Kouji Maeda

Piezoelectric detection of the photoacoustic signals of n‐type GaAs single crystals

Piezoelectric photoacoustic (PA) measurements on liquid‐encapsulated‐Czochralski‐grown n‐GaAs were carried out at room temperature. A continuous broad band below 1.35 eV and a peak at 1.383 eV were observed in the PA amplitude spectra. By comparing with the optical‐absorption spectra, it is concluded that the broad band is due to the electron transition involving the EL2 deep‐lying defect levels. For the observed peak at 1.383 eV, the origin is considered to be dislocation related. The possibility that this peak is an apparent one expected from the proposed models for the PA signal generation is denied.

Misfit dislocation anisotropies in the InGaAs/GaAs(001) interface measured using X-ray topography and reciprocal space mapping

The anisotropies of misfit dislocations (MDs) formed at an InGaAs/GaAs(001) interface grown by molecular beam epitaxy were investigated using X-ray topography and X-ray reciprocal space mapping techniques. The MDs bunched in small regions to form MD bunches. The number of MDs running along the direction (α-MDs) included in one MD bunch was larger than that along the [110] direction (β-MDs). In addition, the bunched α-MDs were aligned more periodically than the other MDs.

Electrical Properties of Layered ZrSe2 Single Crystals Annealed in Selenium Atmosphere.

Temperature dependencies of electron carrier concentration n and Hall mobility µ H of layer ZrSe2 single crystals are investigated for samples annealed in vacuum or Se atmosphere. The high carrier concentration in the order of 1019 cm-3 for the as-grown sample decreases to 1018 cm-3 upon annealing in Se atmosphere. We consider that the dominant donor state in ZrSe2 is produced by a complex involving interstitial Zr atoms and Se vacancies. The temperature dependence of µ H is explained by inter and intravalley electron scattering by acoustic phonons.

Structural characterization for GaAs nanowires Au-assisted grown by pulsed-jet gas epitaxy measured using Raman spectroscopy

We analyzed the crystallinity of GaAs-NWs grown by pulsed-jet gas epitaxy using Raman spectroscopy. The specific optical phonon mode from WZ structures as the defects for the GaAs NWs was observed. The crystallinity was improved and WZ structures were hard to grow with increasing the diameter of NWs.

Formation of Silicon Carbide Using Volcanic Ash as Starting Material and Concentrated Sunlight as Energy Resource

SiC was formed using volcanic ash as starting material and concentrated sunlight as energy resource. The solar furnace was composed of two parts: Fresnel lens and reacting furnace. The reacting furnace was composed of a cylindrical vacuum chamber and quartz glass plate functioning to guide the concentrated sunlight into the furnace and was placed at the focal point of the Fresnel lens. The sample was made from the mixture of silica formed from volcanic ash and graphite and placed in the carbon crucible inside the reacting furnace. The temperature in the carbon crucible reached more than 1500°C. After the reaction using concentrated light, β-SiC was formed. The weight % of formed SiC was 90.5%.

Proposition of a New Valid Utilization for Shirasu Volcanic Ash Using Renewable Energy

SiC was prepared from Shirasu volcanic ash using solar furnace. The solar furnace is composed by two parts; Fresnel lens and reacting furnace. Fresnel lens is used to concentrate sunlight onto the reacting furnace where the sample was put on. The sample was made from the mixture of SiO2 formed using Shirasu volcanic ash and graphite, and placed in the carbon crucible inside the reacting furnace. By using light of sun concentrated with Fresnel lens, the sample was irradiated for 15 minutes and the furnace was left until it cooled down to room temperature. Both irradiated and cooling processes were done under Ar atmosphere. After the experiment, the sample was evaluated by XRD and Raman spectroscopy and the result indicated that β-SiC was formed.