Optical characterization of epitaxial Ga{sub x}In{sub 1{minus}x}As suitable for thermophotovoltaic (TPV) converters

A preliminary investigation of the optical characteristics of Ga{sub x}In{sub 1{minus}x}As epilayers is presented. Ga{sub x}In{sub 1{minus}x}As epilayers with x = 0.465, 0.400, and 0.277 were prepared by metalorganic vapor-phase epitaxy (MOVPE) to represent a wide spectrum of TPV converter applications. Ellipsometric measurements, combined with various characterization techniques and multi-layer modeling, are used to extract n({lambda}) and k({lambda}) for these epilayers. The validity of the results was checked by using the experimentally determined optical constants to calculate expected reflectance, and then comparing this result against measured reflectance. Good agreement was obtained in all cases; larger differences were observed for samples having greater surface roughness. Suggestions for improving the optical constant determination procedure are given.