Intrinsic n-type behavior in transparent conducting oxides: A comparative hybrid-functional study of In2O3, SnO2, and ZnO

We present a comparative study of point defects in In2O3, SnO2 and ZnO based on the hybrid-functional method within the density functional theory (DFT). For In2O3 and SnO2, our results provide strong evidence of shallow donor states at oxygen vacancies. The formation energies of oxygen vacancies are low both for the doubly positive and neutral charge states. In comparison with the semilocal exchange-correlation approximations in DFT the hybrid-functional method lowers strongly the formation energy of the positive charge state and keeps that of the neutral state nearly intact. The trend is analyzed in terms of changes in the lattice relaxation energy and the electron energy levels near the band gap. The existence of shallow donor states at oxygen vacancies and the consequent n-type conductivity are in line with experimental findings. The results invalidate some former theoretical interpretations.