Codoping of magnesium with oxygen in gallium nitride nanowires

Codoping of $p$-type GaN nanowires with Mg and oxygen was investigated using first-principles calculations. The Mg becomes a deep acceptor in GaN nanowires with high ionization energy due to the quantum confinement. The ionization energy of Mg doped GaN nanowires containing passivated Mg–O complex decreases with increasing the diameter, and reduces to 300 meV as the diameter of the GaN nanowire is larger than 2.01 nm, which indicates that Mg–O codoping is suitable for achieving $p$-type GaN nanowires with larger diameters. The codoping method to reduce the ionization energy can be effectively used in other semiconductor nanostructures.