Tuning the electronic structure of the transparent conducting oxide Cu₂O

The electronic structure of Cu₂O is important for its application as a p-type transparent conducting oxide (TCO). To be useful as a TCO, a material needs to show enhanced transparency in the visible range (band gap > 3 eV) as well as good conduction properties. While Cu₂O has too small a band gap, alloys of Cu₂O and Al₂O₃ or Cu₂O and alkaline earth oxides are known to display enhanced transparency, with little degradation of electrical properties. It is of interest to consider how to dope Cu₂O p-type, e.g. Cu vacancies (oxidation) or cationic dopants. We present a study of the electronic structure and effective hole masses of stoichiometric and oxidised Cu₂O and study metal cation doping, using density functional theory (DFT), to analyse p-type doping scenarios. We show that formation of a Cu vacancy is relatively facile, introducing delocalised hole states, with a light hole present. Substitutional cation doping with Al and Au/Ag is found to decrease the band gap but maintains a light hole effective mass necessary for p-type conduction.