Temperature dependence of the optical phonon reflection band in GaP

We explore the effect of temperatures between 80 and 720 K on energy linewidth zone-center transverse (TO) longitudinal (LO) optical phonons in bulk gallium phosphide (GaP) using Fourier transform infrared ellipsometry from 0.03 to 0.60 eV. extract phonon parameters GaP by fitting ellipsometric angles with Lowndes–Gervais model, which applies two different broadening TO LO phonons. In GaP, two-phonon density states is larger for decay than Therefore, we observed a (compared phonon) an asymmetric reststrahlen line shape. This would lead negative imaginary part dielectric function just above but addition absorption avoids this. find temperature-dependent redshift increasing temperature due thermal expansion anharmonic phonon-phonon scattering, involving three four processes. also investigate dependence high-frequency constant. Its variation explained Penn gap.