Photoemission study of the Na/ZnSe(100) interface

We report on a comprehensive study of the ZnSe(100)-c(2×2)-Na interface using x-ray and UV photoemission, and x-ray-induced Auger spectroscopy. Spectra were taken after stepwise Na deposition onto a clean c(2×2)-reconstructed ZnSe(100) surface at room temperature up to a saturation coverage of about 1 ML of Na and after annealing. Based on the analysis of Auger parameters and of the relative intensity evolution of various Na, Zn, and Se species, we present the following model for the ZnSe(100)-c(2×2)-Na interface: below a coverage of 0.5 ML, Na is adsorbed on Zn vacancy sites; above 0.5 ML, a cation exchange reaction occurs between Na and Zn atoms; Zn atoms segregate on top of the Na overlayer forming metallic Zn. In addition, band-bending, surface dipole, valence-band and surface states will be discussed.