Schottky-barrier-free contacts with Janus WSSe 2D semiconductor using surface-engineered MXenes

Forming low-barrier contacts at metal/semiconductor interfaces is an important research area. The Fermi level pinning (FLP) effect is induced by strong interactions between 3D metal/semiconductor interfaces. By using a 2D metal in contact with a 2D semiconductor, the FLP effect can be weakened considerably, resulting in a reduction of the Schottky barrier height (SBH). Surface-engineered MXenes are the best electrode materials available presently. Therefore, herein, the interfacial properties of surface-engineered MXenes (M2CT2) 2 CT 2 ) (M=Hf, M =Hf, Mo, Ta, Zr, Nb; T = F , OH, O)/Janus WSSe (WSSe) heterostructures are systematically investigated using first-principles calculations. OH-terminated MXenes [M2C(OH)2]/WSSe 2 C(OH) 2 ]/WSSe heterostructures are found to form n-type ohmic contacts, and the tunnelling probabilities are high. O-terminated MXenes (M2CO2)/WSSe 2 CO 2 )/WSSe heterostructures tend to form p-type ohmic contacts and p-type Schottky contacts with a very low SBH, and the tunnelling probability is low. Conversely, F-terminated MXenes (M2CF2)/WSSe 2 CF 2 )/WSSe heterostructures form n-type and p-type Schottky contacts readily and n-type ohmic contacts (Hf2CF2/WSSe 2 CF 2 /WSSe and Zr2CF2/SWSe 2 CF 2 /SWSe heterostructures) partially, and the tunnelling probability is found to be low. In addition, the synergistic action of interface and intrinsic dipoles can effectively tune the contact type and SBH of the M2CT2/WSSe 2 CT 2 /WSSe heterostructures, transforming the Mo2CF2/WSSe 2 CF 2 /WSSe and Nb2CF2/WSSe 2 CF 2 /WSSe heterostructures from n-type to p-type Schottky contacts. Through this novel strategy, an SBfree contact can be readily obtained, especially for OH-terminated MXenes (which are the most ideal electrode materials), followed by O-terminated MXenes. This work provides an important reference for the selection of suitable electrode materials and a novel approach for the development of high-performance electronic devices based on Janus WSSe.