High-performance photocurrent generation from two-dimensional WS{sub 2} field-effect transistors

The generation of a photocurrent from two-dimensional tungsten disulfide (WS{sub 2}) field-effect transistors is examined here, and its dependence on the photon energy is characterized. We found from the WS{sub 2} devices that a significant enhancement in the ratio of illuminated current against dark current (I{sub illum}/I{sub dark}) of ∼10{sup 2}–10{sup 3} is attained, even with the application of electric fields of E{sub D} = 0.02 and E{sub G} = −22 mV/nm, which are much smaller than that of the bulk MoS{sub 2} phototransistor. Most importantly, we demonstrate that our multilayer WS{sub 2} shows an extremely high external quantum efficiency of ∼7000%, even with the smallest electrical field applied. We also found that photons with an energy near the direct band gap of the bulk WS{sub 2}, in the range of 1.9–2.34 eV, give rise to a photoresponsivity of ∼0.27 A/W, which exceeds the photoresponsivity of the bulk MoS{sub 2} phototransistor. The superior photosensing properties of WS{sub 2} demonstrated in this work are expected to be utilized in the development of future high performance two-dimensional optoelectronic devices.