Optical Properties of 2H Phase WTe₂ Flakes

Tungsten ditelluride (WTe2) has attracted increasing attention because of its unique properties, such as its relatively narrow bandgap and large carrier transport, which depend on its phases. A mechanically exfoliated ultrathin WTe2 flake was transferred on to a SiO2/Si substrate. A transferred WTe2 flake with a thickness of 10 – 40 nm was determined by using Atomic force microscopy (AFM). We systematically investigated the thickness-dependent optical properties of the WTe2 flakes. The dominant Raman A³₁,A⁴₁,A⁷₁andA⁹₁ peaks were observed. Strong photoluminescence emission peaks with a band gap of 1.83 eV were observed for flakes with thicknesses of 10 nm, possibly because of a radiative transition. We note that the radiative transition efficiency was enhanced with decreasing number of WTe2 flake layers.