Study On Energy Band Structure And Properties Of Two-dimensional Material Heterostructures

In recent years,two-dimensional material have some unique physical and chemical properties,Such as ultra-high carrier mobility,band gap can be controlled,high mechanical strength and so on,receive the attention of many researchers.Transition metal chalcogenides（TMDCs）due to their intrinsic bandgap,strong light-matter interactions,Van der Waals heterostructures can be composed of two-dimensional materials in any order of stacking,making these two-dimensional materials complement each other and play an advantage,gradually arises on Van der Waals heterostructures research.Compared to the traditional semiconductor heterojunction,Van der Waals heterojunction do not consider lattice mismatch and thermal mismatch problems,there is no dangling key on the surface,It is easy to form two-dimensional material heterojunction through Van der Waals forces,preparation method is simple.The graphene material has no bandgap,with ultra-high carrier mobility,fermi level with gate voltage can be controlled and other performances,band structure with dirac cone shape,make it in the optoelectronic devices fields have great potential.It has been found that the MoS₂ material in transition metal chalcogenides belongs to N-type semiconductors,the WSe₂ material belongs to P type semiconductor,there are many new physical phenomenas.therefore,two-dimensional graphene/MoS₂ heterojunction,graphene/WSe₂ heterojunction are the two typical representative.In summary analysis,this article focuses on the band structure and electrical properties of graphene,MoS₂,WSe₂ and the corresponding heterostructures.The main contents include:1.First of all,the mechanical exfoliation of graphene was studied,successfully exfoliated large area,high-quality single-layer graphene.Under normal pressure,monolayer MoS₂ was grown on silicon dioxide by chemical vapor deposition（CVD）.Then graphene is transferred to molybdenum disulfide via fixed-point transfer to form graphene/MoS₂ vertical heterostructure.Starting from the point that the monolayer graphene improves the electrical contact of two-dimensional material heterojunction,in-situ measurement of the band structure of graphene/MoS₂heterostructure by Kelvin probe force microscope（KPFM）,the lower Schottky barrier was observed to be 0.1eV,after annealing Schottky barrier further reduced to 0.079 eV.Heterojunction devices are also tested for electrical performance,current increases by1 order of magnitude,the graphene was verified to improve the electrical contact of the heterojunction,improve the performance of two-dimensional material field-effect transistor devices.2.Graphene and WSe₂ are mechanically exfoliated,fixed-point transfer of graphene/WSe₂ vertical heterojunction.The monolayer graphene fermi level is adjustable by the applied gate voltage,the study further regulates the Schottky barrier height between the graphene/WSe₂ heterojunction,provide guidance on the electrical properties of two-dimensional material heterojunctions.3.Thegrowthofgraphene/MoS₂,graphene/MoS₂/grapheneinplane heterojunctions by chemical vapor deposition and the controllability of two-dimensional lateral heterojunction is realized,with a dark current of pA,low power consumption,current on/off ratio up to 10⁷.Kelvin probe force microscope,Raman spectroscopy and field-effect transistor test,systemically studies the band structure,electrical properties of two-dimensional material heterojunctions.It is proved that two-dimensional material heterojunction has great potential in optoelectronics.