Heterostructure as a Channel Material*

We demonstrate superior performance of PdSe₂/WSe₂ van der Waals heterostructure than PdSe₂ or WSe₂ alone as a channel material for field-effect transistors (FETs), where WSe₂ acts as a buffer between PdSe₂ and Ti metal at the drain/source contacts to alleviate the Fermi-level pinning effect and therefore significantly lower the Schottky barrier and contact resistance. As a result, our PdSe₂/WSe₂ heterostructure-based FETs exhibit a two-terminal electron mobility exceeding 200 cm² V^-1 s^-1 at room temperature and approaching 700 cm² V^-1 s^-1 at 77 K, consistent with phonon-limited electron transport. By contrast, the two-terminal electron mobility of FETs based on a few-layer PdSe₂ or WSe₂ alone is substantially lower, especially at low temperatures suggesting that the electron transport is limited by the contacts. Furthermore, the increase of bandgap with decreasing PdSe₂ thickness leads to a higher ON/OFF ratio without substantial degradation of two-terminal electron mobility in FETs consisting of PdSe₂/WSe₂ heterostructures with thinner PdSe₂. We believe the significantly improved device performance enabled by combining different 2D semiconductors will facilitate real-world electronic applications of 2D semiconductors.