Thermophotovoltaics (TPVs) are a potential technology for waste-heat recovery applications and utilize IR sensitive photovoltaic diodes to convert long wavelength photons (>800nm) into electrical energy. The most common conversion regions utilize Gallium Antimonide (GaSb) as the standard semiconductor system for TPV diodes due to its high internal quantum efficiencies (close to 90%) for infrared radiation (~1700nm). However, parasitic losses prevent high conversion efficiencies from being achieved in the final device. One possible avenue to improve the conversion efficiency of these devices is to incorporate metallic photonic crystals (MPhCs) onto the front surface of the diode. In this work, we study the effect of MPhCs on GaSb TPV diodes. Simulations are presented which characterize a specific MPhC design for use with GaSb. E-field intensity vs. wavelength and depth are investigated as well as the effect of the thickness of the PhC on the interaction time between the e-field and semiconductor. It is shown that the thickness of MPhC has little effect on width of the enhancement band, and the depth the ideal p-i-n junction is between 0.6μm and 2.1μm. Additionally, simulated results demonstrate an increase of E-field/semiconductor interaction time of approximately 40% and 46% for a MPhC thickness of 350nm and 450nm respectively.
In this paper, we investigate extending the operational wavelength of thermophotovoltaic diodes. Our calculations demonstrate that employing a barrier structure can reduce the diffusion current by several orders of magnitude, reducing dark current and improving the overall function of the TPV diode for room temperature operation. We first investigated GaSb/InAs type–II superlattice structures with monovalent barriers targeting wavelength cut-offs of five microns. Simulations were used to optimize the band structure energy levels for superlattice materials and to align the energy bands between different layers in the device. We examine the difference in IV curves between barrier and non-barrier structures for a five micron (Eg=0.248 eV) diode with a barrier of 300 meV.
This work demonstrates metamaterial (MM) selective thermal emitters for potential use with energy harvesting
photodiodes, such as thermophotovoltaic cells. Preliminary structures have been designed, simulated, and fabricated
using CST Microwave Studio and microfabrication techniques including electron beam evaporation, atomic layer
deposition, and electron beam lithography, respectively. Samples were tested to determine the effect of top layer metal
thickness on the absorption of these devices. Preliminary simulation and testing was also performed to design a device
for operation at 500°C.
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