Photoelectrochemical hydrogen generation from water using undoped GaN with selective-area Si-implanted stripes as a photoelectrode

This study examines photoelectrochemical (PEC) cells with undoped GaN (u-GaN) photoelectrodes that feature selective-area Si implantation stripes for hydrogen (H₂) generation using NaCl solution as the electrolyte. Selective-area Si implantation was performed on the u-GaN layer to create n⁺-GaN stripes with higher carrier concentration than the u-GaN area. Si-implanted n⁺-GaN stripes behave like metal lines, but they allow light to penetrate the Si-implanted regions, to facilitate the collection of photogenerated carriers. For a moderate area ratio of Si implantation, the typical hydrogen generation rate of u-GaN working electrodes with and without Si-implanted GaN stripes was approximately 98 μmol h^-1 cm^-2 and 68 μmol h^-1 cm^-2, respectively, when the applied potential was 1 V. These values correspond to an enhanced H₂ generation rate of around 44%. The marked enhancement in the hydrogen generation rate is attributed to the fact that photogenerated electrons can be effectively collected by Si-implanted n⁺-GaN stripes. Microscopy showed an insignificant change in Si-implanted surfaces before and after the PEC reaction. By contrast, the u-GaN area without Si implantation exhibited significant corrosion after the PEC reaction. The findings of this study indicate that the u-GaN epitaxial layer with Si-implanted stripes can be potentially used as a robust photoelectrode to efficiently generate hydrogen.