A classification scheme of oxide sulfides to guide the design of new hole-conducting transparent materials

The addition of S to transition metal oxides has been contemplated as a way to overcome the limitations of pure oxides by producing a hybridized O-S band with lighter hole mass and narrower gap. Here, we show that O-S mixing could lead either to a continuous band broadening and an upward shift of the valence bands (``band amalgamation" scenario) or to the formation of S-localized states deep in the band gap of the host oxide above the O band (``band pinning" scenario). We survey the La-based oxide sulfides by first-principles methods and we observe the following types of VBM wavefunction in relation to the coordination of the O and S atoms: (i) O and S segregate into separate molecular units; the VBM is preferentially localized on the S units (e.g., LaOCuS). (ii) O and S segregate into separate molecular units; the VBM is delocalized on both O and S units (e.g., (LaO)$_{2}$SnS$_{3}$). (iii) O and S are spatially mixed in the lattice; the VBM is preferentially localized on S (e.g., LaGaOS$_{2}$). (iv) O and S are spatially mixed in the lattice; the VBM is delocalized on both S and O (e.g., LaCrOS$_{2}$). Thus, selecting the type of anion coordination is a posible route to tune the hole conductivity in oxide sulfides.