Few-layer α-Sb2O3 molecular crystals as high-k van der Waals dielectrics: electronic decoupling and significant surface ionic behaviors

Inorganic molecular crystal films, particularly α-Sb2O3, have emerged as promising van der Waals (vdW) dielectrics for the large-scale integration of two-dimensional (2D) semiconductors in field-effect transistors (FETs) [K. L. Liu, B. Fin, W. Han, X. Chen, P. L. Gong and L. Huang, et al., Nat. Electron., 2021, 4, 906.]. Nevertheless, a notable gap exists in understanding the electronic and dielectric characteristics of few-layer α-Sb2O3 and the underlying physics governing its interaction with common 2D semiconductors. Herein, we address such issues through first-principles calculations. As the layer number increases, the electronic properties (e.g., band gap and band edges) of α-Sb2O3 exhibit minimal variations, resembling the electronic decoupling behavior, while the out-of-plane high dielectric constant significantly rises, indicating significant surface ionic behavior. These features stem from the weak interlayer quasi-bonding interaction, small atomic Born effective charge at the surface, and the influence of surface-to-volume ratio. Furthermore, exploring device physics, with a focus on complementary metal-oxide-semiconductor FETs, demonstrates that the leakage currents between the N-layer α-Sb2O3 (N ≥ 4) and all our studied 2D semiconducting channels adhere to international standards and the dielectrics with 4 and 5 layers meet the criteria for small equivalent oxide thickness. Unlike other layered vdW dielectrics, few-layer α-Sb2O3 emerges as a novel high-k vdW dielectric with exceptional dielectric performance and distinctive electronic characteristics, inspiring further exploration of inorganic molecular crystals for vdW dielectrics in integrated 2D semiconductor devices.