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 lead to the shallowness of the defect level. When a Ga vacancy forms a complex with two Mn ions located at a distance of about 6Å, which corresponds 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 2 strong Mn–N bonds. Although the broadening and depopulation of the Mn d-band weaken the ferromagnetic stability between the Mn ions, the ferromagnetism was still maintained because of the lack of antiferromagnetic super-exchange 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