First Principles Study Of Janus Ga₂XY (X, Y=S, Se, Te; X≠Y) And Its Heterojunctio

As we all know,two-dimensional semiconductor materials have physical properties such as electrical,mechanical,and optical properties,and have received extensive attention from researchers in the fields of electronics,physics,and chemistry.The emerging Janus materials derived from two-dimensional materials are a class of nanomaterials with asymmetric structures.It consists of two or more regions of different polarity and can integrate two or more physical and chemical properties to produce many novel properties.Janus material has become one of the research directions of condensed matter physics because of its unique structure and excellent properties.The structure and electronic properties of Janus Ga₂XY（X,Y=S,Se,Te;X≠Y）are studied by first principles calculations based on density functional theory in this paper.The calculation results show that Ga₂SSe is an indirect band gap semiconductor with a band gap value of 2.05 eV,Ga₂STe and Ga₂SeTe are direct band gap semiconductors with band gap values of 0.90 eV and 1.22 eV,respectively.Since the structure of Janus materials destroys the inversion symmetry,the difference in electronegativity between atoms will affect the dipole moment of Janus material.It is calculated that the dipole moment of Ga₂STe is the largest and the dipole moment of Ga₂SeTe is the smallest.A large number of researchers can regulate and improve the properties of two-dimensional materials by constructing heterostructures.Two-dimensional van der Waals heterostructures with different properties can be obtained by stacking different two-dimensional materials in numerous stacking modes.Van der Waals heterostructures can not only retain the original properties of 2D materials,but also produce excellent physical and chemical properties.The six stacking modes of graphene/Ga₂SSe,graphene/Ga₂STe and germanene/Ga₂SeTe heterostructures are constructed.The graphene/Ga₂SSe heterostructure at the S-Gr contact interface has a binding energy of-155.97 meV/（?）²,and the structure is the most stable relative to the other five heterostructures.It is found that all six heterostructures form Schottky contact,the graphene/Ga₂STe heterostructure at Te-Gr contact interface forms p-type Schottky contact,and the other five heterostructures form n-type Schottky contact.These results show that the three heterostructures are ideal materials for designing new Schottky electronic devices.In addition,the band structures of the three heterostructures retain the zero-bandgap（Dirac cone）of graphene or germanene.It is found that the effective mass of these heterostructures is very low,indicating that they have ultra-high carrier mobility,which makes them play an important role in the application of high-speed nanoelectronic devices.We also studied the charge transfer mechanism of heterostructures interface.The graphene/Ga₂STe heterostructure at the Te-Gr contact interface exhibits the largest work function and dipole moment.The electric field direction（Ge→Te）generated by the electrostatic potential of the germanene/Ga₂SeTe heterostructure at the Te-Ge contact interface is the same as the built-in electric field direction,which promotes the charge transfer between the interfaces,resulting in the maximum charge transfer intensity of this heterostructure.Finally,the graphene/Ga₂SSe,graphene/Ga₂STe and germanene/Ga₂SeTe van der Waals heterostructures are regulated by changing the interlayer distances.The research shows that the change of interlayer distances will affect the Schottky barrier height and Schottky contact type of these heterostructures.The Schottky contact type transitions from n-type to p-type Schottky contact or from Schottky contact to ohmic contact.These results provide theoretical guidance for the design of controllable Schottky nanodevices based on graphene/Ga₂SSe,graphene/Ga₂STe and germanene/Ga₂SeTe heterostructures.In particular,the band structure of germanene/Ga₂SeTe heterostructure has a small band gap in the Dirac cone（K point）.It is also found that the band gap value of the Se-Ge contact interface heterostructure increases with the decrease of the interlayer distances.An effective method has been theoretically provide to open the band gap of germanene,indicating that TeGa₂Se/Ge heterostructure has important academic significance and potential application value in the research field of high-performance optoelectronic devices.