Odd-even layer effect of bismuth oxychalcogenide nanosurfaces: A first-principles study

Abstract

Recently, a second-type two-dimensional (2D) semiconductor Bi2O2Se with high carrier mobility was successfully fabricated by using the chemical vapor deposition (CVD) method. So far the surface-related property of Bi2O2Se remains a mystery to us. To theoretically explore such surface properties, we investigated the stability and electronic structure of the Bi2O2Se (100) and (110) surfaces by first-principles computations. It is found that (100) surfaces possess both the semiconducting nature and comparable stability as traditional adopted (001) surfaces. Thickness-dependent oscillation behavior is observed in the surface energy and band gap values of (100) surfaces, which can be attributed to the odd-even layer effect. Further studies indicate that odd layers will achieve reduced band gaps compared to the bulk phase while the ones with even layers exhibit larger values, and a similar effect in Bi2O2Te and Bi2O2S is also verified due to the same crystalline structure. To understand such an odd-even layer effect, electronic structure is elaborated and reveals that the local atomic mismatch will result in a different spatial distribution of p orbitals in Bi atoms, thus inducing distinct electronic properties. These new findings demonstrate the potential usage in nanoelectronics and optoelectronics based on the nanoslab of bismuth oxychalcogenides, which opens up a promising way for realizing the manipulation on the band gap in semiconductor.