Theoretical and experimental study of the lattice-dynamical properties of cubic GaN

We report on theoretical and experimental investigations of the lattice dynamics of GaN in the cubic zinc-blende phase. We calculated the phonon dispersion curves of cubic (3C) GaN using an ab initio method based on density-functional perturbation theory. Furthermore, we perform a comparison between the measured second-order Raman spectrum of 3C GaN and the theoretical spectrum determined using ab initio phonon eigensolutions and phenomenological polarizability coefficients. As a test of the method, we performed calculations of the Raman intensities of the prototype zinc-blende semiconductors GaAs. Although the calculation successfully reproduces the experimental spectrum of GaAs, the results for the 3C GaN do not reach the same agreement with the experiment. This is possibly ascribed to the difficulty in growing cubic samples with high degree of purity.