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

TL;DR

This study investigates the electronic properties of Bi$_2$O$_2$Se single crystals, revealing an extraordinarily low metal-insulator transition concentration, giant permittivity, and insights into electron dynamics relevant for 2D device applications.

Contribution

It provides detailed measurements of transport and dielectric properties, explaining the premature metallicity and giant permittivity in Bi$_2$O$_2$Se based on Mott's criterion and dielectric screening effects.

Findings

Critical MIT concentration is around 10^16 cm^-3.

Relative permittivity exceeds 150 in insulating samples.

High mobility at low temperatures due to dielectric screening.

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 ($\rho$) 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 ($n_\textrm{c}\sim10^{16}$ cm$^{-3}$). The relative permittivity of the insulating sample is huge ($\epsilon_\textrm{r}\approx155(10)$) and varies slowly with temperature. Combined with the light effective mass, a long effective Bohr radius ($a_\textrm{B}^*\approx36(2)$ $\textrm{nm}$) is derived, which provides a reasonable interpretation of the metallic prematurity according to Mott's criterion for MITs. The high electron mobility ($\mu$) at low temperatures may result from the screening of ionized scattering centers due to the huge $\epsilon_\textrm{r}$. Our findings shed light on the electron dynamics in two dimensional (2D) Bi$_2$O$_2$Se devices.