Optical transitions in ZrS3-xSexsingle crystals through temperature-modulated reflectivity

Abstract

Thermoreflectance spectra of ZrS3-xSex single crystals have been measured at 50 K. The thermoreflectance spectra of ZrS3 and ZrSe3 are discussed through direct and indirect exciton transitions. The observation of indirect transitions is due to a reflection effect on the back surface of the sample. A calculation that accounts for multiple reflections and agrees with the known values of the absorption coefficient at the indirect fundamental gap is performed. The direct exciton structures are described by a classical oscillator model which includes a dead layer at the surface of the crystal. Both direct and indirect exciton energies of the solid solution ZrS3-xSex are observed as a function of x.