Sustainable Doping via Molecular Adsorption on Thin-film Semiconductor Bi₂O₂Se

Doping in conventional semiconductors is commonly achieved by incorporating foreign atoms into the crystal, which requires precise control. In two-dimensional or thin-film semiconductors, a more straightforward alternative could be surface modification, such as molecular adsorption. However, a non-destructive doping via gas adsorption has not yet been reported. In this work, we present both first-principles calculations and experimental evidence demonstrating the feasibility of this approach in the thin-film semiconductor Bi₂O₂Se, which has recently gained attention for its high carrier mobility, moderate band gap, and excellent air stability. Several molecules are considered. We find that molecules with their LUMOs slightly below the Fermi level, such as NO₂, undergo stable chemisorption with an effective and controllable p-doping effect. Conversely, those with their LUMOs slightly above the Fermi level exhibit only localized charge transfer at the surface. On the other hand, the LUMOs lie far above the Fermi level of Bi₂O₂Se, leading to physisorption and negligible charge transfer, such as NH₃. This NO₂ adsorption-induced p-doping effect significantly modulates the threshold voltage in as-grown n-type samples and remains stable for more than ten days under ambient conditions, markedly improving electrostatic control and switching behavior in Bi₂O₂Se-based devices.