Charged vacancy defects in an AlN nanosheet: A first-principles DFT study

Charged vacancy defects in an AlN nanosheet are studied by first principles calculations. Formation energies values at valence band maximum indicate that the nitrogen vacancy is more stable than the aluminum vacancy in both Al and N rich conditions. Under Al-rich and N-rich conditions, aluminum vacancy presents two transition levels in the band gap: from neutral state to a negative charge-state (0/−1), and from a negative charge-state to a double negative charged state (−1/−2). Nitrogen vacancy at low Fermi energies prefers a positive charged state, then it adopts a neutral charged state, and finally it is stabilized in a negative charge-state. Bond lengths of atoms in vicinity of vacancy and electronic structure are affected by charge states. AlN sheet with vacancy defects could present spin-polarized charge states. Magnetism originated by charged vacancy defects in AlN sheets can serve for potential applications in new spintronic devices.