In Situ Photoluminescence Analysis of GaN Photoanode during Water Oxidation

The behavior of photoexcited carriers in a GaN photoanode was investigated by using photoluminescence (PL) in an electrolyte. The near-band-edge (NBE) emission observed in the electrolyte at around the flat-band potential (EFB), −0.47 VRHE, was stronger than that observed in air because of the disappearance of band bending that existed for the GaN surface in air. A broad PL related to the surface states was observed between the NBE emission and yellow luminescence (YL) and decreased rapidly with an increase of potential above a significant onset of anodic photocurrent. This quenching reflects a deactivation of surface states through the suppressed diffusion of electrons to the surface because of the significant charge separation by band bending. The relative intensity of the YL increased above the significant onset of anodic photocurrent, indicating that the deep levels were partially filled with holes, and photoexcited holes were utilized for oxygen evolution reaction from water.