Tunable Electronic Structure Of Two-Dimensional Van Der Waals Heterostructures

Two-dimensional（2D）van der Waals heterostructures have attracted much attention due to its unique electronic structure and physical properties.Van der Waals heterostructures formed by stacking different two-dimensional materials provide more possibilities for the development of nanoelectronic devices with excellent optoelectronic properties.In this dissertation,tunable interlayer coupling and Schottky barrier in graphene and Janus GaAlSSe heterostructures by applying an external field and electronic structure and regulation of two-dimensional Ⅲ monochalcogenides p?n heterostructure are investigated systematically by using the density functional theory.The formation of van der Waals heterostructures by stacking the graphene with other semiconductor materials provides a new method for studying the physical properties and applications of two-dimensional（2D）materials.In this chapter,based on first-principles calculations,we study the interface bonding and electronic properties of the G/Ga Al SSe heterostructure.The calculation shows that the original properties of monolayer graphene and Ga Al SSe are well preserved in the heterostructure and a small Schottky barrier height（SBH）is formed at the interface.By increasing the interface distance,the n-type Schottky barrier at the interface of the graphene and Ga Al SSe heterostructure can be reduced.In addition,applying a negative electric field can change the Schottky contact to the ohmic contact.What’s more attractive is that adjusting the interface distance or utilizing an external electric field can well control the SBH even change the Schottky contact（n-type and p-type）at the interface of the G/Ga Al SSe heterostructure.These theoretical findings indicate that the coordination of the built-in electric field and surface electronegativity in the heterostructure plays an important role in regulating the Schottky barrier.The controllable electronic properties and contact types in the graphene/Ga Al SSe heterostructure will provide guidance for the design and production of two-dimensional（2D）van der Waals FETs.Some transition-metal dichalcogenides（TMDs）,such as MoSe₂ and WSe₂,are excellent candidates for high efficiency photocatalysts for water splitting.But the high recombination rate of photogenerated carriers hinders their application.Therefore,we have formed a new type of van der Waals（vd W）heterostructures to solve this problem by combining group III sulfides such as BS and BSe and TMDs such as MoSe₂.Based on the first principles,we analyze the electronic structure of the BX/MX₂（M=Mo,W;X=S,Se,Te）heterostructure,it is found that the contribution of conduction band and valence band in the heterostructures of BSe/MoSe₂ and BSe/WSe₂ are all derived from the same material as the main research object.Under the biaxial stress,the band gap of BSe/MoSe₂ and BSe/WSe₂ heterostructures can be effectively adjusted.Under the external electric field,the type of band gap can be effectively controlled.Our theoretical calculation provides ideas for the design of water splitting catalysts and low-dimensional optoelectronic devices based on TMDs.