Study On Electrical And Optoelectronic Properties Of Low-Dimensional Layered Semiconductors

Low-dimensional layered semiconductor materials have increasingly attracted the attention of researchers and have been widely used in fields such as optics,electronics,and thermodynamics since their unique physical and chemical properties distinct from their bulk materials.The electronic properties arising from the existence of the low-dimensional structure enable them to exhibit excellent performance in electronic and optoelectronic devices.However,among traditional low-dimensional layered semiconductor materials,only materials with a type II band alignment structure such as WS₂,MoS₂,and MoSe₂ have been extensively studied,while materials with a type I band alignment structure have been studied less,and their mechanisms are not yet fully understood.In addition,in recent years,a series of new low-dimensional layered semiconductor materials have emerged,such as all-inorganic metal halide perovskites（MHPs）,MXenes,etc.,all of which have excellent physical properties suitable for high performance（HP）devices,such as high carrier mobility and tunable band gaps.Therefore,studying the electrical and optoelectronic properties of these low-dimensional layered semiconductor materials plays an important guiding role in their application in HP electronic and optoelectronic devices.This article focuses on the following three parts of work related to low-dimensional layered semiconductor materials:1.As WSe₂ is one of the few TMDs with a type-I band alignment,this section used a mechanical exfoliation method to transfer layered WSe₂ onto an n-GaN substrate to form a type-I band alignment.XRD,AFM,Raman,and PL spectroscopy were performed to ensure the quality of the transfer and the heterojunction between the substrate material and WSe₂.The heterojunction was made into a photodetector,and the device’s dark current,light response curve,and transient light response were measured.Single material and heterojunction models were created using simulation software,and the band structure,optical absorption coefficient,photon energy function diagram,and local density of states of the single material and heterojunction devices were calculated.The results show that the mechanism of the type-I band alignment WSe₂/GaN heterojunction photodetector under positive and negative bias voltages differs,and the heterojunction band is modulated,leading to a significant increase in visible light absorption.This work realizes a dual-wavelength response photodetector,providing guidance for the application of type-I band alignment structures in dual-wavelength photodetectors and enriching the application of mechanical exfoliation in constructing 2D/3D heterojunctions.2.In this part,the CsPbCl₃ nanocrystals in MHPs were spin-coated onto a p-GaN substrate to form a heterojunction.The materials were characterized using SEM,TEM,EDS,XRD,PL,absorption spectra,and other methods.By simulating the materials and heterojunction,their band structure,projected density of states,electron localization function,and optical absorption coefficient were calculated.The results showed that the bandgap of the heterojunction can be tuned and that the light absorption in the CsPbCl₃ response band is significantly enhanced.By constructing devices and performing optoelectronic performance tests,it was found that there is a sharp drop in the GaN response wavelength under negative bias in the photoresponse graph,but not under positive bias.This phenomenon was explained using band theory and a band diagram.This section investigated the electrical and optoelectronic properties of CsPbCl₃,achieved a dual-band optoelectronic detector based on MHPs and GaN heterojunctions,and discussed its operating mechanism,providing a reference for the application of low-dimensional layered all-inorganic perovskites in dual-band response optoelectronic detectors.3.This section successfully constructed the monolayer（ML）structure of the new MXenes material MoSi₂N₄ through simulation software.It was studied as a channel material for double-gate（DG）field-effect transistors（FETs）,and the electrical properties of the material and the electronic transport mechanism of the device were investigated.Band diagrams,phonon spectra,and projected density of states were calculated to understand the electrical properties of the material.By changing parameters such as carrier transport direction,doping concentration,doping type,and device gate length,a comprehensive understanding of the factors affecting the device transport ability was obtained.By calculating parameters such as the device turn-on current,subthreshold swing,power consumption,and delay time,and comparing them with the high-performance device indicators of international semiconductor technology,it was found that the device still maintained high performance at short gate lengths.Finally,the device’s transport mechanism was analyzed by calculating the device’s local and projected density of states and spectral currents.This section demonstrates that ML-MoSi₂N₄ is a promising channel material for HP short-gate-length DG-FETs.