First-principles calculations of effective-mass parameters of AlN and GaN

The electronic band structures of the wurtzite-type AlN and GaN are calculated by using a self-consistent full-potential linearized augmented plane-wave method within the local-density-functional approximation. In order to clarify the electronic properties near the Brillouin-zone (BZ) center and to give an important guideline on the material designs for short-wavelength optical devices, we link the first-principles band calculations with the effective-mass approximation. The electronic properties are analytically studied on the basis of the effective-mass Hamiltonian, where we consider the hexagonal symmetry of the wurtzite structure. The effective-mass parameters, such as electron effective mass, hole effective masses, or, equivalently, the Luttinger-like parameters, crystal-field splitting and spin-orbit splitting, are determined by reproducing the calculated band structures near the BZ center. The obtained results show that the cubic approximation is fairly successful in the analysis for the valence-band structures of the wurtzite-type nitrides. Further, the calculated parameters for GaN are consistent with the observed ones.