Study Of The Contact Interface Properties Between Two-dimensional Pt Chalcogenides With Metals

In recent years,with the rapid development of nanodevices,two-dimensional（2D）materials with atomic-level thickness,good flexibility and no hanging bonds on the surface have attracted a lot of attention and are expected to replace silicon-based semiconductors as the core material for new nanodevices.In particular,two-dimensional transition metal chalcogenides（2D-TMDCs）are promising for applications in electronics,optoelectronics,gas sensing and catalysis.Among them,2D noble metal sulphides such as Pt X₂,Pt XY（X,Y=S,Se）stand out among other 2D materials due to their high carrier mobility and stability at room temperature.In the preparation of electronic devices from 2D materials,the contact between the 2D material and the metal often results in the Fermi nail effect,leading to the appearance of a Schottky barrier at the contact interface,which affects the carrier transport,a key issue affecting device performance.Therefore,the study of contact interface properties is of great importance for the preparation of electronic devices.In this paper,the contact properties of the 2D Pt chalcogenides PtS₂/PtSe₂/Pt XY have been investigated at the metal interface on the basis of first principles,and some innovative results have been obtained.The main studies and results of this paper are as follows:1.Study of the contact interface between PtS₂ and metalSingle-layer PtS₂ field-effect transistors with two conventional metals（Ag/Au）and four 2D metals（Nb₂CT₂,T=F,O,OH/Nb S₂）as electrodes were constructed,and the contact interface properties of PtS₂ with the metals were investigated using a first-principles approach.By analysing the geometrical structure and electrical properties of the contact interface,it is found that at the vertical interface,PtS₂ forms an ohmic contact with Ag/Au/Nb₂C（OH）₂,and Schottky contacts are formed in the rest of the cases.At the lateral interface,PtS₂ was found to form an n-type ohmic contact with Ag/Nb₂C（OH）₂,an n-type Schottky contact with Au/Nb₂CF₂ and a p-type Schottky contact with Nb₂CO₂/Nb S₂.From these results it can be seen that PtS₂ forms ohmic contacts with both Ag and Nb₂C（OH）₂ electrodes at the contact interface.This work provides theoretical guidance for the design of field effect transistors using PtS₂ as the channel material.2.Study of the contact interface between PtS₂ and metalA monolayer PtSe₂ field-effect transistor with eighteen metals as electrodes was constructed to investigate the properties of PtSe₂ with metals at the contact interface.For PtSe₂ in contact with conventional metals,PtSe₂ formed ohmic contacts with most of the selected metals at the vertical interface,and Schottky contacts with all the selected metals at the lateral contact interface,with the lowestSchottky barrier height（0.19 e V）at the Ag-PtSe₂ contact interface.For PtSe₂ contacts with ten 2D metal electrodes（Nb₂CO₂/M2CT₂（M=Hf,Nb,V;T=F,OH）/Nb Se₂/Ta S₂/borophene）,by calculating the electronic properties of the contact structures,at the vertical interface all contact structures form ohmic contacts except PtSe₂ with Nb₂CF₂/Hf₂CF₂.At the horizontal interface,PtSe₂ forms n-type Schottky contacts with two 2D metal electrodes,V₂C（OH）₂/Hf₂CF₂.p-type Schottky contacts are formed by PtSe₂ with two metal electrodes,Nb₂CF₂ and Ta S₂.p-type ohmic contacts are formed by PtSe₂ with V₂CF₂/Nb Se₂/Nb₂CO₂/borophene,and p-type ohmic contacts are formed with two 2D metals（Hf₂C（OH）₂,Nb₂C（OH）₂）.n-type ohmic contacts were formed.For conventional metal as electrode field-effect transistors,the main reason for the appearance of Schottky contacts is the Fermi pegging effect caused by the metal induced state.When 2D materials are used as electrodes,the Fermi nailing at the interface can be effectively eliminated,resulting in ohmic contacts.This work provides theoretical guidance for the design of high quality field-effect transistors using PtSe₂ as the channel material.3.The effect of tensile strain on the interfacial properties of Nb₂CT₂-PtSSeIn order to study the interfacial contact properties of the Janus material PtSSe with the metal type MXene of Nb₂CT₂（T=F,O,OH）,the Nb₂CT₂-PtSSe interface was constructed,and by calculating the energy band structure,planar average charge density and other properties of the six interfaces,it was found that both heterostructures of Nb₂C（OH）₂ in contact with PtSSe formed an n-type Ohmic contact The two heterostructures of Nb₂CO₂ in contact with PtSSe formed p-type Schottky contacts at the interface;when Nb₂CF₂ was in contact with PtSSe,PtSSe exhibited its dual nature,forming p-type Schottky contacts at the interface of Nb₂CF₂ in contact with SPtSe and n-type Schottky contacts at the interface of Nb₂CF₂ in contact with Se PtS.Subsequent tensile strain on all structures revealed that the band gap of PtSSe decreased with increasing tensile strain and that the Nb₂CF₂-SPtSe heterojunction transformed from an n-type Schottky contact to an n-type ohmic contact at a tensile strain of 4%;the Nb₂CF₂-Se PtS heterojunction was a p-type Schottky contact that transformed under tensile strain to an n-type Schottky contact.This work broadens the scope of interfacial modulation of Nb₂CF₂-PtSSe and provides guidance for the application of Nb₂CF₂-PtSSe in electronic devices.This thesis consists of six chapters:Chapter 1 is the introductory section,which introduces the 2D materials studied in this paper,and the current state of development of metal-semiconductor contact interfaces.In Chapter 2 introduces the theoretical calculations of this paper.In Chapter 3investigates the electronic structure and interface type of the PtS₂-metal contact interface.In Chapter 4 investigates the electrical properties and interface types at the two contact interfaces of PtSe₂ transistors.In Chapter 5 modifies the interface modulation range of Nb₂CT₂-PtSSe by means of tensile strain.In Chapter 6 provides a summary of the work in this paper and an outlook on the future development of 2D Pt metal sulphide to metal contact interfaces.