Temperature Dependence of the First-Order Raman Phonon Lines in GaS$\text{}_{0.25}$Se$\text{}_{0.75}$ Layered Crystals

Systematic measurements by Raman scattering of the frequency and line width of the zone-center optical modes in GaS$\text{}_{0.25}$Se$\text{}_{0.75}$ layered crystal over the temperature range of 10-300 K are carried out. The analysis of temperature dependence of intralayer modes shows that frequency shift and line broadening are successfully modeled by including the contributions from thermal expansion and lattice anharmonicity. The purely anharmonic contribution (phonon-phonon coupling) is found to be due to three-phonon processes.