First Principles Study of Aluminium Vacancy in Wurtzite Aluminium Nitride

We report that the aluminium vacancy in wurtzite AlN brings about two impurity levels e and a₂ in the band gap, not just one single t₂ level. The aluminium vacancy carries a magnetic moment of 1μ_B in the ground state. The molecule orbit of the aluminium vacancy becomes e^↑↑a₂^↓ rather than e^↑↑a₂^↓. The calculation is carried out by using the CASTEP code. The intrinsic symmetry of wurtzite AlN is the driving force for this spin splitting. Finally the symmetry of wurtzite AlN results in an anti-ferromagnetic coupling between the aluminium vacancies, as is predicted. Our findings are helpful to gain a more through understanding of the structural and spin property of aluminium vacancy in wurtzite AlN.