Theoretical study on electronic properties of p-type GaN nanowire surface covered with Cs

By using density functional theory, we have investigated the Cs adsorption mechanism of Mg-doped GaN nanowire photocathode. The results show that in the GaN nanowire, Mg atoms tend to replace the Ga atoms in the central position, because the position has the lowest formation energy, and the carrier concentration is highest, which shows better conductivity. Besides, Mg doping leads to the Fermi level close to the valence band, exhibiting p-type conductivity. After Cs activation, the most stable adsorption site of Mg-doped nanowires is B_N site. After Cs adsorption, the conduction band minimum and the valence band maximum both move to the lower energy, which is favorable for forming the n-type surface state and improving the photoelectron escape probability. This study can be used to guide the Cs adsorption process of Mg-doped GaN nanowires, which is helpful to improve the performance of GaN nanowire-based optoelectronic devices.