Hidden Direct Bandgap of Bi<sub>2</sub>O<sub>2</sub>Se by Se Vacancy and Enhanced Direct Bandgap of Bismuth Oxide Overlayer
Sang Wook Han, Won Seok Yun, Seungho Seong, Zeeshan Tahir, Yong Soo Kim, Minji Ko, Sunmin Ryu, Jong‐Seong Bae, Chang Won Ahn, Jeongsoo Kang
Abstract
The Bi 2 O 2 Se 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 Bi 2 O 2 Se. 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 Bi 2 O 2 Se electronic devices and enhancing photocatalytic activity.