Masahiro Yoshikawa

Fabrication of Bi(Pb)SrCaCuO Thin Film of High-Tc Phase

Lead-added Bi-Sr-Ca-Cu-O (BSCCO) thin film of high-Tc phase has been successfully prepared by means of rf-magnetron sputtering and the post annealing process. The content of lead in the BSCCO thin film was decreased during an ordinary annealing process. In order to minimize the decrease of lead, the BSCCO thin film was placed on a bulk ceramics whose composition was similar to that of the film, and annealed for 50 hours at 855°C in air. As the result, the content of lead in the thin film was almost unchanged during the annealing process. The intensity ratio of the X-ray diffraction lines due to the (002) of high and low-Tc phases was about 4/1. The film showed a superconducting transition at 110 K; a long tail of some residual resistance remained down to 90 K.

Complete Polarization Control of 12×8-Bit Matrix-Addressed Oxide-Confined Vertical-Cavity Surface-Emitting Laser Array

The authors have shown complete polarization control of a 12×8-bit matrix-addressed oxide-confined vertical-cavity surface-emitting laser (VCSEL) array, which has an unstrained active region emitting at 780 nm. By using a combination of an elliptical-shaped post structure fabricated on misoriented substrate and upper p-side metal lines elongated in the substrate off-direction, we observed complete polarization pinning in an index-guide type array device. All of the VCSELs in this array lased in a fundamental transverse mode and linearly polarized along the direction.

Surface Reconstruction of GaP (001) for Various Surface Stoichiometries

The surface stoichiometry and reconstruction of GaP (001) are investigated by means of reflection high-energy electron diffraction and surface photo-absorption. The experiments were carried out using a solid-source molecular beam epitaxy system with a cracker cell as a P source. When the amount of Ga supplied to the surface is over 2 monolayer (ML), the 2×4 reconstruction corresponding to the P-stabilized surface is observed in spite of the existence of excess Ga on the surface. The change of surface reconstruction may be interpreted as follows: the surface is a Ga-terminated structure up to 2 ML of Ga supply, then Ga atoms move to some nonperiodic sites such as Ga droplets.

Characteristics and Reliability of 10 Gbps/Channel 1 ×10 Vertical-Cavity Surface-Emitting Laser Array of 850 nm Wavelength

A 10 Gbps/channel 1 ×10 vertical-cavity surface-emitting laser (VCSEL) array of 850 nm wavelength was demonstrated for a 100 Gbps (10 Gbps × 10) local area network. The VCSEL array was oxidized using an in situ probing technique. The threshold current of each VCSEL on the array is approximately 0.5 mA with the oxide and metal apertures of 8 and 6 µm, respectively. The temperature characteristic of lasing from -40 to 120 °C was stable and the f-3 dB cutoff frequency exceeded 10 GHz at 6 mA. The data transmission test through the conventional multimode fiber of 300 m length was carried out. We also investigated the reliability of the VCSEL array at an ambient temperature of 120 °C and a dc current of 15 mA. We could achieve a failure rate over a decade below 1% at a temperature and current of 60 °C and 7 mA, respectively.

Growth Process in Initial Stage of GaAs/GaP(001) by Molecular Beam Epitaxy.

The growth-mode transition of strained GaAs heteroepitaxial growth on GaP(001) is studied in detail using reflection high-energy electron diffraction (RHEED). The lattice parameter oscillation during layer-by-layer growth and the increase of the critical thickness of the growth-mode transition with increase of the growth rate reflect the elastic strain relaxation around the edge of two-dimensional nuclei and the existence of the kinetically controlled evolution of islands, respectively. The transformation from a strained metastable layer structure to a relaxed stable island structure is revealed through analyses of the RHEED pattern. We propose a model to explain the increase of the critical thickness, which assumes two processes at the surface, the formation of a metastable layer and its transformation to islands.

Preparation of Bi(Pb)SrCaCuO Thin Film with High-Tc Phase

The lead added BiSrCaCuO thin film of high-Tc phase has been successfully prepared by using rf-magnetron sputtering and post annealing process. The content of lead in the thin film was easily decreased during the ordinary annealing process. In order to minimize the decrease of lead, the Pb-doped BSCCO thin film was placed on the bulk ceramics and annealed for over 170 hours at 855°C in air. As the result, the content of Pb was almost unchanged and the film showed superconducting transition at 104 K.