BOND-ROTATION VERSUS BOND-CONTRACTION RELAXATION OF (110) SURFACES OFGROUP-III NITRIDES

The rotation-relaxation model with large layer-rotation angles of abou t 30 degrees is well accepted for the (110) cleavage surfaces of ordin ary m-V compounds. We examine this model for the group-III nitrides BN , AlN, GaN, and InN with larger covalency and polarity of the bonds. W ell converged ab initio calculations using a plane-wave pseudopotentia l method suggest a tendency for a bond-contraction relaxation where th e buckling and the zigzag character of the III-N chains parallel to [1 (1) over bar 0] are reduced. The resulting geometries, energetics, an d electronic structures are analyzed in terms of bond strength and bon d ionicity.