Theoretical Study Of Two-dimensional Silver-chalcogenide Compounds And Their Contact Properties

A class of two-dimensional layered semiconductor materials with excellent electrical,optical and mechanical properties is considered a promising candidate for manufacturing flexible electronic devices and optoelectronic devices in addition to standard semiconductors.For example,graphene has ultra-high carrier mobility,transition metal chalcogenides have a wide band gap,strong light absorption performance and larger specific surface area than bulk materials.Therefore,new two-dimensional layered semiconductor materials can help the next generation of optoelectronic devices break through some of the limitations of traditional semiconductor materials.The greater advantage of two-dimensional layered semiconductor materials is that they rely on strong covalent bonds between their atoms,but they rely on weak van der Waals(van der Waals)bonds to connect between layers.Therefore,when producing ultra-thin two-dimensional materials on flexible polymer substrates,mechanical transfer techniques and layering techniques that do not consider lattice mismatch can be used.In order for two-dimensional materials to evolve into a new generation of electronic devices,it is necessary to consider the contact between metal and channel material(metalsemiconductor contact).Here,contact acts as a link between nanoscale two-dimensional materials and macroscopic applications of materials,which often determine the final performance of the device.Two-dimensional(2D)metal-semiconductor heterojunctions can integrate the excellent performance of 2D metals and 2D semiconductors,which has attracted great interest in future integrated electronics and energy-related applications.In addition,interlayer coupling in two-dimensional metal-semiconductor heterojunctions can also adjust their electrical and catalytic properties,which is very important for artificially regulating their performance.As a member of the two-dimensional silver chalcogeniphacogenic compounds,the Ag2X(X=S,Se)monolayer of two-dimensional semiconductors has recently proved to be very promising in the construction of electronic and optoelectronic devices due to its high carrier mobility and excellent optoelectronic properties.Furthermore,considering that silver atoms are sandwiched between chalcogenides in a single layer Ag2X(X=S,Se),Janus structures can be experimentally synthesized by oxidation processes.The Janus structure can realize transplane intrinsic electron dipoles,which can affect the Schottky barrier height and change its contact type by stacking the Janus structure differently from the metal.Therefore,the G/XAg4Y(X,Y=S,Se,Te)heterogeneous structure is well worth further study for further application in Schottky rectifier devices.First-principles calculations are used in this paper to systematically regulate the Schottky barrier of metal-semiconductor heterojunctions composed of two-dimensional silver chalcogenides and graphene.The following two aspects are the main research results obtained in this paper,which are mainly divided into:(1)The stability of Ag2Te and the electrical properties of XAg4Y(X,Y=S,Se,Te)monolayer are calculated theoretically.The phonon spectrum of Ag2Te has no imaginary frequency indicating that it can be stable and can be synthesized in the laboratory,and it can be seen from the band diagram of XAg4Y(X,Y=S,Se,Te)that they are direct bandgap semiconductors and are expected to be widely used in electronic devices.(2)The G/XAg4Y(X,Y=S,Se,Te)interface was constructed,and the changes of electrical properties of G/XAg4Y(X,Y=S,Se,Te)under the regulation of electric field,layer spacing and transverse stress and its dynamic stability were explored.It is found that G/XAg4Y(X,Y=S,Se,Te)has different G/X interfaces,and Schottky barrier height can be adjusted and different contact types can be obtained by external electric field,vertical strain and transverse strain.At the same time,the relative Dirac cone position of graphene in a metal-semiconductor heterojunction can be adjusted under vertical strain or external electric field control.By theorizing the differential charge density and electrostatic potential,it is shown that the Schottky barrier can be adjusted by external electric field,vertical strain and transverse strain due to interlayer charge transfer or Fermi level movement.