Band edge modulation and interband optical transition in AlN:Mg$_{{\rm{Al}}}$-O$_{{\rm{N}}}$ nanotubes

AlN nanotubes (NTs) have many novel characteristics and great potential applications in electronic and optoelectronic nanodevices. However, little is known about the influence of Mg-O co-doping effects on their optical properties. Here, we focus on investigating the electronic structures, clarify the interband optical transition mechanism and give a clear atomic picture for the important electron/hole localization centre in AlN:Mg-O NTs using the GGA-1/2 method. We find that the Mg doping efficiency can be improved effectively due to O doping in AlN NTs. The Mg and O form Mg-O defect complex easily along the AlN NT axis (C-axis). The Mg-O defect complex can result in a remarkable charge transfer around it and modify the valence band maximum and conduction band minimum significantly. Meanwhile, the Mg-O defect complex also forms the important exciton localization centre and effectively enhances the interband radiative recombination rate. Moreover, the light emission/absorption sensitively depends on its polarization. The parallel polarized light () is much stronger than the perpendicular one (). The Mg-O co-doping thus paves a new way for improving the performance of electronic and optoelectronic nanodevices based on AlN NTs.