Interface dipoles, surface work functions, and Schottky-barrier formation at Au/ZnSe(100) interfaces

Ultraviolet-photoemission studies for Au--n-type ZnSe(100) interfaces show parallel changes in substrate band bending and the surface work function as a function of Au coverage. For the Zn-rich reconstructed c(2\ifmmode\times\else\texttimes\fi{}2) ZnSe(100) surface, the electron affinity is 0.55 eV less than that for the cleaved (110) surface, suggesting the existence of a positive surface dipole. This surface dipole is gradually reduced by 0.19 eV by the deposition of \ensuremath{\sim}2 A\r{} of Au. The deposition of Au results in exponential decay of the Zn 3d core-level emission, but no changes in line shape that would indicate chemical interaction. The final position of the Fermi level is 1.25\ifmmode\pm\else\textpm\fi{}0.10 eV above the valence-band maximum of ZnSe, but changes are very slow. There is a clear correlation of band bending with the surface work function as Au adatoms evolve from a dispersed state to a metallic film, indicating the validity of the original Schottky model for this system.