The Study Of Visible And Infrared Photodetectors Based On Two-Dimensional Heterostructures

Since the discovery of graphene in 2004,two-dimensional materials have received many domestic and foreign researchers'tremendous attention.Thousands of two-dimensional materials with different properties have been successfully discovered and synthesized,as the preparation technologies of nanostructured materials is continuously improved.The properties are extremely sensitive to external condition and easy to be manipulated,due to the atomic thickness.The excellent electrical and optical properties enable it to exert unlimited potential in micro-nanoelectronics and photodetection.However,photodetectors based on two-dimensional materials still have problems needed to be solved,such as slow response speed and limited light absorption efficiency.Fortunately,the improvement of micro-nano processing technology makes it possible for us to combine two-dimensional materials arbitrarily by manual stacking,and we can design some unique structure to improve the detection of photoelectric devices based on two-dimensional materials.In this paper,we mainly focus on the heterojunction based on two-dimensional materials,and explores the effects of these local electric fields on the photoelectric transport of junction photodetectors and their physical mechanism,aiming to realize the effective suppression of dark current and the significantly increased of response speed.The main contents are as follows:1.The mechanism and performance of a vertical Au-WSe₂-ITO Schottky junction photodetector under different bias voltages for detecting visible and near-infrared light were studied.First,the built-in electric field formed by Schottky junction can effectively improve the detector performance.A stable photovoltaic responsivity of 0.1 A/W,fast photoresponse of 50?s and low dark current of 1 pA are achieved in the vertical Au–WSe₂–ITO photodetector.Next,the intrinsic properties of this material enable the fabricated detector achieving a broad spectral response from550 nm?visible light?to 950 nm?near-infrared light?.These results indicate that our vertical Schottky junction can achieve an excellent photoelectric performance.2.The controllable rectification characteristics under different gate voltage were obtained and the photoelectric performances for visible light?520 nm?at zero gate voltage were investigated in van der Waals heterojunction devices based on ReS₂/MoTe₂.The conductivity of MoTe₂ can be tuned from p-type to n-type by the gate voltage.That is to say,the gate voltage can induce the Fermi level of MoTe₂ to shift up or down.As a result,the relative position of the Fermi level between MoTe₂and ReS₂ can be changed by the gate voltage,resulting in a switchable rectifying direction.In addition,the photoelectric performance of heterojunction was measured at zero gate voltage under the visible light?520 nm?illumination.The responsivity and response time can reach 0.5 A/W and 109?s,respectively.This results could offer potential value for the application of 2D materials in the field of electronic and optoelectronic devices.3.The photoelectric performance was investigated in vertical heterojunction devices based on PdSe₂/MoTe₂.It is found that this device has a broad spectral response from visible light?520 nm?to infrared?10.6?m?.In addition,the built-in electric field formed by the two materials has effectively reduced the dark current.The visible light current reaches 10?A with the responsivity of 79 mA/W,the rise response time reaches 160?s and the fall time is 44?s,when the device under the condition of 520 nm light illumination and zero bias voltage.It is the physical property of PdSe₂ make this device achieve an ultra-wide detection range.4.We design the in-plane p-n junction devices based on thin-layer PdSe₂double-gate structure.The thin-layer PdSe₂ exhibits good ambipolar when it is controlled by the gate voltage.By adjusting the size and direction of the voltage applied on the two independent back gates,the form junction can be switched in four states of p-n,p-i,i-n,and n-p.In addition,we tested the photoelectric performance of the device for visible light?637 nm?with a response rate of 3.6 mA/W?external quantum efficiency of 0.9%?.