Gate-TunableCurrent Polarity Switching in p‑NiO/n-ZnGa₂O₄ Heterojunction Field-Effect Phototransistorsfor Secure Optical Communication

Secure optical communication is crucial for protecting sensitive data in modern communication systems. Herein, we report the gate-tunable current polarity switching phenomenon in p-NiO/n-ZnGa₂O₄ heterojunction field-effect phototransistors, offering a novel strategy for secure optical communication. The low carrier concentration in the n-type ZnGa₂O₄ channel layer enables the transistor to persist in the cutoff state under dark conditions. Interestingly, the forward gate voltage application induces a polarity reversal of the drain-source current, with the dark current and photocurrent demonstrating a transition from 0.621 nA/34.53 μA at a gate voltage of 0 V to −0.438 nA/–164.08 μA at a gate voltage of 40 V. Moreover, the device demonstrates outstanding solar-blind ultraviolet (UV) photodetection performance, with responsivities of 53.2 A/W and 252.3 A/W, decay times of 16.44 and 29.35 ms, and rejection ratios exceeding 10⁴ at gate voltages of 0 and 40 V, respectively. By leveraging the gate voltage and solar-blind UV light as inputs, an optoelectronic exclusive OR (XOR) logic gate scheme is designed, where the drain-source current acts as the output. This enables the encoding of optical signals with gate voltage as an encryption signal, ensuring secure information transmission. Even if intercepted, transmitted data remain indecipherable without the encryption signal at the receiver. This research provides a promising avenue for developing advanced secure optical communication technologies.