Anharmonicity of the E2(high) and A(1)(LO) phonons in GaN studied by temperature-dependent Raman spectroscopy

We study the influence of heteroepitaxy as well as intrinsic anharmonicity of the E2(high) and A1(LO) lattice vibrations in wurtzite GaN layers. The intrinsic phonon-phonon scattering of bulk GaN determines the temperature dependence of the width of the E2(high) and A1(LO) Raman lines of GaN layers. The Grüneisen contribution of the GaN layer, which is strongly influenced by the thermal expansion coefficient of the substrate, dominates the temperature dependence of the phonon frequencies.