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GaInAsSb/AlGaAsSb/GaSb epitaxial layers were wafer bonded to semi-insulating GaAs wafers for monolithic series interconnection of thermophotovoltaic (TPV) devices. SiOx/Ti/Au was used as a bonding layer to provide electrical isolation and to serve as an internal back-surface reflector (BSR). The minority-carrier lifetime in WB BSR structures is more than two times longer than that of control structures without a BSR. WB GaInAsSb/AlGaAsSb TPV cells were fabricated and monolithically interconnected in series. These cells exhibit nearly linear voltage building. At a short-circuit current density of 0.4 A/cm2, Voc of a single TPV cell is 0.2 V, compared to 0.37 and 1.8 V for 2- and 10-junction series-interconnected TPV cells, respectively. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

This work summarizes recent data on minority carrier lifetime in n- and p-type double heterostructures (DHs) of 0.5–0.6 eV GaInAsSb confined with GaSb and AlGaAsSb cap layers. Recombination times were measured by time-resolved photoluminescence (TRPL) and by optical frequency response (OFR) to sinusoidal excitation. It was shown that one of the mechanisms responsible for interface recombination in GaSb/GaInAsSb/GaSb DHs is thermionic emission of carriers over the heterobarrier. Considerable improvement of carrier confinement was obtained with 1 eV AlGaAsSb cap layers. Optimization of the epitaxial growth resulted in a recombination velocity at GaInAsSb/AlGaAsSb interface as low as 30 cm/s. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Thermophotovoltaic (TPV) diodes fabricated from 0.52eV lattice-matched InGaAsSb alloys are grown by Metal Organic Vapor Phase Epitaxy (MOVPE) on GaSb substrates. 4cm2 multi-chip diode modules with front-surface spectral filters were tested in a vacuum cavity and attained measured efficiency and power density of 19% and 0.58 W/cm2 respectively at operating at temperatures of Tradiator = 950 °C and Tdiode = 27 °C. Device modeling and minority carrier lifetime measurements of double heterostructure lifetime specimens indicate that diode conversion efficiency is limited predominantly by interface recombination and photon energy loss to the GaSb substrate and back ohmic contact. Recent improvements to the diode include lattice-matched p-type AlGaAsSb passivating layers with interface recombination velocities less than 100 cm/s and new processing techniques enabling thinned substrates and back surface reflectors. Modeling predictions of these improvements to the diode architecture indicate that conversion efficiencies from 27–30% and ∼0.85 W/cm2 could be attained under the above operating temperatures. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

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 (GalnAsSb) ceils epitaxially grown on GaSb substrates to the performance of ternary (GalnSb) 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-ID simulations using appropriate material parameters. [ABSTRACT FROM AUTHOR]

High-performance GalnAsSb/A1GaAsSb/GaSb thermophotovoltaic (TPV) devices with quantum efficiency and fill factor near theoretical limits and open-circuit voltage within about 15% of the limit are reported. This paper discusses detailed studies of GalnAsSb epitaxial growth, the microstructure, and minority carrier lifetime that have led to these results. For further improvements in TPV cell performance, device structures with either a distributed Bragg reflector or a back-surface reflector are described. [ABSTRACT FROM AUTHOR]

This paper presents results of experimental and theoretical research on antimonide- based thermophotovoltaic (TPV) materials and cells. The topics discussed include: growth of large diameter ternary GalnSb bulk crystals, substrate preparation, diffused junction processes, cell fabrication and characterization, and, cell modeling. Ternary GalnSb boules up to 2 inches in diameter have been grown using the vertical Bridgman technique with a novel self solute feeding technique. A single step diffusion process followed by precise etching of the diffused layer has been developed to obtain a diffusion profile appropriate for high efficiency, p-n junction GaSb and GalnSb thermophotovoltaic cells. The optimum junction depth to obtain the highest quantum efficiency and open circuit voltage has been identified based on diffusion lengths (or minority carrier lifetimes), carrier mobility and experimental diffused impurity profiles. Theoretical assessment of the performance of ternary (GalnSb) and binary (GaSh) cells fabricated by Zn diffusion in bulk substrates has been performed using PC-1D one-dimensional computer simulations. Several factors affecting the ceil performances such as the effects of emitter doping profile, emitter thickness and recombination mechanisms (Auger, radiative and Shocldey-Read-Hall), the advantages of surface passivation and the impact of dark current due to the metallic grid will be discussed. The conditions needed for diffused junction cells on ternary and binary substrates to achieve similar performance to the epitaxially grown lattice- matched quaternary cells are identified. [ABSTRACT FROM AUTHOR]

This paper discusses recent efforts to realize GalnAsSb/GaSb TPV cells with an internal back-surface reflector (BSR). The cells are fabricated by wafer-bonding GalnAsSb/GaSb device layers to GaAs substrates with a dielectric/Au reflector, removing the GaSb substrate, and subsequently processing the layers using standard photolithographic techniques. The internal BSR enhances optical absorption within the device, while the dielectric layer provides electrical isolation. This approach is compatible with monolithic integration of series-connected TPV cells and can mitigate the requirements of filters used for front-surface spectral control. [ABSTRACT FROM AUTHOR]