Valence band structure of CuGa(S1−zSez)2 alloys

Abstract

Measurements of wavelength-modulated reflectance have been made in the temperature range 20–300 K on single-crystal samples of the alloy system CuGa(S1−zSez)2 and values of the valence to conduction band transition energies EA, EB and EC determined as a function of temperature. It has been shown that if the quasi-cubic model is used in the analysis of these data to determine values of spin-orbit and crystal-field splittings and their variation with temperature, the results are inconsistent with those from X-ray diffraction measurements of lattice parameters and tetragonal distortion. This is because the quasi-cubic model does not properly allow for the fractional d-character of the valence bands of these materials. The results have therefore been analyzed in terms of a recently developed theoretical model which takes into account the effects of p–d hybridization on both spin-orbit and crystal-field splittings. The analysis gives values of a dimensionless parameter M/E which is a measure of the interaction between the p and d states forming the valence bands and which determines the fractional d-like character [Formula: see text] of those bands. The variations of M/E and [Formula: see text] with both temperature and composition are considered in some detail.