Efficient Ohmic contacts and built-in atomic sublayer protection in MoSi2N4 and WSi2N4 monolayers

<jats:title>Abstract</jats:title><jats:p>Metal contacts to two-dimensional (2D) semiconductors are often plagued by the strong Fermi level pinning (FLP) effect which reduces the tunability of the Schottky barrier height (SBH) and degrades the performance of 2D semiconductor devices. Here, we show that MoSi<jats:sub>2</jats:sub>N<jats:sub>4</jats:sub> and WSi<jats:sub>2</jats:sub>N<jats:sub>4</jats:sub> monolayers—an emerging 2D semiconductor family with exceptional physical properties—exhibit strongly suppressed FLP and wide-range tunable SBH. An exceptionally large SBH slope parameter of <jats:italic>S</jats:italic> ≈ 0.7 is obtained which outperforms the vast majority of other 2D semiconductors. Such intriguing behavior arises from the septuple-layered morphology of MoSi<jats:sub>2</jats:sub>N<jats:sub>4</jats:sub> and WSi<jats:sub>2</jats:sub>N<jats:sub>4</jats:sub> monolayers in which the semiconducting electronic states are protected by the outlying Si–N sublayer. We identify Ti, Sc, and Ni as highly efficient Ohmic contacts to MoSi<jats:sub>2</jats:sub>N<jats:sub>4</jats:sub> and WSi<jats:sub>2</jats:sub>N<jats:sub>4</jats:sub> with zero interface tunneling barrier. Our findings reveal the potential of MoSi<jats:sub>2</jats:sub>N<jats:sub>4</jats:sub> and WSi<jats:sub>2</jats:sub>N<jats:sub>4</jats:sub> as a practical platform for designing high-performance and energy-efficient 2D semiconductor electronic devices.</jats:p>