TEMPERATURE-DEPENDENT FAR-INFRARED REFLECTANCE OF LAYER STRUCTURED III-VI COMPOUNDS

The temperature dependence of the long-wavelength vibrational spectra of III-VI compounds has been studied. The reflectivity of layered semiconductors GaSe and InSe is carried out in the spectral range from 10 to 600 cm-1 as a function of temperature. Features of normal modes from liquid helium up to room temperature are reported. Reflectivity spectra are fitted with a four-parameter dispersion model based on the factorized form of the complex dielectric function. The temperature dependencies of the frequency and lifetime of the phonons are analysed using the anharmonic model with two- and three-phonon decay functions. The cubic and quartic anharmonic parameters are deduced and discussed in relation to the dimensionality of the materials.