In-depth study on defect behavior and electrical properties in Ga-doped ZnO films by thermal-treatment under different chemical equilibrium

Abstract GZO films were sputtered under two contrasting atmospheres of pure oxygen and pure Ar and post-annealed in Zn vapor and vacuum to investigate the effect of the chemical equilibrium during annealing. In an effort to get a deep insight on the correlation between film properties and behavior of defects in the Ga-doped ZnO (GZO) films, in-depth analysis of the prepared GZO films has been also performed using various analytical tools. XPS and EPR investigation clearly demonstrate that after thermal treatment, the activation rate of the doped-Ga atoms as a donor was enhanced and especially, the annealing in Zn vapor resulted in the introduction of the donor-like defect, Zn interstitials in films, further increasing the electron concentration in film, as demonstrated by Hall analysis. By combining EPR results with Hall data, it was evaluated that after thermal treatment in both ambients, the electrical quality of the GZO film sputtered in a strong oxidizing ambient, pure O2, was dramatically converted from highly resistive to highly conductive by fully annihilating acceptor-like defect, Zn vacancies with the lowest formation energy in GZO and it was suggested that this finding would be attributable to the out-diffusion of the oxygen atoms adsorbed or chemisorbed at grain-boundaries and on the film surface and the compensation of Zn vacancies by the incorporated excess Zn ions/atoms in films during thermal treatment.