Oriented Growth of BiOCl High‐κ Dielectrics for Pristine Van der Waals Electronics

High‐κ dielectric materials are pivotal for next‐generation two‐dimensional (2D) electronics. However, integrating high‐κ dielectrics with 2D semiconductors remains challenging in terms of simultaneously achieving superior dielectric properties and high‐quality interfaces. Here, we demonstrate that ultrathin bismuth oxychloride (BiOCl) crystals grown by chemical vapor deposition (CVD) can serve as excellent gate dielectrics, showing a high dielectric constant (>40) and a wide bandgap (∼3.9 eV). Remarkably, the CVD growth mode of BiOCl can be regulated from horizontal to vertical orientation by tuning nucleation rates, enabling residue‐free dry transfer for pristine device integration. Top‐gated BiOCl/MoS 2 field‐effect transistors exhibit a high on/off ratio exceeding 10 8 , a near‐ideal subthreshold swing of 61.2 mV/dec, minimal gate leakage currents of 10 −8 A/cm 2 , and nearly zero hysteresis. This reliable approach to integrating ultrathin single‐crystalline high‐κ dielectrics paves the way for realizing the full theoretical performance of 2D electronics.