Research On Synthesis Of Novel Low-dimensional Narrow Bandgap Semiconductors And Related Optoelectronic Functional Device

Low-dimensional materials,whose physical size scales down to nanometer in one or more dimensions,have unique properties compared to traditional bulk counterpart materials.The low-dimensional materials have potential applications in advanced electronic devices,photodetectors,electrocatalysis as well as bio-wearable devices.In the field of low dimensional materials,the bandgap of these materials has an obvious relationship with thickness and size.For instance,the bandgap of two-dimensional semiconductor increases with the thinning of thickness,even the indirect bandgap would transform to direct bandgap in some specific materials.Among them,the materials with the bandgap smaller than 0.26 e V are called low-dimensional narrow bandgap semiconductors,which can be used to realize sensitive detection of infrared illumination,and is one of the candidates of novel infrared detection materials.However,the application of low-dimensional narrow bandgap materials still faces challenges like large-area synthesis,integration with traditional technology and so on.This paper starts from the materials,contact engineering and device functions,deeply studies the synthesis of low-dimensional narrow bandgap materials,the contact between semiconductor and metals as well as versatile infrared photodetectors.The main content can be divided into three parts.1.Controllable synthesis of large-scale platinum diselenide(Pt Se₂)and related electronic properties study.The large-area Pt Se₂ films with various thicknesses are synthesized by directly selenization of Pt films.The Pt Se₂ patterns are directly achieved by introducting a metal mask during sputtering Pt,which eliminates unnecessary processes like etaching and transfering.Raman,TEM,XPS,XRD are preformed to prove the quality and crystallinity of Pt Se₂ films.Field effect transistors(FET)are fabricated of Pt Se₂ films with different thicknesses.The FETs can be modulated to behave as metallic,p-type and ambipolar characteristics by control the thickness of Pt Se₂ films,in which the p-type FET of 4.7 nm-thick-film behaves high mobility of 6.2cm² V^-1 s^-1 and large on-off ratio of 5×10³.2.Contact studies of tellurium(Te)transistors.Te nanowires and nanoflakes are synthesized by physical vapor deposition.Palladium(Pd)is introduced as contact metal to form alloy with Te at interface.By this alloying,the end-bonded contact is successfully achieved in Te transistors.Compared to side contact,this contact is more effective for carrier injection and extraction.In these end-bonded contacted transistors,the metal insulator transition is easily realized by electrostatic doping form back gate.The transistors exhibit outstanding performance from visible to near infrared radiation when the intrinsic carriers are depleted by gate voltage.Scandium(Sc)atoms diffuse into the entire channel of Te devices when deposited as contact metal.The Sc atoms undergo electrochemical reaction and be oxidized to ions under a proper bias voltage.Sc ions can migrate back and forth in the Te structure and form multi-vacancy Sc Te_xcompounds with Te at the contact region,resulting in the reversible switch between high resistance state and low resistance state in output characteristics.Te nanowire transistors with ultrahigh on-off ratio,Te-based memristors and programmable Te diodes are demonstrated based on this contact type.3.Versatile photodetector based on heterostructure of vanadium dioxide(VO₂)and two-dimensional material.VO₂ is not only the typical functional materials of bolometer,but also a narrow bandgap semiconductor,which is capable of quantum photodetection.Here,a heterostructure of thin VO₂ film and Molybdenum telluride(Mo Te₂)flake is fabricated,combining the bolometric effect with photovoltaic effect in one device.Moreover,considering the metal insulator transition property of VO₂,this photodetector can realize three detection modes including p-n junction detector,Schottky junction detector and bolometer.The heterostructure shows excellent performance including high responsivity,fast response rate and broad detection range covers from visible to long-wave infrared radiation,also,the technology can be integrated with modern VO₂bolometer.In this paper,we synthesized large-scale narrow band gap semiconductor films and one-/two-dimensional atomic crystals,studied the contact characteristics between semiconductor and different metals,also developed a versatile broad spectrum photodetector integrating three functional modes.Our work provides strategies and references for the application of low-dimensional materials in advanced photodetectors.