Hidden Direct Bandgap of Bi2O2Se by Se Vacancy and Enhanced Direct Bandgap of Bismuth Oxide Overlayer

Abstract

The Bi2O2Se surfaces are well-known to possess 50% Se vacancies, yet they have shown no in-gap states within the indirect bandgap (similar to 0.8 eV). We have found that the hidden in-gap states arising from the Se vacancies in a 2 x 1 pattern induce a reduced direct bandgap (similar to 0.5 eV). Such a reduced direct bandgap is responsible for the high electron mobility of Bi2O2Se. Moreover, the Bi oxide overlayers of the Bi thin films, formed through air exposure and annealing, unexpectedly exhibit a large direct bandgap (similar to 2.1 eV). The simplified fabrication of Bi oxide overlayers provides promise for improving Bi2O2Se electronic devices and enhancing photocatalytic activity. © 2024 American Chemical Society