First principles theoretical calculations were used to investigate the effect of the presence of Ga vacancy on the defect and magnetic properties of Mn-doped GaN. When a Ga vacancy (VGa) was introduced to the Mn ions occupying the Ga lattice sites, a charge transfer occurred from the Mn d-band to the acceptor levels of VGa, and strong Mn–N bonds were formed between the Mn ion and the N atoms in the neighborhood of VGa. The charge transfer and chemical bonding effects significantly affect the defect and magnetic properties of Mn-doped GaN. In a Mn-VGa complex, which consists of a Ga vacancy and one Mn ion, the dangling bond orbital of the N atom involved in the Mn–N bond was electrically deactivated, and the remaining dangling bond orbitals of VGa led to the shallowness of the defect level. When a Ga vacancy formed a complex with two Mn ions located at a distance of about 6Å, which corresponded to the percolation length in determining the Curie temperature in diluted Mn-doped GaN, the Mn d-band was broadened and the density of states at the Fermi level was reduced due to two strong Mn–N bonds. Although the broadening and depopulation of the Mn d-band weakened the ferromagnetic stability between the Mn ions, the ferromagnetism was still maintained because of the lack of antiferromagnetic superexchange interactions at the percolation length.

The Effect of Ga Vacancies on the Defect and Magnetic Properties of Mn-Doped GaN. J.Kang, K.J.Chang: Journal of Applied Physics, 2007, 102[8], 083910