Local vibrational modes at AsN in cubic GaN: Comparing ab-initio calculations to a semi-empirical model

We present a study of the local vibrational modes (LVM) at the AsN impurity in cubic GaN. These are of interest, as in the growth of cubic GaN on a GaAs substrate, some As penetrate from the substrate into the layer. Such impurities might be the origin of a large number of sharp Raman modes, which can be observed at low temperatures and certain excitation wavelengths. We focus on the AsN substitutional impurity in the GaN layer. The energies of the LVMs at those centres are calculated using two different approaches: first, a semi-empirical calculation is presented, then an ab-initio one. In the conclusion, we will show, that the results of both calculations produce similar results. The Raman lines of ref. [4] can not be explained by LVMs at isolated As impurities in GaN.