Electronic and optical properties of Ga-doped ZnO

This study adopted density functional theory and the Hubbard-U method in an investigation of the electronic and optical properties of pure ZnO and Ga-doped ZnO. The difference in the lattice constant between calculated results and experimental measurements is less than 1%, while the calculated band gap of pure ZnO is in excellent agreement with experimental values. Three structures, including the substitution of Ga for Zn (Ga-s(Zn)), interstitial Ga in an octahedron (Ga-i(oct)), and interstitial Ga in a tetrahedron (Ga-i(tet)), were considered. Calculations related to formation energy revealed that Ga-s(Zn) forms more easily than Ga-i(oct) and Ga-i(tet). All three of the Ga defect models resulted in an upward shift in the Fermi level into the conduction band, resulting in n-type conductive characteristics and expansion of the optical band gap beyond that of pure ZnO. In the Ga-s(Zn) model, the average transmittance levels in the visible and UV regions were 90.5% and 77.8%, respectively, which are higher than those obtained using the pure ZnO model. However, in both the Ga-i(oct) and Ga-i(tet) models, an increase in effective mass resulted in a decrease in carrier mobility, thereby reducing electrical conductivity. In addition, interestitial Ga atoms within the ZnO crystal reduced transmittance significantly. (C) 2014 Elsevier B.V. All rights reserved.