Single-step, large-area, variable thickness sputtered WS2 film-based field effect transistors

Single-step, uniform, continuous, large-area WS2 films with variable thickness, controlled by the sputtering time, were grown using a magnetron sputtering method to fabricate and then investigate the characteristics of field-effect transistor (FET) devices. Raman measurements showed that WS2 thin films of different thicknesses all give rise to single-phase WS2 that is free of oxide phases. Raman mapping and optical microscope images taken from the interface between the Si/SiO2 substrate and the WS2 region clearly show the formation of a large-area continuous film. X-ray photoelectron spectroscopy (XPS) measurements revealed the sulfur-deficient formation of WS2 for all of the time-dependent series with S/W atomic ratios of around 1.15-1.30. The FET device fabricated on the WS2 layer grown for 1 s showed dominant p-type channel behavior with off-current values in the pA range and on/off ratios spanning almost four orders of magnitude. On the other hand, ambipolar behavior was realized for FET devices fabricated on WS2 continuous films grown for the 5 s, 10 s, and 30 s. Relatively large mobility values of 16.7 and 15.7 cm(2)/(V s) were achieved for the FET devices fabricated on the 10 s and 30 s grown WS2 layers, respectively. The present study shows acceptable FET device characteristics for 2D WS2 materials grown in a single step by sputtering.