A survey of materials options and technologies for GaSb-related thermophotovoltaic (TPV) cells is presented, followed by an overview of device design principles and issues. This device technology has been developed for thermal-to-electric generator systems with thermal emitter infrared sources operated in the 1000–1200 °C range. Significant results for the growth, material characterization and device performance of TPV cells based on InGaAsSb, InGaSb, AlGaAsSb and InAsSbP fabricated by LPE, MOCVD, MBE and diffusion methods are reviewed. For single-junction TPV cells, epitaxial heterostructures with a ~0.53 eV bandgap InGaAsSb base layer and wide-bandgap AlGaAsSb or GaSb window/cladding layers (all closely lattice matched to a GaSb substrate) represent the state of the art. As an alternative, a low-cost Zn-diffusion technology for fabrication of InGaAsSb p–n homojunction structures has been developed for producing the high efficiency TPV cells. External quantum yields as high as 90% at wavelengths (around 2000 nm wavelength), and response edges to about 2400 nm wavelength have been obtained with these TPV cells. Multijunction tandem TPV devices based on GaSb top cells and InGaAsSb bottom cells provide even higher performance. TPV cells based on InAsSbP, also reviewed here, have spectral responses in wavelengths in the 2.5–3.5 μm range, and thus provide a means for utilizing radiation from thermal emitters with lower temperatures.

https://iopscience.iop.org/article/10.1088/0268-1242/18/5/308/pdf

GaSb-related materials for TPV cells

GaSb thermophotovoltaic (TPV) cells are one of the reasons for the renewed interest in TPV technology. Today, they are the most suitable choice for modern TPV generators. This paper reviews the background and the status of the GaSb photovoltaic cell development. GaSb TPV cells are fabricated either by a zinc vapour diffusion technology or by epitaxial methods such as liquid phase epitaxy or metal-organic vapour phase epitaxy. Efficiencies of more than 30% under filtered blackbody spectra were reported.

https://iopscience.iop.org/article/10.1088/0268-1242/18/5/307/pdf

GaSb photovoltaic cells for applications in TPV generators

The vast majority of power generation in the United States today is produced through the same processes as it was in the late-1800s: heat is applied to water to generate steam, which turns a turbine, which turns a generator, generating electrical power. Researchers today are developing solid-state power generation processes that are more befitting the 21st-century. Thermophotovoltaic (TPV) cells directly convert radiated thermal energy into electrical power, through a process similar to how traditional photovoltaics work. These TPV generators, however, include additional system components that solar cells do not incorporate. These components, selective-emitters and filters, shape the way the radiated heat is transferred into the TPV cell for conversion and are critical for its efficiency. Here, we present a review of work performed to improve the components in these systems. These improvements will help enable TPV generators to be used with nearly any thermal source for both primary power generation and waste heat harvesting.

A Review of Advances in Thermophotovoltaics for Power Generation and Waste Heat Harvesting

Ternary semiconductor substrates with variable bandgaps and lattice constants are key enablers for next-generation advanced electronic, optoelectronic, and photovoltaic devices. This chapter presents a comprehensive review of the crystal growth challenges and methods to grow large-diameter, compositionally homogeneous, bulk ternary III–V semiconductors based on As, P, and Sb compounds such as GaInSb, GaInAs, InAsP, AlGaSb, etc. The Bridgman and gradient freezing techniques are the most successfully used methods for growing ternary crystals with a wide range of alloy compositions. Control of heat and mass transport during the growth of ternary compounds is crucial for achieving high-quality crystals. Melt mixing and melt replenishment methods are discussed. The scale-up issues for commercial viability of ternary substrates is also outlined.

Bulk Crystal Growth of Ternary III–V Semiconductors

This chapter gives an overview of thermophotovoltaic (TPV) energy conversion. First, an introduction of the TPV system is given followed by a historical introduction to TPV. After a description of all elements present in a typical TPV system, a detailed overview of the different TPV cell concepts is given. Subsequently, some examples are given of TPV systems built in the world followed by an estimation of the TPV market potential. The chapter is finalized by drawing some conclusions.

1.28 – Thermophotovoltaics

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 GaInSb bulk crystals, substrate preparation, diffused junction processes, cell fabrication and characterization, and, cell modeling. Ternary GaInSb 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 GaInSb 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 (GaInSb) and binary (GaSb) cells f...

GaSb and Ga1−xInxSb Thermophotovoltaic Cells using Diffused Junction Technology in Bulk Substrates

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.

/pdf/performance-limits-of-low-bandgap-thermophotovoltaic-25acl4m321.pdf

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

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.

/pdf/performance-limits-of-low-bandgap-thermophotovoltaic-me07gt4wnj.pdf

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

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.

/pdf/recombination-parameters-for-antimonide-based-semiconductors-4smssfliw6.pdf

R.J. Gutmann

Papers

GaSb and Ga1−xInxSb Thermophotovoltaic Cells using Diffused Junction Technology in Bulk Substrates

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

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

Recombination Parameters for Antimonide-Based Semiconductors using RF Photoreflection Techniques