Doping limits in p-type oxide semiconductors

The ability to dope a semiconductor depends on whether the Fermi level can be moved into its valence or conduction bands, on an energy scale referred to the vacuum level. For oxides, there are various suitable n-type oxide semiconductors, but there is a marked absence of similarly suitable p-type oxides. This problem is of interest not only for thin-film transistors for displays, or solar cell electrodes, but also for back-end-of-line devices for the semiconductor industry. This has led to a wide-ranging search for p-type oxides using high-throughput calculations. We note that some proposed p-type metal oxides have cation s-like lone pair states. The defect energies of some of these oxides were calculated in detail. The example SnTa2O6 is of interest, but others have structures more closely based on perovskite structure and are found to have more n-type than p-type character. Graphic abstract