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Anharmonic line shift and linewidth of the Raman modes in GaS0.75Se0.25 layered crystals

The frequencies and linewidths of five Raman-active modes in a GaS0.75Se0.25 layered crystal have been measured in the 10-300 K temperature range and in the 10-380 cm(-1) frequency region. We observed softening and broadening of the optical phonon lines with increasing temperature. The analysis of the experimental data showed that the temperature dependencies of frequencies and linewidths are well described by considering the contributions from thermal expansion and lattice anharmonicity. The purely anharmonic contribution (phonon-phonon coupling) is found to be due to three-phonon processes.