Quasiparticle band structure of AlN and GaN

The ab initio pseudopotential method within the local-density approximation and the quasiparticle approach have been used to investigate the electronic properties of AlN and GaN in the wurtzite and zinc-blende structures. The quasiparticle band-structure energies are calculated using a model dielectric matrix for the evaluation of the electron self-energy. For this calculation, good agreement with the experimental results for the minimum band gaps in the wurtzite structure is obtained. In the zinc-blende structure we predict that AlN will be an indirect ({Γ} to X) wide band-gap semiconductor (4.9 eV) and that GaN will have a direct gap of 3.1 eV at {Γ} in good agreement with recent absorption experiments on cubic GaN (3.2--3.3 eV). A discussion of the direct versus indirect gap as well as other differences in electronic structure between the wurtzite and zinc-blende phases is presented. Other properties of quasiparticle excitations are predicted in this work and remain to be confirmed by experiment.