Study On The Structure And Photoelectric Properties Of Two-Dimensional Indium Selenide Heterostructure Materials

Since Novoselov and his colleagues discovered graphene experimentally in 2004,two-dimensional materials have been one of the most popular materials.Recently,other two-dimensional(2D)materials have been discovered.Among them,the twodimensional InSe material overcomes the disadvantage of zero band gap of graphene,and has high carrier mobility,significant charge transfer and wide absorption spectrum.It is a potential candidate material for nano electronic and optoelectronic devices.Two-dimensional InSe is a kind of hexagonal lattice structure.However,there are many disadvantages in the traditional InSe devices.At present,several key problems restricting its application are the difficulty to realize large spontaneous polarization,high work function and low hole mobility in InSe,which seriously restrict the efficiency of InSe devices.The construction of heterostructure is a common material-designing method.Twomaterials with different work functions can effectively improve the separation of photogenerated electron-hole pairs.At the same time,for a heterojunction with two component,not only the advantages of the two materials can be integrated,but also new interface will occur,which could lead to a series of new physical phenomena.In this dissertation,we choose the InSe-based heterojunction as the research object,and take the first principles method to calculate different heterostructures,and explore the physical properties such as carrier manipulation,band engineering,light absorption regulation and so on.The main contents of this paper are as follows:1.Single layer two-dimensional boron nitride,also known as white graphite,has become a popular member among the two-dimensional materials.Hexagonal boron nitride(h-BN)is considered to be an ideal two-dimensional insulator because of its excellent stability,flat surface and relatively large band gap.The electrical and optical properties of two-dimensional InSe/h-BN heterostructures are studied by first principles calculations.Our calculation results show that the InSe/h-BN heterojunction has the I-type band alignment.At the same time,there is a strong interlayer coupling at the interface of the heterojunction,which results in extra emerging states.In addition,the properties of the heterostructures with different stacking modes are very almost the same,thus InSe/h-BN heterostructures can be used as excellent candidate materials for optoelectronic devices.2.Although InSe-based devices have high switching ratio,only the band gap can be tuned under external field.We report a class of heterojunction materials of InSe/bismuth with strong spin orbit coupling.Based on first principles calculations,we find that there is a strong spin coupling effect with the composite of InSe and bismuth,which leads to metal-semiconductor transition and topological transition under the external field.The results show that the InSe/Bi heterostructure can be transformed from metal to type-? semiconductor,and the topological nontrivial surface channel can be found,which is conducive to the realization of efficient and stable electronic switching,and can be used as a new type of switch device module material.3.In optoelectronic devices,efficient carrier separation and optical absorption are two key points.The electronic and optical properties of a series of InSe/?-Sb heterostructures with different stacking modes are studied by first principles method,significantly improving charge separation and optical absorption in two-dimensional materials.Our calculation results show that the InSe/?-Sb heterojunction has type-? band alignment,which ensures the separation of photogenerated electron-hole pairs and eliminates the spontaneous recombination of carriers.At the same time,excellent optical absorption properties were observed in the InSe/?-Sb heterojunction.The result provides an effective strategy to improve the photovoltaic performance of twodimensional InSe.