Investigations On The Electronic And Optical Properties Of Novel Two-Dimensional Semiconductor And Metal Heterojunction Interfaces

Since the pioneering work of graphene,researchers have been exploring and researching new two-dimensional?2D?materials outside the carbon family.Among them,transition metal chalcogenides represented by molybdenum disulfide?MoS₂?and group III-V compounds semiconductors represented by hexagonal boron nitride?h-BN?have attracted much attention due to their excellent photoelectric properties.In addition,2D materials often form heterojunction with metals or other 2D materials,which are applied to field effect transistors,photodetectors and other optoelectronic devices to improve device performance and realize their greater potential.Therefore,it is of great scientific value to deeply study the interfacial and photoelectric properties of new 2D materials and metal heterojunction.Based on the DFT,the geometry,electronic and optical properties of 2D III-V semiconductor GaN and 2D transition metal sulfide TiS₃ have been studied theoretically using the first-principle calculation method.The interfacial characteristics of the metal heterojunctions of the two materials and the interfacial properties of indium selenide?InSe?/germanium telluride?GeTe?heterobilayer have been explored systematically.The main research results are as follows:1.The geometry structure,energy band structure and optical absorption characteristics of single-layer 2D GaN are predicted,and the interface model of single-layer GaN in contact with six kinds of common metals with different work functions?WF?is constructed.By calculating the effective potential,projected density of states,electron localization function and other characteristic parameters,the tunneling barrier and orbital overlap,Schottky barrier of the system are discussed and analyzed in detail.The results show that the ohmic contact is realized in a single-layer GaN-Ag and-Ni contact system,which is conducive to the effective carrier injection in the device,thereby achieving high device performance.2.The geometrical structure and transport properties of single-layer TiS₃ in contact with six metals were studied systematically.By calculating the Fat band structure,electron density,electron localization function,and the Milliken population of charge,it is concluded that iridium?Ir?and nickel?Ni?are more suitable metal electrodes for contact with single-layer TiS₃.The calculation of the transport characteristics of the single-layer Ti S₃-Ni,-Ir contact double interface models shows that single-layer Ti S₃ forms an n-type Schottky contact with the metal Ir and forms an ohmic contact with the metal Ni.3.An interface model of 2D InSe/GeTe heterobilayer with small lattice mismatch is constructed.By calculating the energy band structure and optical absorption spectrum of InSe,GeTe single-layer and InSe/GeTe heterobilayer,it is concluded that the absorption intensity of the designed InSe/GeTe heterobilayer increases significantly due to the coupling between the two layers,and the absorption edge expands to the infrared region.The effects of biaxial strain on the Fat energy band,Mulliken population,electron density difference and optical absorption spectrum are further discussed.The results show that biaxial strain can effectively adjust the electronic and optical properties of InSe/GeTe heterobilayer.