High-performance photocurrent generation from two-dimensional WS2 field-effect transistors

The generation of a photocurrent from two-dimensional tungsten disulfide (WS2) field-effect transistors is examined here, and its dependence on the photon energy is characterized. We found from the WS2 devices that a significant enhancement in the ratio of illuminated current against dark current (Iillum/Idark) of ∼102–103 is attained, even with the application of electric fields of ED = 0.02 and EG = −22 mV/nm, which are much smaller than that of the bulk MoS2 phototransistor. Most importantly, we demonstrate that our multilayer WS2 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 WS2, 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 MoS2 phototransistor. The superior photosensing properties of WS2 demonstrated in this work are expected to be utilized in the development of future high performance two-dimensional optoelectronic devices.