GaSb cells are commonly fabricated using Zn diffusion into n-GaSb, and in this paper they have been designed inversely using Te diffusion into unintentionally p-doped GaSb. Numerical simulation is used to analyze the cell performance. We found that a GaSb cell with n-type emitters showed a significantly higher output power density compared with that of the cell with p-type emitters under 1500 K-blackbody radiation. The performance improvement is owing to the good matching of the diffusion length of minority carriers with the depth of their moving regions. Several parameters that affect the cell performance were analyzed, such as doping depth, substrate thickness, and surface recombination velocity. The cell performance was evaluated under low temperature radiations and found to have huge potentials for the use in low-temperature thermophotovoltaic systems.

Performance Improvement of the GaSb Thermophotovoltaic Cells With n-Type Emitters

A novel zinc diffusion process for the fabrication of high-performance GaSb thermophotovoltaic cells

Generally, waste heat is redundantly released into the surrounding by anthropogenic activities without strategized planning. Consequently, urban heat islands and global warming chronically increases over time. Thermophotovoltaic (TPV) systems can be potentially deployed to harvest waste heat and recuperate energy to tackle this global issue with supplementary generation of electrical energy. This paper presents a critical review on two dominant types of semiconductor materials, namely gallium antimonide (GaSb) and indium gallium arsenide (InGaAs), as the potential candidates for TPV cells. The advantages and drawbacks of non-epitaxy and epitaxy growth methods are well-discussed based on different semiconductor materials. In addition, this paper critically examines and summarizes the electrical cell performance of TPV cells made of GaSb, InGaAs and other narrow bandgap semiconductor materials. The cell conversion efficiency improvement in terms of structural design and architectural optimization are also comprehensively analyzed and discussed. Lastly, the practical applications, current issues and challenges of TPV cells are critically reviewed and concluded with recommendations for future research. The highlighted insights of this review will contribute to the increase in effort towards development of future TPV systems with improved cell conversion efficiency.

A Review on Thermophotovoltaic Cell and Its Applications in Energy Conversion: Issues and Recommendations.

GaInAsSb cells may show better performance than GaSb cells in low-temperature thermophotovoltaic systems due to their lower bandgap energies. In this paper, numerical simulation is used to evaluate GaInAsSb and GaSb cells with similar structures under different radiation temperatures. We find that GaInAsSb cells with n-type emitters show slightly higher output power densities compared with those for GaSb cells with n-type emitters below 1500 K given-blackbody radiation, but the power density of the GaSb cells will surpass the former’s above this temperature point. Furthermore, over the temperature range of $1200\sim 2000$ K, the efficiencies of GaSb cells with n-emitters are $1.31\sim 2.32$ times higher than those of GaInAsSb cells with n-emitters if filters with 10% subbandgap losses are used. Several parameters that affect the GaInAsSb cell were analyzed, such as doping profiles, thicknesses of GaInAsSb epitaxial layer and surface recombination velocity. The n-on-p junctions, i.e., n-type emitters vs p-type emitters are better for GaInAsSb cell fabrication, which is similar to that for the GaSb cell.

The Theoretical Performance of GaInAsSb and GaSb Cells Versus IR Emitter Temperature in Thermophotovoltaic Systems

This paper reports a novel zinc diffusion method for forming emitters in GaSb thermophotovoltaic cells. A closed quartz-tube diffusion system using Zn–Ga alloys as the diffusion sources is designed to realize p-type doping in N-GaSb wafers, the surface high-concentration zinc diffusion region is suppressed by this diffusion method, the GaSb cells fabricated using this method shows good quantum efficiency in the near-infrared bands. Compared to the conventional pseudo-closed-box (or semi-closed box) diffusion method using Zn–Sb alloys, the zinc profiles obtained from the novel diffusion method have no surface high-concentration zinc diffusion region which could have shortened the lifetime of photo-generated carriers, thus the controllability of the etch-back process after front-side metallization is significantly improved. The cost of the cell fabrication is reduced since no protective gas is required during the diffusion process.

A Novel Zinc Diffusion Process for Fabrication of High Performance GaSb Thermophotovoltaic Cells

Different diffusion sources were used to study Zn diffusion in n-GaSb. We found that the Ga atoms from the diffusion sources suppressed the formation of the high-concentration surface diffusion fronts in Zn profiles, thus converting the kink-and-tail-shaped profile to the box-shaped profile. Our analysis demonstrated that both the surface and the tail regions in the kink-and-tail profiles showed high-quality regularities. The analysis also revealed that the formation mechanism of the box profiles is the same as that of the tail region of the kink-and-tail profiles. The similarities of the photoluminescence signals between the main region of the box profiles and the tail region of the kink-and-tail profiles substantiated our findings.

Kuijun Li

Papers

The intrinsic relationship between the kink-and-tail and box-shaped zinc diffusion profiles in n-GaSb