Showing papers in "Japanese Journal of Applied Physics in 1979"

Liquid-Crystal Lens-Cells with Variable Focal Length

Abstract: Liquid-crystal cells shaped like a plano-convex lens or a plano-concave lens are prepared. The focal length can be varied from the value fe for an extraordinary ray, where the liquid-crystal cell takes a homogeneous alignment, to fo for an ordinary ray, where it takes a homeo-tropic alignment, by applying an electric field or a magnetic field across the lens-cell. The focal length in the lens-cell with the homogeneous alignment can also be switched between fe and fo. This is done by switching the direction of polarization of the incident light by applying a voltage across a TN cell sandwiched between the polarizer and the lens-cell. Since the thickness of the liquid-crystal layers increases in the lens-cells, the optical transmission properties are investigated as a function of the cell thickness.

A New Method to Determine Effective MOSFET Channel Length

Abstract: An accurate and convenient method to determine an effective MOSFET channel length is proposed. This method is based on a computer aided evaluation of an intrinsic MOSFET channel resistance without using special test devices. N-channel silicon-gate MOSFETs were fabricated, and the channel length and its range of device to device scatter were evaluated . To define an effective channel, a simple model of the source-drain (S-D) diffusion layer is proposed. This model shows that the expected transition layer resistance between the S-D diffusion layer and the inverted channel layer agrees with the experimental results. The accuracy of this method is also discussed. It is found to be better than 0.1 µm.

Deep Level Transient Spectroscopy of Bulk Traps and Interface States in Si MOS Diodes

Abstract: Deep-leve transient spectroscopy (DLTS) of bulk traps and interface states in Si MOS diodes are theoretically studied and energy levels, capture cross-sections and spatial and energy density distributions of majority-carrier traps are measured. In P+-implanted unannealed MOS diodes, four bulk traps are measured at Ec-0.18 eV, Ec-0.20 eV, Ec-0.31 eV and Ec-0.45 eV. Their spatial distributions are found to be the same among them within experimental error and thought to be corresponding to the distribution of implanted ions qualitatively. Bulk traps are distinguished from interface states experimentally. The capture cross-section of interface states in non-implanted MOS diodes are measured to be of the order of 10-16 cm2 in the energy range of Ec-0.15 eV to Ec-0.30 eV. The interface state density measured with DLTS is found to be in a reasonable agreement with those detetmined by other methods.

Electrical Properties of p- and n-Type CuInSe 2 Single Crystals

Abstract: The electrical resistivity and Hall effect of p- and n-type CuInSe2 single crystals are measured in the temperature range from 80 K to 500 K p- and n-type samples are prepared by doping with excess Se and excess In, respectively The acceptor levels at 0020 eV and 0028 eV above the valence band and the donor levels at 0012 eV and 018 eV below the conduction band are identified The mobility data are analysed assuming scattering by acoustic, polar optical, and nonpolar optical phonons and by ionized impurities For some of the n-type samples, the measurements are extended to liquid helium temperature and the result is analysed by the existing theories of impurity band conduction

Temperature Sensitive Threshold Current of InGaAsP-InP Double Heterostructure Lasers

Abstract: The threshold current of InGaAsP–InP double hetetostructure lasers has been investigated through measurements of the temperature dependence of carrier lifetime and radiative efficiency. Both the carrier lifetime and the radiative efficiency decrease noticeably above the break point temperature as observed in the Ith vs. T relation. The decrease of the carrier lifetime is explained by considering additional non-radiative recombination centers with 0.3 eV activation energy. The origin of this center is also discussed.

Studies of Neutron-Produced Defects in Silicon by Deep-Level Transient Spectroscopy

Abstract: Majority-carrier traps produced in silicon by fast neutron irradiation were studied by the deep-level transient spectroscopy (DLTS). The measurement technique of the DLTS was developed, which was similar to that using a lock-in amplifier, but had some advantages over it. Three electron traps (E1, E2 and E3) and two hole traps (H1 and H2) were observed in fast-neutron-irradiated n- and p-type silicon, respectively. The energy levels and majority-carrier capture cross sections for these traps were determined. The introduction rates of E1 (Ec-0.15 eV), E2 (Ec-0.21 eV), E3 (Ec-0.39 eV), H1 (Ev+0.15 eV) and H2 (Ev+0.34 eV) were 4.7, 1.4, 3.2, 1.8 and 5.5 cm-1, respectively. Comparison with other published data was also made.

(Invited) Characterization of Plasma-Deposited Amorphous Si: H Thin Films

Abstract: Amorphous Si: H is a materials system that possesses several distinct local environments for the hydrogen. The evidence discussed in this paper suggests that it is the distribution of the hydrogen between these environments and not the total hydrogen content that is the crucial factor in determining defect density. The material that possesses the "optimum" properties for device applications is a homogeneous silicon hydrogen compound that contains hydrogen bonded as either Si-H or SiH2. The primary structural defect in this system is a void associated with (SiH2)n. These voids are oriented parallel to the growth direction of the film and the dangling bonds on their internal surfaces form deep defect states that act as efficient non-radiative recombination centers.

Optical Constants of Polycrystalline 3d Transition Metal Oxides in the Wavelength Region 350 to 1200 nm

Abstract: The refractive index and the extinction coefficient of polycrystalline oxides of Ti, V, Mn, Fe, Co, Cu, and Zn are determined from the measurement of the ratio of the reflection coefficients for incident light polarized parallel and perpendicular to the plane of incidence. The absorption coefficient and the reflectivity for light of normal incidence are calculated from the data. Among these oxides, CuO has a large extinction coefficient and a rather small refractive index, and hence a large absorption coefficient and a medium reflectivity, over the solar spectrum.

Effects of Heat-Treatment on Crystal Phases, Microstructure and Electrical Properties of Nonohmic Zinc Oxide Ceramics

Abstract: An investigation was carried out of the effects of heat-treatment (h.t.) on the crystal phases, microstructure, and nonohmic properties of ZnO ceramics consisting of ZnO containing dissolved Co and Mn; Zn7Sb2O12 spinel (SP) containing dissolved Co, Mn, and Cr; and β, δ-Bi2O3 containing dissolved Zn and Sb. The properties change with h.t. temperature, and the changes are closely related to each other. The nonohmic exponent α decreases greatly at 700° to 800°C, where the intergranular (i.g.) layer is coarsened by the phase transformation of β, δ-Bi2O3 into γ-Bi2O3. The α-value again changes abruptly and almost recovers at 800° to 900°C, where the dense i.g. layer is reconstructed from the Bi2O3-rich liquid (B.r.l.) formed by the melting of γ-Bi2O3. The α-value gradually recovers at 900° to 1100°C with the decrease of Cr in δ-Bi2O3 solid solution (δ-S.S.) and the decrease of Zn2Bi3Sb3O14 pyrochlore (PY) by reaction with ZnO. The formation of δ-S.S. and the decrease of Cr in it are brought about by the movement of Cr from the SP to the B.r.l. around 900°C and from the B.r.l. to the SP above 900°C, respectively. The PY is formed by partial reaction between the SP and the B.r.l.around 900°C. The phases, microstructure, and α-value recover completely around 1100°C.

A Non-Destructive Method for Determining the Eu2+ Concentration in the Alkali Chlorides

Abstract: Single crystals of NaCl, KCl and RbCl doped with divalent europium up to 600 p.p.m. were grown by the Czochralski technique. Taking advantage that the Eu2+ ion produces two optical absorption bands in these crystals, calibration constants for determining the Eu2+ concentration in the alkali chlorides by optical techniques are reported. Oscillator strengths of the absorption bands were calculated from the knowledge of the divalent europium concentration. In addition, the distribution coefficient of Eu2+ in NaCl, KCl and RbCl single crystals was determined by the use of this nondestructive method.

Fabrication and Characterization of SnO2/n-Si Solar Cells

Abstract: SnO2/n-Si solar cells fabricated by the spray pyrolysis technique display significant photovoltaic effects when exposed to sunlight. These solar cells have a thin insulating layer at the SnO2/n-Si interface. The presence of the thin insulating layer can increase the open-circuit voltage by increasing the diode quality factor and by reducing the dark saturation current. The performance of this heterojunction solar cell was an open-circuit voltage of 0.52 V, short-circuit current of 21.0 mA/cm2, fill factor of 0.53 and conversion efficiency of 7.2%. The relative photospectral response above fifty percent spreads in a range of 420 to 1020 nm and is wider than that of conventional Si p-n solar cells. One possibility for cost reduction lies in the method of junction fabrication, and the idea of a simply deposited SnO2/n-Si junction is very attractive.

Ferroelectric Properties of RF Sputtered PLZT Thin Film

Abstract: A series of technical data for the preparation of ferroelectric thin film PLZT by RF sputtering at substrate temperatures lower than 400°C with subsequent annealing is described. Films with dielectric and optical properties of considerable quality have been obtained under certain conditions. Parametric changes in the dielectric, optical and pyroelectric properties according to sputtering, annealing conditions and film thickness have also been clarified. The dielectric properties depend heavily on film thickness. Well-annealed thick films have dielectric constants nearly equal to those of ceramics. Discussion on the thickness dependence of dielectric properties and on the effects of the packing density of PLZT and other preparation conditions is made.

Photoelectric Emission and Contact Charging of Some Synthetic High Polymers

Abstract: Surface states of nylon 6, polyethylene, and polypropylene are investigated using external photoelectric emission. These polymers seem not to have exact threshold energies. The top edges of the filled surface-states of polymers are located near 4 eV from the vacuum level. From the measurement of electron-irradiated samples, the polymers are found to have traps distributed above and below the top edge of the filled state. The charging tendency of polymers depends on the distribution of both the filled and the trap levels.

Correspondence between Layered Cell Structures and Slip Lines in Deformed Copper Single Crystals

Abstract: Layered cell structures in deformed copper single crystals with the [112] and the [415] tensile axes were observed by transmission electron microscopy on slices with (1), (10), and (001). It was confirmed that cell walls are formed on planes rotated around the axis on the active slip plane to a definite direction with respect to the tensile axis. The rotation angles were measured as a function of tensile stress. The slip line lengths on the two side planes were measured by optical microscopy. The slip line lengths and the ratios of the slip line lengths of edge dislocations to those of screw dislocations agree approximately with the slip distances estimated from the spacing and the rotation angle of the cell walls, assuming that the cell walls of the primary system are obstacles for primary dislocations. It is concluded that the slip line length is mainly determined by the layered cell structure.

Anomalous Transient Currents in High-Density Polyethylene around 50–70°C

Abstract: Transient currents in high-density polyethylene have been investigated at various temperatures and applied fields. A distinct difference between the transient charging and discharging currents suggests that they are attributable to space charge in the sample. The charging current peak around 70°C was explained on the basis of transient SCLC theory, and the carrier mobility was estimated to be 0.5–2.0×10-10 cm2/Vsec at 70°C. Anomalous discharging currents flowing in the same direction as the charging current were observed at 50 and 70°C, and they were concluded to be caused by the injected home space charge and the partial blocking of a metalpolymer contact.

Low Threshold Current Density (100) GaInAsP/InP Double-Heterostructure Lasers for Wavelength 1.3 µm

Abstract: Low threshold current density (100) GaInAsP/InP DH lasers emitting at 1.3 µm with thin active layer were studied experimentally and theoretically. The two phase solution growth technique was applied with low cooling rate of 0.08°C/min, which gave 0.05 µm thick uniform active layer. The threshold current density was minimized down to 770 A/cm2 with 0.13 µm thick active layer by reducing the concentration of Zn dopant, whereas the normal V–I characteristic was kept. The residual internal and the external absorption losses of the active layer were estimated to be about 70 cm-1 and 30 cm-1, respectively, in order to know the theoretical threshold limit. The narrowest beam divergence obtained was 23° for the active layer 0.05 µm thick. Both the threshold current density dependence on the thickness of the active layer and the beam divergence were in good agreement with the theory which was calculated by using the relative refractive index difference of 8.7%. A narrow stripe laser with undoped thin active layer had a tendency to emit in a single longitudinal mode.

Interference Electron Microscopy by Means of Holography

Abstract: Electron holography was applied to interference microscopy by means of the phase-difference amplification technique. Image electron holograms were formed with a field emission electron microscope. Phase-amplified interferograms and contour maps were obtained by the illumination of two laser beams onto the holograms, at the optical reconstruction stage. The method was effectively applied to electron microscopic specimens such as polyhedral fine particles whose phase changes sometimes had not been large enough for interference microscopy.

Spherical-Aberration Correction of an Electron Lens by Holography

Abstract: Electron image holograms of a crystalline fine particle are made with a field emission electron microscope. The spherical aberration of the electron lens is corrected in the optical reconstruction stage, using an optical lens as a compensator. Lattice images separated from the particle in the exactly focused electron microscopic image are formed inside the particle in the spherically corrected image and give correct information on the crystal lattice of the gold particle.

Temperature Dependence of Tetragonal Distortion and Crystal Field Splitting in CuGaS 2

Abstract: The lattice parameters and crystal field splitting of the uppermost valence band in CuGaS2 are measured as a function of temperature. The linear thermal expansion coefficients along the "a" and "c" axes are estimated to be 11.2×10-6 and 4.1×10-6 respectively, and the axial ratio, c/a, changes with a coefficient of -9.0×10-6. This result indicates an "increase" in tetragonal distortion, (2-c/a), with temperature, and hence, an increase in crystal field splitting is expected. However, the apparent crystal field splitting shows a slight "decrease" with temperature. An attempt to explain this contradictory feature is discussed using the concept of the p-d hybridization effect on crystal field splitting.

Electron Microscopic Studies of Structure and Crystallization of Amorphous Metal Oxide Films

Abstract: High-resolution transmission electron microscopy using axial beam illumination was carried out on vacuum-deposited WO3, TiO2, and MoO3 films. In as-deposited WO3 films thinner than 100 A and films heated at 350°C for 2~5 h which gave rise to amorphous haloes in electron diffraction, crossed fringe-like structure images of the order of 10~20 A was observed. This means that the amorphous films consisted of micro-crystallites in which the W–O6 octahedra were arrayed like crystalline WO3. When the films were heated at 350°C for 10 h, they grew to crystallites of WO3 as large as 100 A. On the other hand, in WO3 films thicker than about 200 A, crystals of a few microns grew after shorter heat treatment. Similar results were obtained for the TiO2 and MoO3 films. The differnce in crystallization between the very thin films and the thicker films is interpreted by considering the heat generated during crystallization and its dispersion.

Desities of Amorphous Thin Films

Abstract: The densities of amorphous Ge, C, SiO, Se, and WO3 films prepared by vacuum-evaporation were measured using multiple beam interferometry in combination with an oscillating crystal microbalance. Optically polished quartz crystals were used as both the microbalance sensing elements and the substrates for interferometry. The film densities were found to be independent of thickness. The measurements indicated that the amorphous film densities were 23–31% less than the crystalline bulk densities and 13–14% less than the amorphous or vitreous bulk densities. This density decrease may be attributed to voids, the presence of which is deduced from a microcrystalline model of the amorphous structure confirmed by recent high-resolution electron microscopic observation.

Numerical Solution of Phosphorus Diffusion Equation in Silicon

Abstract: Based on the pair diffusion model that phosphorus in silicon diffuses only via the diffusion of E centers and on the assumptions that the vacancy formation energy decreases with an increase in the phosphorus concentration and that the binding energy between a vacancy and a phosphorus atom is constant, phosphorus diffusion equations are obtained. P+, V+, V0, V-, V-, E0 and E- (P, V and E denote a phosphorus atom, a vacancy and an E center respectively and a superscript denotes the charge state.) are taken into account in the equations. Choosing parameters suitably, anomalies in the phosphorus diffusion, that is, a kink and a tail, are well explained.

Cd1-xZnxS Films for Low Cost Solar Cells

Abstract: Cd1-xZnxS films suitable for use in solar cells have been produced by a low cost chemical spray process A series of technical data to make the films having uniform composition covering the range 0 to 90% ZnS concentration has been presented and the dependence of energy gap, crystal habit, X-ray and electron diffraction patterns on composition are investigated The transition from the wurtzite structure of the zinc blende form takes place at 80 mole% ZnS concentration The band gap has a nearly linear variation with composition except at x=1 where the material becomes amorphous and has a energy gap Eg≈32 eV which is smaller than that in the polycrystalline ZnS case Doping of 5% Indium Cd1-xZnxS (x=01) decreases the resistivity from 104 ohm cm to \Lesssim102 ohm cm which is necessary for optimum photovoltaic effciency in a Cd1-xZnxS–Cu2S solar cell

Cotton-Mouton Effect of Alkyl- and Alkoxy-Cyanobiphenyls in Isotropic Phase

Abstract: The magnetic field induced birefringence Δn has been measured for nCB (n=5–8) and nOCB (n=3, 5–9). Sufficiently above the clearing temperature Tc, all the materials investigated, except 7OCB, satisfy the relation Δn/H2=λKC/(T-Tc*) over a wide temperature range of 20°C or more. Here λ=633 nm is the wavelength used, Tc* a temperature slightly lower than Tc, and KC a constant. The anomaly observed in 7OCB is impurity sensitive. As the alkyl chain length increases, KC drops appreciably; 3OCB has the largest value, KC=2.98×10-10°C cm-1 G-2, while 7CB has the smallest value, KC=0.99×10-10. Near Tc, on the other hand, Δn/H2 becomes larger than the above relation predicts. The two constants Tc-Tc* and KC are not enough to characterize the materials; (Δn/H2)T=Tc is also an important factor. Among the materials investigated, 5OCB has the largest value of (Δn/H2)T=Tc, namely 2.50×10-14 G-2.

Sputtering of Si with keV Ar+ Ions. I. Measurement and Monte Carlo Calculations of Sputtering Yield

Abstract: Sputtering has been studied both in experiment with an ion microprobe analyzer and in theory by a Monte Carlo calculation technique. For the sputtering yield, the experiment has been performed with uniform argon ion beam for polycrystalline silicon and calculations based on the binary collision model have been made for amorphous silicon at ion energies of 3, 5 and 10 keV for angles of ion incidence θ=0°, 45° and 60°, respectively. Monte Carlo calculations are compared the sputtering yields as a function of energy and angle of incidence. Some theoretical results are also shown for angular distributions of the sputtered atoms to see the qualitative tendency of the preferred angle of sputtered atoms with primary ion energy for inclined incidence.

Analytical Approximations in the Theory of Relativistic Thomson Scattering for High Temperature Fusion Plasma

Abstract: The light scattering spectrum from a high temperature plasma is calculated for the second order in v/c (c=light speed) and the second order approximate formula is obtained from the calculation. The blue side shift of the peak derived from the second order approximate formula agrees well with that of the full relativistic spectrum for an electron temperature of several tens of kilo electron-volts and less. The second order apparent temperature and density are deduced with an accuracy of better than 8 percent in the range up to 20 keV and 100 keV for scattering angles θ=90° and 50°, respectively, by application of the least-square procedure.