Layer-modulated, wafer scale and continuous ultra-thin WS2 films grown by RF sputtering via post-deposition annealing

Abstract

Tungsten disulfide (WS₂) is a layered semiconducting material with a tunable bandgap that is promising in next generation nanoelectronics as well as energy harvesting devices. In this study, we presented a continuous and wafer-scale uniform WS₂ layer preparation technique through sulfurization of a RF-sputtered WO₃ film. Various characterization techniques were employed in order to investigate the structural and physical properties of the WS₂ films. It was observed that the thickness of WS₂ films could be controlled by tuning the sputtering time. The fabricated WS₂ transistors exhibited high mobility values of ∼17 and 37–38 cm² V⁻¹ s⁻¹ and on/off ratios in the range of ∼10⁴ and 10⁴–10⁵ for 80–100 s-sputter time and 120–140 sputter time, respectively, which is in the maximum range for CVD-grown WS₂ FETs with an SiO₂ gate oxide. Photoresponse was also studied for a few layers of WS₂ on a transparent quartz substrate and it was observed that the photosensitivity was linearly dependent on bias voltage. The proposed growth technique is attractive for next-generation transparent and nanoelectronic devices, as well as for other potential applications.