Type-dependent hot carrier behavior in photoelectrochemical reduction and oxidation of Au/GaN junction photoelectrodes

[Display omitted] •Hot carrier behavior at the interface between plasmonic nanoparticles (NPs) and semiconductors with opposite doping types is elucidated.•More efficient hot-carrier separation and injection when Au NPs are attached p-doped GaN (Au/p-GaN) compared to n-doped GaN (Au/n-GaN).•A higher enhancement (approximately 8 times) in photoelectrochemical reactions for Au/n-GaN compared to Au/p-GaN is observed.•The difference in the band alignment between the Au/GaN junction systems is responsible for the superior photoelectrochemical performance of Au/n-GaN. In junctions with semiconductors, plasmonic metal nanoparticles (NPs) can be utilized to efficiently harness solar energy by collecting hot carriers. However, the behavior of hot carriers at the interfaces between semiconductors with opposite doping types is not fully elucidated. Here, Au NPs are attached to n-doped (Au/n-GaN) or p-doped gallium nitrides (Au/p-GaN) to examine the photoelectrochemical performance regarding hot carrier behavior. Direct surface potential measurements revealed that electrons are collected in n-type GaN (n-GaN) when illuminated, while hot holes remain in Au NPs for oxidation reactions via the plasmonic process. Conversely, holes are collected in p-type GaN (p-GaN), thereby promoting the reduction reaction by the electrons left in Au NPs. Specifically, the change in surface potential difference induced by green light illumination in Au/p-GaN is four times greater than that observed in Au/n-GaN. Conversely, the changes in open-circuit potential and photocurrent density under light illumination are approximately six times more significant in Au/n-GaN compared to Au/p-GaN. This difference in efficiency can be attributed to the more favorable oxidation reaction occurring in Au NPs at the interface with GaN materials, as opposed to the reduction reaction, due to the difference in band alignment between the Au/GaN junction systems.