Lattice‐Rotating SrTiO ₃ Buffer Enables Self‐Powered DUV/NIR Dual‐Band Ga ₂ O ₃ /GaAs Photodetectors with Wavelength‐Polarity Locking for Optical Encryption

ABSTRACT Heterogeneous integration of wide‐bandgap oxides with mature III‐V semiconductors off promising opportunities for next‐generation multimodal optoelectronics, but remains challenging due to the substantial lattice mismatch between these dissimilar material systems. Here, it is overcome this limitation by introducing a SrTiO 3 (STO) buffer layer that accommodates interfacial strain through a lattice‐rotation mechanism, enabling high‐quality epitaxial growth of Ga 2 O 3 on GaAs substrates. Leveraging this heterostructure, a vertical Au/Ga 2 O 3 /STO/GaAs/Ti photodetector that achieves self‐powered, polarity‐switchable dual‐band detection is fabricated. The device exhibits a responsivity of 55 mA/W with negative polarity photocurrent for 255 nm solar‐blind ultraviolet light and 5 mA/W with positive photoconductor for 940 nm near‐infrared light, accompanied by rapid response times of 1.56 and 1.04 ms, respectively. It is attributed this bidirectional photoresponse to opposing built‐in electric fields established at the top Au/Ga 2 O 3 Schottky junction and the bottom Ga 2 O 3 /STO/GaAs heterojunction, which selectively drive photogenerated carriers in opposite directions depending on the incident wavelength. Exploiting this wavelength‐polarity locking effect, filter‐free wavelength‐division multiplexing (WDM) communication and hardware‐level optical image encryption is demonstrated. This work provides an effective interface engineering strategy for large‐mismatch heteroepitaxy and opens a pathway toward secure, zero‐power optoelectronic systems.