對於以往二維光偵測器的文獻主要限制之一是低響應頻率(<< 1 Hz)。在追求高增益及高響應度的同時，響應速度方面幾乎沒有甚麼大幅改善。在此我們展示一新型光偵測器，具有響應度2.6x10^3 A/W相應的光增益為每一入射光子增益6.3x10^3個電子，在具備高響應度及高增益的情況下依然具有40-60 us的超快響應時間。此一新型光偵測器結構為:石墨烯-二硫化鎢-石墨烯的異質接面結構且在此結構上還有隨機覆蓋的銦吸附原子。此新型結構的光偵測器比傳統的金-二硫化鎢-金結構的光偵測器響應度差了6個數量級。光增益主要由銦吸附原子貢獻，銦原子照光產生的電子轉移至二硫化鎢通道，電洞則留於銦原子內，形成光致閘極效應，使電洞留於銦原子的時間內吸引通道內的電子循環。在靠近石墨烯狄拉克點的閘極電壓下，探測率D*達到 2.2x10^12 jones且亮暗電流比高達10^4。此元件的卓越性能歸功於高品質的石墨烯與二硫化鎢接面和銦吸附原子與二硫化鎢通道的強耦合。

One of the primary limitations of previously reported 2D photodetectors is a low frequency response (<< 1 Hz) for sensitive devices with gain. Yet, little efforts have been made to improve the photodetectors in terms of speed while maintaining high gain and responsivity. Here, we demonstrate a gain of 6.3×〖10〗^3 electrons per photon and a responsivity of 2.6×〖10〗^3 A/W while simultaneously exhibiting an ultrafast response time of 40–60 μs in a hybrid photodetector that consists of graphene-WS2-graphene junctions covered with In adatoms atop. The resultant responsivity is 6 orders of magnitude higher than that of conventional photodetectors comprising solely of Au-WS2-Au junction. The photogain is provided mainly by the adsorbed In adatoms, from which photogenerated electrons can be transferred to the WS2 channel, while holes remain trapped in In adatoms, leading to a photogating effect as electrons are recirculating during the residence of holes in In adatoms. At a gate voltage near the Dirac point of graphene, a detectivity of D^*=2.2×〖10〗^12 Jones and an ON/OFF ratio of 〖10〗^4 are achieved. The remarkable performance of the device can be attributed partly to the transparent graphene/WS2 contact and partly to the strong capacitive coupling of the In adatoms with the WS2 channel, which enables ultrafast carrier dynamics.

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