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ABSTRACT: Given an unknown multicomponent alloy, and a set of standard compounds or alloys of known composition, can one improve upon popular standards-based methods for energy dispersive X-ray (EDX) spectrometry to quantify the elemental composition of the unknown specimen? A method is presented here for determining elemental composition of alloys using transmission electron microscopy-based EDX with appropriate standards. The method begins with a discrete set of related reference standards of known composition, applies multivariate statistical analysis to those spectra, and evaluates the compositions with a linear matrix algebra method to relate the spectra to elemental composition. By using associated standards, only limited assumptions about the physical origins of the EDX spectra are needed. Spectral absorption corrections can be performed by providing an estimate of the foil thickness of one or more reference standards. The technique was applied to III-V multicomponent alloy thin films: composition and foil thickness were determined for various III-V alloys. The results were then validated by comparing with X-ray diffraction and photoluminescence analysis, demonstrating accuracy of approximately 1% in atomic fraction.
Microscopy and Microanalysis 01/2013; · 3.01 Impact Factor
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Progress in Photovoltaics Research and Applications 08/2009; 17(8):587 - 593. · 5.79 Impact Factor
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J.F. Geisz,
Sarah R. Kurtz, M.W. Wanlass,
J.S. Ward,
A. Duda,
D.J. Friedman,
J.M. Olson,
W.E. McMahon,
T.E. Moriarty,
J.T. Kiehl,
M.J. Romero,
A.G. Norman,
K.M. Jones
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ABSTRACT: We demonstrate high efficiency performance in two ultra-thin, Ge-free III–V semiconductor triple-junction solar cell device designs grown in an inverted configuration. Low-stress metamorphic junctions were engineered to achieve excellent photovoltaic performance with less than 3 × 10<sup>6</sup> cm<sup>−2</sup> threading dislocations. The first design with band gaps of 1.83/1.40/1.00 eV, containing a single metamorphic junction, achieved 33.8% and 39.2% efficiencies under the standard one-sun global spectrum and concentrated direct spectrum at 131 suns, respectively. The second design with band gaps of 1.83/1.34/0.89 eV, containing two metamorphic junctions achieved 33.2% and 40.1% efficiencies under the standard one-sun global spectrum and concentrated direct spectrum at 143 suns, respectively.
Photovoltaic Specialists Conference, 2008. PVSC '08. 33rd IEEE; 06/2008
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ABSTRACT: We discuss recent developments in III-V multijunction solar cells, focusing on adding a fourth junction to the Ga<sub>0.5</sub>In<sub>0.5 </sub>P/GaAs/Ga<sub>0.75</sub>In<sub>0.25</sub>As inverted three-junction cell. This cell, grown inverted on GaAs so that the lattice-mismatched Ga<sub>0.75</sub>In<sub>0.25</sub>As third junction is the last one grown, has demonstrated 38% efficiency, and 40% is likely in the near future. To achieve still further gains, a lower-bandgap Ga<sub>x</sub>In<sub>1-x</sub>As fourth junction could be added to the three-junction structure for a four-junction cell whose efficiency could exceed 45% under concentration. Here, we present the initial development of the Ga<sub>x</sub>In<sub>1-x</sub>As fourth junction. Junctions of various bandgaps ranging from 0.88 to 0.73 eV were grown, in order to study the effect of the different amounts of lattice mismatch. At a bandgap of 0.88 eV, junctions were obtained with very encouraging ~80% quantum efficiency, 57% fill factor, and 0.36 eV open-circuit voltage. The device performance degrades with decreasing bandgap (i.e., increasing lattice mismatch). We model the four-junction device efficiency vs. fourth junction bandgap to show that an 0.7-eV fourth-junction bandgap, while optimal if it could be achieved in practice, is not necessary; an 0.9-eV bandgap would still permit significant gains in multijunction cell efficiency while being easier to achieve than the lower-bandgap junction
Photovoltaic Energy Conversion, Conference Record of the 2006 IEEE 4th World Conference on; 06/2006
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M.W. Wanlass,
S.P. Ahrenkiel,
R.K. Ahrenkiel,
D.S. Albin,
J.J. Carapella,
A. Duda,
J.F. Geisz,
S. Kurtz,
T. Moriarty,
R.J. Wehrer,
B. Wernsman
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ABSTRACT: We discuss lattice-mismatched (LMM) approaches utilizing compositionally step-graded layers and buffer layers that yield III-V photovoltaic devices with performance parameters equaling those of similar lattice-matched (LM) devices. Our progress in developing high-performance, LMM, InP-based GaInAs/InAsP materials and devices for thermophotovoltaic (TPV) energy conversion is highlighted. A novel, monolithic, multi-bandgap, tandem device for solar PV (SPV) conversion involving LMM materials is also presented along with promising preliminary performance results.
Photovoltaic Specialists Conference, 2005. Conference Record of the Thirty-first IEEE; 02/2005
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ABSTRACT: Salient advances in the development of thermophotovoltaic (TPV) energy converters based on low‐bandgap, InP‐based, GaInAs/InAsP heterostructures are presented and discussed. InP‐based materials are well‐suited and advantageous for TPV converter applications. Substantial improvements in the quality of lattice‐mismatched (LMM) heterostructures have been realized through an enhanced understanding of the relaxation behavior, and associated microstructure, of InAsP compositionally graded layers and GaInAs/InAsP interfaces. Double‐heterostructure, GaInAs/InAsP test structures with bandgaps as low as 0.5 eV (1.6% lattice mismatch) have been demonstrated with exceptional low‐injection, minority‐carrier lifetimes (several μs) and large estimated diffusion lengths — comparable to those for lattice‐matched materials. The advances in material quality have contributed to a number of notable TPV device achievements. A record in‐cavity efficiency of 23.6% was reported for a 0.6‐eV, GaInAs/InAsP monolithic interconnected module. Additionally, 0.52‐eV GaInAs/InAsP TPV converters were demonstrated with near‐unity internal quantum efficiencies and reverse‐saturation current densities nearly equaling the best reported for lattice‐matched, 0.52‐eV GaInAsSb/GaSb devices. Furthermore, InP‐based, 0.74/0.63‐eV, monolithic, series‐connected, tandem TPV converters are also under development and show promising performance; an in‐cavity efficiency of 11% has been reported for preliminary devices. © 2004 American Institute of Physics
AIP Conference Proceedings. 11/2004; 738(1):427-435.
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ABSTRACT: Low-bandgap, lattice-mismatched GaxIn1−xAs (GaInAs) grown using InAsyP1−y (InAsP) compositional-step grades on InP is a primary choice for lightabsorbing, active layers in high-efficiency thermophotovoltaic
(TPV) devices. The GaInAs/InAsP double heterostructures (DHs) show exceptional minority carrier lifetimes of up to several
microseconds. We have performed a characterization survey of 0.4–0.6-eV GaInAs/InAsP DHs using a variety of techniques, including
transmission electron microscopy (TEM). Dislocations are rarely observed to thread into the GaInAs active layers from the
InAsP buffer layers that terminate the graded regions. Nearly complete strain relaxation occurs in buried regions of the InAsP
grades. The buffer-layer strain prior to deposition of the active layer is virtually independent of the net misfit. Foreknowledge
of this buffer-layer strain is essential to correctly lattice match the buffer to the GaInAs active layer.
Journal of Electronic Materials 02/2004; 33(3):185-193. · 1.47 Impact Factor
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ABSTRACT: Hydrogen-induced exfoliation combined with wafer bonding has been used to transfer ∼600- nm - thick films of (100) InP to Si substrates. Cross-section transmission electron microscopy (TEM) shows a transferred crystalline InP layer with no observable defects in the region near the bonded interface and an intimately bonded interface. InP and Si are covalently bonded as inferred by the fact that InP/Si pairs survived both TEM preparation and thermal cycles up to 620 ° C necessary for metalorganic chemical vapor deposition growth. The InP transferred layers were used as epitaxial templates for the growth of InP/In <sub>0.53</sub> Ga <sub>0.47</sub> As/InP double heterostructures. Photoluminescence measurements of the In <sub>0.53</sub> Ga <sub>0.47</sub> As layer show that it is optically active and under tensile strain, due to differences in the thermal expansion between InP and Si. These are promising results in terms of a future integration of Si electronics with optical devices based on InP-lattice-matched materials. © 2003 American Institute of Physics.
Applied Physics Letters 01/2004; · 3.84 Impact Factor
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ABSTRACT: Thermophotovoltaic (TPV) tandem converter technology is being explored in an effort to improve both the efficiency and power density of TPV systems. Inverted, tandem structures incorporate epitaxially grown 0.74-eV lattice-matched Ga<sub>0.47</sub>In<sub>0.53</sub>As and 0.55-eV lattice-mismatched Ga<sub>0.28</sub>In<sub>0.72</sub>As diodes. Additionally, a strategy has been developed to allow voltage matching between these two subcells. Performance modeling calculations show that, under typical operating conditions, the 0.74/0.55-eV tandem converter should outperform a 0.5-eV single junction converter by 15% on an efficiency basis and by 15% on a power-density basis. This paper will present details regarding the design, growth, fabrication, and electrical, optical, and structural characterization of voltage-matched tandem TPV devices.
Photovoltaic Specialists Conference, 2002. Conference Record of the Twenty-Ninth IEEE; 06/2002
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ABSTRACT: A four-junction cell design consisting of InGaAs, InGaAsP, GaAs, and Ga<sub>0.5</sub>In<sub>0.5</sub>P subcells could reach 1×AM0 efficiencies of 35.4%, but relies on the integration of non-lattice-matched materials. Wafer bonding and layer transfer processes show promise in the fabrication of InP/Si epitaxial templates for growth of the bottom InGaAs and InGaAsP subcells on a Si support substrate. Subsequent wafer bonding and layer transfer of a thin Ge layer onto the lower subcell stack can serve as an epitaxial template for GaAs and Ga<sub>0.5</sub>In<sub>0.5</sub>P subcells. Present results indicate that optically active III/V compound semiconductors can be grown on both Ge/Si and InP/Si heterostructures. Current voltage electrical characterization of the interfaces of these structures indicates that both InP/Si and Ge/Si interfaces have specific resistances lower than 0.1 Ω cm<sup>2</sup> for heavily doped wafer bonded interfaces, enabling back surface power extraction from the finished cell structure.
Photovoltaic Specialists Conference, 2002. Conference Record of the Twenty-Ninth IEEE; 06/2002
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ABSTRACT: We measured the recombination lifetime of degenerate n- In <sub>x</sub> Ga <sub>1-x</sub> As for three different compositions that correspond to x=0.53, 0.66, and 0.78 (band gaps of 0.74, 0.60, and 0.50 eV, respectively) over the doping range of 3×10<sup>18</sup>–5×10<sup>19</sup> carriers/cm <sup> 3 </sup>. The Auger recombination rate increases slowly with decreasing band gap, and it matches the behavior predicted for phonon-assisted recombination. © 2001 American Institute of Physics.
Applied Physics Letters 12/2001; · 3.84 Impact Factor
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ABSTRACT: High-quality, thin-film, lattice-matched (LM) InAs <sub>y</sub> P <sub>1-y</sub>/ In <sub>x</sub> Ga <sub>1-x</sub> As double heterostructures (DHs) have been grown lattice mismatched on InP substrates using atmospheric-pressure metalorganic vapor-phase epitaxy. The low-band gap In <sub>x</sub> Ga <sub>1-x</sub> As layers in the DHs have room-temperature band gaps that range from 0.47 to 0.6 eV. Both the optical and electronic properties of these films have been extensively measured. The band-to-band photoluminescence is quite strong and comparable to that found for LM InP/In <sub> 0.53 </sub> Ga <sub> 0.47 </sub> As DHs grown on InP. Recombination lifetime measurements of undoped DH structures show minority-carrier lifetimes in excess of 1 μs in most cases. The earlier properties make the band gap-flexible InAs <sub>y</sub> P <sub>1-y</sub>/ In <sub>x</sub> Ga <sub>1-x</sub> As DH system attractive for applications in high-performance, infrared-sensitive devices. © 2001 American Institute of Physics.
Applied Physics Letters 03/2001; · 3.84 Impact Factor
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ABSTRACT: Influences of CuPtB atomic ordering on transient photoconductivity in epitaxial Ga0.47In0.53As films grown by metal-organic chemical vapor deposition are examined. Low-injection lifetimes of several ms are measured in double-variant ordered samples at 77 K; these lifetimes decrease rapidly with temperatures above 180 K, giving a thermal activation energy for recombination of 0.19 eV. Single-variant ordered samples exhibit typical lifetimes of 30–60 μs, with no noticeable temperature dependence up to 300 K. Charge separation in double-variant samples may be driven by a type-II band alignment between ordered and disordered regions, or by an alternating internal electrical polarization between ordered variants. Recombination in both double- and single-variant samples may be influenced by inhibited transport across antiphase boundaries. © 1999 American Institute of Physics.
Applied Physics Letters 06/1999; 74(23):3534-3536. · 3.84 Impact Factor
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ABSTRACT: Recent progress in the development of high-performance, 0.6-eV Ga0.32In0.68As/InAs0.32P0.68 thermophotovoltaic (TPV) converters and monolithically interconnected modules (MIMs) is described. The converter structure design is based on using a lattice-matched InAs0.32P0.68/Ga0.32In0.68As/InAs0.32P0.68 double-heterostructure (DH) device, which is grown lattice-mismatched on an InP substrate, with an intervening compositionally step-graded region of InAsyP1−y. The Ga0.32In0.68As alloy has a room-temperature band gap of ∼0.6 eV and contains a p/n junction. The InAs0.32P0.68 layers have a room-temperature band gap of ∼0.96 eV and serve as passivation/confinement layers for the Ga0.32In0.68As p/n junction. InAsyP1−y step grades have yielded DH converters with superior electronic quality and performance characteristics. Details of the microstructure of the converters are presented. Converters prepared for this work were grown by atmospheric-pressure metalorganic vapor-phase epitaxy (APMOVPE) and were processed using a combination of photolithography, wet-chemical etching, and conventional metal and insulator deposition techniques. Excellent performance characteristics have been demonstrated for the 0.6-eV TPV converters. Additionally, the implementation of MIM technology in these converters has been highly successful. © 1999 American Institute of Physics.
AIP Conference Proceedings. 03/1999; 460(1):132-141.
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ABSTRACT: Thermophotovoltaic (TPV) systems have recently rekindled a high level of interest for a number of applications. In order to meet the requirement of low-temperature (∼1000 °C) TPV systems, 0.6-eV Ga0.32In0.68As/InAs0.32P0.68 TPV monolithically interconnected modules (MIMs) have been developed at the National Renewable energy Laboratory (NREL) [1]. The successful fabrication of Ga0.32In0.68As/InAs0.32P0.68 MIMs depends on developing and optimizing of several key processes. Some results regarding the chemical vapor deposition (CVD)-SiO2 insulating layer, selective chemical etch via sidewall profiles, double-layer antireflection coatings, and metallization via interconnects have previously been given elsewhere [2]. In this paper, we report on the study of contacts and back-surface reflectors. In the first part of this paper, Ti/Pd/Ag and Cr/Pd/Ag contact to n-InAs0.32P0.68 and p-Ga0.32In0.68As are investigated. The transfer length method (TLM) was used for measuring of specific contact resistance Rc. The dependence of Rc on different doping levels and different pre-treatment of the two semiconductors will be reported. Also, the adhesion and the thermal stability of Ti/Pd/Ag and Cr/Pd/Ag contacts to n-InAs0.32P0.68 and p-Ga0.32In0.68As will be presented. In the second part of this paper, we discuss an optimum back-surface reflector (BSR) that has been developed for 0.6-eV Ga0.32In0.68As/InAs0.32P0.68 TPV MIM devices. The optimum BSR consists of three layers: ∼1300 Å MgF2 (or ∼1300 Å CVD SiO2) dielectric layer, ∼25 Å Ti adhesion layer, and ∼1500 Å Au reflection layer. This optimum BSR has high reflectance, good adhesion, and excellent thermal stability. © 1999 American Institute of Physics.
AIP Conference Proceedings. 03/1999; 460(1):517-524.
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ABSTRACT: Recent progress in the development of high-performance, 0.6-eV Ga{sub 0.32}In{sub 0.68}As/InAs{sub 0.32}P{sub 0.68} thermophotovoltaic (TPV) converters and monolithically interconnected modules (MIMs) is described. The converter structure design is based on using a lattice-matched InAs{sub 0.32}P{sub 0.68}/Ga{sub 0.32}In{sub 0.68}As/InAs{sub 0.32}P{sub 0.68} double-heterostructure (DH) device, which is grown lattice-mismatched on an InP substrate, with an intervening compositionally step-graded region of InAs{sub y}P{sub 1{minus}y}. The Ga{sub 0.32}In{sub 0.68}As alloy has a room-temperature band gap of {approximately}0.6 eV and contains a p/n junction. The InAs{sub 0.32}P{sub 0.68} layers have a room-temperature band gap of {approximately}0.96 eV and serve as passivation/confinement layers for the Ga{sub 0.32}In{sub 0.68}As p/n junction. InAs{sub y}P{sub 1{minus}y} step grades have yielded DH converters with superior electronic quality and performance characteristics. Details of the microstructure of the converters are presented. Converters prepared for this work were grown by atmospheric-pressure metalorganic vapor-phase epitaxy (APMOVPE) and were processed using a combination of photolithography, wet-chemical etching, and conventional metal and insulator deposition techniques. Excellent performance characteristics have been demonstrated for the 0.6-eV TPV converters. Additionally, the implementation of MIM technology in these converters has been highly successful. {copyright} {ital 1999 American Institute of Physics.}
AIP Conference Proceedings 02/1999; 460(1).
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ABSTRACT: The design for the fabrication of Monolithic Interconnected Modules (MIMs) for thermophotovoltaic (TPV) power conversion described in this paper utilizes a novel, interdigitated contacting scheme that increases the flexibility in the size of the component cells and hence the output current and voltage of the module. This flexibility is gained at the expense of only minimally increased grid obscuration. Because the design uses the grid fingers of the component cells as the interconnect structure, the area of the device used for this purpose becomes negligible. In this paper the authors report on the specifics of the design as well as issues related to the fabrication of the modules. Preliminary performance data for representative modules also are offered.
05/1997;
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K. Emery,
J. Burdick,
Y. Caiyem,
D. Dunlavy,
H. Field,
B. Kroposki,
T. Moriarty,
L. Ottoson,
S. Rummel,
T. Strand, M.W. Wanlass
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ABSTRACT: Photovoltaic (PV) cells and modules are often rated in terms of a
set of standard reporting conditions defined by a temperature, spectral
irradiance and total irradiance. Because PV devices operate over a wide
range of temperatures and irradiances, the temperature and
irradiance-related behavior must be known. This paper surveys the
temperature dependence of crystalline and thin-film, state-of-the-art,
research-size cells, modules and systems measured by a variety of
methods. The various error sources and measurement methods that
contribute to cause differences in the temperature coefficient for a
given cell or module measured with various methods are discussed
Photovoltaic Specialists Conference, 1996., Conference Record of the Twenty Fifth IEEE; 06/1996
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ABSTRACT: Thermophotovoltaic (TPV) generation of electricity is attracting
attention because of advances in materials and devices and because of a
widening appreciation of the large number of applications that may be
addressed using TPV-based generators. The attractions include the wide
range of fuel sources and the potentially high power density outputs.
The two main approaches to TPV generators are: (1) broad-band radiators,
coupled with converters with bandgaps in the range 0.4-0.7 eV; and (2)
narrow-band emitters coupled with lower-cost silicon converters. The key
issues in realizing a viable TPV system are the durability, efficiency
and properties of the radiant emitter; the recuperation of sub-bandgap
photons; the optimization of the converter performance; and the
recuperation of waste heat
Photovoltaic Specialists Conference, 1996., Conference Record of the Twenty Fifth IEEE; 06/1996
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ABSTRACT: Preliminary research into the development of single-junction Ga
<sub>x</sub>In<sub>1-x</sub>As thermophotovoltaic (TPV) power converters
is reviewed. The devices structures are grown epitaxially on
single-crystal InP substrates. Converter band gaps of 0.50 -0.74 eV have
been considered in accordance with modeling calculations. A 1-sun, AMO
efficiency of 12.8% is reported for a lattice-matched, 0.74-eV
converter. Converters with lower band gaps are fabricated using
lattice-mismatched, compositionally graded structures. Functional TPV
converters with good performance characteristics have been demonstrated
for band gaps as low as 0.5 eV
Photovoltaic Energy Conversion, 1994., Conference Record of the Twenty Fourth. IEEE Photovoltaic Specialists Conference - 1994, 1994 IEEE First World Conference on; 01/1995
