Achieving Light-Induced Bipolar Photosensing in III-Nitride Nanowires by Precisely Regulating Ambipolar Carrier-Transport Behavior

The functionality of semiconductor devices primarily relies on their band structure, which governs charge transfer behavior. Achieving precise control of band structures, especially on semiconductor surfaces and at interfaces, remains a long-standing challenge. As semiconductors are miniaturized from bulk to low-dimensional forms (like 2D materials, nanowires, and quantum dots), their unique physical and structural characteristics, especially the high surface-to-volume ratio, make them highly responsive to the surrounding environment. This responsiveness allows for easy alteration of their band structures by external factors. Therefore, the large surface area of low-dimensional materials holds significant promise for surface band engineering, offering opportunities to control charge transfer behavior in nanodevices and develop novel multifunctional nanoelectronics and nanophotonics devices.<br/><br/>Hence, in this study, we developed p-type aluminum-gallium-nitrogen (p-AlGaN) nanowires on an N-type silicon (Si) substrate and introduced a novel post-epitaxy technique to create carbon@p-AlGaN core-shell nanostructures with varying carbon layer thicknesses. As the carbon layer thickens, the electronic interaction at the carbon-AlGaN interface intensifies, causing the degree of surface band bending in the AlGaN alloy. We constructed an innovative electrolyte-assisted photodetector using carbon@p-AlGaN core-shell nanowires as photoelectrodes. By adjusting the carbon layer thickness, we controlled the degree of band bending on the nanowire surface, significantly influencing charge transfer at the p-AlGaN/electrolyte interface. This tunable charge transfer between the adjustable interface and the internal p-AlGaN/n-Si interface ultimately determines the device's photocurrent output, resulting in a spectrally resolved bipolar photocurrent device with adjustable polar switching points across a broad spectral range. Leveraging this unique optical response, we developed a reprogrammable optical switching logic gate capable of performing four logic operations ("XOR," "AND," "OR," and "NOT") within a single device architecture. Additionally, we created an image encryption transmission system where the optical signal is encrypted using the "XOR" logic operation, ensuring secure image transmission. Our proposed bipolar junction device, based on surface energy band engineering, offers a versatile and effective material architecture for creating multifunctional nanophotonic devices.