  Van der Waals heterostructures of two-dimensional materials have opened up
new frontiers in condensed matter physics, unlocking unexplored possibilities
in electronic and photonic device applications. However, the investigation of
wide-gap high-$\kappa$ layered dielectrics for devices based on van der Waals
structures has been relatively limited. In this work, we demonstrate an easily
reproducible synthesis method for the rare earth oxyhalide LaOBr, and we
exfoliate it as a 2D layered material with a measured static dielectric
constant of $\epsilon_{0, \perp} \simeq 9$ and a wide bandgap of 5.3 eV.
Furthermore, our research demonstrates that LaOBr can be used as a
high-$\kappa$ dielectric in van der Waals field-effect transistors with high
performance and low interface defect concentrations. Additionally, it proves to
be an attractive choice for electrical gating in excitonic devices based on 2D
materials. Our work demonstrates the versatile realization and functionality of
2D systems with wide-gap and high-$\kappa$ van der Waals dielectric
environments.
