Photoreflectance of r.f. sputtered Cd_1−xFe_xTe thin films

Abstract

Samples of r.f. sputtered Cd_1−x Fe _x Te (withx = 0.00, 0.05, 0.10 and 0.15) films were studied by photoreflectance spectroscopy. The samples were grown at a substrate temperature of 150°C. The photoreflectance spectra around the fundamental edge were analysed using the generalized theory of electroreflectance in the low-field regime recently developed by Raccahet al. The experimental results forx = 0.00 and 0.05 show a single feature that can be intepreted in terms of optical transitions in a cubic phase structure. In those films wherex =0.10 and 0.15, the experimental results show a double feature spectrum that we attribute to optical transitions in an hexagonal phase structure. Subsequent annealing at 200 and 300° C of the samples produces some changes in the lineshape of the photoreflectance spectra. These changes are interpreted in terms of an increment in the density of polarizable defects as the annealing temperature increases; we associate this effect with an increase in the formation of complex defects composed of Fe³⁺ ions and cadmium vacancies.