Vol.29 No.4(1994.12)
Research Report

First principles pseudopotenital caluculations based on the local-density-functional theory have been performed on GaN and AlN. Due to the localized nature of the valence charge denisity in these materials, the mixed-baseis set which is a linear combination of plane wave and Gaussian orbitals is used to expand the electronic wave functions. We consider two possible crystal structures, , hexagonal wurtzite and cubic zincblende, and predict the equilbrium lattice constants, bulk moduli, electronic band structures , and optical Γ-phonon frequencies. The results are in good agreement with avaiable experimental data: Although the calculated A_l-transverse-optical mode frequency of wurtzite AlN differed by 11% from Raman experimental data published before 1992, the experimental data have been recently revised by two different groups and we have found good agreement between the calculated frequency and the revised ones. The effective mass of the electron appears to be nearly isotropic for wurtzite GaN and AlN. For both nitrides, the wurtzite structure is found to be more stable than the zinc-blende structure.