Preparation of 2D Tungsten Diselenide (WSe2) thin films by selenization of DC-sputtered W precursors

Abstract

Two-dimensional layered transition metal dichalcogenides based on WSe₂ films demonstrated promising properties for nano-electronics and photovoltaic applications. In this work, WSe₂ films were prepared by selenization of DC-sputtered W precursors. The influence of the selenization temperature on the structural, morphology, and optical properties of the WSe₂ films was investigated. The selenization temperature was varied from 350 °C to 450 °C at the interval of 50 °C.  Structural, morphology and optical properties of the WSe₂ were investigated using X-ray diffractometry (XRD), Atomic Force Microscope (AFM), and UV-VIS-NIR spectrophotometer, respectively. XRD analysis revealed that all WSe₂ were polycrystalline and exhibited the co-existence of c-axis perpendicular and parallel substrate texture. Samples selenized at 400 °C demonstrated strong  - types of crystal orientations – perpendicular c-axis substrate texture – dominated crystal growth. The AFM images further revealed the co-existence of parallel and perpendicular crystal orientations for samples selenized at 350 °C and 450 °C. Optical measurement showed that all WSe₂ samples were transparent and consisted of an excitonic peak at the wavelength of around 620 nm. The estimated bandgap values were in the range of 1.22 eV to 1.37 eV which is somchat lower than expected – the presence of W₅O₁₄ phases is suggested to be the main cause.