[en] Resistivity at helium temperatures of uniaxially compressed slightly p-type HgTe decreases greatly by application of a magnetic field along the stress direction. It increases again above a certain magnetic field Hsub(M) showing a large resistance minimum. The minimum position Hsub(M) increases proportionally to the applied compression. These properties are investigated using a magnetic field up to 55 kOe under a uniaxial compression up to about 7 x 10⁸ dyn/cm². By comparison with the magnetic sub-band scheme calculated by the effective mass theory, it is concluded that the resistance minimum is due to a band-crossing at Hsub(M) between the lowest Landau levels of the conduction and the valence bands. A second band-crossing point is also observed by using a magnetic field modulation technique. A shear deformation potential constant of the ₈-band b is deduced; b =(-1.5 +- 0.2) eV. Further, an acceptor impurity band in the stress-induced band gap is found by the analysis of the temperature dependence of weak field Hall coefficient. (author)

[en] Textured Ag tape is one of the most ideal substrates for the next generation high-T_c wires operable in liquid nitrogen. {1 1 0}<1 1 0> textured Ag tapes were obtained by cold rolling and subsequent heat treatments. The texture of the tape after cold rolling (before annealing) was typical 'brass type'. For obtaining the {1 1 0}<1 1 0> texture, oxygen should exist in the Ag tape during the heat treatment. We find a two-step annealing is very effective to achieve the better {1 1 0}<1 1 0> textured Ag tape, compared with the samples annealed in one-step; the better grain alignment and the smoother surface could be obtained. Moreover, 300 deg. C annealing in O₂ atmosphere allow us to obtain the {1 1 0}<1 1 0> texture by only 3 min final heat treatment at around 800 deg. C. This is beneficial to achieve the higher production speed of YBa₂Cu₃O₇ coated conductors

[en] The multiple-stage CVD method is the promising technology, which can be realized for rapid and long formation of YBCO tape. In earlier researches, we have fabricated the six-stage CVD system, and successfully developed 100 m long YBCO tape at the deposition rate of 10 m/h. However, over 500 m long wires are required for the practical applications. In order to achieve this, we have studied the multi-coating of YBCO layer at further high-speed deposition. Five layers of YBCO tape were fabricated on roll milled non-textured Ag substrate directly. Each layer was deposited by the six-stage CVD system at deposition rate of 25 m/h. After each deposition, temperature of YBCO tape went down to room temperature. The distribution of J_c was within 25% and its value is the same as single coating one. No significant degradation of J_c was observed. From these results, it was indicated that the multiple-stage CVD system, which equips more reactors serially, is effective way for making longer YBCO tapes

[en] The self-assembled InAsN quantum dots (QDs) were grown on the GaAs (001) substrates by MOVPE using 1,1-dimethlhydrazine (DMHy) and tertiarybutylarsine (TBAs) as the N and As precursors, respectively. The size distribution of the InAs(N) QDs grown at 450 C and 420 C is found bimodal. The InAsN QDs are typically 4-11 nm in height and 30-41 nm in width. The N incorporation into InAs induces the decrease of the QDs size, due to the increase of the wetting layer thickness. The density of the InAsN QDs with a nominal source supply of 2.6-3.0 ML, increases from 1.1-1.3 x 10¹⁰ cm^-2 for the 450 C growth to 2.1-2.3 x 10¹⁰ cm^-2 for the 420 C growth. The photoluminescence peaks (at 300 K) of the InAs(N) QDs grown at both temperatures clearly show a red-shift to 1200 nm by N incorporation. This red-shift is in contrast with the blue-shift expected from the decrease in the dot sizes (quantum size effect), indicating the huge bandgap bowing induced by N incorporation is dominant over the quantum size effect. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] Self-assembled InAsN quantum dots (QDs) have been grown by rf-plasma-assisted molecular beam epitaxy (RF-MBE) on GaAs(001) substrates via a 2-monolayer (ML)-thick InAs wetting layer. The InAsN QDs are typically 30-70 nm in diameter and 3-7 nm in height. The dot density was 3.6 x 10⁹-2.3 x 10¹⁰ cm^-2 for the fluxes corresponding to the nominal thicknesses of 3.0-4.0 MLs. As the nominal thickness increases, the dot density increases, while the diameter decreases. The low-temperature (10 K) photoluminescence (PL) of the QD samples shows emission spectra in the wavelength range of 1.2-1.6 μm apparently caused by the N incorporation (0.8-2.0%) into the QDs. The QD size distribution causes broad emission spectra. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] Cubic InN (zincblende structure) films have been directly grown on yttria-stabilized zirconia (YSZ) (001)-oriented and vicinal substrates by rf-plasma-assisted molecular beam epitaxy (RF-MBE) (The vicinal substrates are misoriented by 1 toward left angle 110 right angle.), and structurally characterized by X-ray diffraction and atomic force microscopy. Compared with the growth on the (001)-oriented substrate, the surface grain size of the cubic InN film is remarkably large for the growth on the vicinal substrates. From the 2θ/ω and ω X-ray reciprocal space mapping measurements, hexagonal InN is found to be preferentially generated on the c-InN{111} facets. By using the YSZ(001) vicinal substrate, the hexagonal phase incorporation ratio decreased from 16.3% on the (001)-oriented substrate to 11.7% with the same growth condition. And on the vicinal substrate, hexagonal InN is generated predominantly from the c-InN(111) facets which are inclined to the upward direction of the atomic steps. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] InAsN films of N content up to 3.5% without phase separation were grown on GaAs(001) substrates with a 1.9 μm-thick InAs buffer layer by metalorganic vapor phase epitaxy (MOVPE). In order to grow the InAsN films with a high N content at low temperature that assures a non-equilibrium growth environment, 1,1-dimetylhydrazine (DMHy) and tertiarybutylarsine (TBAs), which can be efficiently decomposed at low temperatures, were adopted as the N and As precursors, respectively. The electron concentration evaluated by the Hall measurement increased with increasing N content and the electrons were degenerated, while the fundamental absorption edge which was determined by the FT-IR absorption spectroscopy showed a blue-shift with increasing N content. These results indicate that the Burstein-Moss effect (or band filling effect) is dominant over the bandgap reduction expected from the bandgap bowing. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] The self-assembled InAsN quantum dots (QDs) were grown on the GaAs(001) substrates by MOVPE using 1,1-dimethylhydrazine (DMHy) as the N precursor, and their photoluminescence (PL) properties were investigated. The N incorporation leads to a decrease in the QDs size for an equivalent amount of source supply due to the increase in the wetting layer thickness. It also leads to an increase in the QDs density which is interpreted by the reduced surface migration length. The PL from the electron ground state of the InAsN QDs clearly shows the red-shift to 1159 nm by the N incorporation, indicating that the effect of the huge bandgap bowing is dominant over the quantum size effect in the InAsN QDs. The thermal activation energy of the QDs derived from the temperature dependence of the integrated PL intensity decreases from 176 meV to 140 meV by the DMHy supply, which is explained by the lowering of the electron quantum state of the thicker wetting layer caused by the N incorporation. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] c-InN (zincblende structure) films have been successfully grown on GaAs(001) substrates by rf-plasma-assisted molecular beam epitaxy. The X-ray diffraction analysis has confirmed the growth of c-InN films whose growth temperature was 400-550 C. The structural properties (i.e. surface flatness and crystal quality) of the InN films are obviously improved for the growth condition of the near surface-stoichiometry at the In-rich side. By high resolution transmission electron microscopy images and 2θ/ω X-ray reciprocal space mapping measurements, hexagonal-phase InN (h-InN) is found to be generated from c-InN{111} facets. The volume content of c-InN is estimated to be ∝82% at maximum based on an analysis of the X-ray diffraction intensity. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] A GaAs/InGaAsN p-i-n solar-cell structure on a Ge substrate has been fabricated intending incorporation in high-efficiency InGaP/InGaAs/InGaAsN/Ge four-junction-structure solar cells. An improved InGaAsN MOVPE growth process is adopted in which the Ge(001) vicinal substrates and a two-step-growth GaAs buffer layer combined with post-growth rapid thermal annealing (RTA) are the keys. With a prototype p-i-n photo-cell, the photovoltaic effect and a photo-current edge shift to the longer wavelength of InGaAsN with 1 eV bandgap are demonstrated. After RTA, however, the I-V characteristics are degraded with a significant reverse-bias current leakage. Electrical measurements showed a conduction-type conversion from n-type to p-type and significant increase of the hole concentration. The N-H-VGa complexes acting as shallow acceptors formed through RTA may be the most feasible cause of the drastic change of the electrical property of the InGaAsN film after RTA. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)