CATION DEPENDENCE OF THE ELECTRONIC-STRUCTURE OF III-V NITRIDES

The ab initio pseudopotential method is used to study the effects of the cation potential on the electronic structure of two prototypical III-V nitrides, AlN and GaN. We examine both materials in the wurtzite and zinc-blende structures and compare these results with previous calculations for BN. Effects due to the s, p and d angular components of the Al and Ga potentials are studied. Because the charge densities of both AlN and GaN are dominated by N, the difference in the valence band charge density between these compounds is small. This is the reason that they have similar ground-state structural properties. Individual electronic levels at high-symmetry points, however, are altered by several electronvolts because of changes in the cation potential. This is the origin of the significant difference between the fundamental gaps of these compounds.