Ionicity and relaxation anomalies at III-V nitride surfaces

We present first-principles study of relaxations at nonpolar surfaces of II I-V nitride compounds. These surfaces show up relaxations driven by competi tion between dehybridization and charge transfer mechanisms. For the sake o f comparison additional calculations have been performed for zincblende (11 0) GaAs and wurtzite (10(1) over bar 0) ZnO surfaces. Relaxations at (110) surfaces of zincblende AlN, GaN and InN reveal an anomalous behaviour as co mpared with those occurring at (110) surfaces of ordinary III-V semiconduct ors. On the other hand, for wurtzite (10(1) over bar 0) surfaces the three nitrides show up close analogies with ZnO. We trace back this behaviour to the strong ionic character of the nitrides.