The n-type GaN has stability problem of the surface anodic corrosion during the photoelectrochemical reaction for H2 generation. The photoelectrochemical surface stabilities of n-type GaN dependent on the electrolytes were investigated. The flatband potential in HCl obtained from Mott-Schottky plot shifted 0.1 V to positive direction compared with that in H2SO4. The variation of saturated photocurrent of 1 to 3 cycles in H2SO4 was much larger than that of HCl, NaOH and KOH. The surface morphologies also changed by the electrolytes. These results show the absorbed materials on the GaN electrode surface during the photoelectrochemical reactions were changed by the electrolyte and affected the surface reactions.

Water-splitting by using electric power produced by solar cells is promising system to produce hydrogen without fossil fuels. Oxygen evolving catalyst is, however, major problem to prevent using this system widely because precious materials are used in the catalyst. Considering from the photosynthesis II of plants, the compound of Ca-Mn-O is one of the candidates for the oxygen evolving catalyst. In this study, the synthesis condition and the oxygen evolving electrocatalytic activity of CaMn2O4•xH2O are investigated. The overpotential at 0.1 mA/cm2 was 0.28 V when using the electrode of carbon paste and CaMn2O4•H2O with the weight ratio of 3:1.

Electrochemical reduction of CO2 into useful organics combined with photovoltaics is thought to be one of the promising ways to effectively store and transport the solar energy. In most of the previous researches, CO2 bubbling in different solutions were used as the electrolyte. However, the effects of the electrolyte and the CO2 bubbling are not clear. Therefore, in this research, the effects of different electrolyte, CO2 bubbling, concentration of the electrolyte and temperature on the electrochemical reduction of CO2 on a Cu working electrode were studied. The results showed that the form of the carbon source in the electrolyte, such as HCO3-, CO32- and H2CO3, had a strong effect on this reaction, which was controlled by the pH of the electrolyte. Furthermore, high concentration of the HCO3- and elevated temperature can strongly improve the reaction current density.

Energy storage is a key technology for establishing a stand-alone renewable energy system. Current energy-storage technologies are, however, not suitable for such an energy system. They are cost ineffective and/or are with low energy-conversion efficiency. Hydrogen generation and storage from water by sunlight is one of these technologies. In this study, a simple concept of hydrogen generation from water by using sunlight, “concentrated photovoltaic electrochemical cell (CPEC)” is proposed. It is experimentally shown that the CPEC operates stably and achieves conversion efficiency from light to hydrogen energy of over 12%.

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.

We have fabricated a TE mode InGaAsP active waveguide optical isolator based on the nonreciprocal loss shift in an optical fiber telecommunication wavelength of 1550nm. We demonstrated a TE mode nonreciprocal loss shift of 9.3dB/mm under a magnetic field of +/-1kG in the facricated InGaAsP active waveguide with Fe on an InP substrate at a wavelength of 1560nm. This result opens a way to the monolithic integration of semiconductor-waveguide-type optical isolators with edge emitting semiconductor lasers.

A cometary globule in IC1396 named ”comet tail 6” by Osterbrock (1957), has been observed at CO and 13CO (J = 1-0) lines with a high spatial resolution, 14″, with the 45-m radio telescope at the Nobeyama Radio Observatory. The resolution corresponds to a linear size of 0.05 pc at the distance of 750 pc (Matthews 1979). Two possible pre-main sequence stars, LkHα 349 and LkHα 349/c (Cohen and Kuhi 1979), associated with small nebulosities nestle in the central part of the globule. We have obtained CO and 13CO spectra long NS and EW strips which cross each other at the position of LkHα 349 and have mapped a 1.5′x1.5′ area around the globule center at 13CO. Results from the observations are summarized as follows: