Achieving programmable bipolar photocurrents via <i>p</i> – <i>n</i> junction design for PEPS-based optoelectronic applications

The photoelectrochemical photocurrent switching (PEPS) effect, which enables a single photodetector to generate opposite photocurrent polarities under varied conditions, offers key insights into carrier dynamics at heterojunctions and holds promise for advanced applications in photoelectric logic, optical communication, and self-powered sensing. To achieve wavelength-programmable bipolar photocurrents, this study designed two distinct heterojunctions, such as a p–n junction (Cu2O/α-Ga2O3) and an n–n junction (CdS/α-Ga2O3), and compared their PEPS behaviors. The designed p–n junction successfully realized the desired PEPS effect at 0 V bias, exhibiting a positive photocurrent under 254 nm UV light and a negative photocurrent under 365 nm illumination. In contrast, the n–n junction showed no such polarity switching. This functional difference is attributed to the strong, unidirectional built-in electric field engineered into the p–n junction, which orchestrates wavelength-selective carrier transport and thus dictates the photocurrent polarity. The weaker, diffuse field in the n–n junction fails to achieve this directional control. By leveraging the programmable bipolar photoresponse of the designed p–n device, we further demonstrated its application as a single-element half-adder for simplified logic circuits and its potential for high-density coding and binary phase shift keying modulation in optical communication. This work confirms that intentional band engineering through heterojunction design is the key to materializing the PEPS effect, providing a clear design principle and material platform for developing advanced intelligent photoelectrochemical devices.