Photoemission study of Cu deposition on molecular-beam-epitaxy-grown ZnS(001)

Abstract

The formation, the chemical and electronic properties, and the thermal stability of the Cu/ZnS(001) interface were investigated by x-ray photoelectron spectroscopy, x-ray fluorescence spectroscopy, and low energy electron diffraction (LEED). ZnS(001) films with 16 ML thickness (4.3 nm), grown on bulk GaP(001) were used as a substrate for Cu deposition. During the room-temperature deposition of the Cu film, the initial submonolayer Cu atoms react with ZnS and the reaction is confined to the interface. Beyond 1 ML the Cu starts to display a metallic character. The Cu deposition induced a downward band bending of ZnS. In the S L2,3 emission spectrum, the Cu deposition results in a significant suppression of the Zn 3d-related doublet and creates a component at about 3.6 eV binding energy in the upper valence band. After annealing of room-temperature-deposited Cu films at temperatures higher than 220 °C, as well as Cu deposition at 320 °C, the signals of Ga 2p photoelectrons reappear, as a result of Cu atoms diffusing into the substrate and reacting with GaP. From LEED observation and attenuation of Zn 2p3/2 intensity, we may conclude that the Cu film grows in an island mode at room temperature, whereas a partially ordered arrangement is adopted at the ZnS(001) surface following Cu deposition at 320 °C.