Study on the Growth Parameters and the Electrical and Optical Behaviors of 2D Tungsten Disulfide

Transition-metal dichalcogenides (TMDCs) with atomic thickness are promising materials for next-generation electronic and optoelectronic devices. Herein, we report uniform growth of triangular-shaped (∼40 μm) monolayer WS2 using the atmospheric-pressure chemical vapor deposition (APCVD) technique in a hydrogen-free environment. We have studied the optical and electrical behaviors of as-grown WS2 samples. The absorption spectrum of monolayer WS2 shows two intense excitonic absorption peaks, namely, A (∼630 nm) and B (∼530 nm), due to the direct gap transitions at the K point. Photoluminescence (PL) and fluorescence studies reveal that under the exposure of green light, monolayer WS2 gives very strong red emission at ∼663 nm. This corresponds to the direct band gap and strong excitonic effect in monolayer WS2. Furthermore, the efficacy of the synthesized WS2 crystals for electronic devices is also checked by fabricating field-effect transistors (FETs). FET devices exhibit an electron mobility of μ ∼ 6 cm2 V-1 s-1, current ON/OFF ratio of ∼106, and subthreshold swing (SS) of ∼641 mV decade-1, which are comparable to those of the exfoliated monolayer WS2 FETs. These findings suggest that our APCVD-grown WS2 has the potential to be used for next-generation nanoelectronic and optoelectronic applications.