Photoemission studies of interface chemistry and Schottky barriers for ZnSe(100) with Ti, Co, Cu, Pd, Ag, Au, Ce, and Al.

Abstract

Photoemission has been used to examine the formation of metal overlayers on sputter-annealed ZnSe(100)-c(2\ifmmode\times\else\texttimes\fi{}2) surfaces for transition metals (Ti,Co), noble and near-noble metals (Cu,Ag,Au,Pd), a lanthanide (Ce), and a simple metal (Al). Analysis of Zn 3d core-level emission reflects metal-substrate interaction as well as substrate band bending as a function of metal coverage. Large differences in chemical behavior have been found. In particular, Ag and Au adatoms induce negligible Zn 3d core-level broadening, which is consistent with no substrate disruption. For the other metals, a second Zn 3d component reflects substrate disruption, and two reaction-induced components develop for Ti and Ce. The development of the Schottky barrier is compared with work-function variations. Very different Schottky-barrier heights have been found, ranging from 0.5 eV for Ce to 1.5 eV for Au and Pd. Neither the defect model nor the metal-induced gap-states model is able to describe all the experimental Schottky-barrier data. We do find a general correlation between the barrier height and the metal work function.