Synthesis and Optoelectronic properties of ultrathin Bi2O2Se Nanosheets

Abstract

Bismuth oxyselenide (Bi2O2Se) has garnered significant attention as a promising two-dimensional material for next-generation electronic and optoelectronic devices due to its remarkably high mobility, moderate bandgap, exceptional environmental stability, and possession of a high-dielectric constant native oxide. Bi2O2Se-based field-effect transistors (FETs) have demonstrated outstanding current on/off ratios exceeding 106 with an almost ideal subthreshold swing of approximately 65 mV dec-1, crucial for low-power logic devices. This stratified material exhibits a unique defect structure where the donor state is situated above the conduction band, resulting in exceptional metallicity. In this Thesis, we have investigated the optoelectronic properties of Bi2O2Se nanosheets. In the thesis firstly, we have optimized the growth conditions for synthesizing ultrathin nanosheets of Bi2O2Se on Fluorophlogopite mica. We have developed a non-corrosive dry transfer method to Transfer these nanosheets for studying their electrical Properties. Our transferred nanosheets display outstanding optoelectronic properties, which is attributed to our damage-free transfer method. Then we have investigated the temperature-dependent electronic Transport properties of our samples. Here, we report the observation of metal insulation transition in a few nanometer-thin Bi2O2Se nanosheets by tuning the carrier density via back gate biasing. At high carrier density  = nour devices displayed  1, which tells about the presence of screened coloumb impurity scattering. As we decreased the carrier density below a critical density nC, the charge homogeneity of the system breaks down, resulting in the development of strong inhomogeneity. This leads to a percolation-driven transition in our system. At low carrier density n < nC, the system is in an insulating phase where transport is well described by a thermal activation mechanism where carriers are trapped in localized states, demonstrating the role of disorder in our system. Our extracted value of average percolation exponent  = 1.28 matches well with the theoretical value of 4/3, confirming percolation-based MIT in Bi2O2Se nanosheets.