system acts as a type I (thicker) or type II (thinner) heterostructure due to strain induced changes in the band energies. Temperature dependent photoluminescence reveal that the transition type is also dependent on the temperature with one sample seeming to transform from type II to type I heterostructure as the temperature is increased. These results support previous assertions that it is possible to obtain a zero valence band offset in the InAs/GaAsSb quantum dot system, making it a system of interest for realization of a novel photovoltaic structure, the intermediate band solar cell. The results highlight some of the inherent issues in designing structures with specific band offsets. Some of the implications of these results on the design methodology for quantum dot based solar cells are briefly discussed. (C) 2010 Elsevier B.V. All rights reserved.
  • Strain and crystal defects in thin AlN/GaN structures on (0001) SiC

    Type Journal Article
    Author N. Faleev
    Author I. Levin
    Volume 107
    Issue 11
    Pages 113529-113529-7
    Publication Journal of Applied Physics
    ISSN 0021-8979
    Date Jun 2010
    DOI 10.1063/1.3437632
    Library Catalog IEEE Xplore
    Language English
    Abstract High-resolution x-ray diffraction was used to compare strain relaxation and defect populations in thin GaN/AlN heterostructures (total thickness ?480 nm) grown on (0001) SiC using metalorganic chemical vapor deposition (MOCVD) and hydride vapor epitaxy (HVPE) techniques. The results of high-resolution x-ray diffraction measurements (rocking curves and reciprocal space mapping) were corroborated using transmission electron microscopy. Differently grown films exhibited dissimilar strain relaxation and defect populations that were related to specific growth conditions. In the MOCVD films, grown under lower deposition rates, the elastic strain in the AlN and GaN layers was fully relaxed at the initial stages of the epitaxial growth yielding nearly similar densities of threading dislocation segments (TDS) in layer volumes. Additional, モsecondaryヤ elastic stresses in these layers were attributed to the excess of point defects. In the HVPE films, grown under higher (five to ten times) deposition rates, these layers were over relaxed and the density of TDS in the GaN layer was an order of magnitude larger than that in AlN. The MOCVD-grown sample was devoid of planar defects whereas the HVPE film contains significant densities of stacking faults in both GaN and AlN layers. Formation of モsecondaryヤ extended defects was interpreted in terms of creation and structural transformation of point defects during epitaxial growth. Differences in strain levels, types, and defect populations/distributions for the two heterostructures were attributed to the different growth rates for MOCVD and HVPE.
  • Coherent and diffuse X-ray scattering from a multicomponent superlattice with quantum dots

    Type Journal Article
    Author V. I. Punegov
    Author N. N. Faleev
    URL http://www.springerlink.com/content/x8382tq402470356/
    Volume 92
    Issue 7
    Pages 437-443
    Publication JETP Letters
    ISSN 0021-3640, 1090-6487
    Date 2010-12-16
    DOI 10.1134/S002136401019001X
    Accessed Tuesday, March 6, 2012 12:06:12 PM
    Library Catalog CrossRef
  • Thermal-Quantum Solar Cells

    Type Conference Paper
    Author Adam J. Bailey
    Author Christiana B. Honsberg
    Publisher IEEE
    Date 2011
    Conference Name The 37th IEEE Photovoltaics Specialists Conference, Seattle, WA, 2011
    Abstract The realization of a solar cell with a small number of bandgaps and physical processes which can theoretically attain the maximum possible thermodynamic limits is of substantial interest. Furthermore, achieving the maximum thermodynamic efficiency without concentration is particularly important because of the simpler system configuration. To approach the maximum one-sun efficiency of 68%, a thermal-quantum converter must be used.
  • Investigation of Intersubband Transitions of InAs/GaAsSb Quantum Dots

    Type Conference Paper
    Author K. -Y Ban
    Author S. P. Bremner
    Author S. N. Dahal
    Author C. B. Honsberg
    Place San Diego, CA
    Date 2011
    Conference Name NAMBE Conference
  • Detection of the third transition of InAs/GaAsSb quantum dots

    Type Conference Paper
    Author K.-Y. Ban
    Author S. P. Bremner
    Author D. Kuciauskas
    Author S. N. Dahal
    Author C. B. Honsberg
    Place Seattle, WA, USA
    Date 2011
    Conference Name Conference Record of the 37th IEEE Photovoltaic Specialists Conference
  • Optimizing Educational Approaches for University Photovoltaics Education

    Type Conference Paper
    Author Katherine G. Nelson
    Author Jenefer Husman
    Author Sarah K. Brem
    Author Christiana Honsberg
    Author Stuart Bowden
    Place Seattle, WA, USA
    Date 2011/td>
    Abstract The demands for increasing matriculation and retention in engineering are exceedingly high. To discover future innovations, the Nation needs many more engineers than it produces. This paper reviews the literature regarding some of the most significant barriers to student recruitment and retention in the physical sciences and engineering, especially with regard to underrepresented groups. Many students traditionally find it hard to be successful in engineering, not because they are not as successful in the key competencies (e.g. mathematics), but because they have not been provided with experiences that will provide the motivation required to complete the degree. The focus of this paper is the need to support studentsメ utility value perceptions, Engineering is typically a rigorous and difficult curriculum for all students, not just those at risk. Therefore, educational tools and interventions are needed that aid in overcoming these challenges and enhance learning of material. We argue that an ideal case for supporting student learning and motivation would be to emphasize Photovoltaics (PV) in physical science and engineering curricula. Specifically, we argue that (a) studentsメ perceived value of learning PV is high given the current climate for the need to develop renewable energy technologies, and (b) PV educators and educational researchers need to work together to optimize the motivational opportunities.
    Proceedings Title Conference Record of the 37th IEEE Photovoltaic Specialists Conference
  • Surface characterization of quinhydrone-methanol and iodine-methanol passivated silicon substrates using X-ray photoelectron spectroscopy

    Type Journal Article
    Author B. Chhabra
    Author C. Weiland
    Author R.L. Opila
    Author C.B. Honsberg
    URL http://dx.doi.org/10.1002/pssa.201026101
    Series Phys. Stat. Sol. A (Germany)
    Volume 208
    Issue 1
    Pages 91-5
    Publication Physica Status Solidi A
    ISSN 1862-6300
    Date 2011-01
    DOI 10.1002/pssa.201026101
    Accessed Tuesday, January 31, 2012 4:19:36 PM
    Library Catalog Engineering Village
    Abstract Hydrogen-terminated silicon substrates were passivated with quinhydrone-methanol (QHY/ME) and iodine-methanol (I2/ME), and the chemical changes occurring at the surface were investigated using X-ray photoelectron spectroscopy (XPS). The XPS surface studies demonstrate that QHY/ME passivation provides reduced oxidation, less carbon contamination, and a chemically inert surface. Electrical characterization also demonstrates higher minority carrier lifetimes of QHY/ME passivated substrates as compared to I2/ME passivated substrates. The quality of surface treatment was also characterized using the contact angle measurement, which confirms the presence of a hydrophobic organic layer on the surface after QHY/ME passivation. Si 2p XPS spectra of the QHY/ME, I2/ME samples, and H-terminated silicon. With a peak at 102.9 eV for I2/ME, it is evident that it provides poor surface passivation than QHY/ME where no surface oxidation is observed.
  • Controllability of the subband occupation of InAs quantum dots on a delta-doped GaAsSb barrier

    Type Journal Article
    Author Keun-Yong Ban
    Author Woong-Ki Hong
    Author S.P. Bremner
    Author S.N. Dahal
    Author H. McFelea
    Author C.B. Honsberg
    URL http://dx.doi.org/10.1063/1.3527039
    Series J. Appl. Phys. (USA)
    Volume 109
    Issue 1
    Pages 014312 (6 pp.)
    Publication Journal of Applied Physics
    ISSN 0021-8979
    Date 2011-01
    DOI 10.1063/1.3527039
    Accessed Tuesday, January 31, 2012 4:19:50 PM
    Library Catalog Engineering Village
    Abstract Optical properties of InAs quantum dots (QDs) embedded in GaAsSb barriers with delta-doping levels equivalent to 0, 2, 4, and 6 electrons per dot (e/dot) are studied using time-integrated photoluminescence (PL). When the PL excitation power is increased the full width at half maximum (FWHM) of the 4 and 6 e/dot samples is found to increase at a much greater rate than the FWHMs for the 0 and 2 e/dot samples. PL spectra of the 4 e/dot sample show a high energy peak attributed to emission from the first excited states of the QDs, a result deduced to be due to preoccupation of states by electrons supplied by the delta-doping plane. When temperature dependent PL results are fitted using an Arrhenius function, the thermal activation energies for the 4 and 6 e/dot samples are similar and greater than the thermal activation energies for the 0 and 2 e/dot samples (which are similar to each other). This increased thermal activation energy is attributed to the enhanced Coulombic interaction in the InAs QD area by the delta-doping plane for higher doping levels. It is concluded that delta-doping of the barrier in QD systems is a feasible method for controlling the level of carrier occupation in a QD mediated intermediate band.
  • Effect of Elastic Strain on Band Edge Alignment and Position of Intermediate Band of Isolated and Coupled Quantum Dots

    Type Conference Paper
    Author S. N. Dahal
    Author C. B. Honsberg
    Place Seattle, WA, USA
    Date 2011-06
    Conference Name Conference Record of the 37th IEEE Photovoltaic Specialists Conference
    Abstract Solar cells with quantum dot nanostructure absorbing medium have a potential to overcome single junction limit and achieve the solar energy conversion efficiency up to 63%. Self-assembled quantum dots that are grown by using molecular beam epitaxy(MBE) or metal organic chemical vapor deposition (MOCVD) have significant effect of strain on the band edge alignment and hence the confinement potential of electrons and holes. The energetic positions of confined energy states in quantum dots, which, act as intermediate state or band in intermediate band solar cells (IBSCs) are strongly affected by the strain in and around a quantum dot (QD). This work is focused on the calculation of strain distribution and its effect on band structure of QD array for its potential application in quantum dot intermediate band solar cells (QDIBSCs). Strain distribution in and around a QD is calculated using continuum theory of elasticity. When the inter-dot distance in the growth direction is sufficiently close, there is the interaction in strain distribution of QD layers .The strain distribution due to a vertically aligned QD array is calculated from superposition of the strain due to single quantum dot. The strain calculated this way is given as input for the calculation of band edge alignment and the position of QD confined states.
  • Investigation of the Correlations of Structural and Physical Features of Inas Quantum Dots, Embedded Between Strain-Relief Gaassb Layers with Different Sb Compositions

    Type Conference Paper
    Author N. Faleev
    Author S. P. Bremner
    Author K. -Y Ban
    Author D. Smith
    Author C. B. Honsberg
    Date 2011-06
    Abstract Strong correlations between crystal perfection of epitaxial structures and size, density and PL features of deposited InAs QDs have been found. Rise of Sb composition in GaAsSb strain relief layers from 8% to 37% significantly disturbed crystal perfection of epitaxial structures and increased the density of deposited QDs from 2 ヨ 2.5 ᅲ 1010 cm-2 at 8% Sb structure to 7.5 ヨ 9.5 ᅲ 1010 cm-2 at 16% Sb structure. At 37% Sb initial elastic stress were noticeably relaxed (? 40%) while creation of QDs were fully blocked. Relaxation of elastic stress strongly increased the density of dislocation loops in epitaxial layers and affected atoms migration on the growth front. Observed correlations between densities of dislocation loops and QDs are related with a diminution of the energy of migrated atoms, caused by dislocations. At definite density of dislocation loops reduced energy diminished accumulation of deposited atoms below the level critical for their transformation to QDs.
    Proceedings Title Conference Record of the 37th IEEE Photovoltaic Specialists Conference
  • Absorption coefficient for multiple-quasi fermi level system in quantum well

    Type Conference Paper
    Author K. Ghosh
    Author C. B. Honsberg
    Place Seattle, WA, USA
    Date 2011-06
    Conference Name Conference Record of the 37th IEEE Photovoltaic Specialists Conference
  • Extraction of recombination parameters of a-Si/c-Si solar cell from lifetime spectroscopy

    Type Conference Paper
    Author K. Ghosh
    Author N.-K. Song
    Author M.-S. Oh
    Author D.-S. Kim
    Author S. Bowden
    Place Seattle, WA, USA
    Date 2011-06
    Conference Name Conference Record of the 37th IEEE Photovoltaic Specialists Conference
  • Ultrafast Carrier Relaxation and Nonequilibrium Phonons in Hot Carrier Solar Cells

    Type Conference Paper
    Author S. M. Goodnick
    Author C. B. Honsberg
    Place Seattle, WA, USA
    Date 2011-06
    Conference Name Conference Record of the 37th IEEE Photovoltaic Specialists Conference
    Abstract Third generation concepts in photovoltaic devices depend critically on the dynamics of ultrafast carrier relaxation and electron-phonon interactions on very short times scales in nanostructures. Hot carrier solar cells in particular depend on the reduction in the energy relaxation rate in an absorber material. Here we investigate the short time carrier relaxation in quantum well, hot electron solar cells under varying photoexcitation conditions using ensemble Monte Carlo (EMC) simulation coupled with rate equation models, to understand the limiting factors affecting cell performance. It has recently been argued that nonequilibrium ムhotメ phonons may play a critical role in reducing carrier energy loss, and maintaining energy within the absorber system. Here we explicitly include nonequilibrium optical phonons, in which a detailed balance of emission and absorption events and the phonon population is simulated, and the anharmonic decay of the optical phonon population to acoustic phonons is described using a phenomenological phonon lifetime. We have simulated the average energy versus time of carriers in the quantum well absorber using GaAs effective mass parameters, but varying the effective bandgap to study the effect of this parameter on heating an carrier relaxation, relative to optical excitation at the mean solar spectrum energy at 1000 suns. Results with a 5 ps phonon LO optical phonon lifetime show that the after initial heating, the mean carrier temperature relaxes to relatively low excess temperature, with relatively little extraction through selective contacts, due to the cooling of the photoexcited population, which it turns out are able to effectively lose energy through electron-hole scattering, where the holes in turn have additional relaxation channels through TO modes. However, the inclusion of nonequilibrium phonon effects for all possible phonon modes is expected to reduce this channel for carrier cooling, and improve performance.
  • Hyrbid Advanced Concept Solar Cells

    Type Conference Paper
    Author C. B. Honsberg
    Author S. P. Bremner
    Author J. Lee
    Author A. J. Bailey
    Author S. N. Dahal
    Place Seattle, WA, USA
    Date 2011-06
    Conference Name Conference Record of the 37th IEEE Photovoltaic Specialists Conference
    Abstract Advanced concept or third generation solar cells rely on modification to the basic process of absorption /recombination or collection to increase the efficiency above that from a singe junction solar cell. While there are a number of advanced concept approaches, a feature of theses is that they have focused primarily on inclusion of a single type of physical mechanism. Such single mechanism advanced concept solar cells are in general limited in efficiency to the equivalent tandem solar cell which has the same number of processes. This paper demonstrates that solar cells using combinations of different approaches have higher thermodynamic efficiencies. Some combinations demonstrate higher efficiencies that either of the constituent approaches, and, significantly, even exceed the efficiency of the モequivalentヤ tandem structure. Moreover, such advanced concept hybrid structures have benefits other than efficiency increases, including reduced sensitivity to materials or to physical processes which are difficult to implement, or to non-idealities in the solar cell structure.
  • Limiting Efficiencies of Intermediate Band Solar Cell Assisted with Multiple Exciton Generation

    Type Conference Paper
    Author J. Lee
    Author C. B. Honsberg
    Place Seattle, WA, USA
    Date 2011-06
    Conference Name Conference Record of the 37th IEEE Photovoltaic Specialists Conference
    Abstract We propose and calculate the hybrid thermodynamic model using the intermediate band solar cells assisted with multiple exciton generation. We have been also studied this hybrid thermodynamic model under blackbody radiation and changing concentration to compare the conventional intermediate band solar cells. Because of multiple electron and hole pair on the conduction band edge, its maximum efficiency and optimum bandgap positions have been enhanced compared with conventional detailed balance model of intermediate band solar cells. The maximum efficiencies of this solar cell are both 47.31 percent for one sun and 65.07 percent under maximum concentration. And its corresponding overall bandgap energies are also reduced because of multiple electron and hole pairs.
  • Thermodynamic Limits of Hybrid Photovoltaic Systems Using Multiple Junction Solar Cells with Carrier Transitions at Intermediate Band

    Type Conference Paper
    Author J. Lee
    Author C. B. Honsberg
    Place Seattle, WA, USA
    Date 2011-06
    Conference Name Conference Record of the 37th IEEE Photovoltaic Specialists Conference
    Abstract We have proposed the hybrid thermodynamic approach for multiple junction solar cells introducing the intermediate band. Because of increasing number of transitions inside multiple junction solar cells, it give an effect that small number of stacks can be possible to realize increased number of multiple junction solar. The maximum efficiency of two stacks hybrid solar cells has been enhanced and its value is larger than over 4 stacks tandem solar cells. We have also found optimum bandgap of each stack and studied optimum transition levels of each stack both from valence band to intermediate band and intermediate band to conduction band.
  • Characterization and comparison of silicon nitride films deposited using two novel processes

    Type Conference Paper
    Author V. Sharma
    Author A. J. Bailey
    Author B. Dauksher
    Author C. J. Tracy
    Author S. Bowden
    Author B. O'Brien
    Place Seattle, WA, USA
    Date 2011-06
    Conference Name Conference Record of the 37th IEEE Photovoltaic Specialists Conference
  • Four-point probe characterization of 4H silicon carbide

    Type Journal Article
    Author N. Chandra
    Author V. Sharma
    Author G.Y. Chung
    Author D.K. Schroder
    URL http://www.sciencedirect.com/science/article/pii/S0038110111002620
    Volume 64
    Issue 1
    Pages 73-77
    Publication Solid-State Electronics
    ISSN 0038-1101
    Date 2011-10
    DOI 10.1016/j.sse.2011.07.004
    Accessed Tuesday, February 28, 2012 8:54:15 AM
    Library Catalog ScienceDirect
    Abstract We report on four-point probe measurements on SiC wafers as such measurements give erratic data. Currentヨvoltage measurements on n-type SiC wafers doped to 3 ᅲ 1018 cm-3 are non-linear and single probe IヨV measurements are symmetrical for positive and negative voltages. For comparison, similar measurements of p-type Si doped to 5 ᅲ 1014 cm-3 gave linear IヨV, well-defined sheet resistance and the single probe IヨV curves were asymmetrical indicating typical Schottky diode behavior. We believe that the reason for the non-linearity in four-point probe measurements on SiC is the high contact resistance. Calculations predict the contact resistance of SiC to be approximately 1012 ? which is of the order of the input resistance of the voltmeter in our four-point probe measurements. There was almost no change in two-probe IヨV curves when the spacing between the probes was changed from 10mm to 20cm, further supporting the idea that the IヨV characteristics are dominated by the contact resistance.
  • The Solar Energy Challenge: Engineering Notebook

    Type Conference Paper
    Author K. G. Nelson
    Author C. Foster
    Author M. Crowder
    Author J. Husman
    Author T. Ganesh
    Place Mesa, AZ
    Date 2011-10
    Proceedings Title Arizona Science Teachers Association
  • Observation of band alignment transition in InAs/GaAsSb quantum dots by photoluminescence

    Type Journal Article
    Author Keun-Yong Ban
    Author D. Kuciauskas
    Author S.P. Bremner
    Author C.B. Honsberg
    Volume 111
    Issue 10
    Pages 104302-104302-4
    Publication Journal of Applied Physics
    ISSN 0021-8979
    Date 2012
    DOI 10.1063/1.4717766
    Library Catalog IEEE Xplore
    Abstract The band alignment of InAs quantum dots (QDs) embedded in GaAsSb barriers with various Sb compositions is investigated by photoluminescence (PL) measurements. InAs/GaAsSb samples with 13% and 15% Sb compositions show distinct differences in emission spectra as the PL excitation power increases. Whilst no discernible shift is seen for the 13% sample, a blue-shift of PL spectra following a 1/3 exponent of the excitation power is observed for the 15% sample suggesting a transition from a type I to type II band alignment. Time-resolved PL data show a significant increase in carrier lifetime as the Sb composition increases between 13% and 15% implying that the transformation from a type I to type II band alignment occurs between 13% and 15% Sb compositions. These results taken together lead to the conclusion that a zero valence band offset (VBO) can be achieved for the InAs/GaAsSb system in the vicinity of 14% Sb composition.
  • Lateral spectrum splitting concentrator photovoltaics: Direct measurement of component and submodule efficiency

    Type Journal Article
    Author Xiaoting Wang
    Author Nick Waite
    Author Paola Murcia
    Author Keith Emery
    Author Myles Steiner
    Author Fouad Kiamilev
    Author Keith Goossen
    Author Christiana Honsberg
    Author Allen Barnett
    Volume 20
    Issue 2
    Pages 149-165
    Publication Progress in Photovoltaics: Research and Applications
    ISSN 10627995
    Date 2012
    Journal Abbr Progress in Photovoltaics: Research and Applications
    DOI 10.1002/pip.1194
    Library Catalog Engineering Village
    Abstract To achieve high energy conversion efficiency, a solar module architecture called lateral spectrum splitting concentrator photovoltaics (LSSCPV) is being developed. LSSCPV can concentrate available sunlight and laterally split a single beam into bands with different spectra for absorption by different solar cells with band gaps matched to the split spectrum. Test assemblies of a sample LSSCPV architecture were constructed, each of which contains four p-n junctions and two optical pieces. Independent experiments or simulations had been implemented on the components but by using optimal assumptions. In order to examine the actual performances of all the components, which are dependent on each other and the light source, direct outdoor measurements were made. A set of self-consistent efficiency definitions was articulated and a test bed was developed to measure the parameters required by the efficiency calculation. By comparing the component efficiency items derived from the outdoor measurement and the expected values based on independent simulations, the potential opportunities for efficiency improvement are determined. In the outdoor measurement at the University of Delaware, the optical component demonstrated 891% efficiency. Additional assemblies were tested at the National Renewable Energy Laboratory. One assembly demonstrated 367% submodule efficiency, which compares favorably with the 326% previously reported verified submodule efficiency. Copyright 2011 John Wiley Sons, Ltd.
    Short Title Lateral spectrum splitting concentrator photovoltaics

    Notes:

    • Compilation and indexing terms, Copyright 2012 Elsevier Inc.

  • The role of Sb compositions on the properties of InAs/GaAsSb quantum dots (QDs)

    Type Journal Article
    Author Keun-Yong Ban
    Author Stephen P Bremner
    Author Darius Kuciauskas
    Author Som N Dahal
    Author Christiana B Honsberg
    URL http://spiedigitallibrary.org/proceedings/resource/2/psisdg/8256/1/82561C_1
    Volume 8256
    Issue 1
    Pages 82561C-82561C-6
    Publication Proceedings of SPIE
    ISSN 0277786X
    Date 2012-02-09
    DOI doi:10.1117/12.910834
    Accessed Tuesday, February 28, 2012 10:31:04 AM
    Library Catalog SPIE/AIP
    Abstract QD size, uniformity and density in InAs/GaAsSb material system for increasing Sb content are studied using Atomic Force Microscopy (AFM). AFM results show that QD density and uniformity improve with Sb content increase. The improvement of QD uniformity is ensured by the narrowing of the analysis of AFM scans. To obtain minimum VBO, InAs/GaAsSb with various Sb compositions is investigated by PL and TRPL measurements. PL data shows a blue-shift as excitation power increases as evidence of a type II band structure. Since the PL peak of 8 and 13 % Sb samples did not shift while that of 15 % Sb sample is blue-shifted with increasing the excitation power it is concluded that InAs QDs/GaAs0.86Sb0.14 would have minimum valence band offset. This tendency is supported by the change of a carrier lifetime estimated from TRPL data
  • Modeling carrier relaxation in hot carrier solar cells

    Type Journal Article
    Author Stephen M Goodnick
    Author Christiana B Honsberg
    URL http://spiedigitallibrary.org/proceedings/resource/2/psisdg/8256/1/82560W_1
    Volume 8256
    Issue 1
    Pages 82560W-82560W-10
    Publication Proceedings of SPIE
    ISSN 0277786X
    Date 2012-02-09
    DOI doi:10.1117/12.910858
    Accessed Tuesday, February 28, 2012 10:50:55 AM
    Library Catalog SPIE/AIP
    Abstract Third generation concepts in photovoltaic devices depend critically on the dynamics of ultrafast carrier relaxation and electron-phonon interactions on very short times scales in nanostructures such as quantum wells, wires and dots. Hot carrier solar cells in particular depend on the reduction in the energy relaxation rate in an absorber material, where hot carriers are extracted through energy selective contacts. Here we investigate the short time carrier relaxation in quantum well, hot electron solar cells under varying photoexcitation conditions using ensemble Monte Carlo (EMC) simulation coupled with rate equation models, to understand the limiting factors affecting cell performance. In particular, we focus on the potential role of hot phonons in reducing the energy loss rate in order to achieve sufficient carrier temperature for efficient performance.
  • The thermodynamic limits of tandem photovoltaic devices with intermediate band

    Type Journal Article
    Author Jongwon Lee
    Author Christiana B Honsberg
    URL http://spiedigitallibrary.org/proceedings/resource/2/psisdg/8256/1/82560Q_1
    Volume 8256
    Issue 1
    Pages 82560Q-82560Q-12
    Publication Proceedings of SPIE
    ISSN 0277786X
    Date 2012-02-09
    DOI 10.1117/12.910813
    Accessed Tuesday, February 28, 2012 10:47:53 AM
    Library Catalog SPIE/AIP
    Abstract We present a hybrid thermodynamic model for multijunction solar cells with intermediate bands that demonstrates possible improvements to conventional multijunction photovoltaic systems. Applying this model to selected tandem cell structures shows that the performance of such hybrid solar cells is enhanced and that multiple transitions from intermediate bands can reduce the number of material stacks and boost overall efficiency. We demonstrate the results of detailed simulations for multiple numbers of stacks of hybrid multijunction solar cells. And, we can choose proper materials to compose intermediate band for each junction. Furthermore, we suggest other alternative hybrid solar cell systems to absorb moderate photon energy range and find appropriate materials for hybrid solar cells.
  • Arizona Best Fest

    Type Presentation
    Presenter J. Husman
    URL http://www.az100years.org/arizona-best-fest-series/
    Place Downtown Phoenix
    Date February 11, 2012
  • Characterization and comparison of silicon nitride films deposited using two novel processes

    Type Journal Article
    Author Vivek Sharma
    Author Adam Bailey
    Author Bill Dauksher
    Author Clarence Tracy
    Author Stuart Bowden
    Author Barry O'Brien
    URL http://link.aip.org.ezproxy1.lib.asu.edu/link/doi/10.1116/1.3687423
    Volume 30
    Issue 2
    Pages 021201-1
    Publication J. Vac. Sci. Technol. A
    Date 2012-02-21
    DOI 10.1116/1.3687423
    Abstract Hydrogenated silicon nitride films (SiNx:H) deposited using a PECVD process enhance the performance of crystalline silicon solar cells by functioning as an efficient antireflection coating and passivating layer. In this paper, we compared two SiNx:H novel deposition processes using two different PECVD toolsラone nontraditional in process regime and the other nontraditional in typeラto determine their suitability to solar cell fabrication. The parameter space was explored by employing a design of experiment methodology followed by material characterization using variable angle spectroscopic ellipsometry, reflectance, FTIR, RBS and elastic recoil detection. The thickness and reflectance of Si-rich films changed dramatically after annealing. Further, FTIR results showed that the SiヨH bond peak present at 2160 cm-1 in such films disappeared after a typical Al firing step. Therefore, the optimized films were deposited with a lower SiH4/NH3 ratio to minimize the changes in the film properties after annealing.
  • Photoluminescence Imaging of Silicon Wafers Using High Power Light Emitting Diode Arrays

    Type Thesis
    Author K.C, LaRosa
    Date 2012-3
    University Arizona State University
    Abstract Due to its ability to map the minority carrier lifetime of an entire cell within minutes, photoluminescence has been an increasingly prevalent new technology for solar cell characterization. It is capable of obtaining high spatial resolution with inexpensive Si-CCD cameras. However, it has focused primarily on near-infrared lasers as the excitation source. The development of a photoluminescence system which uses light emitting diode (LED) arrays instead of lasers allows for a cheaper, safer design while increasing the potential functionality. The low cost and versatility of LED arrays make them ideal for inline characterization while also allowing for characterization using a variety of wavelengths. Production of high lifetime solar cells has begun at the Solar Power Lab at Arizona State University, and spatial lifetime mapping is important for characterizing and improving new large area solar cells. Within the last eight months of research, a photoluminescence characterization device has been constructed and verified for high minority carrier lifetime materials. The system designed is an improvement over other systems because of its cost-effectiveness combined with the high resolution spatial variation mapping and short measurement times, making it ideal for the Solar Power Labメs needs.
  • Night of the Open Door

    /tr>

    Type Presentation
    Presenter Jenefer Husman
    Place Qesst offices, asu
    Date March 3, 2012
    Accessed Tuesday, March 6, 2012 1:43:28 PM

    Notes:

    • Participants were

       

  • Solar Energy Technologies - A Comparative Study of Commercial Applications and Government Policies

    Type Thesis
    Author S. Limpert
    Date April 2012
    University Arizona State University
  • ASU|UA Student Conference on Renewable Energy Science

    Type Presentation
    Presenter Arizona State University
    Place Arizona State University
    Date April 19-20, 2012
    Abstract ASU|UA Student Conference on Renewable Energy Science event was held on April 19-20, 2012 at ASU Memorial Union, Turquoise Room, Tempe Campus. There were 60 poster presentations, all are presented by ASU and UofA students. Indeed, this is a student-focused conference exploring renewable energy research activities at both universities in solar fuels, solar electric, and energy policy. Post docs, undergraduate and graduate students were presented their posters at 2 poster sessions, scheduled on April 19 from 5:00 to 7:00 p.m. and on April 20 from 10:15 a.m. to 12:00 noon. Industry representatives who have an interest in ASUメs renewable energy science research, as well as Professors and students from ASU and UofA were attended to poster sessions.
  • Issues in the physical measurement of the intermediate band effect

    Type Conference Paper
    Author S. Bremner
    Author K. Ghosh
    Author N. Ekins-Daukes
    Author C. Honsberg
    Author Stephen Goodnick
    URL http://ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm?arnumber=6317692
    Publisher IEEE
    Pages 000641-000646
    ISBN 978-1-4673-0066-7, 978-1-4673-0064-3, 978-1-4673-0065-0
    Date 06/2012
    DOI 10.1109/PVSC.2012.6317692
    Accessed Monday, March 11, 2013 1:55:39 PM
    Library Catalog CrossRef
    Conference Name 38th IEEE Photovoltaic Specialists Conference (PVSC)
  • Experimental and theoretical verification of the presence of inversion region in a-Si/c-Si heterojunction solar cells with an intrinsic layer

    Type Conference Paper
    Author Kunal Ghosh
    Author Clarence Tracy
    Author Stuart Bowden
    URL http://ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm?arnumber=6317782
    Publisher IEEE
    Pages 001046-001048
    ISBN 978-1-4673-0066-7, 978-1-4673-0064-3, 978-1-4673-0065-0
    Date 06/2012
    DOI 10.1109/PVSC.2012.6317782
    Accessed Monday, March 11, 2013 1:54:51 PM
    Library Catalog CrossRef
    Conference Name 38th IEEE Photovoltaic Specialists Conference (PVSC)
  • Effect of band bending and band offset in the transport of minority carriers across the ordered/disordered interface of a-Si/c-Si heterojunction solar cell

    Type Conference Paper
    Author Kunal Ghosh
    Author Clarence Tracy
    Author Stephen Goodnick
    Author Stuart Bowden
    URL http://ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm?arnumber=6317605
    Publisher IEEE
    Pages 000221-000226
    ISBN 978-1-4673-0066-7, 978-1-4673-0064-3, 978-1-4673-0065-0
    Date 06/2012
    DOI 10.1109/PVSC.2012.6317605
    Accessed Monday, March 11, 2013 1:53:30 PM
    Library Catalog CrossRef
    Conference Name 38th IEEE Photovoltaic Specialists Conference (PVSC)
  • Reassessment of classic recombination mechanisms in silicon point contact concentrator solar cell

    Type Conference Paper
    Author S Herasimenka
    Author P Altermatt
    Author S Bowden
    Author C Honsberg
    URL http://ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm?arnumber=6317784
    Publisher IEEE
    Pages 001055-001058
    ISBN 978-1-4673-0066-7, 978-1-4673-0064-3, 978-1-4673-0065-0
    Date 06/2012
    DOI 10.1109/PVSC.2012.6317784
    Accessed Monday, March 11, 2013 1:58:36 PM
    Library Catalog CrossRef
    Conference Name 38th IEEE Photovoltaic Specialists Conference (PVSC)
  • Realizing Terawatt-Scale Solar Electricity: Nanotechnology-Enabled Physical Mechanisms and Material Properties

    Type Journal Article
    Author Christiana Honsberg
    Author Stephen Goodnick
    URL http://ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm?arnumber=6198867
    Volume 6
    Issue 2
    Pages 6-14
    Publication IEEE Nanotechnology Magazine
    ISSN 1932-4510
    Date 06/2012
    DOI 10.1109/MNANO.2012.2192652
    Accessed Monday, March 11, 2013 1:42:22 PM
    Library Catalog CrossRef
    Short Title Realizing Terawatt-Scale Solar Electricity
  • Statistical analysis of commercial c-Si PV module photovoltaic efficiency distribution over 10-years period

    Type Conference Paper
    Author Joseph M Kuitche
    Author Vivek Sharma
    Author Jaewon Oh
    Author Rong Pan
    Author Govindasamy TamizhMani
    URL http://ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm?arnumber=6318085
    Publisher IEEE
    Pages 002421-002425
    ISBN 978-1-4673-0066-7, 978-1-4673-0064-3, 978-1-4673-0065-0
    Date 06/2012
    DOI 10.1109/PVSC.2012.6318085
    Accessed Monday, March 11, 2013 2:37:55 PM
    Library Catalog CrossRef
  • An overview of the Bangladeshi photovoltaic market, government policies and deployment challenges

    Type Conference Paper
    Author Steven Limpert
    Author Holly Battelle
    URL http://ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm?arnumber=6318092
    Publisher IEEE
    Pages 002455-002457
    ISBN 978-1-4673-0066-7, 978-1-4673-0064-3, 978-1-4673-0065-0
    Date 06/2012
    DOI 10.1109/PVSC.2012.6318092
    Accessed Monday, March 11, 2013 1:00:31 PM
    Library Catalog CrossRef
    Conference Name 2012 38th IEEE Photovoltaic Specialists Conference
  • Peak load offset and the effect of dust storms on 10 MWp distributed grid tied photovoltaic systems installed at Arizona State University

    Type Conference Paper
    Author Vivek Sharma
    Author Stuart Bowden
    URL http://ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm?arnumber=6317682
    Publisher IEEE
    Pages 000590-000595
    ISBN 978-1-4673-0066-7, 978-1-4673-0064-3, 978-1-4673-0065-0
    Date 06/2012
    DOI 10.1109/PVSC.2012.6317682
    Accessed Monday, March 11, 2013 2:35:14 PM
    Library Catalog CrossRef
    Conference Name 38th IEEE Photovoltaic Specialists Conference
  • Laser wafering

    Type Conference Paper
    Author S. Bowden
    Author J. LeBeau
    Pages 001826 -001829
    Date june 2012
    DOI 10.1109/PVSC.2012.6317948
    Library Catalog IEEE Xplore
    Conference Name 2012 38th IEEE Photovoltaic Specialists Conference (PVSC)
    Abstract A new technique for the laser wafering of semiconductors is presented using sub surface laser engraving. In the laser wafering process, a high intensity laser is used to form sub-surface etch pits or defects at multiple depths in an ingot. This allows a rapid, controllable approach to the formation of wafers with thickness ranging from below 10 microns to over 100 microns. Laser wafering provides a way to cut a a brick of silicon into multiple wafers with minimal kerf loss and the possibility to dramatically lower the cost of silicon solar cell production. The techniques relies on the principle that many materials, including silicon and other semiconductors, have a non-linear absorption co-efficient with intensity, such that sub-band gap light is absorbed above a given intensity. This allows a high intensity laser to be focused at an arbitrary point below the surface, and allowing absorption of the high intensity light only at the focal point.
    Proceedings Title 2012 38th IEEE Photovoltaic Specialists Conference (PVSC)
  • Intermediate band solar cell with non-ideal band structure under AM1.5 spectrum

    Type Conference Paper
    Author S.P. Bremner
    Author C.B. Honsberg
    Pages 000021 -000024
    Date june 2012
    DOI 10.1109/PVSC.2012.6317559
    Library Catalog IEEE Xplore
    Conference Name 2012 38th IEEE Photovoltaic Specialists Conference (PVSC)
    Abstract The limiting efficiency of an intermediate band solar cell with a non-ideal band structure is analyzed using the principle of detailed balance. Firstly, the impact of finite band width on the optimum band gap design for AM1.5 spectrum is examined. It is found that the band width may be a determining factor in the optimum band gap arrangement, but that the degradation in efficiency due to the band width up to 200 meV is moderate. It is also found that the band width can determine which band gap combination gives the highest global limiting efficiency. Further to the intermediate band width modification, the inclusion of band tails, analogous to those present in amorphous materials is discussed in terms of realizing an intermediate band using quantum dot arrays. In this model the worst case scenario is assumed, that of low absorption, but maximum emissivity at the band tail edge of the intermediate band. Results show that, with multiple band gap combinations giving several local peaks, the one giving the global maximum efficiency changes with band width. When band tails are included in a materials system proposed for implementing an intermediate band solar cell via quantum dot miniband formation significant drop off in efficiency is seen. The results taken together suggest the intermediate band width and any band tails should be considered in designs for intermediate band solar cells.
    Proceedings Title 2012 38th IEEE Photovoltaic Specialists Conference (PVSC)
  • Simulation of carrier relaxation in hot carrier solar cells

    Type Conference Paper
    Author S.M. Goodnick
    Author S. Limpert
    Author C. Honsberg
    Author P. Lugli
    Pages 001657 -001662
    Date june 2012
    DOI 10.1109/PVSC.2012.6317914
    Library Catalog IEEE Xplore
    Conference Name 2012 38th IEEE Photovoltaic Specialists Conference (PVSC)
    Abstract Hot carrier solar cells depend critically on the energy relaxation dynamics of photo-generated carriers in an absorber material, where hot carriers are extracted through energy selective contacts. Here we combine ensemble Monte Carlo (EMC) simulation with an energy balance equation approach, to simulate the microscopic carrier relaxation processes and corresponding electron and hole temperatures in semiconductor quantum well (QW) hot carrier solar cell structures, both under transient and steady state illumination. We include nonequilibrium optical phonons, in which a detailed balance of emission and absorption events is used to simulate the phonon population in time, with the anharmonic decay of the optical phonon population to acoustic phonons described using a phenomenological phonon lifetime. Simulation of femtosecond laser excitation in GaAs QWs show reduced cooling, depending on the optical phonon lifetime and excitation intensity. Steady state simulation under AM0 solar illumination shows a build-up of hot phonons over long times depending on the phonon lifetime, although they are not readily re-absorbed due to momentum and energy conservation considerations.
    Proceedings Title 2012 38th IEEE Photovoltaic Specialists Conference (PVSC)
  • Theoretical analysis for intermediate band and tandem hybrid solar cell materials

    Type Conference Paper
    Author Jongwon Lee
    Author S.N. Dahal
    Author C.B. Honsberg
    Pages 000068 -000072
    Date june 2012
    DOI 10.1109/PVSC.2012.6317570
    Library Catalog IEEE Xplore
    Conference Name 2012 38th IEEE Photovoltaic Specialists Conference (PVSC)
    Abstract The efficiency limit of an intermediate band (IB) solar cell can be increased by a #x201C;tandem #x201D; configuration of multiple intermediate band devices. Thermodynamic models show that the efficiency of a two-stack tandem of IB devices achieves the efficiency of a six junction series connected solar cell. The efficiency of an IB in conjunction with a single or double stack tandem has similar efficiency advantages. Further, analysis of the materials which can be used to implement IB solar cells in a tandem configuration shows advantages relating to the ability to implement IB materials with quantum wells or quantum dots. For a single IB solar cell, a key difficulty is identifying materials for the barrier and the quantum well which have a small valence band offset and large conduction band offset (or the reverse). The use of an IB solar cell as the bottom solar cell of a tandem allows a larger range of materials with suitable barrier band gaps and a smaller ideal conduction band offset. A further theoretical advantage of such a structure is that it avoids the extremely low open circuit voltages achieved from pn junctions in low bandgap materials; for example, the thermodynamic optimum for a 6 junction tandem solar cell has its lowest bandgap below 0.4 eV. We present a thermodynamic model for IB hybrid tandem configurations which does not assume spectral selectivity among the different solar cells and predicts that a barrier/quantum dot structure can have an efficiency as high as 60 to 70 percent at 1000X blackbody radiation.
    Proceedings Title 2012 38th IEEE Photovoltaic Specialists Conference (PVSC)
  • Limiting efficiencies over 50% using multijunction solar cells with multiple exciton generation

    Type Conference Paper
    Author Jongwon Lee
    Author C.B. Honsberg
    Pages 000062 -000067
    Date june 2012
    DOI 10.1109/PVSC.2012.6317569
    Library Catalog IEEE Xplore
    Conference Name 2012 38th IEEE Photovoltaic Specialists Conference (PVSC)
    Abstract The achievement of solar cells over 50% is a critical goal for photovoltaics. Multijunction solar cells over 5 junctions allow such efficiencies, but are severely limited by material constraints and growth requirements for lattice matching. Nanostructured approaches such as multiple exciton generation (MEG) potentially offer a route to higher efficiency but still require high values of sunlight concentration and large quantum yields. We show an approach that allows for higher efficiencies based on including MEG in a multijunction solar cell. We also present a thermodynamic model for multijunction solar cells with MEG that demonstrates possible improvements.
    Proceedings Title 2012 38th IEEE Photovoltaic Specialists Conference (PVSC)
  • Work in Progress: Towards the development of a model for beneficial use of educational technology through a photovoltaics engineering website.

    Type Conference Paper
    Author K. G. Nelson
    Author R. Koselar
    Author J. Husman
    Place San Antonio, TX
    Date June 2012
    Conference Name American Society for Engineering Education Annual Conference
  • Web applications for: centralization of photovoltaic cell production and characterization data, and processing of Sentaurus simulation files

    Type Conference Paper
    Author Timothy Reblitz
    Author Stuart Bowden
    Author Stanislau Herasimenka
    Date June 22-25 2012
    Abstract Abstract ラ We present the development, architecture, and usage of two web applications for photovoltaic cell research and fabrication on a pilot production line. The first tool, eTraveller, centralizes photovoltaic cell production data and cell measurements from a variety of disparate tools and stores the results in a centralized database. The data is stored alongside uploaded run sheets and reviewing past data is as straight forward as browsing a website. The second tool, Minotaur, provides a web based front end to the semiconductor simulation tool Sentaurus. Minotaur is specifically tailored to the simulation of solar cells and enables the use of sophisticated models in an easy to use package. Index Terms ラ photovoltaic cells, silicon, web applications, Sentaurus, Minotaur, eTraveller
    Proceedings Title proceedings of 22nd Workshop on Crystalline Silicon Solar Cells & Modules, Vail Colorado,
  • Optical absorption dependence on composition and thickness of InxGa1-xN (0.05<ᅲ<0.22) grown on GaN/sapphire

    Type Journal Article
    Author Balakrishnam R. Jampana
    Author Conan R. Weiland
    Author Robert L. Opila
    Author Ian T. Ferguson
    Author Christiana B. Honsberg
    URL http://linkinghub.elsevier.com/retrieve/pii/S0040609012008206
    Volume 520
    Issue 22
    Pages 6807-6812
    Publication Thin Solid Films
    ISSN 00406090
    Date 9/2012
    DOI 10.1016/j.tsf.2012.07.003
    Accessed Monday, March 11, 2013 2:01:14 PM
    Library Catalog CrossRef
  • Optical absorption dependence on composition and thickness of InxGa1 - xN (0.05 < ᅲ < 0.22) grown on GaN/sapphire

    Type Journal Article
    Author Balakrishnam R. Jampana
    Author Conan R. Weiland
    Author Robert L. Opila
    Author Ian T. Ferguson
    Author Christiana B. Honsberg
    URL http://www.sciencedirect.com/science/article/pii/S0040609012008206
    Volume 520
    Issue 22
    Pages 6807-6812
    Publication Thin Solid Films
    ISSN 0040-6090
    Date September 1, 2012
    Journal Abbr Thin Solid Films
    DOI 10.1016/j.tsf.2012.07.003
    Accessed Thursday, February 28, 2013 4:01:26 PM
    Library Catalog ScienceDirect
    Abstract We report the change in optical absorption properties of InGaN epilayers around the critical layer thickness determined from X-ray diffraction. Detrimental sub-band gap absorption is observed in InGaN thin films grown beyond the critical layer thicknesses, and is caused by localized electric fields around extended crystalline defects and aided by V-defects through light channeling. The photoluminescence response from InGaN thin films, grown beyond the critical layer thickness, is reduced owing to absorption of the incident laser light by non-radiative recombination extended crystalline defects. The formation of V-defects is observed to occur beyond the critical layer thickness and continues to grow in areal coverage aiding in sub-band gap absorption. This optical behavior sets constraints to be incorporated in the design of InGaN solar cell and requirement for improvement in epitaxial growth techniques to reduce V-defects.
  • Work in progress: Evaluation of an online education portal from the user's perspective: An empirical investigation of a photovoltaics (PV) engineering learning portal, pveducation.org

    Type Conference Paper
    Author Refika Koseler
    Author Susan Shapcott
    Author Katherine G. Nelson
    Author Jenefer Husman
    URL http://ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm?arnumber=6462492
    Publisher IEEE
    Pages 1-2
    ISBN 978-1-4673-1352-0, 978-1-4673-1353-7, 978-1-4673-1351-3
    Date 10/2012
    DOI 10.1109/FIE.2012.6462492
    Accessed Monday, March 11, 2013 6:59:44 PM
    Library Catalog CrossRef
    Conference Name FIE 2012
    Short Title Work in progress
  • Work in progress: Identification of misconceptions governed by emergent phenomena in photovoltaics content using the Delphi Method

    Type Conference Paper
    Author Katherine G. Nelson
    Author Sarah K. Brem
    Author Jenefer Husman
    URL http://ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm?arnumber=6462382
    Publisher IEEE
    Pages 1-2
    ISBN 978-1-4673-1352-0, 978-1-4673-1353-7, 978-1-4673-1351-3
    Date 10/2012
    DOI 10.1109/FIE.2012.6462382
    Accessed Monday, March 11, 2013 7:01:50 PM
    Library Catalog CrossRef
    Conference Name FIE 2012
    Short Title Work in progress
  • Correlation between lifetime curve and performance of amorphous silicon/ crystalline silicon heterostructure solar cell

    Type Conference Paper
    Author Stuart Bowden
    Date 2013
    Abstract Lifetime curves have been primarily used in a-Si/c-Si heterostructure research for optimization of surface passivation. In this paper, we will provide an analysis of the lifetime curves that allow the determination of the recombination properties and assist in the prediction of the device performance of complete solar cell. The analysis of the lifetime curves are performed on symmetrical stacks of intrinsic/p+ a-Si, intrinsic/n+ a-Si and also on complete solar cell structure with different doping levels in the doped a-Si layers. The results are also presented on the correlation between lifetime curves and the performance of a complete solar cell, particularly fill factor and open-circuit voltage.
  • Non PN junction solar cells using carrier selective contacts

    Type Conference Paper
    Author Stuart Bowden
    Author Kunal Ghosh
    Author Christiana Honsberg
    URL http://dx.doi.org/10.1117/12.2004259
    Volume 8620
    Pages 86200T-86200T-6
    Date 2013
    DOI 10.1117/12.2004259
    Accessed Saturday, September 21, 2013 10:44:15 PM
    Library Catalog Silverchair
    Abstract A novel device concept utilizing the approach of selectively extracting carriers at the respective contacts is outlined in the work. The dominant silicon solar cell technology is based on a diffused, top-contacted p-n junction on a relatively thick silicon wafer for both commercial and laboratory solar cells. The VOC and hence the efficiency of a diffused p-n junction solar cell is limited by the emitter recombination current and a value of 720 mV is considered to be the upper limit. The value is more than 100 mV smaller than the thermodynamic limit of VOC as applicable for silicon based solar cells. Also, in diffused junction the use of thin wafers (< 50 um) are problematic because of the requirement of high temperature processing steps. But a number of roadmaps have identified solar cells manufactured on thinner silicon wafers to achieve lower cost and higher efficiency. The carrier selective contact device provides a novel alternative to diffused p-n junction solar cells by eliminating the need for complementary doping to form the emitter and hence it allows the solar cells to achieve a VOC of greater than 720 mV. Also, the complete device structure can be fabricated with low temperature thin film deposition or organic coating on silicon substrates and thus epitaxially grown silicon or kerfless silicon, in addition to standard silicon wafers can be utilized.
  • Impact of stress relaxation in GaAsSb cladding layers on quantum dot creation in InAs/GaAsSb structures grown on GaAs (001)

    Type Journal Article
    Author S.P. Bremner
    Author K.-Y. Ban
    Author N.N. Faleev
    Author C.B. Honsberg
    Author D.J. Smith
    Volume 114
    Issue 10
    Pages 103511-103511-9
    Publication Journal of Applied Physics
    ISSN 0021-8979
    Date 2013
    DOI 10.1063/1.4819962
    Library Catalog IEEE Xplore
    Abstract We describe InAs quantum dot creation in InAs/GaAsSb barrier structures grown on GaAs (001) wafers by molecular beam epitaxy. The structures consist of 20-nm-thick GaAsSb barrier layers with Sb content of 8%, 13%, 15%, 16%, and 37% enclosing 2 monolayers of self-assembled InAs quantum dots. Transmission electron microscopy and X-ray diffraction results indicate the onset of relaxation of the GaAsSb layers at around 15% Sb content with intersected 60ᄚ dislocation semi-loops, and edge segments created within the volume of the epitaxial structures. 38% relaxation of initial elastic stress is seen for 37% Sb content, accompanied by the creation of a dense net of dislocations. The degradation of In surface migration by these dislocation trenches is so severe that quantum dot formation is completely suppressed. The results highlight the importance of understanding defect formation during stress relaxation for quantum dot structures particularly those with larger numbers of InAs quantum-dot layers, such as those proposed for realizing an intermediate band material.
  • MBE growth of Sb-based nBn photodetectors on large diameter GaAs substrates

    Type Conference Paper
    Author Dmitri Lubyshev
    Author Joel M. Fastenau
    Author Yueming Qiu
    Author Amy W. K. Liu
    Author Edwin J. Koerperick
    Author Jonathon T. Olesberg
    Author Dennis Norton
    Author Nikolai N. Faleev
    Author Christiana B. Honsberg
    URL http://dx.doi.org/10.1117/12.2019039
    Volume 8704
    Pages 870412-870412-10
    Date 2013
    DOI 10.1117/12.2019039
    Accessed Saturday, September 21, 2013 10:41:17 PM
    Library Catalog Silverchair
    Abstract The GaSb-based family of materials and heterostructures provides rich bandgap engineering possibilities for a variety of infrared (IR) applications. Mid-wave and long-wave IR photodetectors are progressing toward commercial manufacturing applications, but to succeed they must move from research laboratory settings to general semiconductor production and they require larger diameter substrates than the current standard 2-inch and 3-inch GaSb. Substrate vendors are beginning production of 4-inch GaSb, but another alternative is growth on 6-inch GaAs substrates with appropriate metamorphic buffer layers. We have grown generic MWIR nBn photodetectors on large diameter, 6-inch GaAs substrates by molecular beam epitaxy. Multiple metamorphic buffer architectures, including bulk GaSb nucleation, AlAsSb superlattices, and graded GaAsSb and InAlSb ternary alloys, were employed to bridge the 7.8% mismatch gap from the GaAs substrates to the GaSb-based epilayers at 6.1 ᅤ lattice-constant and beyond. Reaching ~6.2 ᅤ extends the nBn cutoff wavelength from 4.2 to <5 ᄉm, thus broadening the application space. The metamorphic nBn epiwafers demonstrated unique surface morphologies and crystal properties, as revealed by AFM, high-resolution XRD, and cross-section TEM. GaSb nucleation resulted in island-like surface morphology while graded ternary buffers resulted in cross-hatched surface morphology, with low root-mean-square roughness values of ~10 ᅤ obtained. XRD determined dislocation densities as low as 2 ᅲ 107 cm-2. Device mesas were fabricated and dark currents of 1 ᅲ 10-6 A/cm2 at 150K were measured. This work demonstrates a promising path to satisfy the increasing demand for even larger area focal plane array detectors in a commercial production environment.
  • Inducing a junction in n-type InxGa(1-x)N

    Type Journal Article
    Author Joshua J. Williams
    Author Todd L. Williamson
    Author Mark A. Hoffbauer
    Author Alec M. Fischer
    Author Stephen M. Goodnick
    Author Nikolai N. Faleev
    Author Kunal Ghosh
    Author Christiana B. Honsberg
    Volume 31
    Issue 3
    Pages 03C127-03C127-6
    Publication Journal of Vacuum Science Technology B: Microelectronics and Nanometer Structures
    ISSN 1071-1023
    Date 2013
    DOI 10.1116/1.4797489
    Library Catalog IEEE Xplore
    Abstract The pseudo-binary alloy of indium(x)gallium(1-x)nitride has a compositionally dependent bandgap ranging from 0.65 to 3.42 eV, making it desirable for light emitting diodes and solar cell devices. Through modeling and film growth, the authors investigate the use of InxGa1-xN as an active layer in an induced junction. In an induced junction, electrostatics are used to create strong band bending at the surface of a doped material and invert the bands. The authors report modeling results, as well as preliminary film quality experiments for an induced junction in InGaN by space charge effects of neighboring materials, piezoelectric effects, and spontaneous polarization.
  • Nanoscale Photovoltaics and the Terawatt Challenge

    Type Book Section
    Author Stephen M. Goodnick
    Author Nikolai Faleev
    Author Christiana Honsberg
    Editor Anatoli Korkin
    Editor David J. Lockwood
    URL http://link.springer.com/chapter/10.1007/978-1-4614-5016-0_3
    Rights ᄅ2013 Springer Science+Business Media New York
    Series Nanostructure Science and Technology
    Publisher Springer New York
    Pages 77-116
    ISBN 978-1-4614-5015-3, 978-1-4614-5016-0
    Date 2013/01/01
    Accessed Saturday, September 21, 2013 10:48:14 PM
    Library Catalog link.springer.com
    Language en
    Abstract Achieving a sustainable energy system providing terawatts (TWs) of electricity is one of the defining challenges of the coming decades. Photovoltaic technology provides the most likely path to realizing TW scale conversion of solar energy in the future and has been on a nearly 40% growth curve over the past two decades. In order to maintain this rapid level of growth, innovations in cell design and conversion efficiency are needed that are compatible with existing technology and can lead to improved performance and lower cost. Nanotechnology offers a number of advantages to realizing such innovation, by providing new materials and the implementation of advanced concepts that circumvent the current physical limits on efficiency. This chapter reviews several of the promising applications of nanotechnology to photovoltaic technologies and their prospects for the future.
    Book Title Nanoscale Applications for Information and Energy Systems
  • Role of hot carriers in the interfacial transport in amorphous silicon/crystalline silicon heterostructure solar cells

    Type Journal Article
    Author Kunal Ghosh
    Author Stuart Bowden
    Author Clarence Tracy
    URL http://doi.wiley.com/10.1002/pssa.201228277
    Volume 210
    Issue 2
    Pages 413-419
    Publication physica status solidi (a)
    ISSN 18626300
    Date 02/2013
    DOI 10.1002/pssa.201228277
    Accessed Monday, March 11, 2013 2:05:07 PM
    Library Catalog CrossRef
  • Structural investigations of SiGe epitaxial layers grown by molecular beam epitaxy on Si(0 0 1) and Ge(0 0 1) substrates: IラHigh-resolution x-ray diffraction and x-ray topography

    Type Journal Article
    Author N. Faleev
    Author N. Sustersic
    Author N. Bhargava
    Author J. Kolodzey
    Author A.Yu. Kazimirov
    Author C. Honsberg
    URL http://www.sciencedirect.com/science/article/pii/S0022024812008780
    Volume 365
    Pages 44-53
    Publication Journal of Crystal Growth
    ISSN 0022-0248
    Date February 15, 2013
    Journal Abbr Journal of Crystal Growth
    DOI 10.1016/j.jcrysgro.2012.12.002
    Accessed Saturday, September 21, 2013 10:45:13 PM
    Library Catalog ScienceDirect
    Abstract Epitaxial structures of different SiGe composition grown by molecular beam epitaxy on Si(0 0 1) and Ge(0 0 1) substrates have been studied by high-resolution x-ray diffraction and x-ray topography to establish correlations between epitaxial growth conditions and crystal perfection. It was confirmed that epitaxy under initial elastic stress inevitably led to the creation of extended crystal defects. The type of defects created and their density and spatial distribution, strongly depended on the value and sign of the initial elastic strain, the elastic constants of solid solutions, the temperature of deposition and growth rate, and the thickness of the epitaxial layers. All of the investigated structures were classified by their crystal perfection, using x-ray diffraction with the volume density of dislocation loops as a parameter. It was found that the accommodation and relaxation of initial elastic stress and creation of crystal defects were multistage モchainヤ processes, necessary to stabilize the crystal structure at a level corresponding to the particular growth conditions. Types, density and spatial distribution of crystal defects, related to each stage of defect creation and matched to structural features, as revealed by high resolution x-ray diffraction, were considered for explanation.
    Short Title Structural investigations of SiGe epitaxial layers grown by molecular beam epitaxy on Si(0 0 1) and Ge(0 0 1) substrates
  • Structural investigations of SiGe epitaxial layers grown by molecular beam epitaxy on Si(001) and Ge(001) substrates: IIラTransmission electron microscopy and atomic force microscopy

    Type Journal Article
    Author N. Faleev
    Author N. Sustersic
    Author N. Bhargava
    Author J. Kolodzey
    Author S. Magonov
    Author D.J. Smith
    Author C. Honsberg
    URL http://www.sciencedirect.com/science/article/pii/S0022024812008883
    Volume 365
    Pages 35-43
    Publication Journal of Crystal Growth
    ISSN 0022-0248
    Date February 15, 2013
    Journal Abbr Journal of Crystal Growth
    DOI 10.1016/j.jcrysgro.2012.11.067
    Accessed Saturday, September 21, 2013 10:45:00 PM
    Library Catalog ScienceDirect
    Abstract The creation of crystal defects during epitaxial growth, and their proper characterization and classification are among the most critical issues impacting epitaxial structures and device applications. Epitaxial layers of different SiGe composition grown by molecular beam epitaxy (MBE) on Si(001) and Ge(001) substrates have been studied by Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM). The volumetric and surface structure of crystal defects revealed and characterized by TEM and AFM provided a detailed understanding of the major processes associated with defect creation and structural transformation during epitaxial growth. The main structural features were identified and correlations were made between crystal perfection and epitaxial growth conditions as also revealed by X-ray diffraction.
    Short Title Structural investigations of SiGe epitaxial layers grown by molecular beam epitaxy on Si(001) and Ge(001) substrates
  • Quantitative analysis of the quantum dot superlattice by high-resolution x-ray diffraction

    Type Journal Article
    Author N. N. Faleev
    Author C. Honsberg
    Author V. I. Punegov
    URL http://jap.aip.org/resource/1/japiau/v113/i16/p163506_s1?isAuthorized=no
    Volume 113
    Issue 16
    Pages 163506
    Publication Journal of Applied Physics
    ISSN 00218979
    Date 2013-04-25
    DOI doi:10.1063/1.4802662
    Accessed Saturday, September 21, 2013 10:42:39 PM
    Library Catalog AIP
    Abstract A new high-resolution x-ray diffraction approach for quantitative analysis of superlattice structures (SLs) with self-assembled quantum dots (QDs) was developed. For numerical simulations of the 2D angular distribution of diffracted x-ray radiation, both the coherent and diffuse scattering components have been calculated. Direct comparison of simulated patterns and experimental results revealed good agreement of the calculated intensity distribution with experimental reciprocal space maps for the superlattice GaAs(001)-AlGaAs-{InAs QDs-GaAs}SL with 20 periods of quantum dots. The simulation procedure allows one to obtain data about the shape, average size, elastic strains around the QDs, average density of the QDs, the presence of short- or long-range order in the arrangement of QDs in the semiconducting matrix, the vertical and lateral correlation lengths of the ensemble of quantum dots, and the parameters of the intermediate GaAs and AlGaAs layers.
  • Solar cells without p-n junctions

    Type Journal Article
    Author Stuart Bowden
    Author Kunal Ghosh
    Author Christiana Honsberg
    URL http://www.spie.org/x102605.xml
    Publication SPIE Newsroom
    ISSN 18182259
    Date 2013-07-30
    DOI 10.1117/2.1201307.004681
    Accessed Saturday, September 21, 2013 10:39:37 PM
    Library Catalog CrossRef
  • >750 mV open circuit voltage measured on 50 ?m thick silicon heterojunction solar cell

    Type Journal Article
    Author Stanislau Y. Herasimenka
    Author William J. Dauksher
    Author Stuart G. Bowden
    URL http://apl.aip.org/resource/1/applab/v103/i5/p053511_s1?isAuthorized=no
    Volume 103
    Issue 5
    Pages 053511-053511-4
    Publication Applied Physics Letters
    ISSN 00036951
    Date 2013-08-01
    DOI doi:10.1063/1.4817723
    Accessed Sunday, August 11, 2013 9:57:33 AM
    Library Catalog AIP
    Abstract This paper presents experimental evidence that silicon solar cells can achieve >750 mV open circuit voltage at 1 Sun illumination providing very good surface passivation is present. 753 mV local open circuit voltage was measured on a 50 ?m thick non-metalized silicon heterojunction solar cell. The paper also considers a recombination model at open circuit based on the recent Auger and radiative recombination parameterization and the measured surface saturation current density. The loss mechanisms at open circuit and several practical pathways to achieve >760 mV open circuit voltage in silicon heterojunction solar cells are discussed.