Theoretical analysis of d electron effects on the electronic properties of wurtzite and zincblende GaN

We investigate the electronic properties of the technologically important wide-band-gap semiconductor GaN employing 'state-of-the-art' DFT-LDA calculations using a FP-LAPW code. The Ga 3d electrons are treated both as core or as valence electrons and the wurtzite as well as the zincblende modifications of GaN are investigated. In particular, we address the influence of the lattice configuration and of the d electrons to the electronic structure of w-GaN and c-GaN. Band structures, densities of states, orbital-resolved densities of states, total and partial valence charge densities, and ionicity factors are analysed in great detail. The calculated values of the energy gaps, bandwidths, spin-orbit, crystal-field splittings, and the correct band degeneracies are compared to experimental and/or ab initio results. Several features of w-GaN resemble those of c-GaN. Most of the calculated band parameters, of band gaps, total and upper-valence bandwidths, and antisymmetric gap for w-GaN are close to those of c-GaN within 1%. The charge distributions have similar features meaning that this material has the same ionicity factor with or without Ga 3d hybridization in both structures. By examining the pressure dependence of the energy band gaps, the value of the hydrostatic deformation potential of the band gap has also been calculated.