Table of contents

Most semiconductor crystals are transparent for infrared rays but some of them are difficult to study by X-ray methods if they are composed of heavy elements. An infrared light scattering tomography, which is developed in this paper to characterize semiconductor crystals, successfully gives clear images of micro-defects in a heat-treated Si crystal and dislocation networks in a GaAs crystal grown by a horizontal Bridgman method.

The plasma deposition apparatus developed in this study can realize a deposition of dense and high quality thin films, such as Si₃N₄ and SiO₂, without the need for substrate heating. It does this by enhancing the plasma excitation efficiency at low gas pressures (10^-4 Torr) and by the acceleration effect of ions with moderate energies (10 to 20 eV), using a microwave ECR (Electron Cyclotron Resonance) excited plasma, and a plasma stream extraction onto the specimen table by a divergent magnetic field method. The Si₃N₄ and SiO₂ films deposited are comparable to those prepared by high temperature CVD and thermal oxidation, respectively, in evaluations such as by buffered HF solution etch rate measurement.

It is demonstrated that a high electric field has large effects on the electron distribution and mobility in selectively doped GaAs/n-GaAs heterostructures. An increase of electron density in the AlGaAs layer has been found in the analysis of pulsed Hall effect and SdH oscillations at 4.2 K. At high fields, the mobility of two dimensional (2D) electrons has become slightly higher than the average mobility obtained by the pulsed Hall measurement. The velocity of 2D electrons reaches 3.8×10⁷ cm/s at 4.2 K.

Insulating BN thin-films were prepared at a temperature below 300°C by the rf glow discharge decomposition of a B₂H₆+NH₃+H₂ gas mixture. The structure of the deposited films was amorphous and the optical bandgap was determined to be ∼5.0 eV. Utilizing the plasma-deposited BN films, Al/BN/Si MIS structures were fabricated to test the dielectric properties. The static dielectric constant of stoichiometric BN is found to be 6.5, and the breakdown-field strength exceeds 3×10⁶ V/cm.

A blazed Si grating with a blaze angle of 3° is successfully fabricated using holographic exposure and reactive ion-beam etching. A new two-stage etching technique is developed for a grating with a blaze angle of less than 1° in Si single crystal, combining inclined and normal incident reactive ion-beam etching techniques. These diffraction gratings can be expected to be very useful in a soft X-ray region.

The temperature dependence of the threshold voltage shift has been studied for long term device degradations. The threshold voltage shift strongly depends on temperature and this is mainly caused by the temperature dependence of the effective trap density. The model assuming that the traps with an emission probability higher than 10^-5∼10^-6 are useless as electron traps agrees well with the experimental results.

The microwave breakdown and its suppression by superposing d.c. voltage was investigated at the frequency of 2.45 GHz with regard to the high power microwave techniques for heating fusion plasmas. An increase of about 60% in r.f. breakdown voltage was realized by superposing d.c. voltage of 1000 volts in the cavity, whose height was 2 cm, at the pressure of 1×10^-4 Torr.

A new alloyed-liquid-metal ion source for ion implantation into III-V compound semiconductors has been developed. A ternary alloy consisting of Au, Si & Be is used as the liquid metal for this ion source which is capable of emitting p-type dopant (Be), n-type dopant (Si), and Au ions from a single emitter tip. Threshold voltage for emitting ion current is about 6 kV and Be⁺⁺, Si⁺⁺ and Au⁺ ions are dominant. Energy spreads of Be and Si ion beams are less than 10 eV, while that of Au was greater than 15 eV.

The potential emission from aluminum under argon ion bombardment and an enhanced emission under oxygen ion bombardment have been investigated for an aluminum sample. For this a compact energy analyzer was made to measure energy distribution of secondary electrons at certain detection angle as well as total yield for the energy range from 0.7 to 3.0 keV. The results show that the electron yield owing to potential emission is between about 0.07 and 0.08 for argon ions and the enhancement in kinetic emission by oxygen ion bombardment results in marked increase in the yield of more than one order of magnitude higher than that for argon ions.

An AlGaAs dual-stripe laser, where each stripe has an SBH configuration, has been fabricated by means of chemical etching followed by liquid phase epitaxy. Phase-locked oscillation is observed under pulsed and CW operations. This is confirmed by the coalescence of the two longitudinal modes, as well as by the interference fringe measured in the far-field radiation pattern.

A new optical interferometer system for the absolute determination of lattice constant of a crystal is designed and constructed. It can measure linear displacement accurately within the range of 94% of a period of the interference fringes with long term fluctuation of 50 pm for 14 hours and short term fluctuation of 30 pm. Its high visibility, compact and simple structure will allow various applications to precision measurement of dimension in both scientific and industrial fields.

In S^*_C phase of DOBAMBC, electric field dependence of variance of the helicoidal pitch and of light transmittance was studied using a photodensity analyzer consisting of a video camera and a personal computer. When a temperature deviation from the transition point T_c between S_A and S^*_C is large, the minimum transmittance is observed at the field of the maximum variance of the pitch with both increasing and decreasing field. This shows that an increase in the variance induces an increase in light scattering. The increase in variance is qualitatively explained as the result of imhomogeneous realignment of pitch by applying the field to finite size domains.

Using two pump beams with wavelengths of 1.32 µm and 1.34 µm, a continuum spectrum in a multimode fiber is newly generated with relatively low pump power of 1.5 kW for each wavelength. The continuum spectrum is attributable to the superposition of sequential stimulated Raman scatterings and forced four-photon mixing processes.

Resonance experiments of magnetostatic surface waves (MSSW's) controlled by field gradients in a YIG slab partially shielded in its center with an iron ring are reported. In the configuration, the field profile is bowl-shaped with a minimum at the center of a slab in the propagation direction of MSSW's. The results indicate that MSSW's can propagate in such a geometry with increasing the wavenumbers. In the presence of the field gradients, new mode resonance has also been observed in the transmission spectrum below the bottom field of ordinary MSSW resonance.

Zinc oxide thin films with the resistivity of 5×10^-3Ω·cm and the transparency of above 80% at the wavelength between 400 and 800 nm have been prepared by conventional rf sputtering in pure argon from a zinc oxide target. A close relation of their electrical characteristics with crystallographic characteristics is found using X-ray diffraction analysis. The low resistivity films consist of very small crystal grains, the c-axis of which is not preferentially oriented or is weakly oriented parallel to the substrate surface.

The ablation pressure and the mass ablation rate for a 10 µm CO₂ laser were measured using two methods: a ballistic target pendulum and shifted X-ray emission images which are equivalent to X-ray back-lighting. The measured ablation pressure was 10 Mbar and the mass ablation rate was 10⁶ g/cm²·sec at the absorbed laser intensity of 5×10¹³ W/cm². Comparing the ablation mass rate measured by the pendulum with that derived from the penetration depth of the hot electrons using K_α line emission, we could identify the hot electron driven ablation as the dominant process.

The properties of platinum-diffused MOS structures were experimentally investigated. It is pointed out that the amount of charge at the Si–SiO₂ interface introduced by platinum diffusion is strongly dependent on a sort of diffusion ambient and crystal orientation of the wafers.

The ratio of the quadrupole relaxation probability, W₂ for |Δm|=2 transition to W₁ for |Δm|=1 transition has been measured at 132K at ²³Na site in NaNO₂ by the method of acoustic nuclear magnetic resonance. The orientation dependence of W₁ and W₂ is calculated in terms of the fourth rank M-tensor components using a point charge model. The calculation based on the assumption that the mode of lattice vibrations is completely isotropic shows the opposite tendency to that of the experimental results. Anisotropy of the lattice vibrations and/or other charge distributions of NO^-₂ ion should be taken into account.

Two terminal conductances for GaAs n⁺-n-n⁺ ballistic diodes are calculated by using a simplified diode model. It is found from the results that, due to space charge transit time effects, negative conductances appear in such ballistic diodes at a far infrared frequency range. It is also demonstrated that diode conductance-frequency characteristics are affected significantly by the plasma oscillation frequency.

The frequency of AlGaAs semiconductor lasers with external grating feedback has been locked to a Fabry-Perot interferometer by controlling the external cavity length with a PZT. The lasers were tunable over a wavelength range of 3.0∼4.5 nm. The frequency stability of 8.0×10^-10≧σ_y≧3.2×10^-12 was obtained for 1 ms≦τ≦100 s.

This letter proposes a new, fascinating ICF scheme. The scheme employs the soft x-ray production by hypervelocity projectiles. The soft x-ray of 10¹³ W/cm² and 10 nsec duration, which is focusable onto a small sized pellet, can be efficiently produced.

Photoinduced current has been measured in the range 0.5–3.4 eV in trans-polyacetylene of about 100 µm thickness. The typical photoinduced current spectrum shows a peak at 1.4 eV below the interband absorption edge and a sharp decrease below 0.7 eV. By observing the dependence of photoinduced current spectra on sample degradation and compensation with ammonia, it has been concluded that there exist four distinct spectral regions. Photoinduced current in one of them, the lowest energy region, has been ascribed to the bolometric effects, while those in the other regions are genuine photoconductivity.