Growth Behavior, nucleation control and excellent optical properties of atomically thin WS2 thin films processed via Gas-phase chemical vapor deposition

Improving growth-rate of atomically thin transition metal dichalcogenides (TMDs) with precise thickness-control using a facile-approach is ever growing interest for nanoscale electronic devices. Here, using metalorganic precursors, we demonstrate the growth of WS2 layers on sapphire and SiO2/Si substrates at elevated temperatures via gas-phase chemical vapor deposition (CVD) approach. This choice of precursor for the CVD-process allowed us to rapidly produce the WS2 layers with a growth rate as high as 1-monolayer per 5 min at a growth temperature of 850 degrees C. The layer thickness (number of layers), which linearly scales with growth time, can be manipulated with a monolayer precision. Our findings suggest that the initial-nucleation and growth behavior of the WS2 monolayers are very well controlled by reactor pressure and growth temperature. Grain size engineering and possible growth-mode switching from 2D lateral-growth to 3D vertical-growth is demonstrated by tuning the CVD reactor pressure between 10 and 30 Torr. A possible growth behavior is also discussed for the growth temperature range of 650 to 850 degrees C. The as-grown WS2 monolayers exhibited excellent photoluminescence emission around 2.0 eV with a linewidth of 49 meV. Our gas-phase-precursor assisted CVD approach would enable a pathway for the rapid-production of atomically thin TMDs for electronic industry.