Photoelectrochemical water splitting using semiconductors to produce hydrogen is a promising technique for converting sunlight to chemical energy. However, anodic photocorrosion occurs during the reaction even when n‐type GaN, a chemically stable material, is used for the photo‐illuminated working electrode. We previously demonstrated that the stability is related to the amount of Si doping used to make the GaN to be n‐type. This means that, the surface damage after photoelectrochemical reaction depends on the amount of Si. We have now investigated the relationship between this surface change and the optical properties especially for the near band edge peaks. With the peak shift by the strain relaxation due to the surface change from smooth to rough, new peaks around 3.4 eV were observed after photoelectrochemical treatment. These new peaks are defect‐related emission, which has been reported as Yi lines. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Nitride semiconductors are expected for the working electrodes of photoelectrochemical water splitting due to the chemical stability and band‐gap configuration. The p‐type nitrides are stable under photoelectrochemical conditions but the efficiency of light to hydrogen energy is low. The n‐type nitrides have relatively high energy‐conversion especially for the quantum efficiency, but the photoelectrochemical reaction is not stable because of the anodic photocorrosion. In this article, the relationships between the characteristics of n‐type GaN and the photocurrent stability are discussed. The amount of Si doping was clarified to relate to the stability. The suitable properties for stable photocurrent were different from those for high energy‐conversion efficiency at initial stage. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Photoelectrochemical properties of nitride semiconductors are paid attention due to their possibilities of water splitting by visible light absorption. However, the photocurrent density of InxGa1-xN, which absorbs visible light, is usually lower than that of GaN, which has larger band-gap and absorbing only UV light. The reasons of this are thought to be the band-edge position at the semiconductor-electrolyte interface and the crystal quality. The conduction band-edge decreases with increasing of indium composition and across the hydrogen generation energy at around the indium composition of 0.2. This means that the hydrogen generation ability decreases with increasing of indium composition. Low crystal quality is obtained because the lower growth temperature of InxGa1-xN than that of GaN to achieve the indium incorporation. In order to improve the photocurrent density, band-edge energy control and quantum tunneling effect are tried using the structure of thin GaN layer on InxGa1-xN here. The effect for the photocurrent densities is also discussed.