Huge permittivity and premature metallicity in Bi$_2$O$_2$Se single crystals

Abstract

Bi2O2Se is a promising material for next-generation semiconducting electronics. It exhibits premature metallicity on the introduction of a tiny amount of electrons, the physics behind which remains elusive. Here we report on transport and dielectric measurements in Bi2O2Se single crystals at various carrier densities. The temperature-dependent resistivity (ρ) indicates a smooth evolution from the semiconducting to the metallic state. The critical concentration for the metal-insulator transition (MIT) to occur is extraordinarily low (nc ∼ 10 16 cm −3 ). The relative permittivity of the insulating sample is huge ( r ≈ 155(10)) and varies slowly with temperature. Combined with the light effective mass, a long effective Bohr radius (a * B ≈ 36(2) nm) is derived, which provides a reasonable interpretation of the metallic prematurity according to Mott's criterion for MITs. The high electron mobility (µ) at low temperatures may result from the screening of ionized scattering centers due to the huge r. Our findings shed light on the electron dynamics in two dimensional (2D) Bi2O2Se devices.