In(0.53)Gao(0.47)As/InP conventional and inverted thermophotovoltaic cells with back surface reflector

摘要

Characteristics of conventional and inverted InGaAs/InP thermophotovoltaic (TPV) cells with a back surface reflector (BSR) fabricated on electrically active n-type InP substrates are presented. Thermophotovoltaic cells based on lattice matched InP-In0.53Ga0.47As heterostructures were fabricated with the use of LPE and Zn,P diffusion technologies. In the p-n TPV cells (conventional type, spectral range 600 divided by 1800 nm) with a frontal p-InGaAs layer, BSR was made on a n-InP substrate. In the n-p structure (inverted type, spectral range 1000-1800 mn) with a frontal bulk n-InP-window-substrate, BSR was formed on a p-InGaAs layer. Antireflection coating (ARC) on the frontal cell surface consists of ZnS/MgF2 layers. Results of investigation of sub-bangap photons reflection from InP substrates with a backside MgF2/Au mirror in the range of 1800 divided by 2000nm are described. The reflection of BSR for InP samples with the doping level in the range of 1x10(17) divided by 6x10(18)cm(-3) evidenced a weak dependence on their thickness and doping level. A reflection of 86 divided by 90% has been measured for substrates 100 mu m thick and 80% for ones 400 mu m thick with ARC. Study of sub-bandgap photon reflection of p-InGaAs (Zn,P) layers with surface concentration of 1 divided by 3x10(19)cm(-3) has been also carried out. A reflection of 68 divided by 77% for 2 divided by 4 mu m layers with "hybrid" (ohmic contact plus mirror) back-surface reflector consisted of deposited Cr/Au layers was measured. It was found, that p-n and n-p thermophotovoltaic 1x1cm(2) Cells with identical grid design reveal similar parameters for up to 1A/cm(2) current density (V-OC=465mV and FF=64%) and the 76 divided by 80% reflection of the sub-bandgap photons for wavelengths longer than 1.86 mu m. The developed inverted InGaAs TPV cells have been tested under illumination of silicon carbide high temperature emitter. The photocurrent density J(sc)=7A/cm(2), open circuit voltage V-oc=0.476V and fill factor FF=0.691 have been measured in the inverted (without BSR) InGaAs cell under SiC emitter heated to the temperature of about 1550 degrees C. Both types of devices can successfully be used as TPV cells for conversion of radiation in the range of 1500-1900K, with 14-15% efficiency.