Self-doping of cadmium stannate in the inverse spinel structure

Using first-principles total energy calculations, we have studied self-doping in the ternary transparent conducting oxide, Cd2SnO4. Formation of the CdO and SnO2 binaries limits the inverse spinel Cd2SnO4 phase into a narrow region in the atomic chemical potential (μ) space. This suggests that μSn is not independent of μCd, so a Cd-rich growth or annealing condition also implies Sn-rich, and vice versa. We found that the widely accepted intrinsic donors such as oxygen vacancy and cadmium interstitial are not responsible for the observed conductivity in Cd2SnO4: both require too much energy to form. In addition, the oxygen vacancy is rather deep. We show instead that the Sn-on-Cd antisite defect is the most probable donor responsible for the n typeness under Cd-rich conditions.