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 (I_illum/I_dark) of ∼10²–10³ is attained, even with the application of electric fields of E_D = 0.02 and E_G = −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.