Light-Induced Bipolar Photoresponse with Amplified Photocurrents in Electrolyte-Assisted Bipolar p-n Junction

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, we report a bipolar-junction photoelectrode employed with gallium nitride (GaN) p-n homojunction nanowire array that operates in electrolyte, 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 resulted 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 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-band optical communication system incorporated with such photoelectrode is constructed with using only one photoelectrode to decode dual-channel 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 multi-functional optoelectronic devices for future sensing, communication, and imaging systems.