Stability of native defects in hexagonal and cubic boron nitride - art. no. 125205

We investigate, through first-principles calculations, the stability and el ectronic structure of self-interstitials and vacancies in both hexagonal (g raphite-like) and cubic boron nitride. We find that the self-interstitials N-i and B-i in hexagonal boron nitride (h-BN) have low formation energies, comparable to those of the vacancies V-N and V-B. For instance, we find tha t N-i is the most stable defect in h-BN under N-rich and p-type conditions followed by the nitrogen vacancy. This is consistent with experimental find ings of large concentrations of nitrogen interstitials and vacancies, and o f the trapping of nitrogen in the hexagonal phase of BN thin films grown by ion-bombardment assisted deposition techniques. In contrast, in cubic boro n nitride (c-BN) the self-interstitials have high formation energies as com pared to those of the vacancies. As a consequence, the formation of vacancy -interstitial pairs in kickout processes would typically require much more energy in c-BN than in h-BN. This suggests that a possible role of the ion bombardment in favoring the growth of c-BN films is to generate a much larg er amount of defects in the hexagonal phase than in the cubic phase.