Nitrogen vacancies at InN (11¯00) surfaces: A theoretical study

We present an ab initio atomistic study of the effects of nitrogen vacancies both in InN bulk and at (11¯00) nonpolar surface and confirm that these defects act as n-type impurities. Based on the dependence of the vacancy formation energy on the distance from the surface, we predict that at thermodynamic equilibrium these defects tend to segregate in the outermost surface layers reaching a concentration which is few orders of magnitude higher than in the bulk phase. Considering out-of-equilibrium growth and in view of the large calculated energy barrier that characterize vacancy diffusion, we also predict that the N enriched layer will extend hundreds of angstroms from the surface for typical growth processes. This vacancy accumulation at surface is consistent with the observed high electron accumulation layer.