An ab initio study of the electronic properties of helium in wurtzite gallium nitride

Abstract

Impurities and their complexes with intrinsic point defects, e.g vacancies, can alter the opto-electronic properties of semiconductors. Among such impurities, helium is incorporated into GaN by ion implantation, for wafer splitting and for device isolation purposes. Yet, despite the technological importance of such impurity, it is not known whether or not He is electrically active in GaN or what its impact on n- or p-type dopants is. For this reason, we carried out a density functional theory (DFT) study of substitutional He and related complexes (vacancies and dopants) in wurtzite GaN. We employed the generalized gradient approximation (GGA) and overcame the band gap energy understimation, by a posteriori corrections. It is found that He is unstable at N-sites, moving to interstitial sites and forming a N vacancy (VN). This was observed for the case of substitutional He and for He complexed with n- or p-type dopants. The formation of VN, in such defects, gives rise to donor states close to the valence band edge (EV). On the other hand, the presence of a gallium vacancy (VGa) leads to the formation of an energetically stable complex that gives rise to acceptor states close to the conduction band edge (EC). Our findings are then discussed in the light of previous experimental reports on GaN device isolation.