CVD growth of monolayer WS2 through controlled seed formation and vapor density

Abstract Large area, single layer WS 2 has a high potential for use in optoelectrical devices with its high photoluminescence intensity and low response time. In this work, we demonstrate a systematic study of controlled tungsten disulfide (WS 2 ) monolayer growth using chemical vapor deposition (CVD) technique. With a detailed investigation of process parameters such as H 2 gas inclusion into the main carrier gas, growth temperature and duration, we have gained insight into two-dimensional (2D) WS 2 synthesis through controlling the seed formations and the radical vapor density associated with WO 3 . We confirm that H 2 gas, when included to the carrier gas, is directly involved in WO 3 reduction due to its reductive reagent nature, which provides a more effective sulfurization and monolayer formation process. Additionally, by changing the CVD growth configuration, hence, increasing the tungsten related vapor density and confining the reactant radicals, we succeed in realizing larger WS 2 monolayers, which is still a technological challenge in order to utilize these structures for practical applications. Further optimization of the growth procedure is demonstrated by tuning the growth duration to prevent the excess seed formations and additional layers which will possibly limit the device performance of the monolayer flakes or films when applied.