Atomic structure and relative stability of gallium and nitrogen interstitials in GaN[0001] grain boundaries

The atomic and electronic structures of gallium and nitrogen interstitial created at the 8-interface of the (2330) Sigma= 19 (theta = 13.2 degrees) tilt grain boundary in GaN were investigated by density-functional based tight-binding calculations. We found that the structure of lowest energy of the Ga- or N-interstitial boundary is formed by a mixture of 6- and 5/7-atom rings (Ga-i- or N-i-interface) which is comparable to that of the 5/7-interface. The calculations show that the non stoichiometric Ga-i-interface is energetically more stable than the stoichiometric 5/7-interface, suggesting that both configurations may exist. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.