First principle study of structural stability, electronic structure and optical properties of Ga doped ZnO with different concentrations

Structural, electronic and optical properties of pure and Ga doped ZnO (GZO), with different concentrations (x = 6.25%, 12.5% and 25%) are investigated by the ab initio full-potential linearized augmented plane wave (FP-LAPW) method, using the exchange and correlation potential within the generalized gradient approximation and the modified Becke-Johnson (mBJ) exchange potential. In the present work, some electronic properties, such as the band structure and the density of states as well as some optical properties, such as the dielectric function e(omega), the refractive index n(omega), the reflectivity R(omega) and the electron energy-loss L(omega) were improved. The calculated lattice constants and the optical band gap (3.27 eV) of pure ZnO were found to be in good agreement with the experimental results. We have shown that the increase of the Ga concentration in ZnO creates shallow donor states Ga-4s in the minimum of the conduction band around the Fermi level, increasing the optical band gap and the conductivity. The absorption edge, presents in the imaginary part of the dielectric function, moves to higher energy levels with increasing Ga concentration. The static refractive index and the reflectivity of GZO increased with the increasing Ga concentrations. The L(omega) spectrum shows a single metal property for pure ZnO, and two peaks were observed for GZO, a small one around 2 eV originated from Ga doping and a second moved to higher energies indicating that the metallic character is more present in GZO than in pure ZnO.