Koji Yamano

Effect of Hydrogen and Thermal Conductivity on Nucleation of Polycrystalline Si by Excimer Laser Annealing

The influence of hydrogen on the nucleation of polycrystalline Si (poly-Si) during excimer laser annealing (ELA) of amorphous silicon (a-Si) films was investigated in detail. The results of Raman spectroscopy reveal that the internal stress and defect density in the poly-Si films strongly depend on substrate structures which are made of quartz, SiO2/SiN/glass and SiO2/glass. From the thermal-desorption spectrum and surface morphology characterization using scanning electron microscopy (SEM), it was clarified that the origin of the difference is due to both the hydrogen incorporated in the a-Si from the SiN film by diffusion via SiO2 and the thermal conductivity of the SiO2, SiN and quartz. We also discuss the nucleation process taking into account the hydrogen burst and the thermal conductivity of the substrates.

Property Control for High-Quality Ba1-xKxBiO3 Epitaxial Thin Films Prepared by High-Pressure Reactive rf-Magnetron Sputtering

The electrical properties of Ba1-xKxBiO3(BKBO) epitaxial thin films on SrTiO3(110) substrates have been successfully controlled using high-pressure reactive rf-magnetron sputtering under an 80-Pa discharge gas. We investigated the relationship between the target composition and the electrical properties of BKBO films. The zero resistance temperature (Tce) and the temperature dependence of resistivity above the superconducting onset temperature (Tco) were found to be primarily influenced by the ratio of Ba/K and the Bi content of the target composition, respectively. Electrical measurements showed that the highest Tce of as-grown BKBO epitaxial film was 28 K.

Directional Crystallizing Si Films with a Fundamental Continuous Wave Yttrium Aluminum Garnet Laser (Zone Melting for Film)

To form large-grained polycrystalline-silicon (poly-Si) films on glass substrates, we propose a new lateral crystallization method, zone melting for film, which uses a high-power fundamental continuous wave yttrium aluminum garnet (CW-YAG) laser and an absorption layer. The lasers infrared light is changed into thermal energy at the absorption layer and heats the amorphous Si (a-Si) film. Next, the Si film is zone-melted and solidified in one direction with a scanning laser beam. By this method, columnar structured Si films were successfully formed with scanning velocities from 400 to 1000 mm/s. Very large typical grains of 1 or 2 µm by few hundreds of µm were obtained on both glass and quartz substrates, and the long axes of the grains were almost parallel to the laser scanning direction. Textures were also observed in these columnar structured Si films. Recombination carrier lifetimes of these films were several times longer than those of conventional low-temperature-processed poly-Si films.

Preparation and Characterization of Nb/MgO/Bi2Sr2CaCu2Ox Junctions Using the Cleavage Planes of a Single-Crystal Superconductor

Nb/MgO/Bi-Sr-Ca-Cu-O junctions using the cleavage planes of Bi2Sr2CaCu2Ox single crystals have been fabricated using an artificial barrier for the first time. A large step, in the order of several hundred nm on the cleavage plane, proved to be closely related to the anisotropic behavior of tunneling spectroscopy through the surface of a Bi2Sr2CaCu2Ox single crystal. This effect for the results of quasi-particle tunneling in the Nb/MgO/Bi-Sr-Ca-Cu-O junctions was in good agreement with calculated results for the local density of states in the superconductor/normal-conductor superstructure model.

Study of the Tunneling Characteristics of Ba1-xKxBiO3 Superconducting Thin Films Based on the Gap-Energy Distribution Model

The broadening of the gap edge in the conductance-voltage ( dI/ dV–V) characteristics for native-barrier Ba1-x Kx BiO3-gold (BKBO//Au) and MgO-barrier Ba1-x Kx BiO3-gold (BKBO/MgO/Au) junctions was investigated by using a gap-energy distribution model where the inhomogeneity of the energy gap Δ at the junction interface was taken into consideration. It was demonstrated that the broadening of the dI/ dV–V curves and their temperature dependence (T<2T C/3) in both junctions could be explained by assuming the Gaussian distribution of gap energies (at T=0 K) with Δ0(0)=3.1 meV, δΔ=0.9 meV for the BKBO//Au junction and Δ0(0)=3.5 meV, δΔ=1.1 meV for the BKBO/MgO/Au junction, where Δ0(0) and δΔ represent the center point and the width of the distribution, respectively. It was found that the value δΔ could be regarded as a criterion for the quality of the tunneling junction.

MBE growth and HR-TEM observations of several-nm MgO film on the cleavage plane of Bi2Sr2CaCu2Ox single crystals

Abstract Pinhole-free, several-nm thick MgO films were fabricated for the first time on the cleavage plane of Bi2Sr2CaCu2Ox single crystals by the MBE method, and confirmed by direct HR-TEM observation of the MgO/BSCCO interface. A superconducting energy gap with BCS-like behavior was clearly observed from tunneling spectroscopy for Nb/MgO/BSCCO.

Electric Field Effects on Faraday Rotation of Cd1-xMnxTe Films Prepared by Ionized Cluster Beams

Effects of an electric field on the Faraday rotation of Cd1-xMnxTe films, prepared by ionized cluster beams, have been investigated. A marked change in the Faraday rotation was observed near the band gap energy under an applied electric field perpendicular to the film plane. The maximum change ΔV in the Verdet constant obtained for a Cd0.49Mn0.51Te film was of the order of 0.22°/cmG at an electric field of 174 kV/cm. It was found that this effect could be attributed to the electric field effects on optical absorption by excitons.

Fabrication and Properties of MgO/Bi2Sr2CaCu2Ox Interfaces Using Crystalline and Amorphous MgO Films Grown by the MBE Method

Tunnel-type junctions with pinhole-free crystalline and amorphous MgO barriers on the order of several nm were successfully fabricated on the cleavage plane of BSCCO single crystals. Both MgO films for the tunnel barriers were grown by the molecular beam epitaxy method. The superconducting gap parameters, Δ, of a BSCCO single crystal deposited with crystalline and amorphous tunnel barriers were estimated to be 25 meV and 38 meV, respectively, for the configuration of a Nb/MgO/BSCCO junction from dI/dV-V characteristics. The possibility of different surface superconductivities for BSCCO single crystals was determined by the characterization of the MgO/BSCCO interface.

Far-Infrared Optical Properties of Quenched Germanium; V. Uniaxial Stress Effects on the SA1 Acceptors

Far-infrared absorption spectra of quenched germanium were measured under a uniaxial stress along the , and crystallographic orientations. It is concluded from the analyses of the number of the bands split with stress and from the feature of splitting of each band that the SA1 acceptor, which is the shallowest one in the quenched-in acceptors and has a ground state split into two levels without a uniaxial stress, is constructed from a defect in which the symmetric axis is along a crystallographic axis. From the comparison between the results on the SA1 acceptors and the SA1Au and SA1Ag acceptors which are the perturbed SA1 acceptors, it is proposed that the SA acceptor is constructed from a pair of substitutional and interstitial atoms along the axis and that SA1Au and SA1Ag acceptors are the defects consisting of the SA1 acceptor together with either Au or Ag impurities along the axis, respectively.

Growth and Characterization of BaBiO3 Films by Molecular Beam Epitaxy

The fabrication and characterization of BaBiO3(BBO), which is the mother material of the Ba1-xKxBiO3 superconductor have been successfully performed. BBO films have been grown by molecular beam epitaxy (MBE) using an oxygen radical beam source at the lower pressure of 2.0×10−7 Torr. The BBO films were considered to be sufficiently oxidized from the Bi(4f) core level spectra estimated by X-ray photoelectron spectroscopy (XPS). These results demonstrate that the oxygen radical is effective for the formation of BBO films.