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The p–n junction with bipolar characteristics sets the fundamental unit to build electronics while its unique rectification behavior constrains the degree of carrier tunability for expanded functionalities. Herein, a bipolar‐junction photoelectrode employed with a gallium nitride (GaN) p–n homojunction nanowire array that operates in electrolyte is reported, demonstrating bipolar photoresponse controlled by different wavelengths of light. Significantly, with rational decoration of a ruthenium oxides (RuOx) layer on nanowires guided by theoretical modeling, the resulting RuOx/p–n GaN photoelectrode exhibits unambiguously boosted bipolar photoresponse by an enhancement of 775% and 3000% for positive and negative photocurrents, respectively, compared to the pristine nanowires. The loading of the RuOx layer on nanowire surface optimizes surface band bending, which facilitates charge transfer across the GaN/electrolyte interface, meanwhile promoting the efficiency of redox reaction for both hydrogen evolution reaction and oxygen evolution reaction which corresponds to the negative and positive photocurrents, respectively. Finally, a dual‐channel optical communication system incorporated with such photoelectrode is constructed with using only one photoelectrode to decode dual‐band signals with encrypted property. The proposed bipolar device architecture presents a viable route to manipulate the carrier dynamics for the development of a plethora of multifunctional optoelectronic devices for future sensing, communication, and imaging systems.

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The carrier transport dynamics at the surface/interface of semiconductors determine the electronic and optical properties of devices. Thus, precise control of their dynamic processes while understanding the nature of these characteristics is crucial for modulating device functionalities. Here, a photoelectrochemical-type photosensor is built using monocrystalline p-GaN nanowires on the Si platform, which unambiguously exhibits either positive or negative photocurrent upon different light illumination. Such dual-polarity photocurrents are attributed to photogenerated-carrier-transport competition at two interfaces: the GaN/electrolyte and GaN/Si interface. Particularly, a rational Pt decoration successfully accelerates the carrier migration at the GaN/electrolyte interface that breaks the original balance of carrier transport. This mechanism is further elaborated by Kelvin-probe-force-microscopy characterization, which intuitively reveals the impact of Pt decoration on modulating nanowires' surface band bending and the consequent carrier dynamics at the interfaces. These insights into the control of carrier dynamics shed light on achieving multi-functional PEC devices built upon simple semiconductor architectures.