Mechanistic Insights into High Electron Mobility in 2D Bi₂O₂Se Field-Effect Transistors

Bismuth oxyselenide (Bi₂O₂Se), a two-dimensional (2D) semiconductor, is a promising postsilicon channel material for field-effect transistors (FETs) at sub-3 nm technology nodes. It offers high intrinsic mobility and a stable, lattice-matched interface with its native oxide, Bi₂SeO₅. Reported mobilities are high, reaching 4.7 × 10⁵ cm² V^-1 s^-1 at 2 K and 812 cm² V^-1 s^-1 at 300 K in three-dimensional (3D)-FETs, and 2.0 × 10⁴ cm² V^-1 s^-1 at 2 K and 313 cm² V^-1 s^-1 at 300 K in 2D-FETs. However, the dominant scattering mechanisms that limit this mobility remain unclear. We develop a unified mobility model that incorporates ionized impurity, surface roughness, longitudinal optical phonon, electron-electron, and acoustic deformation potential scattering. The model quantitatively reproduces experimental data from the bulk material to the monolayer limit. We found that in ultrathin channels, surface roughness scattering is strongly reduced, while acoustic phonon deformation potential scattering becomes the dominant limiting mechanism. These insights establish a mechanistic understanding of charge transport in Bi₂O₂Se and provide crucial guidelines for device design at sub-1 nm nodes.