Ab initio studies of strained wurtzite GaN surfaces

In GaN and other group III nitrides the considerable lattice mismatch with the substrates normally employed during growth, such as sapphire, 6H-SiC and ZnO, can lead to the presence of strain which may affect the surface properties. Here we have studied the effect of biaxial strain on the structure, electronic configuration and formation energy of various GaN(0001) and (0001-bar) 1 x 1 surfaces. In particular, we consider the Ga and N tetrahedral (T4), hexagonal (H3) and asymmetric top (atop) configurations. The ab initio total energy calculation studies presented here employ the density functional formalism using a pseudopotential plane-wave basis set approach in order to obtain the minimum energy configurations of the unstrained and biaxially strained structures. We show in bulk GaN a good linearity between the biaxial strain imposed and the calculated structural cell parameters. The calculated formation energies of the GaN surfaces show that the most stable configuration for the different reconstructions is not influenced by the biaxial strain