Ultrathin Rare‐Earth Oxyhalides as High‐κ van der Waals Layered Dielectrics

Abstract Van der Waals (vdW) dielectrics are extensively employed to enhance the performance of 2D electronic devices. However, current vdW dielectric materials still encounter challenges such as low dielectric constant ( κ ) and difficulties in synthesizing high‐quality single crystals. 2D rare‐earth oxyhalides (REOXs) with exceptional electrical properties present an opportunity for the exploration of novel high‐ κ dielectrics. In this study, for the first time, the synthesis of a series of van der Waals layered gadolinium oxyhalides with thicknesses down to monolayer through a space‐confined vdW epitaxy approach and demonstrating their application as a single‐crystalline gate dielectric is reported. It exhibits a remarkable relative dielectric constant exceeding 17 and an impressive breakdown field strength of 13.5 MV cm −1 . The 2D transistors directly gated by the REOXs layer exhibit enhanced electron mobility and a low interface trap density. An ultrahigh on/off current ratio of 10 9 and a near‐Boltzmann‐limit subthreshold swing is achieved. The superior dielectric properties, combined with the universality and scalability of the production method (e.g., millimeter‐scale films are achieved), demonstrate that 2D REOXs can serve as promising gate dielectrics for 2D electronics, thereby expanding the study of high‐ κ vdW materials and potentially providing new opportunities for the development of low‐power electronic devices.