Study On The Fabrication And Mechanisms Of TMDs Photodetectors

In the past decade,two-dimensional?2D?materials have been extensively investigated and exhibited the huge potential in the next-generation nanoelectronic and photoelectronic fields because of the unique properties,such as atomic thin?tunable electronic states?,interlayer van der Waals force?lattice match at heterostructure interfaces?,and abundant electronic band structures?the whole electromagnetic spectrum?.The representative transition metal dichalcogenides?TMDs?with a tunable bandgap,large light absorption efficiency,and anisotropy,provide a feasible route to fabricate high-performance photodetectors with broadband response,high bandwidth,and polarization sensitivity.However,lots of defects?vacancy defects?in TMDs severely limit the carrier transport and the collection efficiency of photo-carriers,which makes the core parameters of detectors,such as the special detectivity and response speed,far from satisfactory.In the light of the operating mechanisms of photodetectors,TMDs photoconductive and photovoltaic photodetectors modulated by charge transfer doping,electrostatic doping,and substitution doping,are investigated in our work,to fabricate sensitive photodetectors with high sign-noise ratio and fast speed at room temperature.The main contents are as follows:1.The fabrication and mechanism of photoconductive photodetector based on TMDs are investigated.The Pt S₂ crystals are grown by chemical vapor transport.The Pt S₂photodetectors are fabricated by the mechanical exfoliation and micro-process.Pt S₂photodetectors exhibit excellent performance with the electron mobility(62.5 cm² V^-1s^-1)and the on/off ratio?10⁶?at room temperature.The low-temperature electrical transport characteristic of Pt S₂ photodetectors are studied.The temperature-dependent conductance and mobility of Pt S₂ transistors show a direct metal-to-insulator transition and carrier scattering mechanisms,respectively.The Pt S₂ photodetectors could detect the light from visible to infrared and exhibit fast speed.2.Charge transfer doping modulation based on TMDs photodetectors is investigated.In-plane WSe₂ photovoltaic photodetectors are fabricated by charge transfer doping with modulating the carrier concentration and types.High quality WSe₂ p-n junctions are obtained by photocurrent mapping characterization.Moreover,WSe₂ photovoltaic devices show low dark current(10^-12 A),high detectivity(10¹¹ Jones)as well as fast speed.Meanwhile,the WSe₂ devices,as the micro-photocells,possess the open-circuit voltage of 0.38 V and power conversion efficiency of 1.4%,which has great potential in integrating with the photodetectors to offer the driven voltage.3.Electrostatic doping modulation based on TMDs photodetectors is investigated.The thin Mo Se₂ is p-type doped by the electrostatic effect since the electronic states of atomic TMDs are easily modulated by the external field.The Mo Se₂ homojunction naturally consists of the thin and thick Mo Se₂ with intrinsic n-type.Mo Se₂ photovoltaic detectors exhibit rectifying characteristics and excellent room-temperature photoelectrical properties.The devices could detect the light from visible to near-infrared at room temperature and possess the responsivity of 2.25 A W^-1 and detectivity over 10¹⁰4.Substitution doping modulation based on TMDs photodetectors is investigated.The Mo atoms in Mo Se₂ are replaced by the donor Ta atoms with five valence electrons to grow p-type Mo Se₂.The electrical properties of Mo Se₂ with different Ta concentration are investigated to fabricated Mo Se₂ photovoltaic detectors.Mo Se₂ photodetectors show obvious rectifying behavior with the rectification ratio over 10³.Moreover,Mo Se₂photodetectors exhibit obvious photoresponse from visible to near-infrared as well as high performance of high detectivity(10¹⁰ Jones),low dark current(10^-12 A),high sign-noise ratio?the ratio of photocurrent and dark current over 10⁶?,faster response speed?the rising and falling time of 30 and 62.7?s?.Additionally,the photovoltaic devices,as the micro-photocells,show the open-circuit voltage of 0.4 V and the short-circuit current of 11.1?A.