Achieving real Ohmic contact by the dual protection of outer layer atoms and surface functionalization in 2D metal Mxenes/MoSi2N4 heterostructures

Abstract

The quality of contact between a metal electrode and a two-dimensional (2D) semiconductor is simultaneously determined by the Schottky barrier height (SBH), the tunneling probability (P_TB), and the Fermi level pinning (FLP), which also impact the performance of the device. Herein, we investigate the contact characteristics of 20 2D metal Mxenes/MoSi₂N₄ heterostructures, which are all stable van der Waals (vdW) heterostructures with various contact types: n/p-type Ohmic/Schottky contact and p-type quasi-Ohmic contact by surface functionalized Mxenes based on density functional theory. Interestingly, it was found that the M₄C₃O₂H₂/MoSi₂N₄ heterostructures have the best contact properties according to the calculated vertical/lateral SBH and comprehensive coefficient C for evaluating P_TB and Fermi pinning factor (S). More importantly, our results indicate that the unique atomic structure of MoSi₂N₄ and surface functionalization of Mxenes can protect the contact properties, i.e., –O and –F terminations can regulate the contact properties, but they will induce a large SBH, carrier polarity, and small P_TB. –OH terminations can protect the excellent contact properties of intrinsic M₄C₃/MoSi₂N₄ heterostructures and achieve real Ohmic contact. Therefore, the degradation of device performance caused by oxidation and fluoridation can be avoided by –OH termination in practical applications. These results are of great significance for realizing the application of the MoSi₂N₄ family of semiconductors in electronic devices.