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

Abstract

Bi${}_2$O${}_2$Se 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 Bi${}_2$O${}_2$Se single crystals at various carrier densities. The temperature-dependent resistivity ($\ddot{I}$) 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 ($n_{\text{c}}\sim 10^{16}$ cm${}^{-3}$). The relative permittivity of the insulating sample is huge ($\hat{I}{\mu }_{\text{r}}\approx 155(10)$) and varies slowly with temperature. Combined with the light effective mass, a long effective Bohr radius ($a_{\text{B}}^{\ast }\approx 36(2)$ $\text{nm}$) is derived, which provides a reasonable interpretation of the metallic prematurity according to Mott's criterion for MITs. The high electron mobility ($\hat{I}¼$) at low temperatures may result from the screening of ionized scattering centers due to the huge $\hat{I}{\mu }_{\text{r}}$. Our findings shed light on the electron dynamics in two dimensional (2D) Bi${}_2$O${}_2$Se devices.

8 pages, 5 figures, accepted by SCIENCE CHINA: Physics, Mechanics & Astronomy