Metal-MoS₂ Schottky Barrier Regulation Based On First-principles

The Schottky barrier between the source,drain（metal material）and channel layer（semiconductor material）is one of the key factors restricting the development of nanoscale thin film field effect transistors.In this paper,the first-principles pseudopotential plane wave method based on density functional theory is used to study the regulation of the Schottky barrier of metal-MoS₂ heterojunction by different metal electrode contact,ZnO transition layer insertion and the doping of theVIA group elements.First of all,It was built that a stable heterojunction structures of Mg,Cd,Be and Au with single-layer MoS₂ to study their geometric structure and electronic properties.The results show that in the four heterojunction structures,metal and MoS₂ are combined by van der Waals force,and Fermi energy levels are pinned in the gap near the bottom of the conduction band to form n-type Schottky contact,the pinning factor S≈0.36,of which the Schottky barrier of Mg-MoS₂is the smallest,and the value is 0.14 eV.The analysis of electronic structure shows that the pinning of Fermi energy level mainly comes from two aspects:（1）The extended wave function of metal disrupts the electronic energy state of MoS₂,and a new state that resonates with the metal state appears in the band gap of MoS₂,that is,the metal-induced gap state;（2）The interface dipole caused by the interface charge transfer leads to the change of the work function of the metal after the adsorption of the semiconductor,thus affecting the relative energy levels of the metal and the semiconductor.Secondly,ZnO transition layer is inserted to regulate the Schottky barrier of Mg-MoS₂.It is found that after inserting ZnO transition layer,Mg and ZnO are combined by chemical bond,and ZnO and MoS₂are combined by van der Waals force,and the interface contact type changes from Schottky contact to ohmic contact.The analysis of electronic properties shows that the introduction of ZnO transition layer:（1）weakens the metal-induced gap state in the MoS₂ band gap;（2）reduces the transfer of electrons at the interface,and reduce the change in work function of the interface dipole after Mg adsorbs MoS₂.The combination of the two leads to the de-pinning of Fermi energy level,and finally realizes the ohmic contact between Mg-MoS₂;（3）reduce the tunneling barrier and increase the probability of tunneling.Finally,it was studied that the influence of the doping of group VIA elements to the Mg-MoS₂ Schottky barrier.The results show that compared with Se and Te doping,O doping can significantly reduce the band gap value of single-layer MoS₂,and when O was doped at the interface,the contact type of Mg-MoS₂ heterojunction changes from Schottky contact to ohmic contact.The study of electronic properties indicates that in addition to the influence of metal induced gap state and interface dipoles,the doping O on the formation of ohmic contact is also an important factor in increasing the electron affinity of single-layer MoS₂.In addition,the analysis of electrostatic potential shows that the tunneling barrier between Mg and MoS₂disappears when the interface O is doped,and the tunneling probability is 100%.This paper uses four metals and semiconductor MoS₂ to construct heterojunction,and successfully adjusts the Mg-MoS₂ heterojunction from Schottky contact to ohmic contact by inserting a ZnO transition layer and doping with theVIA group elements.The research in this paper can provide some reference and guidance for the height control of Schottky barrier at the metal-semiconductor interface.