Optical phonons in InP1−xAsx revisited

Abstract

The transverse (TO) and longitudinal (LO) optical phonons in bulk alloys of InP1−xAsx at room temperature have been studied previously by Kekelidze et al. [J. Phys. Chem. Solids 34, 2117 (1973)] using infrared reflectance spectroscopy. Their analysis based on the classical model yielded results that indicated a linear dependence on composition for all four optical modes, but no actual mode frequencies were reported. We have reanalyzed their spectra using three different methods: the conventional Kramers-Kronig approach, the factorized model fitted to the differential of the reflectivity, and directly fitting the reflectivity. The results obtained for the mode frequencies are found to vary somewhat depending on the method used, but the two LO modes are seen to exhibit a slight nonlinear dependence on x. The results also provide information on the concentration dependence of the damping of the InP-like and InAs-like TO and LO phonons. The InP-like and InAs-like mode oscillator strengths have also been determined and are found to vary differently from that depicted schematically earlier by Kekelidze et al. Comparisons are made with infrared reflectivity results obtained earlier by Oswald [Z. Naturforsch. A 14A, 374 (1959)].