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RF/microwave non-destructive measurements of electrical properties of semiconductor wafers for thermophotovoltaic applications

Description: A radio-frequency/microwave measurement system has been designed for non-contacting determination of sheet resistance and excess carrier lifetime of low-bandgap materials and junctions, specifically GaSb-based alloys for thermophotovoltaic (TPV) applications. The design incorporates RF circuitry in the 100--500 MHz frequency range and utilizes a Q-switched YAG laser at 1.32 microns to photo-generate electron-hole pairs and conductivity modulate the material and/or junction under test. Supplementary measurements with a GaAs pulsed diode laser at 904 nm provides a faster transient response with near-surface photogeneration. Initial measurements on GaSb substrates, Zn-diffused materials and epitaxially grown layers are presented and discussed.
Date: May 1, 1997
Creator: Saroop, S.; Borrego, J.M. & Gutmann, R.J.
Partner: UNT Libraries Government Documents Department

TPV energy conversion: A review of material and cell related issues

Description: This paper presents an overview of thermophotovoltaic (TPV) energy conversion using low band gap semiconductor photovoltaic cells. Physics of PN junctions related to TPV cells is described and the factors that affect overall cell efficiencies are outlined. Current status of bulk and epitaxial growth of TPV materials and cell fabrication issues are also described.
Date: August 1, 1996
Creator: Bhat, I.B.; Borrego, J.M.; Gutmann, R.J. & Ostrogorsky, A.G.
Partner: UNT Libraries Government Documents Department

Modeling of InGaSb thermophotovoltaic cells and materials

Description: A closed form computer program has been developed for the simulation and optimization of In{sub x}Ga{sub 1{minus}x}Sb thermophotovoltaic cells operating at room temperature. The program includes material parameter models of the energy bandgap, optical absorption constant, electron and hole mobility, intrinsic carrier concentration and index of refraction for any composition of GaInSb alloys.
Date: May 1, 1997
Creator: Zierak, M.; Borrego, J.M.; Bhat, I.; Gutmann, R.J. & Charache, G.
Partner: UNT Libraries Government Documents Department

Measurement of the Auger Recombination Rate in p-type 0.54-eV GaInAsSb by Time-Resolved Photoluminescence

Description: Auger recombination in p-type GaSb, InAs and their alloys is enhanced due to the proximity of the bandgap energy and the energy separation to the spin split-off valence band. This can affect the device performance even at moderate doping concentration. They report electron lifetime measurements in a p-type 0.54-eV GaInAsSb alloy, commonly used in a variety of infrared devices. They have studied a series of double-capped heterostructures with varied thicknesses and doping levels, grown by organometallic vapor phase epitaxy on GaSb substrates. The Auger coefficient value of 2.3 x 10{sup -28} cm{sup 6}/s is determined by analyzing the photoluminescence decay constants with a systematic separation of different recombination mechanisms.
Date: June 13, 2003
Creator: Anikeev, S.; Donetsky, D.; Belenky, G.; Luryi, S.; Wang, C.A.; Borrego, J.M. et al.
Partner: UNT Libraries Government Documents Department

Thermodynamic analysis of Thermophotovoltaic Efficiency and Power Density Tradeoffs

Description: This report presents an assessment of the efficiency and power density limitations of thermophotovoltaic (TPV) energy conversion systems for both ideal (radiative-limited) and practical (defect-limited) systems. Thermodynamics is integrated into the unique process physics of TPV conversion, and used to define the intrinsic tradeoff between power density and efficiency. The results of the analysis reveal that the selection of diode bandgap sets a limit on achievable efficiency well below the traditional Carnot level. In addition it is shown that filter performance dominates diode performance in any practical TPV system and determines the optimum bandgap for a given radiator temperature. It is demonstrated that for a given radiator temperature, lower bandgap diodes enable both higher efficiency and power density when spectral control limitations are included. The goal of this work is to provide a better understanding of the basic system limitations that will enable successful long-term development of TPV energy conversion technology.
Date: February 22, 2000
Creator: Baldasara, P.F.; Reynolds, J.E.; Charache, G.W.; DePoy, D.M.; Ballinger, C.T.; Donovan, T. et al.
Partner: UNT Libraries Government Documents Department

Recombination Parameters in InGaAsSb Epitaxial Layers for Thermophotovoltaic Applications

Description: Radio-frequency (RF) photoreflectance measurements and one-dimensional device simulations have been used to evaluate bulk recombination parameter and surface recombination velocity (SRV) in doubly-capped 0.55 eV, 2 x 10{sup 17} cm{sup -3} doped p-InGaAsSb epitaxial layers for thermophotovoltaic (TPV) applications. Bulk lifetimes of 90-100 ns and SRVs of 680 cm/s to 3200 cm/s (depending on the capping layer) are obtained, with higher doping and higher bandgap capping layers most effective in reducing SRV. RF photoreflectance measurements and one-dimensional device simulations are compatible with a radiative recombination coefficient (B) of 3 x 10{sup -11} cm{sup 3}/s and Auger coefficient (C) of 1 x 10{sup -28} cm{sup 6}/s.
Date: March 17, 2003
Creator: Kumar, R.J.; Gutmann, J.J.; Borrego, J.M.; Dutta, P.S.; Wang, C.A.; Martinelli, R.U. et al.
Partner: UNT Libraries Government Documents Department

RF photoreflectance characterization of binary and quasi-binary substrates and antimonide-based TPV devices

Description: Both starting substrates and complete TPV device structures have been characterized using a radio-frequency (RF) photoreflectance technique, in which a Nd-YAG pulsed laser is used to excite excess carriers, and the short-pulse response and photoconductivity decay are monitored with an inductively-coupled non-contacting RF probe. The initial exponential transient decay, indicative of bulk recombination and surface recombination mechanisms as demonstrated previously for doubly-capped sample structures, is approximately 30--40 ns for GaSb substrates, with the decay constant increasing with increasing optical excitation (similar to Shockley-Read-Hall (SRH) high injection behavior). In the InGaAsSb quasi-binary substrates two distinct decays are observed, an initial decay transient of 15--20 ns which is independent of optical intensity and a subsequent decay of 30--60 ns which decreases with increasing optical intensity. This latter dependence on optical intensity was observed with doubly-capped epitaxial layers and is indicative of radioactive recombination. Similar measurements on quaternary device structures indicate that both the pulse amplitude and initial decay are reduced significantly without a front-surface capping layer that reduces surface recombination velocity. With reduction of the front surface recombination velocity, initial decays of 20--25 ns were obtained under open-circuit conditions. These results indicate that the RF photoreflectance technique can be useful in characterizing and qualifying starting substrates and can be used to qualify epitaxial structures as well, particularly when doubly-capped standards are available for initial understanding of recombination processes in the material systems being investigated.
Date: October 1, 1998
Creator: Saroop, S.; Borrego, J.M.; Gutmann, R.J.; Dutta, P.S.; Ostrogorsky, A.G. & Charache, G.W.
Partner: UNT Libraries Government Documents Department

Antimonide based devices for thermophotovoltaic applications

Description: Thermophotovoltaic (TPV) devices have been fabricated using epitaxial ternary and quaternary layers grown on GaSb substrates. GaInSb ternary devices were grown by metalorganic vapor phase epitaxy (MOVPE) with buffer layers to accommodate the lattice mismatch, and GaInAsSb lattice-matched quaternaries were grown by MOVPE. Improved devices are obtained when optical absorption occurs in the p-layer due to the longer minority carrier diffusion length. Thick emitter p/n devices are limited by surface recombination, with highest quantum efficiency and lowest dark current being achieved with epitaxially grown surface passivation layers on lattice-matched MOVPE quaternaries. Thin emitter/thick base, n/p devices are very promising, but require improved shallow high-quality n-type ohmic contacts. Diffused junction devices using quasi-binary substrates offer the possibility of good performance and low manufacturing cost.
Date: December 1, 1998
Creator: Hitchcock, C.W.; Gutmann, R.J.; Borrego, J.M.; Bhat, I.B. & Charache, G.W.
Partner: UNT Libraries Government Documents Department

Recombination Parameters for Antimonide-Based Semiconductors using RF Photoreflection Techniques

Description: RF photoreflection measurements and PC-1D simulations have been used to evaluate bulk and surface recombination parameters in antimonide-based materials. PC-1D is used to simulate the photoconductivity response of antimonide-based substrates and doubly-capped epitaxial layers and also to determine how to extract the recombination parameters using experimental results. Excellent agreement has been obtained with a first-order model and test structure simulation when Shockley-Reed-Hall (SRH) recombination is the bulk recombination process. When radiative, Auger and surface recombination are included, the simulation results show good agreement with the model. RF photoreflection measurements and simulations using PC-1D are compatible with a radiative recombination coefficient (B) of approximately 5 x 10{sup -11} cm{sup 3}/s, Auger coefficient (C) {approx} 1.0 x 10{sup -28} cm{sup 6}/s and surface recombination velocity (SRV) {approx} 600 cm/s for 0.50-0.55 eV doubly-capped InGaAsSb material with GaSb capping layers using the experimentally determined active layer doping of 2 x 10{sup 17} cm{sup -3}. Photon recycling, neglected in the analysis and simulations presented, will affect the extracted recombination parameters to some extent.
Date: October 10, 2002
Creator: Kumar, R.J.; Borrego, J.M.; Dutta, P.S.; Gutmann, R.J.; Wang, C.A.; Martinelli, R.U. et al.
Partner: UNT Libraries Government Documents Department

Performance Limits of Low Bandgap Thermophotovoltaic Antimonide-Based Cells for Low Temperature Radiators

Description: This paper assesses the performance of antimonide-based thermophotovoltaic cells fabricated by different technologies. In particular, the paper compares the performance of lattice matched quaternary (GaInAsSb) cells epitaxially grown on GaSb substrates to the performance of ternary (GaInSb) and binary (GaSb) cells fabricated by Zn diffusion on bulk substrates. The focus of the paper is to delineate the key performance advantages of the highest performance-to-date of the quaternary cells to the performance of the alternative ternary and binary antimonide-based diffusion technology. The performance characteristics of the cells considered are obtained from PC-1D simulations using appropriate material parameters.
Date: August 29, 2000
Creator: Borrego, J.M.; Wang, C.A.; Dutta, P.S.; rajagopalan, G.; Bhat, I.B.; Gutmann, R.J. et al.
Partner: UNT Libraries Government Documents Department