Metal insulator Transition in Bi₂O₂Se Nanosheets.

Bismuth oxyselenide has recently gained tremendous attention as a promising 2D material for next-generation electronic and optoelectronic devices due to its ultrahigh mobility, moderate bandgap, exceptional environmental stability, and presence of high-dielectric constant native oxide. Bi₂O₂Se based field-effect transistors (FETs) have also shown excellent current on/ off ratios of >10⁶ with an almost ideal subthreshold swing (≈65 mV dec−1), which is essential for low-power logic devices[1]. Bi₂O₂Se. possesses a unique defect structure in which the donor state lies above the conduction band leading to unusual metallicity. Furthermore, there is a spatial separation of electrons from donor sites, suppressing the scattering caused by the donor sites resulting in high mobility[2]. In this work, we have synthesized ultrathin single crystalline nanosheets of Bismuth oxyselenide using a Homebuilt Atmospheric Pressure Chemical Vapor Deposition system on Fluorophlogopite Mica substrates. Using a non-corrosive dry transfer method, we transferred as-grown samples to SiO₂/Si substrates and studied their Temperature dependent electrical transport properties. Our Back gated devices show a remarkable increase in field effect mobility with decreasing temperature. Mobility of our sample increases from 900cm²V^-1s^-1at 300K to 4000cm²V^-1s^-1 at 11.5K. Furthermore, our devices show a gate-tunable metal-insulator Transition. At higher gate voltages, our devices display metallic resistivity behavior over the entire temperature range. Our finding helps in understanding the transport mechanism and nature of electronic states in Bi₂O₂Se .