Nucleation and coalescence of tungsten disulfide layers grown by metalorganic chemical vapor deposition

•Lateral growth of nucleated WS2 domains on C-plane sapphire by MOCVD in a commercial showerhead reactor was demonstrated.•The crystalline quality of coalesced WS2 monolayers with 108 and electron mobility of 5 cm2/Vs.•Impact of the change of offcut direction of sapphire, substrate annealing temperature and WS2 growth temperature was investigated. The nucleation of tungsten disulfide WS2 crystallites and coalescence behaviour of monolayer WS2 films grown on C-plane sapphire have been studied in a commercial AIXTRON close coupled showerhead metalorganic chemical vapor deposition (MOCVD) reactor using tungsten hexacarbonyl and di-tert-butyl sulfide as precursors. The influence of sapphire substrates offcut (both orientation and angle), as well as the substrate annealing conditions and growth temperature, on the nucleation and size of the WS2 domains has been investigated. A higher nucleation temperature combined with increased substrate annealing temperatures was found to promote an increase in the WS2 domain size. The dependence of surface coverage and coalescence behaviour of the WS2 domains on the growth duration has also been determined, allowing monolayer WS2 films with