In-depth understanding of the band alignment and interface states scenario in Bi2O2Se/SrTiO3 ultrathin heterojunction

Bismuth oxyselenide (Bi₂O₂Se), a novel quasi-two-dimensional charge-carrying semiconductor, is recognized as one of the most promising emerging platforms for next-generation semiconductor devices. Recent advancements in the development of diverse Bi₂O₂Se heterojunctions have unveiled extensive potential applications in both electronics and optoelectronics. However, achieving an in-depth understanding of band alignment and particularly interface dynamics remains a significant challenge. In this study, we conduct a comprehensive experimental investigation into band alignment utilizing high-resolution X-ray photoelectron spectroscopy (HRXPS), while also thoroughly discussing the properties of interface states. Our findings reveal that ultrathin films of Bi₂O₂Se grown on SrTiO₃ (with TiO₂ (001) termination) exhibit Type-I (straddling gap) band alignment characterized by a valence band offset (VBO) of approximately 1.77 ± 0.04 eV and a conduction band offset (CBO) around 0.68 ± 0.04 eV. Notably, when accounting for the influence of interface states, the bands at the interface display a herringbone configuration due to substantial built-in electric fields, which markedly deviate from conventional band alignments. Thus, our results provide valuable insights for advancing high-efficiency electronic and optoelectronic devices, particularly those where charge transfer is highly sensitive to interface states.