Valence band structure of BaCuSF and BaCuSeF

The origin of high hole conduction in BaCuQF (Q=S,Se) was investigated by photoemission measurements and full-potential linearized augmented plane wave band-structure calculations. In both compounds, the large dispersion near the top of the valence band is realized by admixed states of Cu 3d and S 3p or Se 4p orbitals, indicating that high hole mobility is possible. In addition, the valence band maxima of BaCuQF are much closer to the vacuum level than most p-type transparent oxides, which leads to high hole stability in the valence band. The high hole mobility and stability in BaCuQF relative to most oxides afford a significantly larger p-type conductivity.