Novel Low-dimensional Semiconductor Optoelectronic Devices And Two-dimensional Semiconductor Heterojunctions

Two-dimensional(2D)materials have novel physical properties and have great scientific research,industrial applications,and economic value in the fields of catalysis,energy storage and conversion,and microelectronics.Based on the frontier issues of 2D materials research,this thesis explores 2D materials in four dimensions:new materials,new mechanisms,new applications,and new tools,with the aim of obtaining electronic and optoelectronic devices with excellent performance.The authors have carried out four research works on the new two-dimensional semiconductor material ZnIn2S4,the quasi-one-dimensional layered material Ta2Ni3Se8,the transition metalsulfur compound ReSe2,and the single-element two-dimensional material Te.The paper is divided into six chapters as followsIn chapter Ⅰ,we introduce the development of 2D materials and give a brief overview of the types and properties of 2D materials as well as the current stage of research progress.The physical properties and research status of transition metal ternary sulfur compounds,rhenium diselenide and tellurium nanosheets covered in this thesis are mainly introduced.The common methods of obtaining 2D material films are briefly introduced and the advantages and disadvantages of each method are compared.Then we highlight the background knowledge related to 2D materials in electronics and optoelectronics,and summarize the research progress,technical problems faced,and future directions of 2D semiconductor materials in field-effect transistors,metalsemiconductor contacts,emerging computing technologies,and photodetectors.Finally,we introduce 2D materials based on ionic liquid and ionic solid for electric double-layer field-effect transistors.In chapter Ⅱ,we introduce the novel 2D semiconductor material ZnIn2S4,including crystal structure,defects,photoluminescence spectrum,absorption spectrum,Raman spectrum,and optoelectronic properties.The ZnIn2S4 photodetector and phototransistor are prepared by Micro and Nano fabrication.The ZnIn2S4 photodetector exhibits an extremely low dark state current(7 pA at a bias voltage of 5 V).The photodetectors also exhibit a series of excellent parameters under 405 nm laser irradiation,with responsivity of 230 A W-1,specific detectivity of 1.8 × 1014 Jones,external quantum efficiency of 6.12×104%,rise time of 222 μs and fall time of 158 μs.In addition,the ZnIn2S4 phototransistor,under the gate voltage,achieves the responsivity of 1.0× 104 A W-1,and the result shows the gate voltage tunability of this phototransistor.Subsequently,we have successfully applied ZnIn2S4 in an optical convolutional neural network.We believe that the combination of ultra high sensitivity,ultra fast response and high gate tunability makes the 2D semiconductor material ZnIn2S4 promising as an ideal device for low-energy and high-frequency optoelectronic applications in the future.In chapter Ⅲ,we present the physical study of the new layered quasi-1D semiconductor material Ta2Ni3Se8,including the crystal structure,energy band structure,chemical components,optoelectronic properties and mechanism.The energy band structure is analyzed by first-principles calculations,and the material has a band gap of 0.25 eV,which is a narrow-band semiconductor material with an indirect band gap.Based on the single-crystal sample,we prepare a photodetector of this material and investigat its photoelectric properties in detail and systematically.The photocurrent comes from photo-bolometric effect.Based on the fact that this effect does not depend on photon energy,the detector is expected to be used in the field of mid-infrared or long-infrared photoelectric detection in the future.These results indicate that Ta2Ni3Se8 has the potential to become a material for low-dimensional broad-spectrum optoelectronic applications.In chapter Ⅳ,we present the work on the study of(Pt/Pd)Te2-ReSe2 Schottky heterojunctions.Two metallic 2D layered materials,PtTe2 and PdTe2,are applied to the preparation of Schottky diodes using a dry transfer method,and new applications of PtTe2 and PdTe2 as high power metallic materials are developed.Thanks to the clean van der Waals interface,the Pt/PdTe2-ReSe2 heterojunction exhibits high performance Schottky diode characteristics,indicating the existence of a large Schottky barrier at the Pt/PdTe2-ReSe2 interface.In addition,the device exhibits a significant gate voltage dependent effect and the reason for its extremely low reverse leakage current is analyzed.These results indicate that the 2D materials PtTe2 and PdTe2 with high work function are promising for the preparation of high-performance Schottky diodes and the realization of contact electrodes for high-performance p-type semiconductor fieldeffect transistors.In chapter Ⅴ,we show the application of ionic liquid and solid ionic substrate(SIS)in the 2D materials ReSe2 and Te nanosheets.The band gap of ReSe2 is calculated to be 1.18 eV by the method of SIS gate modulation,which is consistent with that obtained by optical spectrum measurements.The synaptic transistor is successfully prepared using SIS as the substrate and p-type semiconductor tellurium nanosheets as the channel material,and the device can operate stably at room temperature.Compared with the high gate voltage required for conventional oxide dielectric,the operating voltage of the device is particularly small,and the conductance response of the device changes up to 1000 times under the action of a-3 V gate voltage pulse,and it can quickly return to the initial state,indicating that synaptic transistor is promising for brain-like device research.Chapter Ⅵ is the summary and outlook of the entire paper.