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

The effects of Mg doping (Mg-Al) and native N vacancy (V-N) on the electronic structures and transport properties of AlN nanowire (AlNNW) were theoretically investigated by using density functional theory. Either the Mg-Al defect or the V-N defect prefers to be formed on the AlNNW surfaces. Both MgAl and V-N 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 Mg-Al serves as a shallow acceptor rendering the nanowire a p-type conductor. The V-N introduces a deep donor state enabling the nanowire an n-type conductor. The Mg-Al systems exhibit higher conductivity than the V-N ones owing to the narrow subgaps of Mg-Al systems. The conductivity is roughly proportional to the defect concentration in the Mg-Al and V-N defect systems. When the Mg-Al and V-N coexist, the hole state of the Mg-Al defect and the electron state of the V-N 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.