Table of contents

Zn-doped InGaP/Te-doped ZnGaP on n-type GaAsP substrate homostructural light-emitting diodes has been reproducibly fabricated by liquid-phase epitaxy using a supercooling technique. The growth and characterization of Te- and Zn-doped InGaP layers are described. The strongest photoluminescence peak intensity occurs at 1×10¹⁸ and 6×10¹⁷ cm^-3 for electron and hole concentrations, respectively. Diodes fabricated from the p-n homostructure are characterized by current-voltage measurement, electroluminescence, light output power, and external quantum efficiency. A forward-bias turn-on voltage of 1.5 V with an ideality factor of 2.02 and a breakdown voltage as high as 20 V are obtained from the current-voltage measurements. The emission peak wavelength and the full width at half-maximum of electroluminescence are around 5840 Å and 66-55 meV at 20 mA, respectively. The light output power of the uncoated diodes is about 35 µW at a dc current of 100 mA, and an external quantum efficiency of ∼0.02% is observed. The EL spectra are compared to the PL spectra of the Zn-doped InGaP layer at 300 and 50 K.

The optical absorption property of highly beryllium (Be)-doped GaInAsP (λ_g=1.31 µm, p=2×10¹⁹ cm^-3) grown by chemical beam epitaxy (CBE) was investigated. The absorption coefficient was estimated from the transmissivity of a Fabry-Perot resonator formed by selective etching of an InP substrate. We found a fairly large absorption (α\cong400 cm^-1) in Be-doped material in the longer wavelength region (λ>1.35 µm).

Low-resistivity p-type GaN films, which were obtained by N₂-ambient thermal annealing or low-energy electron-beam irradiation (LEEBI) treatment, showed a resistivity as high as 1×10⁶ Ω·cm after NH₃-ambient thermal annealing at temperatures above 600°C. In the case of N₂-ambient thermal annealing at temperatures between room temperature and 1000°C, the low-resistivity p-type GaN films showed no change in resistivity, which was almost constant between 2 Ω·cm and 8 Ω·cm. These results indicate that atomic hydrogen produced by NH₃ dissociation at temperatures above 400°C is related to the hole compensation mechanism. A hydrogenation process whereby acceptor-H neutral complexes are formed in p-type GaN films was proposed. The formation of acceptor-H neutral complexes causes hole compensation, and deep-level and weak blue emissions in photoluminescence.

The irradiation-temperature dependence of light-induced degradation has been studied at temperatures between 300 K and 25 K. Although Si-H₂ bonds have a strong influence on degradation at an irradiation temperature of 300 K, their influence is reduced at low irradiation temperatures. Si-H₂ bonds are thought to have a stabilization effect on newly created defects. Also, the hydrogen atom itself was found to have an influence on light-induced degradation in a-Si solar cells with low Si-H₂ bond density or in the region of low irradiation temperatures below about 60 K.

A detailed characterization of ultrahigh-speed pseudomorphic InGaAs/AlGaAs inverted high electron mobility transistors (pseudomorphic I-HEMT's) is reported. Charge control analysis indicates that the pseudomorphic I-HEMT accomplishes improved transconductance (g_m) and reduced short channel effects due to higher concentration and excellent confinement of two-dimensional electron gas (2DEG) in the InGaAs channel. The 0.2 µm gate pseudomorphic I-HEMT's reported here exhibit superior DC and RF performances, i.e., maximum transconductance (g_m^max) of 565 mS/mm, cutoff frequency (f_T) of 110 GHz and propagation delay times (τ_pd's) of 6.6 ps/gate at R.T. and 4.9 ps/gate at 120 K. Delay time analysis reveals the reduction of both the electron transit time (τ_transit) and the channel charging time (τ_channel) in the pseudomorphic I-HEMT, which are significant factors in the ultrahigh-speed performance. Higher electron saturation velocity (υ_s:2.1×10⁷ cm/s) and improved g_m are considered to contribute to the reduction in τ_transit and τ_channel.

We propose and demonstrate a new functional optoelectronic device, the "self-scanning light-emitting device (SLED)." The SLED consists of light-emitting thyristors whose turn-on voltages interact with each other through the resistor network. The SLED acts as an optical shift register, and the light-emitting element is automatically transferred by input clock pulses. We successfully demonstrated GaAs SLED operation using three-phase transfer clock pulses, and obtained 3 MHz as the maximum transfer rate. Moreover, we propose here the diode-coupled SLED, where the turn-on voltages of the thyristors interact through the pn diode in order to obtain the transfer operation driven by a two-phase clock pulse. The SLED has several unique functions and will become a new key device in the optoelectronic field and in optical information processing.

CW Nd:YAG laser (1.065 µm wavelength) anneal of B¹¹ and BF₂ implanted silicon yields sheet resistance values matching those of the thermally annealed ones. The samples annealed at low laser powers show a narrowing of the secondary ion mass spectroscopy (SIMS) dopant profile compared to the as implanted cases, accompanied by a shift in the profile peak towards the bulk. The anomalous dopant redistribution when annealing is done at low laser powers is explained on the basis of a new phenomenon, termed damage enhanced diffusion.

The improvement in electrical characteristics of oxides, including oxide leakage current, radiation hardness, and hot-carrier resistance, in metal-oxide-semiconductor (MOS) capacitors by irradiation-then-anneal (ITA) treatments is studied. The ITA treatment is performed by Co-60 irradiation with a suitable dose followed by annealing in pure nitrogen at 400°C for 10 min. It is found that samples receiving ITA treatments exhibit better performance in oxide properties than those not receiving an ITA treatment. For the examination of oxide leakage current, the charge-then-decay method is employed. Devices with two ITA treatments exhibit a very slow gate voltage decay behavior even in a moist environment. Both the radiation hardness and the hot-carrier resistance are improved by the ITA treatment. The gate area dependence and the total dose effect in ITA treatment are also discussed.

The GaAs(100) surface is modeled, using a cluster to study the interaction with hydrogen. On the basis of ab initio theory including electron correlations, the most stable structures for the As-terminated surface with adsorbed hydrogen atoms are established. The optimized structure of the modeled cluster without the adsorbate is also obtained. From the computational results of total energy, the activation energy of the dissociation of the hydrogen molecule on the surface was estimated. The cluster with adsorbed hydrogen atoms is more stable than that without hydrogen, although the approach of the hydrogen molecule toward the surface causes an increase in the total energy.

Measurements of currents for a GaAs metal-semiconductor field-effect transistor (MESFET) when a negative bias was applied to a nearby ohmic contact (sidegate) showed that significant hole injection from the gate occurs for large negative sidegate voltages. This is in agreement with a proposed model, in which the presence of an inversion layer under the Schottky gate due to the pinning of the Fermi level at the channel surface causes hole injection into the channel when the gate is positively biased with respect to the sidegate. Upon increasing negative sidegate voltage the substrate-channel depletion region is expanded, and consequently, the neutral region of the channel is shrunk. This results in more holes being injected into the substrate from the gate.

Silver-added YBa₂Cu₃O_7-x (Y123) composites have been prepared for study of the effects of noble metal on the fracturing of Y123 grains. The microscopic results show that the planar-type microcracks are frequently found in large Y123 grains, which are delaminated by a uniaxial pressure as low as 150 MPa. Planar-type microcracks, characterized by the Wulff Net operation, are laid on the basal (001) plane which is the weakest plane in the Y123 crystal system. The formation of glassy material above eutectic temperature, the effect of Ag on green density, eutectic liquid, and the reaction of Ag grains with glassy material will be discussed. Moreover, compression tests of Ag/Y123 depict that more than 20 vol% silver additive can improve the ductility of the composite and prevent delamination of large Y123 grains.

Bi(Pb)-Sr-Ca-Cu-O superconducting tubes with different critical current densities were fabricated to examine the effect of the critical current density on the magnetic shielding property. The shielding magnetic flux density, at which the flux started to penetrate into the tube center, was proportional to the critical current density at zero magnetic field. These experimental results agreed with the calculations based on the critical state model.

Structure, resistivity and susceptibility have been measured in the Bi₂Sr_2-xRE_xCaCu₂O_8+δ (RE=Nd and Ce) system. The samples with 0≤x≤1 (RE=Nd) and 0≤x≤0.25 (RE=Ce) have almost single phases of the Bi₂Sr₂CaCu₂O_8+δ structure. The x-dependence on T_c in the Ce-substituted system is almost twice as strong as that in the Nd-substituted one. The valences of Nd and Ce ions in the samples were determined from susceptibility measurement as trivalent and tetravalent, respectively. The hole concentration was determined from the Hall effect measurement. The results confirm that the hole concentration in the Ce-substituted system becomes twice as strong as that in the Nd-substituted one, as expected from the universal relationship between the T_c and the hole concentration in the Bi₂Sr₂CaCu₂O_8+δ system.

Yttrium-excess Y_xBa₂Cu₃O_y (1.00≤x≤1.25) superconductors have been fabricated by a combination process of ordinary solid-state reaction and partial melting. Sintering the yttrium-excess Y_xBa₂Cu₃O_y results in extremely small grains, which in turn produce uniformly distributed fine Y₂BaCuO₅ during partial melting. Y₂BaCuO₅ acts as the nucleation site for peritectic reaction. The unreacted Y₂BaCuO₅ seems to act as a flux pinning center. Due to this flux pinning force, the yttrium-excess Y_xBa₂Cu₃O_y superconductors have very high critical current densities of about 22,000 A/cm² (at 77 K, 1 T).

A new compound, YBa₂SnO_5.5 was found forming in YBa₂Cu₃O_7-x-SnO₂ system. Preparation of YBa₂SnO_5.5 as a single phase compound by solid state reaction method is reported for the first time. This new compound has a cubic structure with a lattice parameter a=8.42 Å. Kinetics of sintering and its dielectric properties are briefly discussed. No chemical reaction between YBa₂Cu₃O_7-x and YBa₂SnO_5.5 was observed even at an elevated temperatue of 950°C. Sintered YBa₂SnO_5.5 is proposed as a new substrate material for the preparation of superconducting YBa₂Cu₃O_7-x thin films.

Both the surface crystalline structure and chemical composition of Y-Ba-Cu-O film were examined in situ using reflection-high-energy-electron-diffraction and total-reflection-angle X-ray spectroscopy (RHEED-TRAXS). The chemical composition determined by TRAXS agreed well with that determined by inductively coupled plasma spectroscopy. The compositional deviation from Y₁Ba₂Cu₃O_7-x affected the surface crystalline structure of films, as was detected by RHEED and confirmed by scanning electron microscopy. RHEED-TRAXS is a powerful tool for in situ examination of the crystal growth of Y-Ba-Cu-O films.

Critical current distributions in superconducting composite wires of Nb₃Sn alloyed with Ti were studied using the second-derivative analysis of the flux flow voltage state. Specimens were prepared for a reaction time of 1 to 8 days at a heat treatment temperature of 675°C and measurements were carried out with short samples. It has been shown that the critical current distributions were mainly determined by variations in the areas and the thermodynamic critical fields of the Nb₃Sn filaments.

The transport critical current J_c of the Nb/Al₂O₃ superconducting multilayer films has been measured at 4.2 K and 1.5 K under both the parallel and the perpendicular magnetic fields to the film plane. From the obtained J_c values, the pinning force density F_p in the parallel (F_p//) and the perpendicular (F_p⊥) directions is estimated. F_p⊥ enhancement is drastic in comparison with F_p// but F_p// itself is also remarkably enhanced by the multilayer structure. The pinning mechanisms are discussed in reference to the pinning function curve F_p//,⊥ (h). It has been found that for F_p⊥ of multilayers showing quasi-two-dimensional superconductivity the temperature scaling law breaks down. F_p// of all multilayers roughly obeys the scaling law and shows some characteristics of usual core pinning.

Growth conditions in the KCl-flux method were refined to reduce defects in the platelike crystals of Bi₂Sr₂CaCu₂O_8+y. Crystals were grown from high-temperature solutions by slow-cooling and subsequent isothermal processes in a horizontal temperature gradient. As a result, we succeeded in excluding defects that had been observed as etch pits in our previous study.

In the photoemission spectra of the κ-(BEDT-TTF)₂Cu(NCS)₂ surface, two characteristic structures were observed at the binding energies of ∼-7.5 eV and ∼-11.5 eV, which were attributed to the π- and σ-bonding states, respectively, in comparison with the results of the molecular orbital (MO) calculations. Polarization dependence appearing in the spectra was comprehensively interpreted by the electronic structures calculated for those states, which is in good agreement with the results previously obtained using a scanning tunneling microscope.

Maghemite films with coercivity of 1200-1300 Oe, saturation magnetization of around 5000 G, and squareness ratio of 0.63-0.66 have been routinely prepared by spray-pyrolysis onto heated substrates of alumina, MgO(100) and Corning 7059 glass from aqueous nitrate solutions containing Fe, Co, and Mn. Composition and reduction-oxidation treatments were found to dominate coercivity. Glancing angle X-ray diffraction showed a single phase maghemite structure. Transmission electron microscope (TEM) studies on detached film material showed that ultrafine equiaxed particles of 40 to 90 nm contribute to high coercivity. Post-annealing was found to enhance coercivity substantially. These films are potential candidates for magnetic recording media.

The effect of intergrain exchange and magnetostatic interactions on remanence and coercivity is calculated numerically for an isotropic Nd-Fe-B model magnet composed of 8000 grains. The intergrain exchange interaction affects the magnetizing process markedly when the grain size L is small, but the magnetostatic interaction does not have substantial effects. The calculated remanence which takes the intergrain exchange interaction into account increases with decreasing L from M_s/2 (M_s: the saturation magnetization) to M_s and agrees roughly with the experimental results. The calculated coercivity decreases with decreasing L from 0.48H_A (H_A: the anisotropy field) to 0. Our results suggest that the large remanence above M_s/2 observed experimentally in isotropic Nd-Fe-B magnets can be explained by the intergrain exchange interaction between Nd₂Fe₁₄B grains.

Unstable superoxide, ^·O₂^-, and semiquinone can be stabilized when hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ is crystallized from aqueous solutions containing these radicals. The inorganic microcrystals surround the radicals and stabilize them for nearly a year at room temperature. Radicals adsorbed on the surface of apatite showed spectra different from those obtained by doping. Semiquinone radicals in apatite were almost stable up to about 600°C. Effects of additional Fe³⁺ and F^- impurities on the electron spin resonance (ESR) spectrum of superoxide-doped apatite were studied to determine the site of the radicals in the lattice. Superoxide may be substituted at the OH^- site.

Using the slab waveguide composed of spin-coated vinylidene cyanide/vinyl acetate (VDCN/VAc) organic copolymer having the square-shaped corrugation of nonlinear optical susceptibility χ⁽²⁾ with corona discharge in the guiding layer, and taking quasi-phase matching between the dominant modes of both fundamental and second-harmonic waves, enhancement of second-harmonic generation (SHG) has been demonstrated at Nd:YAG 1.06 µm and Er:YAG 2.94 µm laser lines. The SHG power with this χ⁽²⁾ corrugated slab guide is theoretically evaluated, together with its enhancement factor (E.F.) to a bulk scheme. The E.F. of 500 to 800 obtained in the experiments is consistent with the theoretical estimates.

Very low threshold current densities of 640 A/cm², 400 A/cm² and 200 A/cm² were obtained in 1.5 µm GaInAs/AlGaInAs lattice matched, compressive and tensile strained-layer quantum well laser diodes (SL-QW LDs) respectively, grown by organometallic chemical vapor deposition, with continuously graded-index separate-confinement-heterostructure. The polarization of output power for a tensile SL-QW LD showed transverse magnetic (TM) mode, while that for a lattice matched and a compressive SL-QW LDs showed transverse electric (TE) mode. A very low threshold current of 3.6 mA was obtained in a buried heterostructure compressive SL-QW laser diode grown by two-step organometallic chemical vapor deposition.

We measure the growth temperature dependence of the magnetic and optical properties of lanthanum- and gallium-substituted yttrium iron garnet films deposited on gadolinium gallium garnet substrates by the liquid-phase-epitaxial-growth method for use as integrated optical waveguides. The magnetization of the film can be saturated in the film plane by a weak external-magnetic field (<45 Oe). The refractive index is controlled in a range of 2.192 to 2.204 by the growth temperature, which ranges from 893 to 835°C. Rib waveguides with low propagation loss (2.3 dB/cm at 1.55 µm wavelength evaluated by measuring the contrast in Fabry-Perot cavity resonance signals) are also fabricated.

A thin film waveguide consisting of newly-developed polymer p-NAn-PVA was fabricated and characterized. The thin film was formed by spin-coating and poled by applying an electric field. The electro-optic (EO) coefficient r₃₃ was measured to be 14 pm/V, which is as large as half of the r₃₃ of LiNbO₃. As an application of this waveguide, a waveguide EO grating switch was proposed and demonstrated. The switching operation was confirmed preliminarily.

A parametric and unsupervised method of automatic threshold selection for image segmentation is presented. An optimal threshold is selected by the fuzzy risk criterion, namely, so as to separate a given picture into meaningful gray level classes under the assumption of object and pixel gray level values being normally distributed. The effectiveness of the proposed approach is illustrated using some experimental images with 256 gray-levels, and the results are compared with minimum error thresholding method using the criterion functions such as uniformity, shape, and edge measures.

In order to control the polarization direction of surface emitting lasers, we have introduced biaxial tension in the active layer. By making an elliptical etch well, we introduce the anisotropic strain in the active region. We experimentally demonstrated polarization stabilization along the major axis of the elliptically holed region.

Manganese-doped zinc sulfide electroluminescent (EL) films were prepared for the first time by a hot wall technique with Mn planar doping. Undoped and Mn-doped ZnS films on glass substrates exhibit preferred cubic (111) orientation at the substrate temperature of 280°C. The Δ2θ value (full width at half-maximum) of the 111 reflection of the ZnS:Mn film in an X-ray diffraction pattern was found to be improved with an increase in Mn concentration and film thickness. By means of secondary ion mass spectroscopy (SIMS) and electron spin resonance (ESR) analyses, it was confirmed that this doping technique was very efficient in obtaining a homogeneous Mn²⁺ distribution which yielded highly luminescent EL devices. For an optimum device with double insulators of stacked Ta₂O₅/Al₂O₃ layers, the maximum luminance and efficiency at 1 kHz sinusoidal excitation were 3200 cd/m² and 1.3 lm/W, respectively.

Dielectric properties of two polymer-liquid crystal composites, comprised of the polymer, poly (methyl methacrylate) (PMMA), and liquid crystal, octyl cyanobiphenyl (K-24) and a biphenyl-terphenyl mixture (E-8), are reported as function of frequency (100 Hz-1.0 MHz) and temperature (20-80°C). Two distinct dispersion regions in dielectric permittivity are observed; one at ∼500 Hz due to space charge relaxation at the liquid crystal droplet-polymer interface and the other at ∼50 kHz due to dipolar relaxation. Correspondingly, dissipation factor `D' peaks are also seen in the low- and high frequency regions. Temperature variation studies show that the low-frequency dispersion becomes more and more prominent with increasing temperature, attains a maximum at ∼55°C and then disappears completely beyond 72°C. Correspondingly, `D' also shows a broad peak at ∼55°C. The above results are explained in terms of the Maxwell-Wagner interfacial polarization which arises due to the presence of liquid crystal or liquid microdroplets of higher conductivity in a resistive polymer matrix. Dielectric behavior of polymer-liquid crystal composites is not so much affected by the mesophase transitions, as by the glass transition temperature of the polymer.

A method is introduced to determine the statistical distribution of energetically degenerate but geometrically inequivalent states in a temperature induced phase transition in solids. The method has been employed to calculate the ratio of the rhombohedral and tetragonal phases in the Pb(Zr_xTi_1-x)O₃ solid solution of the morphotropic phase boundary (MPB) composition. Our results indicate that the MPB determined by Jaffe, Cook and Jaffe [Piezoelectric Ceramics (Academic Press, London, 1971) p. 136] from structural measurements should be shifted to the rhombohedral side, which is more consistent with the MPB determined from dielectric measurements.

The depletion edge region must be taken into account in the determination of the capture rate of minority carriers from a transient capacitance after the application of an injection pulse to a reverse-biased pn junction. A simple expression to evaluate the edge effect is proposed, with which the capture rate of minority carriers can be determined if the capture rate of majority carriers is known. Measurements are performed on an Au-doped Si p⁺n diode to determine the hole capture rate of the Au acceptor level.

Thin single crystals of NaCl were deeply colored by intense electron irradiation to introduce Na clusters in the crystal, and were heat treated at 473 K. Dependence of the photoacoustic (PA) signal on the absorption coefficient and on modulation frequency reveals a smaller concentration of clusters near the heated surface compared with the other surface. Recombination of hole centers with the Na clusters is suggested from temperature dependence of the Na cluster concentration.

Dielectric and Ferroelectric (D-E) hysteresis loop measurements were conducted for evaporated organic thin films by utilizing a newly developed sample cell. A vinylidene fluoride-trifluoroethylene (VDF/TrFE) copolymer sample with 54 mol% VDF content clearly exhibited a ferroelectric nature when an electric field of 30 MV/m was applied during the evaporation process.

Measurements of the soft-mode and electroclinic behavior in the smectic A^*-phase of a compound with very high spontaneous polarization (about 5 mC/m² (0.5 µC/cm²) in the smectic C^*-phase) are presented. It is found that for large induced tilt angles, one observes a strip texture giving rise to a strong characteristic light scattering. Once created this periodic stripe pattern remains even when the field is turned off. Furthermore, the electric field-induced modulation of the pattern allows scattering intensity modulation, resulting in anomalous electroclinic behavior.

Smectic layer structures of some surface-stabilized ferroelectric liquid crystal cells were studied using high-resolution X-ray analysis. The cells were constructed of two glass plates coated with a polymer aligning film rubbed in parallel and exhibited a typical chevron layer structure. The correlation between the layer tilt angle and the molecular tilt angle was investigated in detail, taking into account the differences between the molecular tilt and apparent tilt angles. It was confirmed that the layer tilt angle correlated with the molecular tilt angle though it was slightly smaller, and the ratio of the layer tilt angle to the molecular tilt angle gradually decreased as the molecular tilt angle increased.

The characteristics of the diffusion process of quasicrystals are studied for one-dimensional and two-dimensional models by the conventional Monte Carlo simulation. For the one-dimensional model, the tracer diffusion coefficients of an isolated particle are calculated for the three types of lattice models, i.e., single crystal, binary solid solution and quasicrystal. The characteristics of diffusivity of the one-dimensional quasicrystal model are derived from comparisons among the three types of models. For the two-dimensional model, the characteristics of diffusivity of a quasicrystal are discussed in comparison with those of the honeycomb lattice. In particular, the concentration dependence of diffusivity on the two-dimensional Penrose lattice is calculated and the effects of interatomic potential are discussed.

The change in properties with composition of Mg-doped LiNbO₃ crystals at ∼10% MgO, reported by Hu et al. [Jpn. J. Appl. Phys. 30 (1991) 1412] may be reinterpreted in terms of a different change in solid solution mechanism to the one proposed by Hu et al. For Mg contents greater than ∼10%, phase diagram studies indicate that any crystals would be constrained to have compositions close to or on the stoichiometric join of constant overall cation content, with substitution mechanism 3Li⁺+Nb⁵⁺\rightleftharpoons4Mg²⁺ rather than to have A site vacancies as suggested by Hu et al. The Curie temperature, T_c, varies with composition. In addition to the well-established decrease in T_c associated with cation vacancy creation, a second mechanism must also operate to reduce T_c, probably associated with substitution of Mg onto B(Nb) sites.

Hexagonal boron nitride-aluminum nitride (75-25, 50-50, 40-60, 30-70, 20-80 wt%) ceramic composites are synthesized by uniaxial hotpressing. Their thermal and mechanical properties are evaluated. The anisotropy of thermal conductivity and thermal expansion coefficient decreases and the mechanical strength increases with increasing aluminum nitride content. Hexagonal boron nitride gives large anisotropies of these properties of the composites even for aluminum-nitride-rich compositions.

The synthesis of diamond films using radio-frequency (13.56 MHz) glow discharge plasma chemical vapor deposition (CVD) is investigated. A variety of films are prepared from a mixture of ethyl alcohol and hydrogen, and they are evaluated using Raman spectroscopy. Diamond films grow when external heating is used in combination with the radio-frequency glow discharge. The films grow at temperatures between 350 and 800°C. In this temperature range, film of reasonable quality is obtained at 550∼600°C. The diamond grows even at the low temperature of 350°C although it contains a few nondiamond carbons. These temperatures are considerably lower than those generally regarded as the optimal regime for diamond growth.

Aiming at the precise profile control of Si_1-xGe_x, selective epitaxial growth (SEG) conditions and Si_1-xGe_x growth were investigated by ultrahigh-vacuum chemical vapor deposition (UHV-CVD) using Si₂H₆ and GeH₄. As long as the total amount of Si₂H₆ did not exceed the critical amount, Si- and Si_1-xGe_x-SEG were both achieved independent of source gas flow rate and substrate temperature. The Ge fraction x of Si_1-xGe_x could be decided by the flow rate ratio between Si₂H₆ and GeH₄, independent of substrate temperature. Fast gas flow switching realized the formation of a Si(120 Å)/Si_1-xGe_x(69 Å) strained layer superlattice at 587°C.

The thermal annealing properties of B⁺ implantation in HgCdTe are investigated by the electrolyte electroreflectance technique. The various thermal annealing conditions, such as temperature, time, and presence or absence of ZnS encapsulated passivation, are used as parameters to study the surface properties of HgCdTe and are characterized by electrolyte electroreflectance spectroscopy. We found that Hg accumulates near the surface region of an encapsulated sample, and Hg is lost at a depth of 1600 Å. The quality of the crystal is much improved when the sample is annealed at 200°C for a duration of over 30 minutes.

The apparent surface corrugation of highly oriented pyrolytic graphite (HOPG) was investigated with a scanning tunneling microscope (STM) in air using mechanically polished PtIr tips. It was found that the tunneling resistance was the most dominant parameter governing the observed atomic corrugation. The tunneling resistance was defined by the ratio of bias voltage to tunneling current required for STM measurements. The maximum corrugation of about 0.3 nm was attained at the tunneling resistance around 10⁷ Ω. The dependence of the corrugation upon tunneling resistance is qualitatively explained taking into account the variation of tip function, by means of both the elastic deformation of the sample surface and the separation change of the tip and surface.

The microstructure of TiN and TiO_xN_y films deposited on Si(100) substrates in an Ar-N₂ or an Ar-N₂-O₂ gas mixture was evaluated with a high-resolution field emission scanning electron microscope (FE-SEM). The TiN films deposited under an applied negative substrate bias have an extremely dense microstructure with hillocks on the film surface caused by the high compressive stress. The addition of oxygen modifies the microstructure of TiN film, i.e., the hillocks disappeared on the surface of TiO_xN_y by virtue of the stress relaxation effect. It has been found through the experiment of internal thermal diffusion by annealing Al/TiN (or TiO_xN_y)/Si in a vacuum that the diffusion barrier performance of the films is associated with the microstructure and internal stress in addition to the oxygen content itself.

A direct Monte Carlo simulation of secondary electron emission from Al is carried out in order to describe its dependence on the incident angle. The results show that the dependence of the electron yield at low energy is under the inverse cosine of the angle measured from the surface normal. At high energy, however, it is slightly over the inverse cosine at least for angles of less than 60°. These are mainly caused by small penetration and large backscattering of primary electrons for high incident angles. The calculation describes the experiment better than the conventional simulation based on continuous slowing-down approximation. Furthermore, the energy and angular distributions of emitted secondary electrons are insensitive to the incident angle. In electron emission statistics at higher energies than an energy where the secondary electron yield is maximum, the probabilities for no emission and high n electron emission (n>2) are larger than the Poisson distribution, being enhanced for high incident angle due to the backscattering.

Time-resolved luminescence spectra and electron spin resonance (ESR) spectra were measured at 300 K and 77 K in CdSSe-doped glass. Intense light irradiation accelerates the decay of luminescence. The change in ESR spectra is indicative of the creation of recombination centers by irradiation.

The ultralow resistivity in Langmuir-Blodgett heterofilms reported by T. Hino and M. Kushida is deliberated in this paper. A false ultralow resistivity may be caused by the very thin and nonuniform top Au films and by the miscounting the total current, I, as the current in the top Au films only.

The W values and Fano factors for 5.3 MeV alpha-particles have been measured with a gridded ionization chamber and are found to be 43.3±0.3 eV and 28.9±0.2 eV, and 0.24±0.02 and 0.11±0.02 for pure helium and helium+argon (1%), respectively. The W values for both gases agree fairly well with theoretical estimates as well as with previous experimental results and especially with the results of Jesse. The corresponding Fano factors, however, are significantly large compared with those theoretically calculated for the case of electron incidence. The reasons for this difference are discussed.

With the development of the pseudospark device, glow discharge with high power has recently become of interest. In this study, the voltage across a gap, the discharge current and the glow duration have been measured during transient glow discharge in the pressure range of 40-130 Torr in nitrogen. The results show that there exists a large difference between a previous investigation by Chalmers (1971) and the present study in the quantity of energy dissipated in the gap during the transient glow. However, in regard to the volume density of energy dissipated in the cathode fall, the values obtained by Chalmers and the present authors almost agree. From this result it is considered that the energy density is more essential than the energy quantity with respect to the transition of discharge from a transient glow to an arc.

A multi-ring-cusp-type surface magnetic field is tested for production of large-diameter electron cyclotron resonance (ECR) plasma. The density and its distribution are improved by means of a new launching system consisting of an adjustable antenna and a microwave suppressor inserted into the vacuum chamber, which forces the microwave to propagate into the plasma from the stronger side of the surface magnetic fields.

A microwave magnetron plasma source which excited the plasma inside the open-end of a coaxial line is described. Experiments are carried out to measure plasma parameters and external circuit elements. The coupling of the plasma and microwave is analyzed for the magnitude of the reflection coefficient. It was found that the self-bias between plasma and inner conductor of coaxial line is dependent on the reactance of the external circuit elements.

In atomic vapor laser isotope separation (AVLIS), an ion collection method which has a short collection time and low applied potential is required. We demonstrated that by using a positively biased wire electrode, the ions are collected from the laser-induced plasma in a shorter time at the same applied potential or at lower electric potential in the same collection times compared with the conventional parallel electrode method. The ion collection times could be estimated using simple one-dimensional models for both the wire electrode method and the parallel electrode method.

Plasma cleaning by use of hollow-cathode discharge, where RF voltage was supplied with the same phase on both electrodes, was investigated in a CHF₃-SiO₂ parallel-plate-type dry-etching system. The plasma cleaning by use of the hollow-cathode discharge has achieved a high plasma-cleaning rate, because the electrons were confined by the opposite ion sheaths' electric field and high-density plasma was generated between the electrodes. With the heating of the reaction chamber wall, the plasma-cleaning rate was increased and the deposition rate of the plasma-polymer was decreased. The temperature of the reaction chamber wall was found to be one of the important parameters affecting the etching characteristics, such as the SiO₂/poly-Si selectivity.

An electron cyclotron resonance (ECR) plasma is produced with a slotted Lisitano coil, and the axial distribution of the plasma parameters is measured in detail for different magnetic field configurations. It is found that the plasma density in uniform magnetic fields axially decreases more slowly than that in divergent magnetic fields. Furthermore, carbon films are formed by ECR plasma chemical vapor deposition (CVD), and the deposition rate obtained in the uniform magnetic fields is found to be larger than that obtained in the divergent magnetic fields.

Electron energy distribution functions in a low-pressure rf discharge (<1 mTorr) were measured with an electrostatic energy analyzer facing the powered electrode and the bulk plasma. Electrons with high energy were observed in the former case, whereas the distribution of electrons was almost Maxwellian in the latter case.

Kinetic calculations in microwave discharges have been carried out for experimental conditions currently employed to grow diamond layers. The effects of plasma parameters such as the nature of the electron energy distribution function (eedf), the electron density (N_e), and the electron temperature (T_e) have been investigated. It has been pointed out that ion-molecule reactions do not notably modify the plasma composition in the range of electron density 10¹⁰-2×10¹² cm^-3. In addition, the plasma chemistry is greatly influenced by the amount of H atoms present in the discharge. Finally, the hydrocarbons produced in the discharge have been classified into two categories, CH_x (0≦x≦3) radicals and C₂H_y (0≦y≦6) neutrals, and diamond deposition can be related to plasma compositions.

Basic characteristics of a particle detection method using laser breakdown were studied for a system of polystyrene standard particles dispersed in ultrapure water. The method was able to detect 0.02 µm particles. The detection sensitivity decreased with the particle size due to size dependence of the laser breakdown threshold. The plasma emission delay time from the laser pulse decreased with particle size (9.8±0.8 ns for 0.04 µm, 5.7±0.8 ns for 3.0 µm). The above results suggested the possibility of concentration and size measurement of fine particles in liquids by the proposed method.

A microwave caliper used for performing noncontact measurements of the thickness of dry sheet materials is developed using a microwave coaxial cavity resonator. Since the coaxial cavity is open-ended on one side, even a thick sheet material can be measured. High resolution of thickness is obtained due to a strong electric field on the open circuit plane of the cavity. The fringing electric field distribution of the open-ended coaxial cavity, which has been difficult to observe, is monitored as a thermal distribution by a thermography. The frequency shift of a resonance peak is found to be closely related to the dielectric constant.

In conventional semiconductor high-energy photon detectors, photon-counting sensitivity decreases with increasing photon energy. To use semiconductor detectors for dosimeters, we need to reduce this energy dependence of the sensitivity to within ±20% variation in the photon energy range of 60 keV to 6 MeV. This can be realized by detecting secondary electrons generated by high-energy photons in the undepleted region around the depleted region. In studies on the design of an efficient pattern and size for such electrodes based on this principle, we found that, for an a-Si:H/c-Si heterojunction detector, an asterisk-patterned electrode composed of a 1-mm-dia. circle with 4 to 6 projections can satisfy the required energy dependence of the sensitivity.

A measurement system for the velocity distribution of sputtered neutral particles by means of multiphoton resonance ionization spectroscopy (MPRIS) combined with the time-of-flight (TOF) technique was formulated using the simple linear response theory in matrix form. The relationship between each parameter for the measurement and the observed TOF spectrum could be indicated visibly in the present form. It was demonstrated that the optimum condition for the velocity distribution measurement can be derived easily with the present method. It was also demonstrated that the velocity distribution measured is seriously affected by the pulse shape of the primary ion beam.

The key processes of silicon-wafer direct bonding (SDB), including hydrophilic surface formation and optimal two-step heat treatment, have been developed However, H₂SO₄/H₂O₂ solution being a strong oxidized acid solution, native oxide is found to have grown on the wafer surface as soon as a wafer is treated in this solution. In the case of a wafer further treated in diluted HF solution after hydrophilic surface formation, it is shown that the wafer surface can not only be cleaned of its native oxide but also remains hydrophilic, and can provide excellent voidless bonding. The N⁺/P and N/P combination junction mesa diodes fabricated on the wafers prepared by these novel SDB technologies are examined. The ideality factor n of the N/P mesa diode is 2.4∼2.8 for the voltage range 0.2∼0.3 V; hence, the lowering of the ideality factor n is evidently achieved. As for the N⁺/P mesa diode, the ideality factor n shows a value of 1.10∼1.30 for the voltage range 0.2∼0.6 V; the low value of n is attributed to an autodoping phenomenon which has caused the junction interface to form in the P-silicon bulk. However, the fact that the sustaining voltage of the N/P mesa diode showed a value greater than 520 V reveals the effectiveness of our novel SDB processes.

The sidewall damage induced by reactive ion-beam etching (RIBE) with Cl₂ has been studied. The sidewall damage depth was estimated from the ion-beam-angle dependence, and the photoluminescence (PL) emitted from the etched sidewall of a GaInAsP/InP DH wafer was directly measured. The sidewall damage depth of an InP substrate was estimated as less than a few hundred angstroms at an extraction voltage of 400 V. The PL intensity from the sidewall of a GaInAsP/InP DH wafer decreased considerably after RIBE, compared with that of a cleaved facet. The deteriorated PL intensity was recovered remarkably through passivation with (NH₄)₂S_x.

The range profile of the most abundant stable boron isotope, ¹¹B, implanted into three wafers made of the three stable silicon isotopes, ²⁸Si, ²⁹Si and ³⁰Si, in the energy range between 0.4 to 2.0 MeV, has been studied by the Monte Carlo program TRIM. It is found that the implantation profile depends strongly on the isotopic state of the silicon wafer. Also, it is concluded that the presence of the least abundant stable silicon isotope, ³⁰Si, in a silicon wafer of natural abundance, influences the shallow tail of the implantation profile.

An improved multilayer structure of a metal pad is developed for Au wire bonding to a monolithic IC. The proposed structure of the pad is Ti(2.5 nm)/Cu(800 nm)/Ti(70 nm)/Al(130 nm) on SiO₂/Si substrates. Thermosonic Au wire bonding to the pad shows good bondability after heating at 473 K for the storage time of 3.6 ks in air. During heat treatment at 473 K after bonding, the bond between the Au wire and the pad is not degraded.

The monostatic radar cross-sectional spectra of rotating multiple skew-plated metal fan blades are investigated. The theoretical treatment of such a slowly rotating and electrically large scatterer is based on the quasi-stationary method together with physical optics/physical theory of diffraction (PO/PTD) equivalent current techniques. Only the θθ polarization case is considered here, but the φφ polarization case can be treated in the same way. This solution is applicable to any observation angle, and is represented by such a general form as one which enables us to treat a similar scatterer with multiple blades and with different skew angles. Three rotating skew-plated blades are taken as an example, and the agreements between the theoretical and experimental results are satisfactory.

It is known that thiol-containing compounds form monolayer membranes on a gold surface via chemisorption from organic solvents in terms of a strong connection ability between thiol and the metal. Here we prepared different kinds of thiol-containing lipids and fabricated monolayer membranes on the gold disk electrode whose surface structures were similar to biological membranes. Responses of this lipid-coated electrode to odor substances were examined by an electrochemical method of a cyclic voltammetry. Blocking ability for the redox reaction of Fe(CN)₆^3- was found to change upon adsorption of odor substances into monolayer membranes. The order of threshold values to detect the odorants was β-ionone<β-citral<chloroform≦n-amyl acetate; this order was the same as that in the human olfactory sense. The present study indicates that the monolayer membrane of thiol-containing lipids can be useful as a transducer of an odor sensor.