Unlocking Photodetection Mode Switching from a Simple Lateral Design

ABSTRACT Achieving multi‐mode photodetection within a single device is crucial for next‐generation optical communication systems, where multidimensional optical information must be efficiently and safely transmitted, processed, and encrypted. Yet, integrating multiple distinct photoresponse modes and dynamically switching between them in real‐time typically requires complex architectures or device stacking, which limits scalability and practicality. We present a simple lateral photodetector based on a single semiconductor layer directly integrated on a standard SiO ₂ /Si substrate, enabling three well‐defined and light‐controllable detection modes: transient spikes, continuous square wave, and a hybrid transient‐continuous state. This multimodal behaviour emerges from the cooperative interplay of substrate‐mediated capacitive coupling, generating ultrafast spike responses (∼53 µs), and photovoltaic‐driven photoconductive transport responsible for steady‐state photocurrents. By modulating illumination intensity and wavelength, the relative contribution of these mechanisms is precisely tuned, allowing real‐time switching among three photoresponse states without altering the device structure or bias. Using this light‐programmable behaviour, we demonstrate a light‐controlled triple‐channel secure optical communication platform capable of time‐varying encryption keys and multi‐modal information encoding and decoding. This work introduces a simple but powerful device concept, multi‐mode photodetection within a single photoactive layer, marking a significant step toward compact, efficient, and intelligent optical communication technologies.