Study On Density Functional Theory Of Graphene-based Heterostructures

Since the advent of graphene,it has been widely used in many applications because of its excellent electrical and thermal conductivity,and it has also opened the door to the era of two-dimensional materials.Two-dimensional materials have always been at the forefront of research due to their thickness reaching atomic scale and unique photoelectric properties.High-quality two-dimensional crystal materials are not only conducive to exploring novel physical phenomena under two-dimensional extreme conditions,but also show many novel applications and bright prospects in the field of optoelectronic device applications.Based on the previous work,this paper focuses on the research of graphene-based heterostructures,and constructs three bilayer heterostructures:G/WS2,G/GaN,G/SiC and a trilayer heterostructure GaN/G/WS2(TLH2).We systematically studied their inter-layer coupling,applied electric field,biaxial strain and other conditions on the heterostructures in the band gap size,Schottky barrier control,ohmic contact transition,internal interlayer charge transfer and other aspects influences.Firstly,study the G/WS2 heterostructure.Compared with the intrinsic.WS2 band gap,the band gap of WS2 in the G/WS2 heterostructure is reduced by 0.57 eV,forming an n-type Schottky contact with a barrier height of 0.22 eV.In addition,the application of a vertical electric field can realize the G/WS2 heterostructure from n-type to p-type Schottky contact transition.The variation of ΦBn and ΦBp of the graphene/WS2 heterostructure with strain is sensitive,but plane strain can only change the height of the schottky barrier and cannot change from n-type to p-type with in-plane biaxial strain.Then,the heterostructures of GaN and SiC stacked by G was studied.Under the influence of an external electric field,both heterostructures have their own Schottky contact transition points,and the transition from p-type Schottky contact to ohmic contact occurs when Eext>0.10V/A.For biaxial strain,both heterostructures maintain good p-type Schottky barriers.The difference is that GaN in G/GaN transforms into a direct band gap within the strain range of-7%to-9%,while SiC in G/SiC always maintains an indirect band gap.The ohmic contact of G/GaN occurs at ε>7%,while G/SiC occurs at ε>5%.By analyzing the electrostatic potential under different biaxial strains,the charge transfer between the two heterostructure layers was further explored.Finally,the effects of doping and biaxial strain on the electronic properties of the GaN/G/WS2(TLH2)vdW heterostructure are studied.Mg or Se doping can adjust the doping type of TLH2 vdW heterostructure.The band gap decreases with increasing positive strain and maintains a p-type Schottky barrier contact;the band gap increases with negative strain and then increases first and then decreases.When |ε|≥|-5|%becomes indirect band gap,when |ε|≥|-7|%,the Schottky barrier contact changes from p-type to n-type.The charge under strain is transferred from the GaN layer to the G and WS2 layers,and the electron transfer increases with increasing strain.Under positive strain,more electrons are transferred to WS2,and under negative strain,more electrons are transferred to G.It is believed that the research in this paper will promote the graphene-based heterostructures in many fields such as optoelectronic devices,nanodevices,and sensor design,and also have certain reference value for well-designed Schottky devices and large power devices.