Anharmonic phonon decay in polycrystalline CdTe thin film

Abstract

The anharmonic decay of both the longitudinal optical phonon (LO) and its overtone (2LO) was found to decay asymmetrically into a transverse optical (TO) and a transverse acoustic (TA) phonon, both of which are at the L point along the Γ-L direction of the Brillouin zone. For the LO and its overtone 2LO, both the Raman shift and Raman linewidth were decreased/increased almost linearly with the temperature in the range of 78–523 K. This temperature-dependent phonon decay characteristics were induced by LO anharmonic decay to the TA phonon with an energy of only ∼29 cm−1. A TA phonon mode with such low energy is readily excited, and its phonon density is almost linearly increased with increased temperature. Strong multi-phonon scatterings, which involved the LO, the surface optical mode, and the TO, were funded to contribute to the anharmonic decay of the 1LO, especially at temperature higher than room temperature.