The effect of Ga vacancies on the defect and magnetic properties of Mn-doped GaN

Abstract

We perform first-principles theoretical calculations to investigate the effect of the presence of Ga vacancy on the defect and magnetic properties of Mn-doped GaN. When a Ga vacancy (V-Ga) is introduced to the Mn ions occupying the Ga lattice sites, a charge transfer occurs from the Mn d band to the acceptor levels of V-Ga, and strong Mn-N bonds are formed between the Mn ion and the N atoms in the neighborhood of V-Ga. The charge transfer and chemical bonding effects significantly affect the defect and magnetic properties of Mn-doped GaN. In a Mn - V-Ga 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 is electrically deactivated, and the remaining dangling bond orbitals of V-Ga 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 6 angstrom, which corresponds to the percolation length in determining the Curie temperature in diluted Mn-doped GaN, the Mn d band is broadened and the density of states at the Fermi level is reduced due to two strong Mn-N bonds. Although the broadening and depopulation of the Mn d band weaken the ferromagnetic stability between the Mn ions, the ferromagnetism is still maintained because of the lack of antiferromagnetic superexchange interactions at the percolation length. (C) 2007 American Institute of Physics.