Bipolar Modulation in a Self‐Powered Ultra‐Wide Photodetector Based on Bi₂Se₃/AlInAsSb Heterojunction for Wavelength‐Sensitive Imaging and Encrypted Optical Communication

Broadband photodetectors (PDs) have garnered significant attention due to their ability to detect optical signals across a wide wavelength range, with applications spanning military reconnaissance, environmental monitoring, and medical imaging. However, existing broadband detectors face several practical challenges, including limited detection range, uneven photoresponse, and difficult to distinguish multispectral signals. To address these limitations, this study presents a self-powered ultra-wide PD based on the Bi₂Se₃/AlInAsSb heterojunction. The device can detect signals across a wide wavelength range from 250 nm to 1900 nm, exhibiting outstanding optoelectronic performance with a maximum responsivity of 0.5 A W^-1, a detectivity of 4.2 × 10¹² Jones, a switching ratio of 1.1 × 10⁴, and an external quantum efficiency of 71.4%. Furthermore, the detector achieves a detectivity greater than 10¹⁰ Jones across the entire broadband range, significantly improving photoresponse uniformity. Notably, due to the differential band alignment of the two materials across spectral ranges, this detector exhibits a photocurrent polarity reversal in the 650-680 nm range. Leveraging its broadband and bipolar characteristics, this PD successfully enables secure information encryption in communication systems. This study significantly advances broadband PD technology, enhancing its practical uses and introducing innovative solutions for secure communications, thus strengthening communication security and confidentiality.