Wide Bandgap Lanthanide Oxybromides High‐ κ Dielectrics for High‐Performance Two‐Dimensional Electronics

High‐ κ single‐crystal dielectrics serve as fundamental components in next‐generation 2D electronics. However, the inevitable high leakage current caused by Schottky emission, which stems from the absence of a sufficiently wide bandgap in high‐ κ dielectrics, limits device performance. Here, we show that 2D lanthanide oxybromides ( Ln OBr, Ln = La, Ce, Nd, Sm, Eu, Gd, Ho, and Er) synthesized by the chemical vapor deposition method exhibit a wide bandgap (>5.7 eV), tunable thickness, and feature of high‐quality single crystal. Meanwhile, 2D LaOBr single crystal displays high dielectric constant (14.8), low leakage current density (<10 −6 A cm −2 ), and high breakdown field strength (14.2 MV cm −1 ), suggesting good insulating property. As a result, the LaOBr top‐gate MoS 2 transistors demonstrate competitive electrical performances, including a negligible hysteresis (0.72 mV/(MV cm −1 )), high on/off ratio (10 7 ), near‐Boltzmann‐limit subthreshold swing (63 mV dec −1 ), excellent electrical reliability and thermal stability (up to 450 K). Accordingly, the well‐performed inverter is integrated, with a steep voltage transition and high gain. This work develops abundant dielectric materials with a wide bandgap and a high dielectric constant for innovative high‐performance 2D electronics.