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Electronic structure of oxysulfide (LaO)CuS and ( La 1 − x Ca x O <…

2003; American Physical Society; Volume: 68; Issue: 3 Linguagem: Inglês

10.1103/physrevb.68.035112

1095-3795

Hitoshi Sato, H. Negishi, Asami Wada, A. Ino, S. Negishi, C. Hirai, H. Namatame, M. Taniguchi, Koichi Takase, Yumiko Takahashi, Tomohiro Shimizu, Yoshiki Takano, Kazuko Sekizawa,

ZnO doping and properties

Valence-band and conduction-band electronic structure of the transparent p-type semiconductor (LaO)CuS and the Ca and Ni co-doped system $({\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}\mathrm{O}){\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x}\mathrm{S}$ $(x<~0.10)$ has been investigated by means of photoemission and inverse-photoemission spectroscopies. It is confirmed that the valence bands of (LaO)CuS are composed of the bonding and antibonding states of the Cu $3d$ ${(t}_{2g})$ and S $3p$ orbitals as well as the nearly localized Cu $3d$ ${(e}_{g}),$ and the O $2p$ states. With increasing x up to $x=0.03,$ the structure due to the Cu $3d$ ${(e}_{g})$ states shifts away from the Fermi level ${(E}_{F})$ and the energy separation between the valence-band maximum and conduction-band minimum decreases rapidly, followed by an appearance of new density of states (DOS) derived from the Ni $3d$ and S $3p$ states just above ${E}_{F}$ of (LaO)CuS. For $x>~0.03,$ the new DOS shows up with x, while the energy position of the Cu $3d$ ${(e}_{g})$-derived structure no longer shifts. The finite DOS at ${E}_{F}$ has been observed as a clear structure for $x=0.10.$ These results are not understood in terms of a rigid-band model. We propose a different band model for $({\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}\mathrm{O}){\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x}\mathrm{S}$ taking into account the Ni $3d$ and S $3p$-derived new DOS.