A comparative device performance assesment of CVD grown MoS₂ and WS₂ monolayers

In this study, optical and electronic transport properties of chemical vapor deposition (CVD) grown 2D WS₂ and MoS₂ based transistors and photodetectors are investigated and compared in ambient air by using 2D flakes grown with the same CVD system. To assess the performance variations between these two materials and understand the underlying mechanisms, it is essential to utilize identical growth methods (i.e. using the same CVD system), identical substrate and dielectric materials with the identical device fabrication methods and geometries. Transistor devices fabricated out of these flakes are examined in terms of their field effective mobility, current ON/OFF ratio, and photoresponsivity. Our results show that the MoS₂ based devices have higher mobility and photoresponsivity than the WS₂ based devices. However, the hysteresis curve of WS₂ based transistors is smaller when compared to that of MoS₂ based transistors. The mobilities of MoS₂ and WS₂ are estimated from measurements as 1.45 and 0.98 cm² V⁻¹ s⁻¹, respectively. The electronic transport performance of MoS₂ based devices (FETs and photodetectors) are found to be unexpectedly better than the WS₂ based devices in terms of effective carrier mobility and photoresponsivity at ambient atmosphere and temperature. Our results suggest that WS₂ is more sensitive to ambient conditions in comparison to MoS₂, in spite of its theoretically estimated superior performance.