Dual-gate MoS2 phototransistor with atomic-layer-deposited HfO2 as top-gate dielectric for ultrahigh photoresponsivity.

An asymmetric dual-gate (DG) MoS2 field effective transistor (FET) with ultrahigh electrical performance and optical responsivity using atomic-layer-deposited HfO2 as top-gate (TG) dielectric was fabricated and investigated. The effective DG modulation of MoS2 FET exhibited an outstanding electrical performance with a high on/off current ratio of 6×108. Furthermore, a large threshold voltage modulation could be obtained from -20.5 to -39.3 V as a function of the TG voltage in a DG MoS2 phototransistor. Meanwhile, the optical properties were systematically explored under a series of gate biases and illuminated optical power under the 550 nm laser illumination. And the ultrahigh photoresponsivity of 2.04×105 AW-1 has been demonstrated with the structure of DG MoS2 phototransistor because the electric field formed by DG can separate photogenerated electrons and holes efficiently. So, the DG design for the 2D materials with ultrahigh photoresponsivity gives promising opportunity for the application of optoelectronic devices.