Therefore we compare in the next sections, the GF LMTO results with the FP LMTO supercell calculations. We study here the cubic phase, believing that there is little difference in impurity level positions of the two phases. There are very similar tendencies in the positions of native defect levels in GaN and AlN, but the absolute values are different mainly due to the different values of the energy gaps. Comparing GaN and AlN, the same sequence of states is seen for all the native defects. The V Ga level position in GaN is 0.2 eV above the VBM, and in AlN V Al lies 0.5 eV above the VBM, in agreement with the pseudopotential calculations by Boguslawski et al.
Outward relaxation is found for cation vacancies.
This agrees with other theoretical results. While the cation vacancy level positions are very similar in GaN and AlN, the nitrogen vacancy behaves quite differently in the two compounds. In contrast, the V N levels in AlN are moved into the band gap. The relaxations in AlN were found to be vanishingly small. Antisites Antisite defects introduce deep levels both in GaN and AlN. Lattice relaxations connected with these defects are very pronounced, but quite different for cation and nitrogen antisites.