First-principles density-functional theory calculations were used to investigate the structural and electronic properties and formation energies of N vacancies in wurtzite InN. An extensive study was made of the favorable atomic and electronic configurations of up to 6 vacancies in large super-cells. The isolated vacancy acts as a donor in a p-type material where there was very little interaction between the singly positive charged vacancies. Their spatial distribution was therefore predicted to involve random arrangements of single defects. However, in more n-type materials, the neutral charge state becomes favored and it was found that the vacancies then prefer to be situated close to one another on the nearest-neighbor (like species) sites, forming so-called vacancy complexes or clusters. In the highest positive charge state of the complexes, the clustering was unstable with respect to isolated single positive charged vacancies. However, the negatively charged and lower positively charged (e.g., 1+ and 2+ charge states for three N vacancies) complexes also exhibited an attractive interaction between the vacancies, thus also favoring clustering. The formation of such N vacancy clusters gives rise to local In- rich regions with metallic-like bonding. The effect that these defect structures had upon the nature of the electronic states in the region of the band-gap was considered with regard to recent experimental results obtained by infra-red photoluminescence, X-ray diffraction and transmission electron microscopy.

Nitrogen Vacancies in InN - Vacancy Clustering and Metallic Bonding from First Principles. X.M.Duan, C.Stampfl: Physical Review B, 2008, 77[11], 115207 (9pp)