Investigation of water splitting using III-N structures

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 (N_D−N_A ∼ 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).