Light-Induced Bipolar Photoresponse with Amplified Photocurrents in an 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, 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.

Automated summary

This research reports a bipolar-junction photoelectrode with a gallium nitride (GaN) p-n homojunction nanowire array, operating in electrolyte, and demonstrating bipolar photoresponse controlled by different wavelengths of light. By rationally decorating the nanowires with a ruthenium oxide (RuOx) layer, guided by theoretical modeling, the resulting RuOx/p-n GaN photoelectrode exhibits significantly boosted bipolar photoresponse compared to the pristine nanowires. The loading of the RuOx layer optimizes surface band bending, promotes charge transfer, and enhances the efficiency of redox reactions, leading to improved positive and negative photocurrents. Lastly, a dual-channel optical communication system is constructed using only one photoelectrode to decode encrypted dual-band signals.