Effects of GaN thin layer on InGaN at electrolyte-semiconductor interface for the application of photoelectrochemical water splitting

Photoelectrochemical properties of nitride semiconductors are paid attention due to their possibilities of water splitting by visible light absorption. However, the photocurrent density of In_xGa _1-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 In_xGa_1-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 In_xGa_1-xN here. The effect for the photocurrent densities is also discussed.