Defect Engineering in β-Bi₂SeO₅/Bi₂O₂Se Heterostructures for High-Resolution Phototransistor Arrays

Analogous to the pivotal SiO₂/Si junction in modern electronics, the β-Bi₂SeO₅/Bi₂O₂Se architecture has been demonstrated to enhance the performance of electronic devices. However, its potential to improve the optoelectronic properties of Bi₂O₂Se, such as responsivity and detectivity, remains unexplored. The photodetection performance of Bi₂O₂Se is primarily limited by intrinsic selenium vacancies at its surface, which lead to low photocurrent and instability. To address this, a defect-engineered β-Bi₂SeO₅/Bi₂O₂Se heterojunction is constructed with an atomically sharp interface via a developed UV-assisted oxidation strategy. This heterostructure successfully suppresses surface vacancies while enabling dual functionality-surface passivation and photoactive charge separation, resulting in substantially enhanced optoelectronic performance. First-principles calculations confirm a stable type-II band alignment with interfacial transitions enabling efficient carrier dissociation. The visible-near-infrared transparency and high-k of β-Bi₂SeO₅ further enable top-gated phototransistors with dynamically tunable photoresponse, achieving the largely improved metrics of responsivity (1.2 × 10⁴ A W^-1), detectivity (1.5 × 10¹³ Jones), and on/off ratio (2.3 × 10⁶). Additionally, by using thermal scanning probe lithography, a high-resolution (pixel pitch = 6.5 µm) β-Bi₂SeO₅/Bi₂O₂Se phototransistor array is fabricated and its imaging capabilities are demonstrated. The results establish an effective defect-engineered strategy with in situ large-area growth capability of β-Bi₂SeO₅ and high-resolution device patterning, making β-Bi₂SeO₅/Bi₂O₂Se a promising photoresponsive platform for advanced optoelectronic devices.