X-ray photoelectron spectroscopy ofCuInSe2

In x-ray photoemission, we have observed negative shifts of the valence-band maximum with conduction-type conversion from p to n type, induced by a decrease in the [Cu]/[In] ratio of the ${\mathrm{Cu}}_{1\pm \mathrm{\delta }}$ ${\mathrm{In}}_{1\mp \mathrm{\delta }}$ ${\mathrm{Se}}_2$ thin films, deposited by a molecular-beam method. We found no evidence of Cu 2p poorly screened peaks, representing Cu ${\mathit{d}}^9$ electron configuration in the p-type films. Holes in the p-type films are located at the d-p antibonding orbital, dominated by the Se p state in the crystal. The binding energy of the Cu d state, dominating the d-p bonding orbital, is larger than that of the Se p state.