To identify chronological changes in the marine reservoir effect in southwest Japan, the radiocarbon ages of eight pairs of marine shells and terrestrial plants were measured from the same horizons of one core of Holocene sediments. This core was obtained from the northern part of the Sukumo Plain in southwestern Shikoku Island, which faces the warm Kuroshio Current. The drilling site is located in an area of subsidence associated with the convergence of the Philippine Sea Plate and the Eurasian Plate. On analyses of lithology, molluscan assemblages, and radiocarbon dating, we interpreted, from oldest to youngest, nine units: basement rock, a braided river channel, a meandering river channel, an estuary, a transgressive inner bay, Kikai-Akahoya volcanic ash, a deltaic inner bay, a tidal flat, and artificial soil. Changes in the depositional environment were mainly associated with sea-level rise after the end of the last glaciation. The reservoir ages of the eight pairs, 330 ± 70 yr, were obtained from a transgressive inner bay to deltaic inner bay sediments, formed during 4100–9200 cal BP. The chronological change in the reservoir effect allows us to correlate the Sukumo Core sediments with previous results from southwestern Japan, the Korean Peninsula, and Taiwan Island.

The macro and micro morphology of the Si surface, depending on noble metal ion concentration in etching solution, prepared by metal assisted etching were investigated. We defined the morphology of etched Si in four types, and developed the phase diagram of Si morphology. Mixture of silver nitrate (AgNO3) and hydrofluoric acid (HF) was used as an electroless-plating bath of Ag, as well as etching solution of Si. The morphology of the etched Si surface as function of concentration of AgNO3 in etching solution was observed by SEM. With increasing concentration of the AgNO3 in the etching solution, the surface of etched Si tended to be porous structure with very fine pores of a few nm (porous Si). When concentration of AgNO3is low, single crystal Si nanowires with a smooth surface without pores were observed.

We present comparative micro-photoluminescence measurements on InGaN/GaN quantum well and quantum dot samples. Single sharp emission lines were investigated for both kinds of samples as a function of temperature and excitation density. For the sharp emission lines of the quantum dots and the strong localization centers in the quantum well samples comparable experimental findings were obtained such as the independence of their spectral position of the excitation density and the observation of binding and antibinding multiexcitonic states giving clear evidence for the quantum dot nature of localization centers.

The surface morphology of thin InxGa1-xN layers in uncapped structures and the overgrowth using GaN or InxGa1-xN with a lower In content than the InxGa1-xN layer as the protection layer of the InxGa1-xN layer were investigated in addition to their dependence on growth temperature during the growth by metalorganic vapor phase epitaxy (MOVPE). It was necessary to decrease the growth temperature of the InxGa1-xN layer in order to realize homogeneous dots. In order to obtain a high luminescence efficiency, on the other hand, it was essential to increase the growth temperature of the protection layer. Sharp lines related to the localized electronic states, which are attributed to InGaN quantum dots, were observed by micro-photoluminescence (μ-PL) for the samples with the InxGa1-xN layers protected by the InxGa1-xN layers grown at 700∼740°C.

The growth of InGaN on GaN (0001) by plasma-assisted molecular beam epitaxy was investigated with special focus on the dynamics of the formation of the dots. A metastable 2D growth regime, where the surface changes from smooth to rough by thermal treatment during growth interruption, existed previous to the 2D-3D transition. Both small regular-shaped dots and large irregular-shaped islands were observed. The large islands were suppressed by choosing correct growth conditions. The critical thickness for the transition from 2D to 3D growth also depended on the growth conditions. The growth of GaN capping layer to cover InGaN dot-structure was also attempted.

This paper describes studies on high-quality InN growth on sapphire by RF-MBE. Critical procedures to obtain high-quality InN films were investigated and (1) nitridation process of sapphire substrates prior to growth, (2) precise control of V/III ratio and (3) selection of optimum growth temperature were found to be essential. Detailed structural characterizations by XRD, TEM, Raman scattering and EXAFS indicate that InN films obtained in this study have ideal hexagonal wurtzite structure. FWHMs of ω-2Θ mode XRD and E2(high)-phonon-mode of Raman scattering are as small as 28.9 arcsec and 3.2 cm-1, respectively. True band gap energy of InN is also discussed based on optical characterization results obtained from well-characterized hexagonal InN grown in this study. PbS, instead of InGaAs, was used as a detector for PL study in order to solve the problem coming from the cut-off wavelength of InGaAs detector. Based on these systematic studies on structural and optical property characterizations using high-quality InN, true band-gap energy of InN is suggested to be less than 0.67 eV and approximately 0.65 eV at room temperature. Single-crystalline InN films are also successfully grown on Si substrates by a brief nitridation of the Si substrates. Significant improvement of InN crystal quality on Si substrates by the insertion of an AlN buffer layer is also demonstrated.

A newly reported narrow bandgap for indium nitride means that the indium gallium nitride system of alloys can be a candidate for new high efficiency solar cells covering most of the solar spectrum. In this paper, n-InN films were grown on p-Si (100) substrates. We characterize, for the first time, photovoltaic properties using n-InN/p-Si hetero-junction grown by RF-MBE.

InN films were grown on Si (111) substrates by radio-frequency plasma-excited molecular beam epitaxy. InN films highly oriented to the c-axis were obtained by optimizing growth conditions in the direct growth on Si. Growth of single crystalline InN films was realized on Si substrates with substrate nitridation for 3 min. On the other hands, when the substrate nitridation was lasted over 30 min, obtained InN films were polycrystalline due to the amorphous SiNx layer formed on a substrate surface. We also studied the local atomic structure in the single crystalline InN film using extended X-ray absorption fine structure measurements.

InN films were grown on sapphire (0001) substrates by radio-frequency plasma-assisted molecular beam epitaxy. The InN buffer layers deposited at low temperature were either grown on a substrate with nitridation or on a substrate without nitridation. The InN buffer layers on the nitridated substrates were always single crystalline, whereas the buffer layers on non-nitridated substrates were always polycrystalline. However, even without nitridation process, single crystalline InN films could be grown on the polycrystalline InN buffer layers; in this case, the orientation was always [1120] InN//[1120] sapphire epitaxy, which differed from the [1010] InN//[1120] sapphire epitaxy in films grown with nitridation.

InN films with excellent surface morphology were grown by controlled the V/III ratio of InN epitaxal layer. It was found they were single crystal of InN films with wurtzite structure by X-ray diffraction (XRD) measurement and reflection high-energy electron diffraction (RHEED) observation. Hall mobility as high as 760 cm2/Vs was achieved for InN film grown at 550°C with 240 W of RF plasma power with a carrier density of 3.0×1019 cm−3 at room temperature. To our knowledge, this electron mobility is the highest value ever reported.