Ga-doping effects on electronic and structural properties of wurtzite ZnO

The electronic properties of Ga-doped ZnO with wurtzite structures are studied using the frozen-core projector augmented wave method based upon the density functional theory with the Perdew-Wang generalized gradient approximation. Among a series of doped cases with atomic ratio of 1.85%, 2.78%, 6.25%, and 12.5%, the system with a 12.5% level of doping yields the lowest cohesive energy in the hexagonal structure. A sharp resonance attributed to the Ga 4s orbital shows up just below the low-lying Zn 3d valence bands. The width of this peak becomes broader as the amount of the Ga dopant is increased, reflecting an increased interaction with the 2p orbitals of the surrounding O atoms. The calculated result reproduces the pronounced Burstein–Moss shift and the shrinkage of the fundamental band gap. Furthermore, an increase of the Ga content leads to the amplification of the volume of the unit cell. The present work seems to indicate that, when doping is introduced, the effective mass of the electron in conduction bands becomes slightly smaller than that in pure ZnO.