bluuebunny/crossref_metadata_2025 huggingface dataset:
Voltage fluctuations in low-current atmospheric arcs
Authors: Gray Eoin W.
Published: February 2004

Large amplitude fluctuations in the arc potential in the initial phase of an arc have been examined for a low-current resistive break arc at atmospheric pressure. These fluctuations were accompanied by an increase in the emitted intensity of the light coming from Pd I, N2+, and N2*, and a leveling of the light from Pd II, suggesting that the initial metallic vapor arc maintains itself by ionizing the surrounding gas. As the gap increases, the arc characteristically enters a second phase in which the discharge is maintained in the gaseous environment.
GaAs diode-pumped Nd : YAG laser
Authors: Rosenkrantz L. J.
Published: February 2004

Using a single chip heterostructure GaAs laser diode as a pump source, and temperature tuning its output wavelength to achieve a spectral overlap with the 8680-Å absorption line in Nd : YAG, lasting was observed in a 1.5-mm-diam×25.4-mm-long laser rod. Pump light was directed through a special multilayer dielectric coating on one end of the laser crystal. This coating was designed to transmit 90% of the GaAs light, but still reflect internally 99.9% of the YAG laser light at 1.06 μ. The purpose of the end-pumping technique was to maximize the single-pass absorption of GaAs pump light by making the effective optical path within the laser rod as long as possible, thus compensating for the relatively weak absorption at 8680 Å in YAG laser crystals.
Lattice match in the heteroepitaxy of III-V compound alloys
Authors: Moriizumi Toyosaka , Takahashi Kiyoshi
Published: February 2004

By using Pauling's tetrahedral covalent radii, the procedure for choosing the pair of a III-V compound semiconductor and a III-V alloy semiconductor with good lattice match is discussed in general. When a III-V compound is given for a substrate crystal, the composition of the alloy to be grown with the best lattice match on the substrate is easily determined from the fundamental equations derived in this study. It is demonstrated that for the GaAs substrate the grown alloy should be AlxGa1−xAs (if the alloy contains no P), or AlxGa0.5−xIn0.5P (if the V atoms in the alloy are P atoms only).
Surface barrier energies on strontium titanate
Authors: Neville R. C. , Mead C. A.
Published: February 2004

The metal-semiconductor surface-barrier systems consisting of the metals gold, palladium, copper, or indium on chemically prepared or cleaved strontium titanate surfaces have been investigated in detail. Surface-barrier energies have been studied by photoresponse, forward current versus voltage, and thermal activation energy techniques yielding values in excellent agreement with each other. Forward current-voltage characteristics were in quantitative agreement with simple diode thermionic theory as modified by the inclusion of image force lowering. The reverse current-voltage characteristic of these stable barriers also is in agreement with that expected from thermionic theory including simple image force lowering over a bias range from −0.1 to −4 V.
Spin-wave correlator
Authors: Schulz M.
Published: February 2004

Real-time convolution has been obtained by parametric mixing of two opposite traveling spin waves in a thin YIG platelet. The efficiency of this spin-wave correlator is very relative to acoustice surface-wave correlators because of the inherent nonlinearity of the spin waves. For frequencies below 2500 MHz the correlator can be operated in a phase-matched mode. Experimental results for 1.8 and 4.1 GHz show a high efficiency and a frequency dependence in accord with theory. For a phase-matched operation at 1.8 GHz an outpout of 1 mW has been obtained for 10 mW total input power. The measured dynamic range of the correlator was 80 dB.
Wave-vector dependence of rare-earth relaxation in yttrium iron garnet
Authors: Scotter D. G.
Published: February 2004

A wave-vector dependence of the parallel-pump spin-wave linewidth in rare earth doped YIG is reported. The spin-wave linewidth (ΔHk) has the form ΔHk = a + a′c + (b + b′c)k. The a's and b's are constants with the primed values dependent on the particular rare earth and c is the rare-earth doping level. Values of b′ are 1.8±0.2, 3.55±0.3, and (11.6±0.5)×105 Oe cm/at.% rare-earth doping level for samarium, holmium, and terbium, respectively. The k dependence may be due either to a k dependence of the longitudinal relaxation mechanism or to a transit-time phenomena. These results show that the rare earths are more effective at increasing the high-power capability of ferrites than the extrapolated ΔHk→0 results would suggest.
Cd displacement threshold in CdS at liquid-helium temperatures
Authors: Elsby C. N. , Meese J. M.
Published: February 2004

The energy required to displace Cd atoms in CdS at 10 °K by irradiation with energetic electrons has been measured by observing the production of a cathodoluminescent band at 1.03 μm. This band is observed to increase in intensity for irradiations above a threshold of 125 keV in CdS platelets containing excess sulfur. A significant increase in the rate of growth of this band is observed above a second threshold at 314 keV which is attributed to cadmium displacements. This rate is proportional to the square of the electron beam energy near the second threshold.
Backscattering of electrons from gallium arsenide
Authors: Klein Wolfgang
Published: February 2004

The percentage of backscattered electrons from a 50–4000-eV primary electron beam was measured for clean (100), (110), (111)A, and (111)B GaAs surfaces. The incident beam angle vaired between 0° and 60° from the surface normal. The influence of cesium and cesium oxide layers on the backscattering coefficient was investigated for (100) GaAs.
Effect of nitrogen on the electrical and structural properties of triode-sputtered tantalum films
Authors: Willmott David J.
Published: February 2004

The structural and electrical properties of nitrogen-doped tantalum films, sputtered in a dc triode system, have been investigated. For constant sputtering voltage and current, the tantalum deposition rate decreased with increasing nitrogen flow rate; at a flow rate of 12 cm3 min−1, the deposition rate was 75% of the rate obtained without the addition of nitrogen. The density of the films decreased from 15.4 to 9.8 g cm−3 as the nitrogen flow increased from 0 to 12 cm3 min−1. The net effect on the film thickness is an increase from 2700 to 3800 Å for films on glass substrates. Films were also deposited on ceramic substrates at the same time. Both x-ray diffractometer and powder camera analysis showed that the films consisted of the bcc Ta phase at nitrogen flows up to 3 cm3 min−1 but the lattice was approximately 3% larger than for bulk Ta. The hcp Ta2N phase appeared at flow rates above 3 cm3 min−1 and the change from bcc Ta to hcp Ta2N was accompanied by an increase in the room-temperature coefficient of resistance from positive to negative values. For films on glass, the resistivity was approximately 250 μΩ cm as the nitrogen flow increased from 4 to 8 cm3 min−1 but the resistivity had a monotonic increase for films on ceramic substrates. The hcp Ta2N phase was replaced by the fcc TaN phase as the flow rate increased in this range; the latter phase had a preferred (111) orientation on the substrate. As the flow rate increased from 8 to 12 cm3 min−1, the resistivity increased rapidly for both types of substrates and the temperature coefficients became rapidly more negative. It is suggested that this behavior is due to the presence of an insulating nitride phase in the film.
Acoustic radiation by interdigitated grids on LiNbO3
Authors: Daniel Michael R. , Emtage P. R.
Published: February 2004

Measurements are presented which show the acoustic power radiated as a function of frequency by an interdigitated transducer on the surface of a lithium-niobate boule. Several peaks are seen which are identified as either surface waves or bulk longitudinal waves travelling close to the boule surface. The transducer is seen to cause radiation at all frequencies above that for fundamental surface-wave generation. Additionally, the signal radiated to a nearby transducer is measured. This signal comprises just surface waves and a weaker bulk longitudinal wave. These are associated with the peaks in the launched power spectrum if reflections are suppressed. In finite regular-shaped samples reflections cannot be entirely suppressed and cause many anomalous signals. Over-all the results show that the average strength of bulk-wave generation is at least an order of magnitude more than that of surface-wave generation.
A field-emission illumination system using a new optical configuration
Authors: Veneklasen Lee H. , Siegel Benjamin M.
Published: February 2004

A field-emission electron-beam illumination system employing an ``oxygen processed'' field emitter and a specially adapted optical configuration is described and experimentally evaluated. A preaccelerator lens, acting directly upon the beam emerging from the field-emission diode, allows the accelerator section to be used in a field-lens mode where the gun crossover remains stationary within the accelerating lens for a wide range of operating conditions. The gun is particularly insensitive to accelerator aberrations and to changes in the high voltage, tip voltage, and beam current, making it particularly suitable for high-voltage microscopy. Operating at 50 kV under conditions favorable for conventional transmission electron microscopy, measurements indicate a brightness of over 108 A/cm2/sr at a beam current of 10−8 A with 10 μA total emission current in satisfactory agreement with theoretical predictions. The discussion includes some general design considerations and performance predictions necessary for optimizing the field-emission system for application in conventional transmission electron microscopy.
Diffraction of electromagnetic plane wave by an infinite slit embedded in an anisotropic plasma
Authors: Hongo Kohei
Published: February 2004

Two-dimensional diffraction of an H-polarized electromagnetic plane wave by a slit embedded in an anisotropic medium is studied. The problem is formulated using the discontinuity characteristic of the Weber-Schafheitlin integral (WSI), and expressions for the diffracted fields and the surface wave trapped in the vicinity of the conducting screen are derived. The numerical results for the radiation pattern of a diffracted field are presented. The pattern is found to show an asymmetry for normal incidence. The solutions are valid for arbitrary small slit width and arbitrary anisotropy.
Electrical measurements in silicon under shock-wave compression
Authors: Coleburn N. L. , Forbes J. W. , Jones H. D.
Published: February 2004

The electrical behavior of p-type silicon in the (111) orientation was studied under shock stresses from 8 to 160 kbar. Positive electrical signals are induced in the crystals during passage of elastic shock waves. Maximum signal amplitude was detected below the Hugoniot elastic limit (55 kbar). Resistance-vs-stress measurements were made when the polarization signal was zero, i.e., no elastic waves were in the crystals. The resistance becomes very small near the elastic limit, indicating that a metallic state is reached. The relative resistance, R/Ro, then increases significantly at 133 kbar where a phase transition is indicated.
I-V characteristics of MOS capacitors with polycrystalline silicon field plates
Authors: Neugebauer C. A. , Burgess J. F. , Joynson R. E. , Mundy J. L.
Published: February 2004

The I-V characteristics of MOS capacitors utilizing polycrystalline p-type silicon field plates were investigated. It was found that sizable current flow is observable in both directions under pulsed dc conditions at voltages much below those at which current flows under applied dc. This suggests that the polycrystalline silicon film can be driven into avalanche and thus inject electrons into the oxide as well as the single-crystal Si wafer. Charge trapping during passage of avalanche injected currents was observed to occur principally at the silicon/oxide interfaces. The rate of trapping depended strongly on the boron content of the oxide.
Plasma parameters in gas discharges for positive-column He–Se+ lasers
Authors: Goto Toshio , Kano Hiroyuki , Hattori Shuzo
Published: February 2004

Electron temperature and density in gas discharges used for positive-column He–Se+ lasers measured with the probe method are described and compared with those for positive-column He–Cd+ lasers. It is shown that the electron temperature in the positive-column He–Se+ laser does not decrease very rapidly with increasing metal vapor pressure although it decreases significantly in the positive-column He–Cd+ laser. The changes of the electron densities in the two also are different. The importance fo the charge-exchange excitation mechanism and the difference of excitation mechanisms in the two are discussed.
Experimental study of argon ion laser discharge at high current
Authors: Wang C. P. , Lin Shao-Chi
Published: February 2004

Argon ion laser experiments have been performed in a large-bore segmented metal plasma tube. The tube is capable of maintaining a steady-state discharge current up to 500 A in low-pressure argon without excessive contamination. The experimental results on the discharge and lasing characteristics agree with recent theory. So far the maximum visible laser output at high discharge current is not yet limited by resonance radiation trapping or other saturation effects, but rather by a low inversion-utilization efficiency. A major cause of such low utilization efficiency is presently attributable to a severe optical degradation of the dielectric cavity mirrors when the internal-radiation flux density exceeds a certain limit (i.e., a few kW/cm2).
High-frequency electro-optic prism deflector with application to optical demultiplexing and multiplexing
Authors: Tsai C. S. , Yao S. K. , Kraushaar J. M.
Published: February 2004

The dc and the high-frequency performance of a LiNbO3 prism light beam deflector is described. A method was devised for the detection and measurement of the high-speed scanning laser beam. Optical demultiplexing of two simulated 37.5-Mbits/sec PCM channels using the deflector is demonstrated. Optical multiplexing of two simulated 75-Mbits/sec PCM channels is also demonstrated by using the same deflector in reverse. The crosstalk between the demultiplexed channels was measured as a function of the rf driving voltage. The salient features of the electro-optic prism demultiplexer and multiplexer are discussed.
Refractive indices and electro-optic coefficients of the eulitities Bi4Ge3O12 and Bi4Si3O12
Authors: Bortfeld D. P. , Meier H.
Published: February 2004

Measurements are reported on the refractive index n and of the static electro-optic coefficient r41 as a function of wavelength throughout the visible for Bi4Ge3O12 and Bi4Si3O12. Both materials exhibit large dispersion. At 633 nm, n=2.0975 for the germanate and 2.0211 for the silicate. The corresponding values for r41 are 0.95×10−10 cm/V and 0.54×10−10 cm/V, respectively.
Slow Gunn domains with field-independent trapping
Authors: Kroemer Herbert
Published: February 2004

A model for the Gunn-effect-domain dynamics in the presence of trapping is studied, both analytically and by computer simulation. The model assumes that in addition to the conventional donors there is a much larger density of traps present which are neutral when empty. The capture- and release-time constants are assumed to be field independent. It is found that the electron-dipole domain is coupled to an ion-dipole domain which can move only by charging and discharging ions and which slows down the overall domain speed by a factor equal to the ratio of untrapped free electrons to ionized donors. The same factor also determines the fraction of the total domain voltage supported by the electron dipole; the remainder is supported by the ion dipole. For sufficiently strong trapping the net ion charge throughout part of the ion domain is actually negative, resembling an npn structure with a punched-through traveling p-type base.
Temperature and intensity dependence of photoconductivity in amorphous (GePbSn)0.5Te0.5 films
Authors: Scharnhorst K. P. , Riedl H. R.
Published: February 2004

Amorphous films of [Ge1−y(Pb0.8Sn0.2)y]0.5Te0.5 were prepared by coevaporation of Ge0.5 Te0.5 and (Pb0.8Sn0.2)0.5Te0.5. The temperature dependence of the photoconductive response, Δσ, between 120 and 300 °K in the region of band-to-band excitation at nominal flux densities of 1015 photons/cm2 sec was measured for the compositions y=0.15, 0.19, and 0.32. At these intensities the response has an absolute maximum near 200 °K for all compositions. The temperature dependence of Δσ is exponential in 1/T on both sides of the maximum. The positive and negative activation energies of photoconductivity, Δ+ and Δ−, respectively, were found to be related to the activation energy of dark conductivity Ec*, by the expression Ec*=2|Δ−|+Δ+. The intensity dependence of Δσ for the y=0.19 alloy was studied over three orders of magnitude. At high intensities and low temperatures, recombination is biomolecular. At low intensities, recombination is monomolecular at all temperatures. The speed of response in the region of bimolecular recombination was determined for the y=0.19 alloy. Temperature and intensity dependences of Δσ are qualitatively similar for all compositions. A model for recombination kinetics recently proposed for a number of IV-V-VI amorphous alloys by Bube et al. is applied to interpret the results. A recombination-rate equation is proposed for these alloys and the steady-state and time-dependent photoconductive response characteristics of the y=0.19 alloy are evaluated on the basis of this equation.
Schottky barriers on ZnTe
Authors: Baker W. D. , Milnes A. G.
Published: February 2004

Metal surface barriers consisting of gold, nickel, tantalum, and aluminum on zinc telluride have been investigated. The behavior of gold and nickel barriers agrees with simple thermionic Schottky barrier theory. The barrier height found for gold is 0.64 eV and for nickel 0.65 eV. Tantalum and aluminum barriers were found to have characteristics dominated by recombination currents. The barrier height found for tantalum is 1.50 eV and for aluminum 2.00 eV.
Density-matrix method for a weakly ionized plasma
Authors: Fisher David M. , Willett Joseph E.
Published: February 2004

A density-matrix formalism for a system consisting of dynamically independent electrons interacting with random scattering centers and arbitrary electromagnetic fields is considered. The method of deriving the equation of motion for the density matrix averaged over scatterer positions is generalized to apply to any order in the electron-field interaction. A solution of the linearized equation of motion is employed to determine the power absorbed by a weakly ionized plasma with a realistic electron-neutral-atom interaction. In an approximation in which the neutral atoms do not change states, results similar to those obtained using a simple potential approximation are derived.
Optical Technique for the Measurement of Surface Charges of Electrets
Authors: Ballik E. A.
Published: February 2004

The paper reports a new technique for the measurement of surface charges of electrets which is based on optical measurements of the displacement of a reflecting membrane. The latter is used as the movable reflector in a Michelson interferometer. Simple calibration procedures and analyses allow calculation of the electret potential in terms of the displacement. Initial evaluation of the technique makes use of the electret material in the form of a membrane, specifically Mylar type S polyester film, 24 μ thick. Typical electret charge growth and decay data is presented which illustrates that the technique is simple, has high accuracy and resolution, and is reliable. Furthermore, the method is nondestructive.
Electromigration-Induced Failures in, and Microstructure and Resistivity of, Sputtered Gold Films
Authors: Blair J. C. , Fuller C. R. , Ghate P. B. , Haywood C. T.
Published: February 2004

Sputtered gold film conductors have been subjected to high current densities in the range of 2.0–3.5×106 A/cm2 in 150 °C air ambience, and data on the mean time to failure (MTF) vs current density J are presented. In this study, a corrosion-resistant Ti: W–Au metallization system is used. The microstructure and resistivity of the sputtered gold films have been examined and the observed excess resistivity of the sputtered gold films is attributed to gaseous impurities in the film. The average grain size of the sputtered films is 2000 Å. The MTF-vs-J data are compared with those of aluminum film conductors and an activation energy of 0.90 eV has been estimated for electromigration in sputtered gold films.
Dielectric Properties of KCl Ice
Authors: Maeno Norikazu
Published: February 2004

The dielectric properties of KCl ice were investigated as functions of frequency, concentration, and temperature. The values of the dielectric constant and loss factor were extremely large compared with those of pure ice when the KCl concentration and the temperature were higher than about 5×10−3 M (g mol/liter) and −10.7 °C, respectively. The dielectric polarization was explained as the Maxwell-Wagner effect caused by the liquid inclusions of KCl solution entrapped in the ice. The dielectric properties at low concentrations were rather similar to those of pure ice, showing a dispersion with an activation energy of 13.5 kcal/mole. When the concentration was above 10−3M and the temperature was below −10.7 °C another dielectric dispersion was observed at high frequencies, the activation energy of which was 6.6 kcal/mole.
Electromechanical Properties of Oxygen-Octahedra Ferroelectric Crystals
Authors: Yamada Tomoaki
Published: February 2004

A phenomenological theory of the electromechanical properties of various types of oxygen-octahedra ferroelectrics is presented. The electrostrictive constants reduced to those of the perovskite-type oxide are nearly constant with the values Q11p≈0.10 m4/C2, Q12p≈−0.034 m4/C2, and Q44p≈0.029 m4/C2. These constants are obtained by assuming that the piezoelectric effect in the ferroelectric phase is due to the electrostrictive effect in the paraelectric phase biased by the spontaneous polarization. The oxygen-octahedra ferroelectrics can be treated approximately as elastically isotropic and the stiffnesses normalized to those of the perovskite-type oxide c11p and c44p are shown to be proportional to their melting points TM, i.e., c11p≈1.3×108TM(°K) N/m2 and c44p≈0.47×108TM(°K) N/m2. The potential usefulness for ultrasonic applications of oxygen-octahedra ferroelectrics is discussed for dielectrically isotropic plates under perpendicular field excitation. The orientation of the plate which has the largest coupling factor to the extensional mode coincides with the direction of oxygen-transition metal-oxygen bonds in each ferroelectric. For the extensional modes a z-cut plate of 4mm structures has the advantage of a large coupling factor, while a y-cut plate of mm2 structures is shown to have possibly the largest coupling factor to the pure shear mode among oxygen-octahedra ferroelectrics.
Positive Ion Species and Degree of Dissociation of SO2 in dc Discharges of He–SO2 Mixtures
Authors: Kuehn D. G. , Chanin L. M.
Published: February 2004

Positive ion sampling measurements have been conducted on dc discharges containing 0.33% and 1.2% SO2 in He. Ions from SO2 include S+, O+, O2+, SO+, SO2+, and SO3+. Studies were made of the functional dependencies on gas pressure and discharge current. Interpretation of these results led to the conclusion that appreciable dissociation of SO2 occurred within the discharge. This hypothesis was confirmed by sampling the neutral gas components with and without a discharge. Measurements show the degree of dissociation increases with discharge current and reaches a limiting value which is relatively constant over the pressure range studied. For 1.2% SO2 in He, the degree of dissociation can become as large as 80% at 6.5 Torr and for a 20-mA discharge current. The results moreover suggest that an appreciable fraction of the dissociated particles is in the form of SO.
Frequency Stability of Methane-Stabilized He–Ne Lasers
Authors: Hellwig Helmut , Bell Howard E. , Kartaschoff Peter , Bergquist James C.
Published: February 2004

Free-running laser stabilities of 1.5×10−11 for the millisecond region and methane-locked stabilities of 10−13 for 10-sec averaging time are achieved with a minimum of shock and vibration isolation in an ordinary laboratory environment. Superior stability performance is obtained with dc excitation as compared to rf excitation. The experimental setup is described in some detail.
Photovoltages Larger than the Band Gap in Thin Films of Germanium
Authors: Kallmann H. , Spruch G. Marmor , Trester S.
Published: February 2004

Photovoltages much larger than the band gap were investigated in thin films of germanium deposited obliquely onto Pyrex substrates. The voltages were studied as functions of angle of deposit, film thickness, intensity of illumination, temperature, and ambient atmosphere. A model is presented which explains the following observations. Positive and negative photovoltages exist simultaneously in a single sample; which of these predominates changes with time. Dark resistance and photovoltage exhibit the same temperature dependence with identical activation energies, indicating that both dark resistance and photovoltage arise from the same elementary processes.
Transient Photoconductivity Effects in an Insulator-Semiconductor Powder System
Authors: Salaneck W. R. , Lind E. L.
Published: February 2004

An investigation of transient photoconductivity effects associated with semiconductor particles suspended in a transparent insulator has been carried out. II-VI compound crystalline solid solutions of CdSxSe1−x and CdSeyTe1−y were used as the photoconductors and poly (N-vinyl carbazole), PVK, as the transport medium, or matrix. Interparticle distances (∼ 5 μ) were large compared with particle diameters (∼ 1 μ). Transient photoconductivity as well as xerographic discharge measurement techniques were employed to study the quantum yield of the system as a function of applied electric field, wavelength of the incident radiation, temperature, and certain surface parameters of the components. Ideal geometry samples, consisting of single-crystal semiconductor-PVK-metal capacitors, were also studied to observe directly the photoemission of holes from the semiconductor into the PVK. The magnitude of the injection efficiency is found to depend upon the surface parameters of the components as well as the applied electric field. The data indicate the electric field dependence of the discharge in these systems to be due to electric field penetration of the surface of the semiconductor.
Temperature Dependence of Nonlinear Optical Coefficients in Ferroelectric NaNO2
Authors: Chern Mao-Jin , Phillips Richard A.
Published: February 2004

In ferroelectric NaNO2, optical rotation as a function of temperature was found to be linearly proportional to the spontaneous polarization as a function of temperature. When a single-domain crystal was switched by applying a dc electric field, the sense of optical rotation was reversed. Multiple-domain crystals exhibited no net rotation. The temperature behavior is explained in terms of the long-range order parameter and crystal symmetry. It is concluded that coefficients for nonlinear effects which are elements of odd-rank tensors will have a similar temperature dependence. The predicted temperature dependence of each second-harmonic coefficient Xijl is given by Xijl(T)=KijlPz0(T), where Kijl is constant and P0 the spontaneous polarization. This prediction is in good agreement with measurements reported by Yanagi et al.
Measurement of the Extrinsic Room-Temperature Minority Carrier Lifetime in GaP
Authors: Bachrach R. Z. , Lorimor O. G.
Published: February 2004

The room-temperature time decay of the near band-gap luminescence in GaP for time decays longer than about 5 nsec is shown to measure the minority carrier lifetime. Rise-time measurements with mode-locked argon laser pulses confirm this interpretation. Minority carrier lifetimes in n- and p-type GaP LPE dipped material at room temperatures have been measured and range up to 450 nsec. The minority carrier lifetime in Zn- and Te-doped GaP is determined by unintentionally present recombination centers. Annealing in GaP green material is found to produce random changes in the minority carrier lifetime. This method of using the green luminescence decay time for measuring the room-temperature minority carrier lifetime has also been applied to Zn, O-doped GaP. In this case, the measurement can be aided by the introduction of trace nitrogen. Spectral line-shape measurements which closely approximate the internal emission spectra have shown that phonon-assisted free-exciton recombination is the primary source of the green emission in non-nitrogen-doped (N < 1017 cm−3) GaP at room temperature. Bound-exciton recombination dominates in nitrogen-doped material (N ∼ 1018−1019 cm−3).
Preparation and Microstructural Properties of NiFe2 O4 Thin Polycrystalline Films
Authors: Suran Gabriel , Heurtel Alain
Published: February 2004

Thin polycrystalline NiFe2O4 films in the thickness range 0.1–0.7 μm were prepared by subsequent oxidation of a metallic film deposited under vacuum. The experimental requirements to obtain a stoichiometric single-phase ferrite film are described in detail. The influence of preparation parameters on crystallographic and magnetic properties is extensively studied. It is shown that when the sintering temperature is increased from 930 to 1130°C, the film density increases and the grain growth occurs. During the grain growth a |111| fiber texture is formed and a surface roughness is created. The formation of the |111| fiber texture which is more pronounced for higher sintering temperatures is explained in terms of surface energy. It is shown that the magnetic properties measured by ferromagnetic resonance are determined by the density and microstructure of the thin film, but the surface roughness has no marked effect on the position and linewidth of the main resonance mode. The thermally induced strains are much lower than predicted by calculation, and this observation is explained by grain boundary cracks. The relevance of this study for the epitaxy of thin ferrite films is pointed out.
Effects of an Ion Bombardment on the Characteristics of a Metal/n-GaAs Tunnel Contact
Authors: Guétin P. , Schréder G.
Published: February 2004

Gallium arsenide surfaces have been submitted to low-energy ion bombardment. Metal/n-GaAs tunnel contacts realized on the surfaces prepared in this manner present features which depend greatly on the ion energy. At very low energy (50 eV) gas ions provide a ``cleaning'' of the interface and yield tunnel characteristics which are essentially identical to those of a vacuum-cleaved analogous contact. This technique may be used to define the origin of tunneling anomalies. Higher-energy bombardments (100–150 eV) lead to strong changes of the tunnel properties which can be summarized as a large resistance increase in spite of a strong barrier lowering and the appearance of inelastic processes. A model based on the creation of structural defects accounts qualitatively for all of the observed phenomena. Tunneling represents, therefore, a promising technique in the study of very-low-energy ion bombardments.
Large-Optical-Cavity (AlGa) As–GaAs Heterojunction Laser Diode: Threshold and Efficiency
Authors: Kressel H. , Lockwood H. F. , Hawrylo F. Z.
Published: February 2004

Detailed operating properties and first-order theory of the large-optical-cavity (LOC) laser diode are described, including threshold current density, efficiency, mirror damage under pulsed operation, and cw operation at room temperature. This new structure differs from the single-heterojunction and conventional double-heterojunction laser in that the optical-cavity thickness can be made very large and is varied independently of the pair recombination region which is always less than a diffusion length thick. Large optical cavities are possible with high differential quantum efficiencies at room temperature because the radiation propagates predominantly in low-loss n-type material, allowing the design of lasers for specific applications. The problem of catastrophic degradation in the wide-cavity devices is reduced because of the lower optical flux density. The threshold current density depends on the width of the mode-guiding region, increasing with increasing thickness of that region. Power conversion efficiency values of 22% have been achieved at room temperature with narrow-cavity lasers.
High-Efficiency Zn-Diffused GaAs Electroluminescent Diodes
Authors: Herzog A.H. , Keune D.L. , Craford M.G.
Published: February 2004

Electroluminescent GaAs diodes have been fabricated in heavily doped (n > 1018 cm−3) GaAs using ZnAs2 or a Zn–Ga solution as a diffusion source. Using the Zn–Ga source, efficiencies of 1.3–1.4% for planar uncoated devices and 3.2–3.5% with an Epoxy lens are reproducibly obtained, and uncoated devices with efficiencies as high as 1.7% have been observed. A variety of GaAs crystals were evaluated in order to determine the type most suitable for the fabrication of diffused electroluminescent diodes. The optimum material was found to be Si-doped GaAs with n in the range (2–3) × 1018 cm−3. Both Czochralski and boat-grown GaAs were investigated. The device efficiency has been found to depend strongly on the etch-pit density of the crystal, with maximum efficiencies obtained for boat-grown GaAs with Δ < 103 cm−2. A series of zero dislocation crystals grown using the Czochralski technique was investigated and found to yield lower efficiency devices than boat-grown GaAs with an etch-pit density between 102 and 103 cm−2.
Stochastic Theory of Particle Flow under Gravity
Authors: Mullins W. W.
Published: February 2004

A discrete theory of cohesionless particle (radius a) flow under gravity is developed, which assumes particle positions are restricted to the sites of a (random) lattice. Downward particle flow toward and through an orifice is represented in terms of an equivalent upward-biased random flight of voids (unoccupied lattice sites) originating at the orifice. The void migration rate is assumed limited by the time required for a particle above a void to fall freely through a distance of 2a into the void. Because of the strong + z (upward) void-jump bias, the theory of random flight yields for the steady-state concentration c of voids the equation ∂2c∂x2+∂2c∂y2=1α∂c∂z  ,from which the usual term ∂2c/∂z2 is absent. Since this equation is formally identical to the two-dimensional diffusion or heat flow equation under the substitution (time) → z, steady-state problems in gravitational particle flow, termed stochastic flow on our model, may be converted to boundary value problems in ordinary diffusion theory. Solutions representing a point orifice and a finite orifice (radius R) in the floor of a semi-infinite bed and a point orifice in the bottom of a pipe are given. Particle flux lines and marker motion and exit times are defined and calculated. Time-dependent flow is discussed briefly. Finally, an idealized theory of flow in the immediate vicinity of the orifice is given, which pictures the transition between stochastic flow in the particle bed and bulk free fall in the orifice vicinity as occurring abruptly on a dome-shaped interface surmounting the orifice. Calculated values of the total rate of particle flow through the orifice show the observed particle size effects and agree well with measured values in the literature for 5<R/a ≲ 25. All main results are given in both two and three dimensions; the former may apply to certain traffic problems.
Ion Implantation of Nitrogen into Cadmium Sulfide
Authors: Shiraki Y. , Shimada T. , Komatsubara K. F.
Published: February 2004

Ion implantation of nitrogen into n-type cadmium sulfide has been investigated with energy up to 200 keV at dose levels 1015–1017 cm−2. The measurements of I-V, C-V characteristics, and photoelectric properties of diodes made on implanted CdS have given evidence for p-type layer formation. EPR studies have clarified the nitrogen center and lattice-defect centers produced by the ion implantation. Current of the implanted diodes can be expressed by I=I0[exp(eV/nkT) −1] and the parameter n was remarkably reduced from 10 to 2.7 by a 10-min anneal at 400°C. Overannealing degraded the diode characteristics. The peculiar C-V characteristics and the negative photovoltage were observed for the implanted diode, which can be understood only by presuming a series structure of the p-n junction formed by nitrogen implantation and a Schottky barrier on a p-type surface. The relative spectral response of photovoltage of the diode had a peak at 800 mμ, i.e., at 0.85 eV below the band edge after annealing below 400°C. The 800-mμ peak is reasonably ascribed to implanted nitrogen ions, because of the absence of the peak in both unimplanted and neon-implanted CdS. Optical quenching level due to radiation damage produced by implantation was also observed for photocurrent of heavily implanted samples. EPR measurements assured the existence of nitrogen centers in implanted CdS. A new EPR spectrum led to the model of N22− molecular-ion center substitutional for sulfur ion. The center was observed after annealing at 400°C, while the density of lattice-defect centers decreased.
Superradiant Laser Emission from Rhodamine 6G and Rhodamine B Using a Coaxial Flashpump
Authors: Mumola P. B.
Published: February 2004

Superradiant laser emission has been observed from ethanol solutions of rhodamine 6G and rhodamine B using a coaxial flashlamp pump. The dependence of input threshold energy on dye concentration is examined. The possibility of exciting other dyes to superradiance is discussed.
Formation of Amorphous Silicon by Ion Bombardment as a Function of Ion, Temperature, and Dose
Authors: Morehead F. F. , Crowder B. L. , Title R. S.
Published: February 2004

The dose (fluence) of 200-keV boron, phosphorous, and antimony ions required to produce a continuous amorphous layer in silicon is determined as a function of target temperature. EPR measurements are used to monitor the process which is also then related to annealing effectiveness. The continuous amorphous layer recrystallizes at 550°C, after which only the implanted ions within that layer are completely electrically active. Carrier concentration profiles indicate the position of the amorphous layer and allow an approximate determination of the distribution with depth of damage. At the low dose rates used, reasonable agreement with a simple model for the formation of amorphous silicon as a function of ion, temperature, and dose is obtained.
Xerographic Discharge Characteristics of Photoreceptors. II
Authors: Chen Inan
Published: February 2004

The xerographic discharge characteristics under space-charge-perturbed conditions have been studied theoretically. The surface potential at time t, V(t), and dV/dt are calculated by numerical iterations, as functions of the carrier emission efficiency, carrier mobility, optical density of the photoreceptor, light flux, and exposure time. It is observed that, unlike the case of emission-limited discharge, the carrier mobility is as important as (sometimes more than) the emission efficiency in determining the speed of discharge. A large field dependence in mobility leads to a high residual potential. An exposure with penetrating light (carrier emission in the bulk) has been found to lift the space-charge limitation and lower the residual potential. In the case of flash exposure with strongly absorbed light, where analytical calculation of the discharge characteristic is possible, the numerical iterative method yields results in excellent agreement with the analytical ones.
Performance of cw HF Chemical Laser with N2 or He Diluent
Authors: Spencer Donald J. , Mirels Harold , Durran Donald A.
Published: February 2004

Recent experimental results on the performance of a continuous HF (or DF) chemical laser are reported. In this device, an arc-heated diluent is mixed in a plenum with SF6 to provide F atoms. The mixture is expanded to form a supersonic jet into which H2 (or D2) is diffused. Population inversion and lasing are due to the reaction H2+F=HF(v)+H; v≤3 and Δ H=−31.7 kcal. Power levels above 1 kW have been obtained in a N2 diluent gas flow, and levels above 1.7 kW have been obtained in a He diluent gas flow. Specific power yields are 43 and 108 kW sec/lb for the N2 and He systems, respectively. The variation of laser power and efficiency with cavity optical axis location and SF6 mass flow are reported for both N2 and He systems. A spectrum of the HF laser operating in a He flow is also presented that gives evidence of v=3 partial inversion.
Far-Infrared Interference Technique for Determining Epitaxial Silicon Thickness
Authors: Saifi M. A. , Stolen R. H.
Published: February 2004

Interference technique in the frequency range 30–200 cm−1 has been used for the first time to determine the thickness of low-conductivity epitaxial films deposited on a highly conducting silicon substrate. It is shown that for thick epitaxial films (d≥4 μm) the frequency at which half-order minimum occurs is highly sensitive to the epilayer-substrate interface carrier concentration profile. In general the far ir thickness is close to that obtained by angle-stain technique. A combination of ir and far-ir measurements therefore yields valuable information regarding the interface carrier concentration profile. The far-ir technique can replace the costly and destructive methods presently used, such as angle stain, and capacitance-voltage measurements made on specially fabricated diodes. The paper also discusses the optical constants of silicon in the far ir. The calculations show that it is necessary to use the energy-dependent anisotropic scattering time to correctly evaluate the optical constant in the far ir.
Effect of Substrate Preparation on the Perfection of GaP Liquid-Phase Epitaxy Layers
Authors: Rozgonyi G. A. , Saul R. H.
Published: February 2004

X-ray topographic studies of GaP substrate wafers have shown that mechanically polished (MP) substrates exhibit a substantial amount of surface damage, whereas chemically polished (CP) substrates have strain-free surfaces. In this work, we used x-ray topography to determine the effect of the residual surface damage on the perfection of GaP liquid-phase epitaxy (LPE) layers. Of primary concern was the quality of the substrate-LPE-layer interface since, for GaP LPE diodes, the radiative recombination occurs within several microns of this interface. The results were correlated with the quantum efficiency of red-emitting LPE diodes fabricated from both MP and CP substrates. It has been found that the bulk perfection of an LPE layer is essentially unaffected by the surface damage remaining after substrate preparation. The surface damage of the substrate, however, results in imperfections at the substrate-LPE-layer interface. The efficiency of the red electroluminescence was found to be reduced by at least 30–40% for diodes fabricated from MP substrates, and this degradation is attributed to the interfacial defects. It is also shown that thermal decomposition of a substrate surface prior to initiation of LPE can significantly reduce residual surface damage. Finally, the nature of a vapor-etched substrate surface has been found to be altered by traces of water vapor in the growth ambient.
Diffusion of Beryllium into Gallium Phosphide
Authors: Ilegems M. , O'Mara W. C.
Published: February 2004

The acceptor Be has been diffused into GaP from a liquid Ga–Be–P diffusion source at temperatures ranging from 600 to 1000°C. The diffusion behavior was found to be a function of the growth origin of the substrates, and the depth of the diffused junctions was not proportional to the square root of the diffusion time over part of the temperature range investigated. Diffusion profiles were obtained in liquid encapsulated Czochralski material at 1000, 900, and 800°C by the atomic absorption technique, and the 1000 and 900°C profiles were analyzed by the Matano method. In the high-concentration range investigated it is found that the diffusion coefficient varies nonmonotonically with concentration and reaches a maximum value of 8.5×10−8 cm2/sec at a concentration of 2.5×1019 cm−3 at 1000°C. Comparison with Zn diffusion shows that the diffusion coefficient of Be is approximately one order of magnitude larger than that of Zn at 100°C and that a strong similarity exists in the concentration dependence of the diffusion coefficient of these two impurities.
Exact First-, Second-, and Third-Order Photocounting Cumulants for Lognormally Modulated Mixtures of Coherent and Chaotic Radiation
Authors: Rosenberg S. , Teich M. C.
Published: February 2004

In this paper we investigate the photocount statistics of mixed coherent plus Gaussian light that has suffered lognormal fading, such as produced by the turbulent atmosphere. The Gaussian component need not be stationary, may have an arbitrary spectral distribution, and the mean frequency of the coherent and Gaussian components need not coincide. The first three cumulants of the phototelectric counts for a single detector and for an array of detectors are obtained for arbitrary ratios of counting time to source coherence time, β, while assuming the fading to be fully time correlated over the detection interval. In particular, the cumulants are evaluated for Gaussian light of Lorentzian spectrum. The variation of the cumulants with degree of turbulence and detector separation is exhibited graphically, for several values of β, and ratio of coherent to chaotic component, y. The effect of increasing the degree of turbulence is shown to cause the ratio of the second-order cumulant for Gaussian light to the same cumulant for coherent light to approach a nominal value of 2, indicating the extent to which the fading dominates the counting statistics. As the detector separation is varied, the twofold cumulant exhibits the spatial correlations of the turbulence, when the source radiation alone is assumed to be approximately spatially coherent at the detector array. Furthermore, the cumulants are shown to increase exponentially with the turbulence level σ, the log-intensity standard deviation.
Autocorrelation Function of Barkhausen Noise in Simple Materials
Authors: Baldwin John A. , Pickles Gregory M.
Published: February 2004

The experimental work was done completely with a single tape-wound core of grain-oriented 50–50% NiFe. The hysteresis loop tracer employed feedback to the effect that the flux in the core was made to vary linearly in time. Under these conditions, Barkhausen noise (in the usual sense of the word) could not occur. It does appear, however, as noise on the mmf (magnetomotive force) signal. In this paper, it is this mmf noise which is referred to as Barkhausen noise. Barkhausen noise is analyzed in terms of the spring model, which explains the noise as being due to statistical fluctuations in the number and strengths of the defects with which a wall is interacting. An expression is derived for the autocorrelation function R(τ) of the noise. Comparison of theoretical and experimental R(τ)'s determines the value of two parameters of the model: S′ Z and N. The values of S′ Z found (S′ Z ≃ 1.7 × 10−3) agree well with values obtained earlier by six completely different methods. The value of the density parameter N is new and is ≃ 1.5 × 1012 m−3. It is concluded that the spring model not only explains the average shape of hysteresis loops of materials meeting the criteria for simplicity, but also explains statistical fluctuations from the average.