Heterohalogen Polarization for 2D High-κ Rare-Earth Oxyhalide Dielectrics.

Two-dimensional field-effect transistors (2D FETs) are promising candidates for next-generation semiconductor technologies, yet their adoption has been limited by the absence of gate dielectrics that simultaneously possess high dielectric constant (κ) and atomically smooth surfaces. Here, we present a heterohalogen polarization engineering strategy to boost the dielectric constants of LaOCl, LaOBr, PrOCl, PrOBr, NdOCl, and NdOBr by markedly improving the ionic and electronic polarizations. For example, F-polarized monolayer LaOCl (0.8 nm) achieves a record-high κ of 36.4 (a 5-fold enhancement over pristine LaOCl), an equivalent oxide thickness of 0.086 nm (0.8 nm thickness, 1 MHz frequency, 40 μm2 top electrode area), and a breakdown field (EBD) of 15.28 MV cm-1, meeting the dual requirements of high κ and high EBD in contemporary dielectric engineering. This study establishes a new paradigm for high-κ dielectric design via heterohalogen polarization engineering, paving the way for ultrascaled nanoelectronics with unprecedented performance.