Cu and Ag deposition on layeredp-typeWSe2: Approaching the Schottky limit

Abstract

The interaction of Cu and Ag on the van der Waals (0001) face of p-type ${\mathrm{WSe}}_2$ has been investigated in relation to Schottky-barrier formation and Schottky solar cells using x-ray and uv photoelectron spectroscopy (XPS,UPS), low-energy electron diffraction (LEED), and surface photovoltage measurements. XPS and UPS results show the growth of a metallic overlayer for small coverages without detectable formation of any interfacial reaction layer. In addition, the LEED experiments indicate epitaxially grown (111) metal layers in the form of clusters. Therefore, we conclude that an atomically abrupt interface between the semiconductor and the M(111) overlayers is formed. The observed band bending obtained from binding-energy shifts corresponds to the work-function difference following the Schottky-Mott theory. However, the surface photovoltage measured at 300 and 100 K is not in good correspondence to the thermionic-emission model of Schottky barriers. Therefore, an alternative interface model is suggested considering n-type doping of the semiconductor interface due to intercalation of the adsorbed metal atoms.