LAUSR

The development of dielectrics with atomic planes and van der Waals (vdW) interfaces is essential for enhancing the performance of 2D devices. However, vdW dielectrics often have smaller bandgaps compared to traditional 3D dielectrics, limiting their options. This study introduces AZBX (AZn₂BO₃X₂, where A = K or Rb, X = Cl or Br), a nonlinear deep‐ultraviolet optical crystal, as a quasi‐vdW layered dielectric ideal for 2D electronic devices. Focusing on KZBB, it's excellent dielectric properties, including a wide bandgap, high dielectric constant (high‐κ), and smooth interfaces are demonstrated. When used as the top gate dielectric in a KZBB/MoS₂ field‐effect transistor (FET) with MoS₂ channels and graphene contacts, the device exhibits outstanding performance, with a steep subthreshold swing (≈ 73 mV dec−1), high on/off ratio (≈ 10⁷), negligible hysteresis (0–8 mV), and stable, low leakage current (≈10⁻⁷ A cm−2) before breakdown. This work expands the 2D material and dielectric landscape and highlights the strong potential of AZBX as high‐performance dielectrics.