Plasma Assisted Low Temperature Synthesis of WSe2

The two-dimensional layered structure of transition metal dichalcogenides (TMDs) materials has attracted much attention due to their particular structure. The electrical properties show large differences depending on the choice of the metal employed. These TMD layered materials may exhibit metallic, superconducting, or semiconducting properties. Particularly, tungsten disulphide (WSe₂) shows a semiconducting electronic structure that varies with their thickness. Previous studies using exfoliated WSe₂, have demonstrated a particular ambipolar behavior with large on/off ration and large mobilities. Despite the exceptional electrical and optical properties of WSe₂ reliable synthesis methods on large area are still in early stages. The use of large processing temperatures (over 800°C) restricts the use of substrates used for synthesis, which are able to bear high temperature. Furthermore, the films have to be transferred to an additional substrate due to the damage caused to the original substrate used for synthesis. In this work, we present a method to synthesize WSe₂ from the reduction and later selenization of WO3. The oxygen atoms are replaced selenium in a plasma assisted chemical vapor deposition (CVD) system. By controlling the plasma power the process temperature can be further lowered from 800°C to 250°C. The thickness can be defined by precisely controlling the thickness of predeposited WO₃. The plasma assisted synthesis of WSe₂ develops a new approach that can be extended to other TMD layered materials; and due to the low temperature does not requires further transfer and is compatible with current silicon semiconductor processes (300°C)