First-principles calculations for AlN, GaN, and InN: bulk and alloy properties

First-principles density-functional calculations utilizing ab initio pseudopotentials and plane- wave expansions are used to determine lattice parameters, bulk moduli, and band structures for AlN, GaN, and InN. It is found that large numbers of plane waves are necessary to resolve the nitrogen 2p wave functions and that explicit treatment of the gallium 3d and indium 4d electrons is important for an accurate description of GaN and InN. Several properties of ternary zinc-blende alloys are determined including their bond-length and bond-angle relaxation and their energy-gap bowing parameters. The similarity of the calculated zinc- blende and wurtzite direct gaps also allows estimates to be made of the energy gap versus composition for wurtzite alloys.