Dashiell, M. W., Ehsani, H., Sander, P. C., Newman, F. D., Wang, C. A., Shellenbarger, Z. A., … & Anikeev, S. (2008). Triple-axis X-ray reciprocal space mapping of InyGa1− yAs thermophotovoltaic diodes grown on (1 0 0) InP substrates. Solar energy materials and solar cells, 92(9), 1003-1010.
Analysis of the composition, strain-relaxation, layer-tilt, and the crystalline quality of InyGa1−yAs/InP1−xAsx thermophotovoltaic (TPV) diodes grown by metal-organic vapor phase epitaxy (MOVPE) is demonstrated using triple-axis X-ray reciprocal space mapping techniques. In0.53Ga0.47As (Egap=0.74 eV) n/p junction diodes are grown lattice matched (LM) to InP substrates and lattice-mismatched (LMM) In0.67Ga0.33As (Egap=0.6 eV) TPV diodes are grown on three-step InP1−xAsx (0<x<0.32) buffer layers on InP substrates. X-ray reciprocal space maps about the symmetric (4 0 0) and asymmetric (5 3 3) reciprocal lattice points (RELPs) determine the in-plane and out-of-plane lattice parameters and strain of the InyGa1−yAs TPV active layer and underlying InP1−xAsx buffers. Triple-axis X-ray rocking curves about the LMM In0.67Ga0.33As RELP show an order of magnitude increase of its full-width at half-maximum (FWHM) compared to that from the LM In0.53Ga0.47As (250 vs. 30 arcsec). Despite the significant RELP broadening, the photovoltaic figure of merits show that the electronic quality of the LMM In0.67Ga0.33As approaches that of the LM diode material. This indicates that misfit-related crystalline imperfections are not dominating the photovoltaic response of the optimized LMM In0.67Ga0.33As 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 In0.67Ga0.33As 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.