A density functional theory study of two-dimensional bismuth selenite: layer-dependent electronic, transport and optical properties with spin-orbit coupling.

Recently, atomic-thickness van der Waals (vdW) layered bismuth selenite (Bi2SeO5) has been successfully synthesized, not only expanding the family of two-dimensional (2D) materials, but also playing a pivotal role in the advancement of 2D electronics as a high-κ dielectric. In this work, we systematically study the basic properties of 2D Bi2SeO5 through first-principles calculations, focusing on the spin-orbit coupling (SOC) effect and layer-dependent behaviors. The results show that SOC can adjust the bandgap of bulk/2D Bi2SeO5 from direct to indirect, with the bandgap decreasing upon increasing the thickness due to quantum confinement. Importantly, we observe that SOC has a negligible effect on the valence band edge but significantly impacts the conduction band edge, due to the specific distribution of the Bi-p orbital. We also explore the vdW magnetic tunneling junction based on 2D Bi2SeO5, which can exhibit significant tunneling magnetoresistance between the parallel and antiparallel magnetic alignments of electrodes, e.g. 900% for 1L and 1800% for 2L. As for the optical properties, strong layer dependence is also verified, and the large absorption coefficient is determined to be ∼106 cm-1. At last, we also explore the piezoelectric properties. Overall, layered Bi2SeO5 is a potential candidate material for electronic device and optoelectronic applications, as well as nano-spintronic applications.