Mechanism of Fermi Level Pinning for Metal Contacts on Transition Metal Dichalcogenides and Their Interface Thermal Stability

Transition metal dichalcogenides (TMDs) have demonstrated immense potential for application in state-of-the-art electronic, optoelectronic, and spintronic devices because of their outstanding electronic, optical, mechanical, and magnetic properties. However, the failure of tuning the Schottky barrier height by the work function of metal contacts strongly limits the efficiency of carrier injection and hence the electronic performance of TMD-based devices. This dissertation focuses on the interface between covalent and van der Waals metal contacts and TMDs to study the origin and mechanism of Fermi level pinning. Firstly, the interface chemistry and band alignment of Ni and Ag contacts on MoS2 is studied. Then the mechanism of Fermi level pinning of metal contacts on other Mo- and W-based TMDs are uncovered by considering interface chemistry, band alignment, defects and impurities of W-TMDs, contact metal adsorption mechanism and the resultant electronic structure. Also, the thermal stability of Ni/MoS2 systems is investigated in the aspects of interface chemistry, elemental diffusion, and band alignment.