Resonant Ta Doping for Enhanced Mobility in Transparent Conducting SnO2

Transparent conducting oxides (TCOs) are ubiquitous in modern consumer electronics. SnO₂ is an earth abundant, cheaper alternative to In₂O₃ as a TCO however, its performance in terms of electrical properties lags behind that of In₂O₃. Based on the recent discovery of mobility and conductivity enhancements in In₂O₃ from resonant dopants, we use a combination of state-of-the-art hybrid density functional theory calculations, high resolution photoelectron spectroscopy and semiconductor statistics modelling to understand what the optimal dopant is to maximise performance of SnO₂-based TCOs. We demonstrate that Ta is the optimal dopant for high performance SnO₂, as it is a resonant dopant which is readily incorporated into SnO₂ with the Ta 5d states sitting ~1.4 eV above the conduction band minimum. Experimentally, the electron effective mass of Ta doped SnO₂ was shown to be 0.23m₀, compared to 0.29m₀ seen with conventional Sb doping, explaining its ability to yield higher mobilities and conductivities.