Mg doping and native N vacancy effect on electronic and transport properties of AlN nanowires

Abstract

The effects of Mg doping (MgAl) and native N vacancy (VN) on the electronic structures and transport properties of AlN nanowire (AlNNW) were theoretically investigated by using density functional theory. Either the MgAl defect or the VN defect refers to be formed on the AlNNW surfaces. Both MgAl and VN defects could increase the conductivity owing to introducing a defect band inside the band gap of AlN and split the AlN band gap into two subgaps. The defect concentration has little influence on the magnitude of the subgaps. The MgAl serves as a shallow acceptor rendering the nanowire a p-type conductor. The VN introduces a deep donor state enabling the nanowire an n-type conductor. The MgAl systems exhibit higher conductivity than the VN ones owing to the narrow subgaps of MgAl systems. The conductivity is roughly proportional to the defect concentration in the MgAl and VN defect systems. When the MgAl and VN coexist, the hole state of the MgAl defect and the electron state of the VN defect will compensate each other and their coupling state appears just above the valence-band maximum leading to a little decrease of the band gap compared with the pure AlNNW, which is unfavorable for the enhancing of the conductivity.