Ohmic contacts in MXene/MoSi2N4 heterojunctions

Efficient Ohmic contacts are highly preferred in metal/semiconductor (M/S) junctions to achieve the exceptional intrinsic characteristics of the two-dimensional (2D) semiconductor channel. However, due to the strong Fermi level pinning effect, it is difficult to predict the Schottky barrier heights of heterojunctions, especially those between the M/S electrode and the channel region (i.e., the lateral Schottky barrier heights), which severely hampers the rational design of Ohmic contact. Herein, by using first-principles quantum transport simulations, it is found that the difference between the intrinsic band edges of pristine MoSi2N4 and the work function of pristine MXenes plays a major role in the Schottky barrier heights of vertical contacts. Furthermore, phase diagrams of Schottky barrier heights dependent on metal work function are established, which can facilitate the screening of Ohmic contacts. By selecting nine MXene/MoSi2N4 heterojunctions as demos, it is found that W3N2(OH)2 and V2C(OH)2 form n-type Ohmic contacts to MoSi2N4 in both vertical and lateral directions with 100% tunneling probabilities due to their ultralow work functions, while p-type Ohmic contacts are formed between MoSi2N4 and V3C2O2, V4C3O2, or Ti4N3O2 due to their relatively large work functions. Our findings not only demonstrate great potential of fabricating coherent dopant-free all-2D devices based on MXene/MoSi2N4 contacts but also more importantly deliver a general strategy for fast screening efficient Ohmic contacts.