Research On Photodetection And Functional Devices Based On Two-Dimensional Black Phosphorus Semiconductor

With the rapid development of modern information technology,low-power broadband photodetectors have been widely used in remote sensing imaging,optical communication,military reconnaissance,unmanned driving and many other fields.While commercial optoelectronic detectors utilizing silicon-based materials have achieved a mature process technology,they are constrained by their structural characteristics and encounter numerous challenges in achieving miniaturization,wide spectral range coverage,and multifunctional applications.Two-dimensional（2D）materials are excellent candidates for novel broadband photodetectors owing to their low-dimensional structure,multi-physical properties and strong light-matter interaction.Graphene-based photodetectors can achieve ultra-broadband detection from visible to far-infrared range with a fast response speed,but the response and photoconductivity gain are still required to be improved due to the zero bandgap characteristics of graphene.Among the various2D materials,black phosphorus（BP）semiconductors have tunable bandgaps,high carrier mobility,bipolar conductive characteristics and optoelectronic anisotropy,which providing more regulatory dimensions for high-performance photodetectors with broadband detectable range or integrated optoelectronic functions.Therefore,2D BP semiconductors show great application prospects for high-performance self-driven broadband photodetection,and provide more regulatory dimensions for functionally integrated optoelectronic devices.In this thesis,we focus on narrow-bandgap BP semiconductor,study the application of asymmetric contact strategy in BP semiconductor,and explore the performance and physical mechanism of asymmetric BP devices for self-driven broadband photodetection.A new method of regulating BP bipolar is further developed,and the deal photovoltaic characteristics of the dual-gate BP device under electrostatic doping method for self-driven broadband photodetection is studied,which provides a basis for realizing diversified band coupling types under dual-gate control.Finally,the reconfigurable broadband photoresponse for dual-gate BP device is studied,and its application in sensor-computing integrated image processing is explored,and a multifunctionally integrated optoelectronic device for broadband sensing and computing is realized.Based on this,the thesis mainly focuses on the photodetection and multifunctionally integration of 2D BP semiconductors,and the specific research contents and results are as follows:1.Self-driven broadband photodetector induced by asymmetric contact on BP.Based on the alignment relationship of band structure,asymmetric device with Chromium/black phosphorus/Tungsten ditelluride（Cr/BP/WTe₂）configuration is designed,in which 2D semimetal tungsten ditelluride（WTe₂）is selected to realize ohmic contact with narrow-bandgap BP semiconductor,while conventional metal chromium（Cr）achieves Schottky contact with BP.The combination of the asymmetric strategies of ohmic and Schottky contacts for the first time constructs a large unilateral built-in electric field in narrow-bandgap BP channel,enabling a self-driven broadband photodetector covering from the visible to infrared spectrum.Under zero bias,when the device is irradiated at 532 and1550 nm lasers,the device exhibits responsivity of～283 and～193 mA W^-1,respectively,with corresponding detectivity of～2.3×10¹¹ and～1.2×10¹¹ Jones.The results show that a well-designed band structure can construct an good Schottky and ohmic contact on narrow-bandgap 2D materials,and a self-driven broadband photodetector can be achieved under the combined effect of the photovoltaic effect induced by the Schottky barrier and the inherent photothermal and electric effect of black phosphorus.2.Self-driven broadband photodetector based on in-plane BP homojunction.To optimize the photovoltaic characteristics of photodetector,a novel method to tune BP bipolarity is developed here by using thermal evaporation Al followed with natural oxidation to prepare Al₂O₃ capping layer with controlled thickness on BP nanosheets.A pn junction with strong build-in electric field is constructed in the device by using electrostatic doping of dual-gate structure for electron and hole doping.In the device,the photogenerated electron-hole pairs in a wide spectral range can be separated spontaneously,thus realizing a self-driven wide-spectrum photodetector covering form the visible to infrared spectrum.The device can achieve responsivity of～226 and～153mA W^-1 under 532 and 1550nm illumination,respectively,with corresponding detectivity of～7.6×10¹⁰ and～5.1×10¹⁰ Jones under zero bias.At various wavelengths,the photoresponse of the device shows a constant photoresponsivity and the fittingαclose to1,which proves that the photoresponse mechanism of the device comes from the ideal photovoltaic effect.3.Broadband reconfigurable photovoltaic detection and sensor-computing integrated image sensing based on BP homojunction device.The theoretical simulation and electrical results show that the dual-gate structure can realize the reconfigurable pn homojunction in the device by tuning the gate voltage,and realize the self-driven photovoltaic detection in broadband spetrum.The positive and negative photovoltaic characteristics of the device in the broadband spectrum are linearly dependent on the gate voltage in a large window,and the change of responsivity can correspond to the weight update of the convolution calculation process in the neural network,so that the broadband convolution operation covering the infrared band can be realized in the device.Finally,the image sharpening and edge enhancement are realized in the device.At the same time,in the digital image recognition and classification function of wide spectrum,the recognition accuracy reaches～100%after only 5 training cycles.It is proved that 2D BP homojunction with electrostatic doping can be further used as a prototype of a broadband sensor-computing integrated image sensor to realize both image sensing and convolution computing functions.