Origin of a Wide and Asymmetric Blue Luminescence Band in AlN Nanowires: VN, VAl, ON, and 3ON–VAl Surface Defects

Abstract

The physical origin of a wide and asymmetric blue luminescence (BL) band from 350 to 750 nm in AlN nanowires (NWs) is clarified by first-principles calculations based on density functional theory and GW approximation together with the Bethe–Salpeter equation. Our results show that the band gap of the AlN NW with 1 nm diameter is 8.40 eV due to the strong one-dimensional quantum confinement, which is larger than that of AlN bulk (6.2 eV). The exciton binding energy is 1.75 eV owing to incomplete dielectric screening in AlN NWs. The defects including N vacancy (VN), Al vacancy (VAl), O impurity (ON), and 3ON–VAl have low formation energy and prefer to stay at the surface layer of AlN NWs. It is the combination of the optical transitions from the exciton ground state to these defect levels that determines the wide and asymmetric BL band in AlN NWs. Our work is useful for understanding the defect-related luminescence mechanism and improving the performance of AlN NW-based optoelectronic nanodevices.