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Hidden Direct Bandgap of Bi2O2Se by Se Vacancy and Enhanced Direct Bandgap of Bismuth Oxide Overlayer
Sang Wook Han1, Won Seok Yun2, Seungho Seong3
1Basic Science Research Institute and Energy Harvest Storage Research Center, University of Ulsan, Ulsan 44610, Republic of Korea.
Abstract:
The Bi2O2Se surfaces are well-known to possess 50% Se vacancies, yet they have shown no in-gap states within the indirect bandgap (∼0.8 eV). We have found that the hidden in-gap states arising from the Se vacancies in a 2 × 1 pattern induce a reduced direct bandgap (∼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 (∼2.1 eV). The simplified fabrication of Bi oxide overlayers provides promise for improving Bi2O2Se electronic devices and enhancing photocatalytic activity.
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