VALENCE BAND-STRUCTURE OF CUGA(S1-ZSEZ)2 ALLOYS

Measurements of wavelength-modulated reflectance have been made in the temperature range 20-300 K on single-crystal samples of the alloy system CuGa(S//1// minus //zSe//z)//2 and values of the valence to conduction band transition energies E//A, E//B, and E//C 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 minus d hybridization on both spin-orbit and crystal-field splittings. The results are presented and discussed.