Lisa Sugiura

Tokyo Metropolitan Institute | TMU · Department of Language Sciences, Graduate School of Humanities

Learning a second language (L2) proceeds with individual approaches to proficiency in the language. Individual differences including sex, as well as working memory (WM) function appear to have strong effects on behavioral performance and cortical responses in L2 processing. Thus, by considering sex and WM capacity, we examined neural responses duri...

The genetic basis controlling language development remains elusive. Previous studies of the catechol-O-methyltransferase (COMT) Val(158)Met genotype and cognition have focused on prefrontally guided executive functions involving dopamine. However, COMT may further influence posterior cortical regions implicated in language perception. We investigat...

Previous neuroimaging studies in adults have revealed that first and second languages (L1/L2) share similar neural substrates, and that proficiency is a major determinant of the neural organization of L2 in the lexical-semantic and syntactic domains. However, little is known about neural substrates of children in the phonological domain, or about s...

The primary objective of the current prospective study was to examine developmental patterns of voxel-by-voxel gray and white matter volumes (GMV, WMV, respectively) that would predict psychosis in adolescents with 22q11.2 deletion syndrome (22q11.2DS), the most common known genetic risk factor for schizophrenia. We performed a longitudinal voxel-b...

A large-scale study of 484 elementary school children (6-10 years) performing word repetition tasks in their native language (L1-Japanese) and a second language (L2-English) was conducted using functional near-infrared spectroscopy. Three factors presumably associated with cortical activation, language (L1/L2), word frequency (high/low), and hemisp...

A randomized pilot experiment examined the neural substrates of response to cognitive training in participants with mild cognitive impairment (MCI). Participants performed exercises previously demonstrated to improve verbal memory and an active control group performed other computer activities. An auditory-verbal fMRI task was conducted before and...

We investigated the far-field patterns perpendicular to the junction plane under room-temperature current excitation and analyzed the transverse modes of nitride-based laser diodes with various types of AlGaN cladding layers. It was found that nitride-based laser structures with thin AlGaN cladding layers induce leakage of high-order transverse mod...

The individual elements attributing to the excess voltage drop in the nitride-based laser diodes were investigated. The specific contact resistivity ρc to p-type GaN was estimated by transmission line model (TLM) method and was estimated to slightly vary from 3.2×10−3 to 6×10−4 Ω cm2 in the current range of 1–10 kA cm−2. It is found that a low spec...

The analysis of the perpendicular far field patterns of nitride-based laser diodes with various types of AlGaN cladding layers is demonstrated. Other results obtained with our nitride-based laser diodes are also demonstrated and discussed

The characteristics of Mg-doped GaN and AlGaN grown by H2-ambient and N2-ambient metalorganic chemical vapor deposition are compared and discussed. While as-grown Mg-doped GaN and AlGaN grown under H2-ambient show high resistivity, p-type GaN and AlGaN with high acceptor concentration were obtained by N2-ambient growth without any post-treatment. T...

The room temperature photoluminescence (PL) of InGaN-based multiple quantum well (MQW) structures was studied. The PL intensity was significantly dependent on the well width and depth. The maximum PL intensity from an MQW with In0.15Ga0.85N wells was produced for a 2nm well; the intensity decreased significantly for thinner and thicker ones. Also,...

We have clarified the effect of H2 and NH3 on the passivation of Mg acceptor in p-type GaN films grown by metalorganic chemical vapor deposition. It has been found that the small amount of H2 carrier gas strongly influences the electrical property of the Mg-doped GaN films. Low-resistivity p-type GaN has been obtained by H2-free growth without any...

Dry etching and overgrowth process techniques have been developed for the fabrication of InGaN inner stripe laser diodes. The dry etch damage at the etched surface and the overgrown interface was estimated using X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectrometry (RBS). As a result, the etch damage at the overgrown int...

Two energetically-separated resonance structures were found in photoreflectance (PR) spectra of three-dimensional InxGa1−xN epilayers (0.05 ⩽ x ⩽ 0.2) grown by metalorganic chemical vapor deposition. Energy difference between the two structures was nearly constant about 50 meV for all x examined. The broadening parameter of each structure was nearl...

The surface morphology and crystalline quality of GaN layers grown by metalorganic chemical vapor deposition on sapphire (0001) substrates were investigated for various thermal treatment conditions of low-temperature (LT)-grown GaN buffer layers. The surface morphology and crystalline quality of subsequently grown high-temperature (HT) GaN layers s...

In0.15Ga0.85N/GaN and In0.15Ga0.85N/In0.05Ga0.95N multi quantum well (MQW) structures grown on (0001) sapphire substrates were investigated by high-resolution x-ray diffraction and cross-sectional transmission electron microscopy. The results show that ultrathin MQWs with fairly good crystallinity and precisely controlled clear parallel interfaces...

Dislocation glide velocities in GaAlAs/GaAs, InGaAsP/InP, and GaN-based light-emitting devices are estimated. These results are consistent with device degradation rates related to dislocation motion. It is clarified that the long lifetime of GaN-based devices with high dislocation density is principally due to extremely small dislocation mobility,...

In this study, dislocation motions in GaN-based materials and devices were quantitatively estimated in order to determine why GaN-based light-emitting diodes have remarkable reliability and longevity in spite of extremely high dislocation density. The dislocation velocity of GaN-based materials was calculated by estimating the activation energy of...

Advantages of applying III-V nitride materials for short wavelength light-emitting devices despite their extremely high dislocation density are discussed from the viewpoint of dislocation motion. There are also difficulties proper to these materials, which make it difficult to fabricate laser diodes. We present recent works to realize high performa...

We demonstrate room temperature pulsed operation of nitride based multi-quantum-well (MQW) laser diodes with cleaved mirror facets grown on a conventional C-face sapphire substrate. Cleavage was performed along the (1120) direction of the sapphire substrate, and the resultant facet was analyzed using an atomic force microscope (AFM) and theoretical...

Orientation dependence of HgCdTe epilayers grown by MOCVD on Si substrates was studied. Substrate orientation is considered to be one of the most sensitive factors to enable hetero-epitaxial growth on silicon substrates, especially in the case of a low temperature growth process. The present work was carried out with characterized features of a low...

The effects of interfacial lattice mismatch upon Hg1-xCdxTe epitaxial layers grown by metalorganic chemical vapor deposition (MOCVD) were investigated. HgCdTe was found to be easily affected by lattice mismatch of less than ±0.1%. It has been shown that mismatched HgCdTe layers in tension tend to deteriorate more easily than those in compression. T...

Differences between the progress of lattice relaxation in (111)CdTe / (100)GaAs and (133)CdTe / (211)GaAs heterostructures, in which large 14.6% lattice mismatches exist, were revealed by lattice images obtained by transmission electron microscopy and photoluminescence spectra of the layers. The lattice of the (133)CdTe layers on the (211)GaAs subs...

The relationship between twin formation and the growth conditions for (111) HgCdTe epitaxial layers grown by metalorganic chemical vapor deposition was investigated. The existence of twins was confirmed by x-ray diffraction and cross-sectional transmission electron microscopy. The x-ray diffraction intensity of the 180°ø rotated 422 asymmetric refl...

The influence of lattice mismatch on the electrical and structural properties of HgCdTe epilayers grown on CdZnTe substrates has been investigated. A slight lattice mismatch of the order of less than ±0.1% between the epilayer and the substrate brings about a conductivity-type conversion of HgCdTe layers, which is related to the presence of misfit...

The effects of mercury partial pressure on the defect density in HgTe grown by metalorganic chemical vapor deposition (MOCVD) have been investigated. A large number of mercury clusters were revealed by transmission electron microscopy in high mercury partial pressure specimens. There were some dislocation loops that seemed to originate on tellurium...

There are two growth methods in Hg1−xCdxTe metalorganic chemical vapor deposition (MOCVD) growth, namely direct alloy growth (DAG) and the interdiffused multilayer process (IMP). HgCdTe layers have been grown by both methods onto CdZnTe (111)B substrates and their structural and electrical properties were investigated. The composition fluctuated si...

LaNi4.5 Al0.5 alloy compacted with organic compounds was used as negative electrode material of a Ni-metal hydride(MH) type rechargeable battery. The charge and discharge characteristics of Ni-composst metal hydride(CMH) cell were similar to those of conventional Ni-Cd cell. The energy density of CMH electrode was twice as high as that of Cd electr...