First-principles study of oxygen and aluminum defects in beta-Si3N4: Compensation and charge trapping

Formation energies for oxygen and aluminum defects in hexagonal silicon nitride (beta-Si3N4) were calculated from first-principles. Aluminum induces a deep donor level at the thermodynamically preferred interstitial site. Oxygen donors substituted into lattice nitrogen sites are found to ionize at 3.5 eV above the valence band and might readily compensate acceptor levels induced by native silicon micro-cluster defects. This is rationalized by examining the electronic structure of a model Si micro-cluster defect, and of the oxygen substitutional impurity. Specifically, this article describes the influence of oxygen and aluminum impurities on the number of states available for electron capture in silicon nitride as trapping layer.