Density-functional pseudopotential calculations were performed in order to investigate the electronic structures, atomic configurations and formation energies of native point defects and impurities in AlN. Among the native defects, the N vacancy had the lowest formation energy in p-type material and the Al vacancy had the lowest formation energy in n-type material. Under n-type conditions, the formation energy of the N vacancy was high; thus indicating that it would not occur in high concentrations. It was found that the N vacancy exhibited differing behaviors in the zincblende and wurtzite structures with respect to the higher-lying defect-induced levels. In zincblende material, this level was a resonance in the conduction band; causing the vacancy to act as a shallow donor. In wurtzite, the level lay well below the conduction-band edge; causing the vacancy to act as a deep donor. In the case of the zincblende structure, it was also found that the Al interstitial had a low formation energy in p-type material. The results indicated that these defects could be important compensation centers. This was considered with regard to dopant impurities (O, Si, Mg). Impurity complexes (MgO, Mg2O2) were also investigated. A comparison of the results obtained using the local-density approximation and the generalized-gradient approximation for the exchange-correlation functional showed that the results were qualitatively very similar.

Theoretical Investigation of Native Defects, Impurities, and Complexes in Aluminum Nitride. C.Stampfl, C.G.Van de Walle: Physical Review B, 2002, 65[15], 155212 (10pp)