Creating wafer-scale 2D WS2 monolayers for next generation nanoelectronic devices: an investigation of epitaxial growth
Semiconducting two-dimensional (2D) transition metal dichalcogendes like MoS2 and WS2 are attracting great interest for application in ultra-scaled nano-electronic devices because of their monolayer thickness, large band gap, low dielectric constants, lack of dangling bonds and structural stability. A key prerequisite for their industrial exploitation is the availability of manufacturable deposition techniques, like chemical vapor deposition (CVD), to create semiconducting 2D monolayers at wafer-scale. Although CVD of 2D semiconductors on large area substrates has been demonstrated, there are still challenges related to achieving high quality structures and good semiconductor properties, especially for WS2. Impurities, defects and crystal grain boundaries can degrade the carrier mobility. A lack of fundamental understanding of the growth mechanism and the impact of templates prevents the accurate control of the crystallinity during epitaxial growth by CVD. The first objective of this project is to generate fundamental understanding of the growth and nucleation mechanisms during the epitaxial growth of 2D WS2 monolayers by CVD. The second objective is to provide insight into the impact of possible resulting defects on the charge carrier mobility. We focus on WS2 because of its much higher intrinsic carrier mobility as compared to MoS2.