Yutaka Ohno 교수

The effect of Si3N4 surface passivation on breakdown of AlGaN/GaN high-electron-mobility transistors was studied in detail by investigating dependences of the off-state breakdown voltage on temperature and gate reverse current, and by measuring electroluminescence distribution. Impact ionization in the channel which was triggered by the gate reverse current was responsible for the off-state breakdown. Surface passivation by Si3N4 film was effective to improve the off-state breakdown voltage. Thi

1-beta-D-Arabinofuranosylcytosine (ara-C) is an effective antileukemic agent which acts as an inhibitor of DNA synthesis. The precise mechanism responsible for this inhibitory effect, however, remains unclear. The present work has examined the effects of the triphosphate derivative, ara-CTP, on purified DNA polymerase beta. These studies were performed on M13 phage DNA templates of defined sequence. The results demonstrate that ara-C is incorporated into DNA by DNA polymerase beta. The results a

The in vitro production of interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha) by monocytes was examined in patients with insulin-dependent diabetes mellitus (IDDM), in those with noninsulin-dependent diabetes mellitus (NIDDM), and in healthy volunteers. The production of IL-1 and IL-6 by monocytes was significantly lower in IDDM patients than in NIDDM patients and normal subjects whereas the TNF-alpha production by monocytes did not differ between IDDM patien

We have developed an in situ TEM/PL apparatus, which enables us to excite PL emissions from a microscopic area of a specimen inside a TEM. The microscopical area of 20 μm can be examined by TEM, PL, and CL methods under the same experimental conditions. The apparatus may be applied to a transmission electron microscope of side-entry type with a minor modification. The apparatus is extremely useful for microscopic characterization of structural and electronic properties in an inhomogeneous materi

Optical properties of wurtzite ZnO bulk single crystals in which an arbitrary number (typically 109–1010 cm−2) of fresh dislocations were introduced intentionally by the plastic deformation at elevated temperatures (923–1073 K) were examined. Deformed specimens showed excitonic light emission with photon energies of 3.100 and 3.345 eV, as well as their LO phonon replicas at 11 K. The light intensities increased with increasing dislocation density. The activation energy for a thermal quenching of

Bonding mechanism at room temperature (RT) in GaAs/Si heterointerfaces fabricated by surface-activated bonding (SAB) is examined using cross-sectional scanning transmission electron microscopy combined with low-temperature focused ion beam and time-of-flight secondary ion mass spectrometry. In the bonding process at RT, atomic intermixing at the interfaces, presumably due to the transient enhanced diffusion assisted by the point defects introduced in the surface activation process, is confirmed.

We grew ZnSe needle-like nanowires on a ZnSe∕GaAs epilayer using Fe catalysts by means of molecular-beam epitaxy operated at low temperatures of 250–350 °C, which are comparable to the usual temperatures for fabrication of ZnSe-based optoelectronic devices. The diameters at the tops of the nanowires ranged from 8 to 20 nm, and the typical length was about 200 nm. The number density of the nanowires was the order of 109cm−2. A nanowire was the zinc blende structure and the longitudinal direction

Three-dimensional distribution of impurity atoms was determined at functional Σ5{013} and small-angle grain boundaries (GBs) in as-grown mono-like silicon crystals by atom probe tomography combined with transmission electron microscopy, and it was correlated with the recombination activity of those GBs, CGB, revealed by photoluminescence imaging. Nickel (Ni), copper (Cu), and oxygen atoms preferentially segregated at the GBs on which arrays of dislocations existed, while those atoms scarcely seg

Three-dimensional distribution of impurities (boron, phosphorus, oxygen, and copper) at Σ3{111} grain boundaries was determined in a Czochralski-grown silicon single crystal by laser-assisted atom probe tomography (APT) combined with transmission electron microscopy, with a detection limit as low as the order of 0.001 at. %. The location of a boundary was determined by APT even when the boundary was not contaminated. Unlike the boundaries in multicrystalline silicon grown by the casting method,

Variation in stacking fault energy with annealing at 1173 K were identified in Czochralski-grown silicon crystals heavily doped with n- or p-type dopant atoms. In n-type crystals, the energy decreased with increasing annealing time. The higher the concentration of dopant atoms, the larger the degree of the decrease. On the other hand, the energy was unchanged during annealing in p-type and nondoped crystals. These results imply that n-type dopant atoms segregate nearby a stacking fault, via thei

We have studied the mechanism of off-state breakdown in AlGaN/GaN high electron mobility transistors (HEMTs). The off-state breakdown voltage (BVoff) had a positive temperature coefficient of 0.12 V/K. BVoff was represented by a monotonous decreasing function of gate leakage current (Ileak), which was analytically derived from the impact ionization coefficient. Our results suggest that off-state breakdown in AlGaN/GaN HEMTs originated from impact ionization in the channel, which was caused by th

Electron-radiation-enhanced glide of 30°-Si(g) partial dislocations bringing about an expansion/shrinkage of Shockley-type stacking faults in 4H-SiC was observed in-situ by transmission electron microscopy. Geometrical kinks on 30°-Si(g) partials did not migrate in the dark, indicating that the kink migration is enhanced by electron irradiation. The direction of the enhanced glide was reversible depending on the irradiation intensity, which can be interpreted in terms of a sign reversal of the d

Temperature distributions in AlGaN/GaN high-electron-mobility transistors under bias voltage have been measured by micro-Raman scattering spectroscopy. The temperature was estimated from the Raman shift of E2 phonons of GaN. The spatial and temperature resolutions are 1 µm and 10 K, respectively. When the power dissipation was 248 mW at a drain voltage of 40 V, the peak temperature of 443 K was observed at the gate edge on the drain side at the center of the channel. This position corresponds to