Bi2OS2: a direct-gap two-dimensional semiconductor with high carrier mobility and surface electron states

Abstract

Two-dimensional (2D) semiconductors with desirable band gaps and high carrier mobility are highly sought after for future application in nanoelectronics. Herein, by means of first-principles calculations, we predict that a new 2D material, namely a Bi₂OS₂ nanosheet, possesses not only a tunable direct band gap, but also ultra-high electron mobility (up to 26 570 cm² V⁻¹ s⁻¹). More interestingly, an anomalous layer-dependent band gap is revealed, derived from the synergetic effect of the quantum confinement and intrinsic surface electron states. 2D Bi₂OS₂ also exhibits excellent absorption over the entire solar spectrum and the absorption coefficient is comparable to that of inorganic–organic hybrid perovskite solar cells. Moreover, the Bi₂OS₂ monolayer maintains good structural integrity up to 1000 K and has a relatively small exfoliation energy from its layered bulk. The excellent electronic and optical properties, together with high stability and great experimental possibility, render 2D Bi₂OS₂ a promising material for future nanoelectronic and optoelectronic applications.