First-principle Studies On Transport Properties Of Graphene-like Two-dimensional Materials And Heterostructures

Since graphene was first successfully prepared by mechanical exfoliation in 2004,two-dimensional(2D)materials with graphene-like hexagonal structure have received researchers'extensive attention.Based on the discovery and successful preparation of a variety of new graphene-like 2D materials,the emergence of graphene-like 2D heterostructures provides a new direction for the development of materials science.Compared with 2D materials,2D heterostructures formed by two different materials may exhibit comprehensive properties of their constituent materials,and other new properties may appear.The novel performance indicates their potential application in electronics,optics,and spintronics,etc.Currently,the graphene-like 2D materials and 2D heterostructures have been widely studied in both experiments and theories and great progress has been achieved in various functional applications.The purpose of this research is to open the connection between functional design,device construction,performance characterization and structure optimization of graphene-like 2D materials and their heterojunctions,and propose a methodology from design to device realization based on two-dimensional materials.Basing on the structure modulation of graphene nanoribbons,a reference table for building heterostructures is proposed,which also provides guidance for the subsequent functional design of materials.Next,the research on In P₃ is a supplement to the lack of magnetism of graphene nanoribbons,and on the other hand,it focuses more on the performance of electrons in non-equilibrium states.Finally,for the study of the thermoelectric properties of In P₃,the properties of phonons are added into consideration.Therefore,a complete research system of material screening and design-device performance evaluation is realized.For the structural design of materials,this study aiming for solving the problem of lack of the large-scale on-demand design for materials and device.By taking graphene antidot nanoribbon(GANR)as an example,a variety of different structures were constructed by modifying them,and their structure,physical and transport properties were systematically studied,and the transport properties and different components of the system were discussed.The functional design of the graphene-like 2D material and heterostructure has been preliminarily completed,and the effective screening and regulation of its device performance has been realized.Steered via first-principle calculations,three different methods including antidots-shape modification,width tailoring and doping are applied to effectively modulate the electronic properties of GANR.As a result,the formation of 2DLH with both type-I and type-II band alignment can be achieved.Especially,a reference table of possible formation of heterostructures is presented which is a recipe for designing the electronic devices with different requirements.Moreover,the transport properties of two typical heterostructures show the manifestation of the type-I and type-II band alignment.On this basis,this project conducts a detailed study to solving the problem that the poor performance of graphene-like 2D materials and heterostructures in application.To improving the performance of indium triphosphide(In P₃)in spin polarized devices,optoelectronic devices and thermoelectric device,this project further conducts doping and stretching modulation of In P₃ with a graphene-like structure.The spin-dependent transport properties of Ge-doped In P₃ monolayer are studied.A 100%spin injection effect and an obvious negative differential resistance were found under small bias.In addition,100%spin-polarized photocurrents can also be generated by illuminating linearly polarized light,which can be tuned by photon energy and polarization angle.The remarkable SIE and NDR suggest that Ge-doped 2D In P₃ has great potential for future applications in 2D spin devices.Finally,we have studied the thermoelectric properties of the In P₃ monolayer by using the quantum transport calculations within the ballistic transport region.A large ZT of 1.92 is obtained at room temperature,which is contributed significantly by the lower thermal conductivity and the larger power factor.Moreover,even if a mechanical tension of 1%is applied on the lattice,a large ZT of 1.67 can also be obtained at room temperature.Such remarkable thermoelectric performance of the In P₃monolayer shows that the In P₃ monolayer is a promising thermoelectric material.In summary,this project proposes a research route of functional application design-performance characterization-structure optimization of graphene-like two-dimensional materials and their heterojunctions.Its regularity research results can be further promoted to other 2D materials,and the research efficiency of graphene-like two-dimensional materials and their heterojunctions will be significantly improved.