The role of oxygen vacancies in the transparent conducting oxides (TCOs) In2O3, SnO2 and ZnO has remained controversial, with some studies indicating that they act as shallow donors, but many computational studies using plane-wave supercell techniques claiming that they act as deep traps. Using the hybrid QM/MM embedded cluster technique via the ChemShell code, we calculated the formation and thermal ionisation energies of oxygen vacancies in the three TCOs.
We found that, in In2O3 vacancies acted as shallow donors and accounted for the large n-type carrier concentrations observed experimentally in undoped samples. Furthermore, we computed equilibrium defect and carrier concentrations, showing that, even in ZnO and SnO2, where the vacancies formed deep centres, they contributed significantly to intrinsic carrier concentrations.
J. Buckeridge, C. R. A. Catlow, M. R. Farrow, A. J. Logsdail, D. O. Scanlon, T. W. Keal, P. Sherwood, S. M. Woodley, A. A. Sokol, and A. Walsh, “Deep vs shallow nature of oxygen vacancies and consequent n-type carrier concentrations in transparent conducting oxides“, Phys. Rev. Materials, 2018, 2, 054604.