Specifics of the water photoelectrolysis in KOH‐base aqueous solution using GaN‐based structures as working electrodes are studied. The structures were grown by HVPE and MOCVD techniques on sapphire substrates. In highly Si‐doped HVPE‐grown GaN layers (ND−NA ∼ 3 × 1018 cm−3) a barrier at the E1 offset potential dominates the current–potential (I–E) characteristics. The same dominant E1 offset potential was observed in MOCVD‐grown GaN/InGaN nanopillar structures after the treatment. The Debye screening effect in high‐concentration of KOH electrolyte (20–40 wt.%) that reduces the potential barrier was observed clearly in the defectless nanopillar structures. The corrosion process is initiated in the top p‐type layers via channels associated with threading defects and can penetrate deeply into the structure. It further proceeds in a lateral direction in n‐type layers forming voids and cavities in the structure. The H2 production rate of 0.3–0.6 ml cm−2 h−1 was measured for n‐GaN‐based structure in KOH electrolyte under the Xe‐lamp illumination (concentration factor ×15).

GaN, GaN/AlGaN and GaN/InGaN-based structures were used to study water photoelectrolysis in KOH-based electrolyte, measurement of current-potential characteristics, investigation of electrode corrosion and for hydrogen generation. The corrosion process of p-n AlGaN/GaN structure starts in the p- layers, spreads via vertical channels associated with threading defects, and continues laterally along the n- layers, where large local hollows and voids were observed. The H 2 production rate of 0.3-0.6 ml/cm 2 ×h was measured for n-GaN structure.