Triple-axis X-ray Reciprocal Space Mapping of In(y)Ga(1-y)As Thermophotovoltaic Diodes Grown on (100) InP Substrates

Abstract Analysis of the composition, strain-relaxation, layer-tilt, and the crystalline quality of In y Ga 1− y As/InP 1− x As x thermophotovoltaic (TPV) diodes grown by metal-organic vapor phase epitaxy (MOVPE) is demonstrated using triple-axis X-ray reciprocal space mapping techniques. In 0.53 Ga 0.47 As ( E gap =0.74 eV) n/p junction diodes are grown lattice matched (LM) to InP substrates and lattice-mismatched (LMM) In 0.67 Ga 0.33 As ( E gap =0.6 eV) TPV diodes are grown on three-step InP 1− x As x (0 x y Ga 1− y As TPV active layer and underlying InP 1− x As x buffers. Triple-axis X-ray rocking curves about the LMM In 0.67 Ga 0.33 As RELP show an order of magnitude increase of its full-width at half-maximum (FWHM) compared to that from the LM In 0.53 Ga 0.47 As (250 vs. 30 arcsec). Despite the significant RELP broadening, the photovoltaic figure of merits show that the electronic quality of the LMM In 0.67 Ga 0.33 As approaches that of the LM diode material. This indicates that misfit-related crystalline imperfections are not dominating the photovoltaic response of the optimized LMM In 0.67 Ga 0.33 As material compared with the intrinsic recombination processes and/or recombination through native point defects, which would be present in both LMM and LM diode material. However, additional RELP broadening in non-optimized LMM In 0.67 Ga 0.33 As n/p junction diodes does correspond to significant degradation of TPV diode open-circuit voltage and minority carrier lifetime demonstrating that there is correlation between X-ray FWHM and the electronic performance of the LMM TPV diodes.