Table of contents

A Josephson logic OR gate suitable for high speed logic circuits is proposed and tested. This gate has a structure modified from Variable Threshold Logic (VTL) to obtain large operating margin and small occupation area. The operating margin is calculated as ±19% for fan-out of 2, even with the critical current variation of ±20%. The circuit area is 40×60 µm². A chain of 5-stage OR gates was fabricated. The gates had Josephson junctions of 4 µm and 7 µm diameter made with Pb-alloy technology. The minimum gate delay of 9 ps was measured using a Josephson sampler.

EXAFS measurements were made on Ni-fine particles (14–5 nm in size) prepared by the gas evaporation technique. Data were analysed by the fine adjustment method developed by Teo et al. Substantial lattice relaxation shows an increase in the nearest Ni-Ni bond distance (R₁), a decrease in the coordination number (N₁) and an increase in the Debye-Waller factor (σ₁). These facts can be explained as a result of the chemisorption of oxygen on the surface of fine particles.

Depth distribution of implanted Si into GaAs using a focused-ion-beam (0.2 µm diameter, 160 keV) was profiled by means of differential Hall effect measurement and secondary ion mass spectroscopy. As compared to conventional unfocused-ion-beam implantation, implantation with a focused ion beam of high current density at high doses results in broadened profiles of the implanted Si at greater depths. This is probably caused by radiation-enhanced migration of the implanted Si during implantation.

Solving the rate equations without spatial averaging reveals the existence of a relaxation resonance peak in the frequency spectrum of an anti-reflection coated low reflectivity laser diode. This peak occurs at >20 GHz which has not been reported previously. Such a diode may have potential applications in high frequency microwave transmission.

Numerical analysis of a Co-Cr medium-ring type head system for perpendicular recording are performed using a two dimensional model with a finite element method. A new magnetization model of the Co-Cr medium is proposed, a columnar structure being taken into consideration. The medium is divided into elements for the calculation and an additional field, H_ad∝( M_upper+ M_lower) is assumed to be applied from upper and lower elements within a column, where M is the magnetization of the element. The results of the simulation show that the interaction between elements plays an important role in the magnetization process of the Co-Cr medium.

Self annealing experiments were performed on thermally insulated (100) Si samples, implanting 100 keV P⁺ ions at beam power densities of 15 and 25 W/cm². Cross and plan section characterization by TEM of the specimens lead to two main conclusions about the dynamic annealing mechanism: 1) ion bombardment enhances the rate of amorphous to crystalline transformation; 2) residual crystalline islands are present on the surface. They allow a regrowth of the amorphous region both from the front and the bottom of the layer.

Stability was examined for an AlAs/n-GaAs superlattice (SL), whose Si donors were confined to the GaAs layer. The SL was grown by MBE at 520°C and was annealed at a temperature (T_a) from 560 to 800°C. Up to T_a=600^°C, no sign of Al-Ga mixing was observed, and the amount of a DX centerlike trap was proportional to exp (-0.65 eV/kT_a). The increase in the trap was due to Si diffusion to the AlAs/GaAs interfaces with the activation energy of 1.3 eV for its diffusion coefficient. As increasing T_a above 650°C, Al-Ga mixing was accelerated and a decrease in carrier concentration and an increase in persistent photoconductivity were observed.

For the first time, a model is presented that takes the effects of concentration-dependent coefficient diffusion into account to determine the lateral distribution of injected carriers in an active layer of gain-guided stripe-geometry lasers. In high carrier concentration cases, computed examples demonstrate the lack of accuracy of the other classical models.

A new type of amorphous silicon-carbide film is produced by the glow discharge decomposition of an intermediate species SiF₂, CF₄ and H₂ gas mixture. Optical band gap and photoconductive properties of this film are measured as a function of carbon content. It is found that the optical band gap can be increased up to 2.2 eV by increasing carbon content without apparent degradation of film properties such as photoconductivity and photosensitivity.

A study of the equilibrium trajectory of the superconducting magnetic levitation system is in progress for the absolute determination of the magnetic flux quantum φ₀. The temporary reproducibility of the evaluation factor K' is about 100 ppm. Problems concerned with higher reproducibility turned out to be the fluctuation of the environmental magnetic field and the stability of the SQUID system in controlling the flux-up process.

Grain boundaries of sintered Fe₇₇Nd₁₅B₈ permanent magnets with different heat-treatments have been examined by high resolution electron microcopy. A b.c.c. phase with the lattice constant of a=0.29 nm was found at most of the boundaries of Fe₁₄Nd₂B grains. The b.c.c. phase and Fe₁₄Nd₂B grains are joined with smooth interfaces in the samples annealed at 870 K, which have a coercivity as high as 1000 KA/m. In samples quenched from 1350 K with a coercivity of about 500 KA/m, however, thin plates of the b.c.c. phase extend from the interfaces to the inside of the Fe₁₄Nd₂B grains, and deform the lattice spacings of (001) planes of the Fe₁₄Nd₂B matrix. These thin plates are considered to act as nucleation centers of reverse magnetic domains which reduce the coercivity of the specimen.

By the irradiation of light on the conducting polymer like polythiophene doped with diaryliodonium salts, its absorption spectrum changes remarkably, which can be explained in terms of an insulator-metal transition due to light induced doping. The application of this phenomenon as an optical memory element which can be written by the light irradiation, is proposed.

The threshold voltage scattering of GaAs metal-semiconductor field-effect transistors (MESFET's) fabricated on commercially available LEC-grown undoped semi-insulating GaAs substrate was investigated with varied annealing methods. It was found that the threshold voltage scattering greatly depended on annealing method. SiO₂ capped annealing under arsenic vapor pressure allowed very uniform threshold voltage of GaAs MESFET's over the full water.

Two methods are proposed to measure EXAFS by monitoring the direct photoemission from a solid sample as a function of photon energy for a randomly oriented sample. One is to measure it in the special direction, at the magic angle, and the other is to measure the average intensity over a hemisphere. For a fixed sample, one cannot expect to measure EXAFS by monitoring the direct photoemission.

Two kinds of energy filtered atomic structure images of Si crystal in (011) orientation formed by no-loss and plasma-loss electrons were photographed using the energy analyzer of a sector type magnet which was attached to the bottom of a high resolution electron microscope. The behavior of plasma-loss electrons in the crystal was discussed on the basis of the dynamical theory of electron diffraction. The contrast of the crystal lattice image formed by the plasma-loss electrons was calculated and compared with the observed image.

Initial current densities under constant voltage anodic oxidation are measured to estimate aluminum oxide film thickness on aluminum. It is shown that the logarithm of initial current density ratio with and without a thin aluminum oxide on aluminum is proportional to the logarithm of the exposure time to dry air. Auger electron spectroscopy measurements show that the surface of aluminum exposed to dry air is covered with a thicker aluminum oxide film than an aluminum surface just after aluminum oxide etching by an aqueous 5% sulfamic acid.

New photoluminescence (PL) recovery effects induced by below band-gap excitation have been observed for the fatigued emission bands associated with the deep donor EL2 in undoped semi-insulating liquid encapsulated Czochralski-grown GaAs crystals. The PL intensity quenched by a pre-excitation with a 1.06-µm light is restored gradually by a persistent irradiation of the same 1.06-µm light with a reduced excitation intensity in some samples and by a 1.32-µm light in all the samples. These recovery effects are explained by the occurrence of optical transition from the metastable state to the normal state of the EL2 level.

This letter demonstrates the single crystallization of thin films on unordered substrates (amorphous materials) with a discrete surface energy distribution, even if the substrate surface is flat. This crystallization, called periodic surface energy driven single crystallization, arises from the periodic stripe patterns of different materials with different surface energy. An example that facetted KCl single crystals can be grown on the SiO₂-Si₃N₄ stripe patterns is shown.

Transient characteristics of luminescence from single quantum well (SQW) structure have been examined using a time-correlated single photon counting method. The decay time of the SQW luminescence is shorter than that of bulk sample. The rapid decay is considered to reflect the enhancement of recombination due to localization of excitons. The disagreement between the present results and those reported by other researchers is discussed.

Crystal orientations of SrF₂ and (Ca, Sr)F₂ films on Si(100) and (111) substrates were controlled by intermediate CaF₂ films which were grown on the substrates prior to growth of lattice-mismatched fluoride films. SrF₂ films with good crystalline quality were grown epitaxially on the CaF₂/Si(100) structure, though the SrF₂ films directly grown on Si(100) were mainly composed of preferentially (111) oriented crystallites. Similarly, (Ca, Sr)F₂ films on Si(111) changed from epitaxial films with internal boundaries between regular and rotationally twinned crystallites to single crystal ones by use of the intermediate CaF₂ films.

To assist in the study of the power balance in a linear confinement machine, atomic hydrogen-density profiles in plasmas of the RFC-XX-M device were measured using laser fluorescence spectroscopy tuned to the Balmer alpha line. Measured profiles showed marked decreases of neutral densities in the centre of the plasma, which are explained by charge-exchange and electron ionization pumping by the plasma. It is important to note that the neutrals are well burned out in the central cell, N_l/N_e \lesssim0.01. Further, charge-exchange losses are quantitatively evaluated and discussed from the neutral-density profiles and parameters of the plasma.

A new method of Fourier analysis is shown by which both concentration and atomic displacement modulations existing in multilayer structures can be reproduced from the measurement of the integrated intensities of satellite reflections. By applying the present method to a molecular beam epitaxy grown (GaAs)₈(AlAs)₈ superlattice, the atomic displacement modulation in interface region is given as well as concentration modulation.

Striations in undoped semi-insulating GaAs grown by liquid encapsulated Czochralski (LEC) technique were revealed by photoetching with diluted AB etchant and X-ray transmission topography. The striations had two different periods; one with shorter period of about 30 µm was due to crystal rotation, and the other with longer period of about 300 µm was due to melt convection. The formation of the striations in undoped semi-insulating GaAs was ascribed to stoichiometric inhomogeneity.

The liquid encapsulated Czochralski technique using a ceramics AlN crucible has been investigated for the growth of InP single crystals. High purity crystals, typically having a carrier concentration of 2.2×10¹⁵ cm^-3 and a Hall mobility of 30100 cm²/(V·s) at 77 K for the first-to-freeze portion, are grown without serious contamination of electrically active impurities from the crucible. Impurity analyses of the grown crystals and the B₂O₃ encapsulants are carried out. The results are compared with those for the crystal grown from a pBN crucible.