Exploring the high dielectric performance of Bi2SeO5: from bulk to bilayer and monolayer

Abstract

Bi2SeO5 has garnered considerable attention as a van der Waals (vdW) layered dielectric material featuring excellent electrical insulation properties. However, the related theoretical understanding of the dielectric properties of atomically thin films is still lacking. Here, we conducted the first-principles calculations to determine the dielectric performance of Bi2SeO5, showing a high average dielectric constant (ε) of >20 ranging from bulk to bilayer and monolayer. Besides, the conduction and valance band offsets between the monolayer Bi2SeO5 and bilayer Bi2O2Se were calculated to be greater than 1 eV, suggesting that monolayer Bi2SeO5 works well as the dielectric for atomically thin Bi2O2Se. Unlike h-BN or other two-dimensional (2D) vdW insulators, ε of Bi2SeO5 is dominated by its ionic component and remains nearly constant as the thickness decreases, demonstrating an ultralow equivalent oxide thickness (EOT) of 0.3 nm for its monolayer form. Moreover, the high ε of monolayer Bi2SeO5 survives under tensile or compressive strains up to 6%, which greatly facilitates its integration with various 2D semiconductors. Our work suggests that Bi2SeO5 ultrathin films can serve as excellent atomically flat encapsulation and dielectric layers for high-performance 2D electronic devices. (Figure presented.)