High-k Monolayer CaF₂ as the Gate Dielectric for Two-Dimensional SiC-Based Field-Effect Transistors

Exploring gate insulators suitable for two-dimensional (2D) semiconductors that can be extended to the nanometer range is of great importance for the development of nanoelectronics. In this paper, the structural and electrical properties of a high-k CaF2 monolayer serving as the gate dielectric for 2D SiC-based field-effect transistors are systematically investigated using first-principles calculations. It is found that a stable van der Waals (vdW) contact can be formed between CaF2 and 2D SiC. In addition, ab initio molecular dynamics simulations show that the interface structure of 2D SiC/CaF2 possesses high thermal stability. Compared with the available vdW gate dielectric hexagonal boron nitride (hBN), CaF2's interactions with 2D SiC exhibit higher structural stability with a lower lattice mismatch rate and a stronger binding energy. In addition, the valence band offset of 2D SiC/CaF2 is as high as 3.5 eV, which could overcome the unacceptable gate leakage current for hBN serving as the gate dielectric. It is further found that the dielectric properties of CaF2 are not deteriorated by carbon antisite and interstitial defects on the 2D SiC surface.