Surface photovoltage and electron energy‐loss spectroscopy of oxygen adsorbed on (1120) CdSe

The surface electronic structure of oxygen adsorbed on (112̄0) CdSe has been studied by surface photovoltage and electron energy‐loss spectroscopy. These techniques have been combined for the first time to compare the extrinsic energy levels associated with observed surface electronic transitions. In addition, x‐ray photoelectron spectroscopy was used to monitor surface chemical composition and valence band photoemission features. Surface photovoltage spectra of the O‐adsorbed surface indicated a pronounced transition to an extrinsic state ∠0.14 eV below the conduction band edge and less intense transitions involving at least four other discrete levels distributed across the band gap. Only minor variations of this structure were observed over a range of oxygen coverages 0.15?ϑ?0.98. Electron energy‐loss spectra of these surfaces exhibited modified ’’interband’’ transitions consistent with x‐ray photoelectron valence‐band spectra and a d‐band transition to an unoccupied extrinsic state near the conduction band edge, in agreement with the strongest photovoltage transition.