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Direct synthesis of submillimeter-sized few-layer WS2 and WS0.3Se1.7 by mist chemical vapor deposition and its application to complementary MOS inverter

This study investigated the direct synthesis of submillimeter-sized few-layer tungsten disulfide (WS2) and tungsten sulfoselenide (WS0.3Se1.7) using the mist chemical vapor deposition (CVD) method as a channel layer for metal-oxide-semiconductor field-effect transistors (MOSFETs). The atomic mono/bilayers WS2 and WS2−x Se x were deposited on thermally grown SiO2 and mist-CVD-grown high-κ amorphous aluminum titanium oxide coated on p+-Si substrates by an intermittent mist supply in a closed quartz tube from (NH4)2WS4 dissolved in N-methyl-2-pyrrolidone. Further, the furnace temperatures, supply/storage times of the precursor mist per cycle, and precursor concentration were considered variables. Consequently, few-layer WS2 and WS0.3Se1.7 with grain sizes of 700–800 μm were obtained on the high-κ a-Al0.74Ti0.26O y dielectric layers through adjustments to the deposition conditions. Subsequently, this few-layer WS2 and WS0.3Se1.7 were applied as channel layers in MOSFETs, which showed n- and p-channel behaviors using gold and platinum source/drain electrodes, respectively. Further, average mobilities of ∼52 and ∼41 cm2 V−1 s−1 were obtained with a threshold voltage of −0.2 (0.3) V and on-off ratios of ∼1 × 106 and ∼6 × 105 in n-WS2 and p-WS0.3Se1.7 channel FETs, respectively. Moreover, this n- and p-channel FETs were used to design an electrically isolated complementary inverter circuit, and a gain of 4–5 was obtained. The findings of this study suggest that mist CVD can be a consistent manufacturing technique for both the channel and gate insulating layers applied in FETs.