First-principle study on GaN(1010) surface structure

We have calculated the atomic and electronic structures of the non-polar surface of GaN (1010) by employing the full potential augmented plan wave and local orbital method (APW + lo). The calculated lattice constant and bulk modulus of zinc-blend GaN crystal are in excellent agreement with the experimental data. Using the slab and supercell model, we find that the surface is characterized by a top-layer bond-lenth-contracting rotation relaxation. The surface Ga atom moves inward with 0.014nm and form a planar sp(2)-like bonding with its three N neighbors. While the surface N atom moves outward with 0.013nm and tends to a taper p(3)-like bonding with its three Ga neighbors. The surface layer rotation angle is 8.5degrees. From the calculated results of the desity of states of GaN (1010) surface we find that the surface relaxation induces the transformation from semi-metallic to semiconducting characteristic. Furthermore, it is also shown that the surface charges have a large transfer, and the surface bonds have a rehybridization, which makes the ionicity reduce and the covalence increase, we believe that it causes the surface bond shortening and rotating.