Argon Plasma Thinning of Bi₂O₂Se and the Impacts on Transistor Performance

The argon plasma etching is used to uniformly thin thickness of as-exfoliated 2D Bi₂O₂Se nanoflake, because the interlayer binding energy of Bi₂O₂Se (76.8 meV/Ų) is much larger than that of graphene (21.1 meV/Ų) or MoS₂ (26.3 meV/Ų) which makes it difficult to obtain ultra thin film. The clean surface morphology and good crystalline quality of Bi₂O₂Se nanoflakes after etching are obtained and characterized. The X-ray photoelectron spectroscopy results show that the O and Se vacancies on the top surface of Bi₂O₂Se nanoflakes are created during etching, which can be passivated by forming an ultrathin oxide layer with UV ozone treatment. The on-current/off-current (<i>I</i>_on/<i>I</i>_off) ratio of bottom gate Bi₂O₂Se FET increases with argon etching time, and is further improved by UV ozone treatment. Eventually the thickness-controlled Bi₂O₂Se FET obtains a high <i>I</i>_on/<i>I</i>_off ratio of &gt;5.0×10⁴. Importantly, the variation trend of <i>I</i>_on/<i>I</i>_off ratio and the electronic transport properties for Bi₂O₂Se FETs are well described by parallel resistor model and corresponding energy band diagram. Moreover, the <i>I</i>_ds-<i>V</i>_gs hysteresis and its inversion with UV irradiation are interpreted by charges trapping/detrapping and tunneling mechanism, respectively.