The WSe2/Tungsten‐Oxide Interface: Structure and Photoluminescence

A “mixed” surface of WSe2, which contains both the |c and τc facets was produced by mechanical indentation, followed by photoelectrochemical etching, and chemical cleaning. This surface was shown to exhibit low surface recombination velocity, and consequently high solar to electrical conversion efficiency, in the past. Using O18 as a tracer for nuclear activation analysis it is shown that, after the above surface treatment, the surface of the ||c facet is covered with a thin (3–5 monolayers) film of tungsten oxide. The structure of the crystalline oxide phases that comprise the tungsten‐oxide/WSe2 interface are investigated with powder X‐ray diffraction. X‐ray photoelectron spectroscopy is used to study the chemical bonding at the interface. A model is proposed to explain the absence of surface recombination at this interface. A strong above the bandgap luminescence is observed from ||c facets of “mixed” surfaces, and from crystal edges (||c) which were allowed to “age” fcr a few weeks in the air. The origin of this luminescence was investigated in some detail, and a mechanism, involving partially oxidized ||c surface which possibly leads to quantum confinement of excitons in ||c edges of WSe2, is proposed.