Defect Engineering in Thickness-Controlled Bi₂O₂Se-Based Transistors by Argon Plasma Treatment

Area of Science:

• Materials Science
• Nanotechnology
• Condensed Matter Physics

Background:

• Two-dimensional (2D) materials offer unique electronic properties.
• Controlling the thickness and defects of 2D materials is crucial for device performance.
• Bismuth oxychloride (Bi2O2Se) is a promising 2D material for electronics.

Purpose of the Study:

• To develop a controllable method for thinning Bi2O2Se nanoflakes.
• To investigate the effect of thickness and defects on the electronic properties of Bi2O2Se field-effect transistors (FETs).
• To explore the potential of Bi2O2Se FETs for nonvolatile memory applications.

Main Methods:

• Thinning of Bi2O2Se nanoflakes using Ar+ plasma treatment.
• Surface morphology and crystalline quality analysis using Atomic Force Microscopy (AFM) and Raman spectroscopy.
• Defect passivation using UV O3 treatment and characterization via X-ray Photoelectron Spectroscopy (XPS).
• Fabrication and characterization of bottom-gate Bi2O2Se-based FETs.
• Analysis of electronic transport properties using a parallel resistor model.
• Investigation of gate-source/drain voltage hysteresis and its dependence on UV irradiation.

Main Results:

• Ar+ plasma treatment uniformly thinned Bi2O2Se nanoflakes with minimal impact on surface morphology and crystallinity.
• UV O3 treatment effectively passivated oxygen and selenium vacancies created during etching.
• The on-current/off-current (Ion/Ioff) ratio of Bi2O2Se FETs increased with decreasing thickness and was further improved by UV O3 treatment.
• Thickness-controlled Bi2O2Se FETs achieved a high Ion/Ioff ratio of 6.0 × 10^4 and field-effect mobility of 5.7 cm^2 V^-1 s^-1.
• Electronic transport properties were well described by a parallel resistor model.
• Clockwise hysteresis was observed before UV irradiation, attributed to charge trapping/detrapping at the interface and in the bulk.
• Anticlockwise hysteresis was observed after UV irradiation, linked to tunneling between deep-level oxygen defects in SiO2 and the Si gate.

Conclusions:

• A simple, effective, and controllable method for thinning Bi2O2Se nanoflakes was established.
• Thickness control and defect passivation significantly enhance the performance of Bi2O2Se FETs.
• The observed hysteresis characteristics suggest potential applications of Bi2O2Se-based devices in nonvolatile memory.