Raman scattering and transverse effective charge of MOCVD-grown GaN films between 78 and 870 K

Abstract

First-order Raman scattering of a hexagonal GaN film is studied in the temperature range T = 78-870 K. The temperature dependence of its five Raman modes is obtained, where both the line width and Raman shift exhibit a quadratic dependence on temperature in our measured temperature range. Excellent agreement was obtained between the experimental data and the calculated results based on a model involving three-phonon and four-phonon coupling. In addition, the splitting between the longitudinal-optical (LO) and transverse-optical (TO) phonons was found to decrease with increasing temperature. From these data, a weak non-linear decrease of the transverse effective charge with increasing temperature is derived. Comparison of the transverse effective charge eT* at room temperature was made between experimental data and theoretical calculations by a pseudopotential expression and bond orbital model (BOM). Good agreement between theory and experiment was achieved.