p-Type Semiconduction in Oxides with Cation Lone Pairs

Semiconducting oxides are valuable as thin-film displays or solar cell electrodes and are recently of interest as back-end-of-line devices. There are numerous high-mobility n-type semiconducting oxides, but there is a lack of p-type oxides with similar mobility. This led to a search for additional p-type oxides using high-throughput calculations. We find that many of these proposed oxides possess cation s-like lone-pair states. The defect energies of some of these oxides are calculated here in detail. SnTa2O6 is found to be promising p-type oxide based on its low effective hole mass owing to its cation lone-pair character, wide stability range, and absence of compensating native defects. This leads to a desirable p-type doping limit range, which includes the valence band edge, but other oxides with structures more closely based on perovskite configuration are more n-type rather than p-type. The experimentally observed p-type conductivity in related niobium compounds is also discussed. The valence band edge of the disordered SnTa2O6 phase has a mixed O(p)–Sn(s)–O(p) character; thus, it is relatively insensitive to disorders, indicating that it could also make an effective p-type amorphous semiconductor.