Electrical And Photoelectrical Properties Of Nanoscale Van Der Waals Heterostructure

The PN junction is a core component of electronics and optoelectronics devices.With device further scaling,it is vitally important to investigate nanoscale PN heterojunctions.However,due to the existence of dangling bonds and lattice mismatch,it is impossible to realize atomic flat heterojunctions with traditional materials,which limits the development of nanoscale PN heterojunctions.Fortunately,two-dimensional(2D)materials are layered materials without dangling bonds.The layer interaction of 2D material is van der Waals force.We can realize^any ftinctional heterostructure by simply stacking these two-dimensional materials into heterojunctions.Therefore,two-dimensional materials provide xxs with an ideal platform to investigate nanoscale heterojunctions.In this thesis,we mainly investigated three kinds of heterojunctions.All of them show novel electrical and photoelectrical properties.Therefore,nanoscale van der Waa^s heterojunctions are suitable for investigating new physics and new applications.By characterizing the performance,we demonstrate that nanoscale van der Waals heterojunctions have great potential applications in nanoelectronics and optoelectronics.First,we investigated electrical transport properties including gate-tunable rectification inversion and polarity inversion in atomically-thin graphene/WSe2 heterojunctions.And also,such atomically thin heterostructure shows excellent performances on photodetection.Even with a zero bias voltage,the responsivity and detectivity of the device can reach 66.2 mA W-1 and 1013 cm Hz1/2/W,respectively.Then,we reported the photoelectric property of b-AsP/MoS2 heterojunctions.We demonstrated a general strategy to suppress dark current and noise to dramatically improve the performance of photonic devices by stacking narrow-band and wide-band materials into PN heterojunctions.The performance of b-AsP/MoS2 is superior to all commercial room temperature mid-IR photodetector.Finally,we demonstrated a ballistic avalanche phenomenon in InSe/BP heterostructure for the first time.Based on this phenomenon,we demonstrated a ballistic avalanche photodetector and a ballistic avalanche transistor.The ballistic avalanche photodetector shows high photon multiplication and low noise properties.The noise can be even less than the theoretical excess noise limit of conventional avalanche photodetector above a certain frequency.The average subthreshold swing of the ballistic avalanche transistor is 0.25 mV/dec.To confirm the ballistic transport in BP vertical direction,we measured the Fabry-Perot interference pattern which is the direct demonstration of the ballistic transport.