bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling of self-breakdown voltage statistics in high-energy spark gaps
Authors: Donaldson A. L. , Hagler M. O. , Kristiansen M. , Hatfield L. L. , Ness R. M.
Published: July 2002

A model which incorporates the influence of electrode surface conditions, gas pressure, and charging rate on the voltage stability of high energy spark gaps is discussed. Experimental results support several predictions of the model; namely, that increasing the pressure and the rate of voltage charging both produce a broadening of the self-breakdown voltage distribution, whereas a narrow voltage distribution can be produced by supplying a copious source of electrons at the cathode surface. Experimental results also indicate that two different mechanisms can produce this broadening, both of which can be taken into account with the use of the model presented. Further implications of the model include changes in the width of the self-breakdown voltage probability density function as the primary emission characteristics of the cathode are modified by, for example, oxide or nitride coatings and/or deposits from the insulator. Overall, the model provides a useful and physically sound framework from which the properties of spark gaps under a wide variety of experimental conditions may be evaluated.
Laser fabrication of electrodes on zinc oxide varistors
Authors: Modine F. A. , Lowndes D. H. , Martinelli J. R. , Sonder E.
Published: July 2002

Near surface properties are reported for ZnO varistors irradiated with high-intensity pulses from both KrF excimer and CO2 lasers. Electrical, optical, and Rutherford backscattering measurements reveal that a thin conducting film is formed by pulsed-laser heating of a varistor surface. The conductive film is evaluated as a varistor electrode.
Reply to ‘‘Comment on ‘Elastic stiffness coefficients of nickel-iron single-crystal alloys at room temperature’ ’’
Authors: Ghosh U. S. , Kanrar A.
Published: July 2002

Ledbetter’s critical discussion on our work on the elastic stiffness coeffficients of nickel-iron single-crystal alloys at room temperature clearly shows that our conclusion regarding the linear dependence of the shear constants of this alloy crystal on the composition is, in general, not valid throughout the whole range of composition. The linearity is destroyed by the onset of instability of the fcc phase of the alloy crystal at about 45% Ni. However, so long as the alloy crystal remains in the stable fcc phase (from 100% to 45% Ni) shear constants do follow a linear dependence on composition.
Temperature of molecular vapor in laser ablation of CuCl
Authors: Rothenberg Joshua E. , Koren G. , Ritsko J. J.
Published: July 2002

Optical emission spectra are studied from the vapor produced by irradiation of polycrystalline CuCl, under vacuum, by pulsed excimer laser radiation at 248 and 308 nm. For fluences φ≲0.4 J/cm2 (intensity I≲20 MW/cm2), well-resolved molecular CuCl emission bands and weak atomic Cu lines are observed. At higher fluences, the CuCl emission increases and develops into a broad continuum due to the broadening and overlap of the bands, whereas the Cu atomic line emission increases more rapidly. At even higher fluences (φ≳1 J/cm2, I≳50 MW/cm2), the Cu atomic emission dominates the entire spectrum. A thermal equilibrium model is used to calculate the vibrational-rotational temperature of the emitting CuCl molecules as a function of fluence by fitting the experimentally observed emission bands. Temperatures in the range 500<T<2000 K for fluences in the range 0.27<φ<0.4 J/cm2 were obtained.
New current probing method for superconducting integrated circuits
Authors: Hanyu I. , Suzuki H. , Tamura H. , Hasuo S.
Published: July 2002

A new current probing method for measuring the current level in superconducting integrated circuits is proposed. In this method, a SQUID (superconductive quantum interference device) is used to pickup unknown superconductive current and a negative feedback loop is used to automatically compensate the unknown current. We have experimentally obtained a resolution of less than 2 μA and a high accuracy of better than 1%.
The pressure dependence of the yield strength of shock-loaded Manganin gauges
Authors: Rosenberg Z. , Partom Y.
Published: July 2002

The variation of the yield strength with shock pressure of Manganin foil gauges can be determined by analyzing their dynamic calibration curve. The analysis is based on the assumption that the material behaves as an elastoplastic work-hardening solid and on the general expression for the resistance change of Manganin which we derived in previous works. It is found that the strength increases by a factor of about 3.5 for shock stresses in the range of 0–160 kbar.
Models for electron mobility and temperature of two-dimensional electron gas at low and moderate fields
Authors: Lee H. P. , Vakhshoori D. , Lo Y. H. , Wang Shyh
Published: July 2002

A theoretical model of electron temperature and electron mobility as a function of electric field has been formulated for GaAs/AlxGa1−xAs heterostructures. The predicted results from this model agree well with available measurements at low and moderate fields (E>200 V/cm). Furthermore, this model enables us to predict the electron temperature and mobility at high fields which are crucial to the understanding of the potential performance of GaAs/AlxGa1−xAs modulation-doped field effect transistor and other novel heterostructures.
Photo-optical devices by amorphous As-S waveguides
Authors: Tanaka Keiji , Imai Yoh , Odajima Akira
Published: July 2002

Principles and fabrications of photo-optical devices based on the photoinduced refractive index changes observed in amorphous chalcogenide films are described. In these devices, propagation of a light beam in optical waveguides constructed with amorphous As-S films is controlled with blue- (and red-) light illumination which can modify the refractive index of the films. The devices operate as single-throw or double-throw photo-optical switches, having switching times ranging between 20 ms and 2 s.
Steady-state plasma production and fluid flow in ion beams with step-function density profiles
Authors: Lemons Don S. , Jones Michael E. , Kadish Abraham , Lee Huan , Newberger Barry S.
Published: July 2002

The steady-state fluid equations for plasma production and transverse flow in an ion beam with a step-function density profile are solved exactly in both slab and cylindrical geometries. The beam edge is treated as both a neutral and a non-neutral sheath. In the former, the beam density falls from its value inside the beam to zero in a distance much greater than a Debye length, while in the latter the Debye length is much greater than the beam falloff distance. Physical solutions with plasma density profiles which decrease monotonically from the beam center are shown not to exist for negative ion beams with a non-neutral sheath.
Demagnetizing fields in magnetic measurements. II. Bulk and surface imperfections
Authors: Brug J. A. , Wolf W. P.
Published: July 2002

Imperfections such as pores, cracks, surface pits, and scratches perturb the magnetization in an otherwise uniform material as a result of the long-range nature of magnetic dipole forces. A number of simple computer simulations have been made which allow semiquantitative estimates of the effects of imperfections in typical experimental situations. The results show that the perturbations will be particularly significant near phase transitions and in experiments using very thin samples and a localized measuring probe.
Improved performance of surface-passivated solar cells by chlorine-containing oxides
Authors: Jackson M. A. , Rao B. B. , Anderson W. A.
Published: July 2002

Many metal-oxide-semiconductor (MOS) devices rely upon surface passivation for improved performance. An oxide grown in the presence of Cl was evaluated using highly efficient, surface-passivated, photovoltaic cells. The Cl-containing oxide gave increased efficiency, increased stability, and reduced surface-state density. Spectral response, Auger, and secondary ion mass spectrometry (SIMS) data support these conclusions. Preliminary results regarding stoichiometry of the oxide are presented.
Current amplification in nonhomogeneous-base structure and static induction transistor structure
Authors: Nishizawa Jun-ichi , Nonaka Ken-ichi , Tamamushi Takashige
Published: July 2002

Current-amplification mechanisms for a nonhomogeneous-base bipolar phototransistor (BPT) and a static induction phototransistor (SIPT) are discussed in this paper, and comparisons are made to the homogeneous- and or the gradually-graded-base BPT. It is shown that the current-transport mechanism of the BPT with a nonhomogeneously doped ⋅ ⋅ ⋅p+pp+p ⋅ ⋅ ⋅(⋅ ⋅ ⋅ n+nn+n ⋅ ⋅ ⋅) base is similar to that of the SIPT if the p (n) base potential is capacitively controllable both by the p+ (n+) base and collector voltages. For the n-channel SIPT in the open-gate mode of operation, the potential-barrier height for holes stored in the p+-gate region is higher than the potential-barrier height for electrons in the source region by the value of VbiGS−VbiG*S, where the VbiGS is the built-in potential between the p+-gate region and the n+-source region of the SIPT and VbiG*S is the potential-barrier height between the intrinsic gate G* in the channel and the n+-source region. In fact, a very high dc optical gain G of more than 108 (at 3×10−15 W incident optical power level, λ=6550 Å) has been obtained. An average gain-bandwidth product of more than 108 Hz has been obtained at subpicowatt incident power levels. The steady-state and transient optical response of the SIPT with an open gate is studied experimentally and theoretically. It is concluded that if the base region of a homogeneous-base BPT is replaced by a nonhomogeneous-base structure and or SIPT structure, the sensitivity and response time will be much improved.
Current-voltage characteristics of ion-implanted metal-semiconductor field effect transistor
Authors: Kwong D. L.
Published: July 2002

In this paper, a general analytic expression for the current-voltage (I-V) characteristics of an ion-implanted metal-semiconductor field effect transistor with a Gaussian channel doping profile is presented. The results are based on a closed-form solution of the static Poisson’s equation in the depletion layer and the integration of the total charge carriers in the undepleted section of the conduction channel. Approximate explicit expressions for the depletion-layer widths at the source and drain electrodes as a function of implantation energy, implant dose, drain voltage, and gate voltage are derived. The explicit I-V characteristic equation incorporating these approximate expressions are then obtained and compared with that of using numerical solutions for the depletion-layer widths, and the difference between them is shown to be negligible. The closed-form expression for the current-voltage equation is well suited for computer-aided design of integrated circuits.
Deep levels in vapor epitaxial indium phosphide grown in the presence of ammonia
Authors: Sun S. W. , Wessels B. W.
Published: July 2002

Deep levels in vapor epitaxial indium phosphide grown in the presence of ammonia were investigated by transient capacitance spectroscopy. A total of three hole traps associated with nitrogen doping was observed with activation energies of 0.21, 0.3, and 0.45 eV. The traps H(0.21) and H(0.3) are tentatively attributed to a nitrogen-impurity complex. Concentrations of deep trapping states as high as 8×1014 cm−3 were observed in the as-grown layers.
Mass spectrometric transient study of dc plasma etching of Si in CF4 and CF4/O2 mixtures
Authors: Brandt W. W. , Honda T.
Published: July 2002

dc plasma etching experiments were carried out on polycrystalline Si wafers using CF4 and CF4/O2 mixtures as etchants. The etchants were injected into a slow stream of Ar while a continuous discharge was maintained. The resulting transients of intermediate and product species were determined mass spectrometrically; some of these were found to depend very much on the oxygen concentration, even though hysteresis effects which complicated earlier results were not noticed in this study.The results do not support existing simplified models, but yield some detailed information concerning the etching mechanism. The etch rates increase when small amounts of oxygen are added to the CF4, probably due to an increase in the atomic fluorine concentrations, while at larger oxygen concentrations they decrease, in part because the fragmentation of the etchant gas CF4 is then suppressed. CF2 radicals are found to be present in the plasma in appreciable concentrations; presumably, this species is directly involved in the formation of SiF4 at the surface.
Properties of InxGa1−xAs-GaAs strained-layer quantum-well-heterostructure injection lasers
Authors: Laidig W. D. , Lin Y. F. , Caldwell P. J.
Published: July 2002

Some of the properties of InxGa1−xAs-GaAs strained-layer quantum-well-heterostructure (SL-QWH) injection lasers are described. The laser structures are grown by molecular beam epitaxy on n+ GaAs substrates. Following the growth of a 0.5-μm n+ GaAs buffer layer, a 2-μm Al0.45Ga0.55As n-type cladding layer is grown. Next an undoped active region is grown, consisting of ∼1600 Å of GaAs with three ∼40-Å In0.35Ga0.65As quantum wells separated by two ∼30-Å GaAs barrier layers. Following the active region, a 2-μm Al0.45Ga0.65As p-type cladding layer and a 0.5-μm p+ GaAs cap layer are grown. Broad-area SL-QWH lasers operate under pulsed conditions at room temperature with threshold current densities as low as 465 A/cm2. The operating wavelength is near 1 μm. Lasers have operated for up to 1000 h with less than 25% increase in current density to maintain a constant output of 2 mW/facet. Data are also presented describing the temperature dependence of threshold current density. Values of T0 between 80 and 103 K are observed near room temperature, indicating that these SL-QWH lasers are somewhat more sensitive to temperature changes than conventional laser structures.
Series expansions for the vector potential and field components produced by a toroidal conductor
Authors: Caldwell J.
Published: July 2002

Alternative solutions for the vector potential and the magnetic-field components produced by a toroidal conductor of rectangular cross section are considered. Series expansions are obtained and found to agree with those obtained independently by M. W. Garrett [J. Appl. Phys. 22, 1091 (1951)]. Results are obtained for a particular coil geometry by using only a few terms from the series expansions and, by comparing with the exact results, are found to be highly accurate at points close to the coil axis.
Two-dimensional modeling of high explosive driven plasma opening switches
Authors: Greene A. E. , Bowers R. L.
Published: July 2002

Calculations of high-explosive (HE) driven plasma opening switches have been extended to two dimensions. The goal of our calculations is to determine the role of mixing in the resistance increases that are observed experimentally. We have not included a magnetic field, but have looked at the hydrodynamics of the interface between the cool HE detonation products and the hot plasma. Our calculations indicate that significant mixing can occur if perturbations exist along the interface. We estimate the sensitivity of our results to the wavelength and amplitude of these perturbations.
Dopant segregation in electroepitaxy: Variation of effective distribution coefficient
Authors: Bryskiewicz T.
Published: July 2002

Variation of the effective distribution coefficient keff with the current density J in electroepitaxy of semiconductor compounds is analyzed, taking into account the thickness L of the solution. On the basis of the analytical expression for (keff−k0)/k0 derived in this paper, where k0 is the interface distribution coefficient, both the changes in dopant concentration with J and the homogeneous distribution of dopants parallel to the growth direction are explained. It is shown that in electroepitaxy from a limited solution volume (L≲0.1 cm) the difference between keff and k0 is negligible even when J becomes very high. Thus, we can carry out direct measurements of k0 vs J in order to conduct a quantitative study of dopant incorporation mechanisms.
Photocarrier transport and trapping processes in doped polyethylene terephthalate films
Authors: Kurtz S. R. , Arnold C.
Published: July 2002

The radiation-induced conductivity of polyethylene terephthalate film is modified by doping this polymer with electron acceptor molecules. Detailed results of x-ray induced thermally stimulated current and photoconductivity experiments are reported for one dopant, 2, 4, 7-trinitro-9-fluorenone. At dopant concentrations≲1019 molecules/cm3, this impurity acts as a deep trap for photocarriers, radically decreasing the radiation-induced conductivity of the doped film. The kinetics of photocarrier trapping in a host material exhibiting dispersive transport is discussed. At dopant concentrations ≳1020 molecules/cm3, the radiation-induced conductivity increases due to the onset of photocarrier transport among the electron acceptor molecules. Utilizing the physical processes discussed in this work, it is possible to develop dielectric materials displaying selected levels of radiation-induced conductivity.
Nb films sputtered with a (Ar, H2) mixture and application to superconductor-insulator-superconductor junctions
Authors: Kobayashi Takeshi , Sakuta Ken , Fujisawa Kazuo
Published: July 2002

Effects of hydrogen trapping in Nb base electrodes on the superconductivity of Nb itself and superconductor-insulator-superconductor (SIS) junction characteristics have been investigated. The Nb films were prepared by sputter deposition in an atmosphere of (Ar, H2) mixture. The gap parameter ΔNb and the critical temperature Tc gradually decreased with increasing H2 partial pressure. The SIS junctions exhibited a sudden extinction of the Josephson current Ic when ΔNb was lowered to or less than 1.1 meV by H2 trapping. Such a junction could be used as a quasiparticle tunneling junction for microwave detection with no requirement for an external magnetic field.
Collective flux pinning in a defective flux vortex lattice
Authors: Mullock S. J. , Evetts J. E.
Published: July 2002

The Larkin and Ovchinnikov (LO) theory for the summation of local pinning forces on flux vortices in type II superconductors describes the collective interaction between a perfectly elastic vortex lattice and a subthreshold pinning potential. Using a similar minimization procedure, it is shown that the elastic solution derived by LO does not always represent the lowest energy state of the vortex lattice. It is argued that as the magnetic field approaches Bc2, the vortex lattice inevitably becomes defective and that the defect structure determines the total pinning force, the static and dynamic response of the vortex lattice, and history effects when they occur. Calculations are presented for two and three dimensions, in two dimensions, the equilibrium defect structure predicts a peak effect in good agreement with observed critical currents. It is suggested that the situation in three dimensions is always nonequilibrium.
Microwave spectroscopic measurement of the electron density in a planar discharge: Relation to reactive-ion etching of silicon oxide
Authors: de Vries C. A. M. , van Roosmalen A. J. , Puylaert G. C. C.
Published: July 2002

It is demonstrated that microwave cutoff can be used to measure absolute electron densities for CHF3, Ar, and O2 plasmas in a batch-mode planar reactor excited at 13.56 MHz. The densities obtained are between 1015 and 1016 m−3 for all gases and a large set of conditions (pressure, rf power, electrode spacing). A comparison with selective etching of SiO2 over Si in the same reactor shows a qualitative agreement between the substrate ion flux calculated from the electron density and the etch rate of silicon oxide; the apparent sputter yield ranges from 0.4 to 1.4 molecules per ion.
Allowed and forbidden transitions of singlet helium high Rydberg states
Authors: Ganguly B. N. , Garscadden Alan
Published: July 2002

Allowed and forbidden transitions of singlet helium from 2s1S to ns1S, np1P, and nd1D states have been measured between n=8 and 31 by optogalvanic spectroscopy in a dc discharge positive column. The addition of neon in the discharge was found to increase the relative intensities of the forbidden transitions. For similar photon flux, the optogalvanic signal reaches a maximum at n=11 and decreases thereafter. Neutral collisional ionization of the excited states from n=13 and above was found to be responsible for the increased ionization efficiency of the high Rydberg states.
Temperature dependence of the Mössbauer linewidth of superparamagnetic particles of ferric hydroxysulfate
Authors: Morais P. C. , Tronconi A. L. , Neto K. Skeff
Published: July 2002

The Mössbauer linewidth broadening of superparamagnetic particles of ferric hydroxysulfate, near the point where the paramagnetic lines begin to appear, has been investigated as a function of temperature. This behavior is explained by a geometric picture of an assembly of magnetically ordered single-domain particles whose magnetic moments move within an asymmetric double-well potential. A relaxation model is presented which combines the conventional theory of superparamagnetism with an exponential distribution of energy barriers.
Practical dual-wavelength light-emitting double diode
Authors: Chin A. K. , Chin B. H. , Camlibel I. , Zipfel C. L. , Minneci G.
Published: July 2002

A practical dual-wavelength light-emitting double-diode (LEDD) device structure is presented. This device is relatively simple to fabricate and requires a single device-to-fiber alignment for packaging. Additionally, the individual wavelengths can be selected within the 0.8 to 1.6-μm low-loss spectral region of optical fibers. A dual-wavelength LEDD emitting at 1.3 and 1.1 μm is demonstrated. Powers exceeding 10 μW for each wavelength at 50-mA drive current are coupled into a lensed, graded index, 62.5-μm core, 0.29-NA optical fiber.
Investigation of the ESR modes in Cu-Mn spin glasses via swept frequency spectroscopy (abstract)
Authors: Gullikson E. M. , Schultz S.
Published: July 2002

We have developed a new swept frequency spectrometer (8–12 GHz) which is designed to allow direct observation of all the ESR modes in Cu-Mn spin-glass samples. When the rf and dc magnetic fields are perpendicular, we readily observe the ω+ mode either by sweeping the field (corresponding to the usual spectroscopy) or sweeping the frequency (our new approach). When the fields are parallel, we observe signals when sweeping the frequency which appear to correspond to the longitudinal mode ωL, but the signal behavior is not as simple as expected from the current triad theory and observations.
Transverse magnetoresistance of DyNi single crystal
Authors: Maezawa K. , Wakabayashi S. , Sato K.
Published: July 2002

The transverse magnetoresistance of a DyNi single crystal was measured at a temperature of 4.2 K over the magnetic field range 0–100 kOe. It was found that a negative magnetoresistance was observed with a spin flopping of the magnetization along the c axis when the magnetic field was applied along the c axis and the current was parallel to the b axis. On the other hand, the negative magnetoresistance was not observed when the current was parallel to the a axis, and the magnetoresistance increased monotonically with increasing magnetic induction B. Information was also obtained about features of the Fermi surface from the field dependence of the magnetoresistance. It was inferred from the present results that there are open orbits along the a axis and the c axis.
Change in the diode quality factor with insulator layer thickness in a metal-insulator-n-semiconductor solar cell
Authors: Goel Anju , Sharma T. P.
Published: July 2002

The theoretical calculations for the diode quality factor n for a metal-insulator-n-semiconductor solar cell under illumination are presented here. These calculations show that, under illumination, n increases with increasing d and decreases slightly for d>18 Å at JL =36 mA cm−2. Results of the calculations compare well with experimental results observed by H. C. Card [Solid-State Electron. 20, 971 (1977)].
Laser damage studies of polymer oxide coated silica optics at 350 nm
Authors: Yoldas B. E. , Smith H. D. , Milam D. , Lowdermilk W. H.
Published: July 2002

A single layer SiO2 film with graded porosity applied from a polymer solution derived from organometallic silicon compounds on fused silica lenses provides antireflectivity over the transmission range covering the first, second, and third harmonics of neodymium glass lasers. The damage thresholds of initial samples at 350 nm (3ω) varied from less than 1 to 9 J/cm2. The main causes of this large variation in the damage threshold were determined to be substrate polishing, substrate surface cleaning, and the coating solution chemistry and processing, which, under certain conditions, leads to carbon formation during the heat treatment of the coating.
Optical studies of impurity trapping at the GaAlAs/GaAs interface in quantum well structures
Authors: Meynadier M. H. , Brum J. A. , Delalande C. , Voos M. , Alexandre F. , Liévin J. L.
Published: July 2002

We present low-temperature photoluminescence studies of nominally undoped GaAs quantum wells in which weak acceptor-related emissions can be observed. We investigate the influence of different sequences of prelayers, in which the number and the aluminum concentration of the layers are varied, on the impurity concentration in the quantum well, and show that thin layers of low aluminum percentage act as very efficient impurity trapping centers. We also present calculations of the electron to acceptor photoluminescence line shape, which show that the acceptor distribution has its maximum at the well interface, extending about 7 Å in the barrier and 12 to 30 Å in the well.
Liquid-phase epitaxial growth and characterization of low carrier concentration n- and p-type In0.53Ga0.47As
Authors: Rao Mulpuri V.
Published: July 2002

Both n- and p-type In0.53Ga0.47As layers with low carrier concentrations (∼1015 cm−3) were achieved reproducibly by adding Zn-doped GaAs to the liquid-phase epitaxial growth melt. The distribution coefficient of Zn in In0.53Ga0.47As (kZn) is found to be 0.52±0.08. Analysis of hole mobility data in the temperature range 10–300 K has revealed that the combination of nonpolar-optical-phonon and acoustic-deformation-potential scattering mechanisms play a more significant role in the high-temperature range. Photoluminescence measurements were also performed on the ternary layers.
Tellurium and zinc doping in In0.5Ga0.5P grown by liquid-phase epitaxy
Authors: Wu M.C. , Su Y. K. , Chang C. Y. , Cheng K. Y.
Published: July 2002

In0.5Ga0.5P epitaxial layers doped with Te and Zn were grown on (100) GaAs substrates by liquid-phase epitaxy using a supercooling method. The lattice mismatch between the InGaP layer and the GaAs substrate decreases with increasing Te or Zn impurity concentration. The electrical properties of doped layers were determined by Hall measurements at 300 and 77 K. Room-temperature carrier concentrations ranging from 2×1017 to 3×1018 cm−3 for n-type and from 2×1017 to 2×1019 cm−3 for p-type dopants were obtained reproducibly. The full width at half maximum value of the 300 K photoluminescent spectrum increases with carrier concentration for both Te- and Zn-doped layers. The relative intensity of the 300 K photoluminescent peak increases with electron concentrations up to 3×1018 cm−3 for Te-doped layers, but it presents a maximum value at 1×1018 cm−3 for Zn-doped layers. The 14 K photoluminescent spectra show three distinctive peaks and their relative intensities change with hole concentrations. Finally, the relationship between the acceptor ionization energy and hole concentration is described.
The effects of hydrogen in sealed electrical contacts
Authors: Schubert Rudolf , Gray Eoin W.
Published: July 2002

Hydrogen has been an integral atmospheric component of sealed electrical contacts for decades because of its effect on reliability. It is well known that hydrogen is a needed component to prevent high contact resistance due to carbon-spot formation. This hydrogen benefit has been attributed to hydrogenation of hydrocarbons (HC), enhanced volatilization of previously deposited carbon, enhanced catalytic activity, and thermal cooling. By a variety of physical and chemical laboratory techniques, this paper shows that the hydrogen is not itself directly active. However, some of the hydrogen is converted to water during the glass sealing process. It is this water which plays the active role in the process of quenching carbon formation from hydrocarbon impurities and also acts as a diluent of HC’s adsorbed on the contact surface and in the arcing volume. This limits the carbon accumulation on the contacts and increases lifetime reliability.
An extremely sensitive heterostructure for parts per million detection of hydrogen in oxygen
Authors: Fonash S. J. , Li Zheng , O’Leary M. J.
Published: July 2002

The fabrication and performance of a new type of solid-state hydrogen detector is described. This device is extremely sensitive at room temperature to parts per million of hydrogen in the interesting situation of an oxygen-rich ambient. The device is a heterostructure whose key layer is a TiOx film produced by low-pressure chemical vapor deposition. Due to the presence of this layer, the device switches from one conduction state in oxygen to another in a hydrogen-rich ambient. This transition from one state to the other is a function of the ambient hydrogen concentration and is caused by the evolution of a barrier in the TiOx layer.
Effect of a conductive layer on copper electromigration in the CuxS/CdS photovoltaic system
Authors: Buhks Ephraim , DeFillipo Lawrence
Published: July 2002

Theoretical and experimental studies of ionic electromigration effects were performed on a photovoltaic system Au/CuxS/CdS. The steady-state lateral distributions of holes and their electrochemical potential were derived for CuxS in the constant-current case. The theory predicts (1) a substantial reduction in CuxS nonuniformity caused by lateral Cu+ electromigration and (2) a large increase (from 100 to ∼400 mV) in the value of the critical voltage for copper precipitation. Experimental data on electrochemical potential distributions in polarized CuxS agree well with theoretical results. Electromigration effects are shown to depend upon the electronic conductivity of the Au layer.
Nature and distribution of electrically active defects in Si-implanted and lamp-annealed GaAs
Authors: Dhar Sunanda , Seo Kwang S. , Bhattacharya Pallab K.
Published: July 2002

The nature and spatial distribution of deep levels arising from defects in device-quality, Si-implanted, and lamp-annealed liquid encapsulated Czochralski GaAs have been investigated. The best activation and mobility values are obtained for annealing times and temperatures of 3–5 s and 900–950 °C, respectively. Further improvements are obtained for a two-step annealing in which a second step at 840–850 °C for 15–40 s follows the main anneal step. From Hall measurements, average layer mobilities of 4000 cm2/V s and activation of 55–65% are obtained for a Si+ dose of 6.5×1012 cm−2 at 100 keV. Electrically active deep-level traps were studied by sensitive deep-level transient spectroscopy (DLTS) and optical DLTS techniques. A dominant 0.57-eV electron trap, which is also present in furnace-annealed GaAs, originates from implantation damage and is possibly related to VGa. Additional electron traps with activation energies of 0.35 and 0.40 eV are present only in lamp-annealed GaAs. Commonly observed hole traps have activation energies of 0.27–1.1 eV. The origins of these centers are discussed. Trap densities in single-step lamp-annealed samples are extremely low in comparison with furnace-annealed samples. Typical values of NT/n are 10−2–10−4. Concentrations are even lower in samples undergoing two-step annealing. The spatial variation of trap density seems to be principally determined by the variation of defect density in the substrate. It is apparent that high-quality implanted and annealed GaAs can be obtained by the two-step lamp annealing procedure.
Investigation of surface mobility in thin-gate oxide metal-oxide-semiconductor field-effect transistors
Authors: Chan T. W. , Cheng Y. C.
Published: July 2002

Thin gate oxide metal-oxide-semiconductor field-effect transistors with different oxide thickness (180–1000 Å) are fabricated with both the as-grown and etching back methods. In order to segregate the geometrical effect and the growth effect of thin oxides, the surface mobilities of these devices at both room temperature and 77 K are investigated. It is found that the mobility in general decreases with the decrease in gate oxide thickness. The surface mobilities of thin-gate oxide devices fabricated with dual trichloroethylene (TCE) techniques are also studied and it is found that the surface mobility drops with the increase of TCE concentration in the oxidizing ambient. Explanations for these observations based on coulomb scattering and surface roughness scattering mechanisms are suggested.
Statistics for the interpretation of deep level transient spectroscopy on insulator-semiconductor interfaces
Authors: Engström O. , Shivaraman M. S.
Published: July 2002

The information obtained by deep level transient spectroscopy (DLTS), used to investigate insulator-semiconductor interfaces, is studied by using basic statistical theory. It is shown that in a modified form of DLTS the Gibbs free energy of the interface traps is obtained, while the standard DLTS gives the enthalpy values. An important consequence is that the ‘‘electronic degeneracy factor’’ cannot be obtained from this type of measurement.
Experimental observation of unstable resonator mode evolution in a high-power KrF laser
Authors: Izawa Shingo , Suda Akira , Obara Minoru
Published: July 2002

For a pulsed high-power laser with unstable resonator, the mode evolution time is important from the viewpoints of beam focusability and laser-energy usefulness. We observed temporal and spatial behavior of the mode evolution in a several-tens-joule KrF laser with a positive branch confocal unstable resonator, which is pumped by electron beams with a pulse width of 65 ns (FWHM). The beam divergence angle was decreased by a factor of 1/M2 (M:magnification) per round trip in the resonator and resulted in a full angle divergence of 0.6 mrad.
Effect of UV laser preionization on CO2-laser-induced optical breakdown
Authors: Yoshida S. , Sasaki J. , Arai Y. , Uchiyama T.
Published: July 2002

The effect of UV preionization by a KrF laser on CO2-laser-induced optical breakdown is studied experimentally. The electron number density as well as the breakdown probability is measured as a function of KrF-laser energy. The results show that the KrF-laser preionization is quite effective in initiating the optical breakdown. Once a breakdown is initiated, however, the number of produced electrons is found to be independent of the KrF-laser energy.
Ion trapping in the emitter sheath in thermionic converters
Authors: Lundgren Lennart
Published: July 2002

The effect of ion trapping in the emitter sheath in ignited thermionic converters is studied. The ion trapping prevents the emitter-sheath barrier from being higher than approximately 0.1 eV, when the current decreases in the converter. This gives a condition for the constriction of the arc. I-V curves are calculated for an ignited thermionic converter with a hydrodynamic plasma theory that takes into account the effect of Coulomb scattering and volume recombination, but assumes that the electron temperature is constant in the plasma.
Measurement of a long diffusion length in a GaAs film improved by metalorganic-chemical-vapor-deposition source purifications
Authors: Partain L. D. , Cohen M. J. , Cape J. A. , Fraas L. M. , McLeod P. S. , Dean C. S. , Ransom R. A.
Published: July 2002

The vacuum metalorganic-chemical-vapor-deposition (Vacuum MOCVD) process was combined with two source purifications to grow p-GaAs epitaxial films of high quality. Theoretical modeling of quantum yield spectra measured on a specially configured n+-p sample determined the minority-carrier electron diffusion length to be 10 μm to within a factor of 2 in the p layer. The p doping was reduced to the 5×1017 cm−3 level to avoid suppression of the diffusion length by Auger recombination. Multiple vacuum sublimations of dicyclopentadienyl magnesium (CP2Mg), the source of Mg for p doping, reduced the contamination by air and by cyclopentadiene (CP) by an order of magnitude. A dry ice/acetone cold trap was operated at slightly below 180-Torr pressure to reduce the water vapor content of arsine, used as the As source, from the hundreds of ppm down level down to the 2 ppm range. The vacuum growth process reduced residual gas contamination. These techniques were combined to grow a p on n GaAs solar cell with an efficiency of 24% at air mass 1.5 (AM1.5).
Influence of Josephson currents on superconductor-insulator-superconductor mixer performance
Authors: Jablonski Daniel G. , Henneberger Mark W.
Published: July 2002

Superconductor-insulator-superconductor (SIS) mixers are currently the lowest-noise devices available for mixing in the 26–110 GHz frequency range. However, a major source of noise is anticipated to be the increased effects of Josephson oscillations within the mixer as higher operating frequencies are achieved. Simulations have been done to demonstrate these effects. Results indicate that the commonly used three-port analysis is valid over a wide range of conditions, but that even minimal Josephson oscillations have a deleterious effect on mixer performance. The junction shunt capacitance, which serves to short out the Josephson oscillations, is thus an extremely important parameter. However, the characterization of the mixer in terms of an ‘‘ωRC’’ product appears to be an oversimplification. A more elaborate approach to mixer characterization is suggested.
Laser surface treatment of high-phosphorus cast iron
Authors: Li Zaiguang , Zheng Qiguang , Li Jiarong , Hu Weiguang , Wang Hansheng , Tian Hongye
Published: July 2002

Samples of high-phosphorous cast iron were treated with a cw CO2 laser to produce superficial martensitic layers by transformation hardening and superficial ledeburitic layers by surface melting. These layers were tested for resistance to cavitation erosion by magnetostrictive vibratory cavitation analysis. Both the ledeburitic and martensitic layers were found to be less prone to cavitation erosion than the untreated surface.
Borophosphosilicate glass flow for solid-state imager application
Authors: Susa Masahiro , Hiroshima Yoshimitsu , Senda Kohji , Kuriyama Toshihiro , Matsumoto Shigenori , Terakawa Sumio , Takamura Tohru
Published: July 2002

A new fabrication process for solid-state imagers based on the borophosphosilicate glass (BPSG) flow has been developed. It was found that well-designed tapered steps can be obtained even at low temperatures with the use of BPSG, which can be cleaned in a hot NH4OH/H2O2/H2O solution. As a result, a solid-state imager fabricated using the above process is characterized by satisfactory shapes of tapered steps made of intermediate oxide which give complete metal interconnect lines.
Incorporation of Al and Ga in AlGaAs grown by low-pressure triethyl gallium metalorganic vapor-phase epitaxy
Authors: Chang C. Y. , Chen L. P. , Nee C. Y.
Published: July 2002

Low-pressure metalorganic vapor-phase epitaxy was adopted to grow AlGaAs epitaxial films by using triethyl-gallium, trimethyl-aluminum, and AsH3 as the Ga, Al, and As sources, respectively. Growth rate, incorporation rates, and AlAs solid composition versus growth temperature have been investigated by electron probe microanalysis with the following results: the growth rate, the AlAs fraction in AlGaAs, and the Al and Ga incorporation rates increase with increasing growth temperature under reduced pressure. The Al incorporation rate increases more quickly than that of the Ga in AlGaAs. The above results are consistent with one another.
Analysis of grating couplers for planar dielectric waveguides
Authors: Wlodarczyk Marek T. , Seshadri S. R.
Published: July 2002

Output and input grating couplers for step index planar dielectric waveguides are investigated taking into account the interaction between a guided mode with a finite number of radiative and an infinite number of nonradiative space harmonics. For transverse electric and transverse magnetic modes, and for shallow gratings of arbitrary profiles located at either the upper or the lower guide surface, the governing equation for the slowly varying amplitude of the guided wave is deduced, and therefrom the real and the imaginary parts of the correction to the wave number of unperturbed guide are evaluated, the power conservation relation is established, and the output and the input coupling efficiencies are defined. For the input coupler, the excitation by a two-dimensional radiation beam is also included. The role of the space harmonics which, like the guided wave, carry power along the guide in modifying the real and the imaginary parts of the wave number of the guided wave is discussed. The effect of the choice of the profile and location of the grating on the distribution of the outgoing radiation between the cover and the substrate, and between harmonics of different orders are examined. In a multimode coupler, significant improvements in input coupling efficiency can be achieved by a suitable choice of the grating profile and the excitation region. The effect of tapering the relative depth of the grating on the amplitude profile of the radiated beam of the output coupler, and on the coupling efficiency of the input coupler are investigated.
Monte Carlo calculation of electron scattering from surface films
Authors: Williamson William , Antolak A. J.
Published: July 2002

The electron backscattering coefficient and reflected energy for surface films on bulk substrates have been computed using the photon-electron Monte Carlo transport code sandyl. The calculations were done for the film/substrate configurations Al/Pt, Ag/Pt, Ag/Al, and Au/Al with incident electron beam energies of 20, 40, 60, and 100 keV at different angles of incidence and various film thicknesses. The backscattering results are compared with available experimental data taken at normal incidence.
Enhancement of the microwave magneto-Kerr effect in semiconductors using dielectric matching techniques
Authors: Perger W. F. , Vernon R. J. , Lee C. M.
Published: July 2002

Enhancement of the microwave magneto-Kerr effect in semiconductors is discussed for the semiconductor being preceded by a semi-infinite dielectric and by a quarter-wave dielectric slab for both plane-wave and guided-wave cases. Expressions are developed that relate the amount of the enhancement to the relative permittivity of the dielectric. Experimental results are compared to the theoretically obtained expressions for the quarter-wave case and the experimentally obtained values compare favorably with the theory.
Diffused germanium dichroic mirror for optically pumped far-infrared lasers
Authors: Rutt H. N. , Selden A. C. , McNeil B. W. , Denning R. G.
Published: July 2002

A new type of dichroic reflector has been developed for the far-infrared region of the spectrum, based on n-type germanium with a diffused conduction layer. A 111-axis single-crystal plate of 40-Ω cm optical-grade germanium was implanted with 5×1014 As+ ions/cm2 by ion bombardment at 200 keV; the donor impurity ions were subsequently diffused into the substrate at a temperature of 850 °C (held for 20 h). The measured power-reflection spectrum displayed a shallow minimum at ∼70 cm−1, rising steeply below 50 cm−1 to reach 80% reflectivity at 10 cm−1. Computer modeling of the infrared reflectance of a thermally diffused conducting layer in n-type germanium—with the assumption of Conwell–Weisskopf mobility variation for the conduction electrons—gave an excellent fit to the observed reflection spectrum for an integrated column density of 1014 cm−2 and 10-μm half width, the latter being in good agreement with the value √Dt=11 μm calculated for thermal diffusion under the conditions indicated.
Spectrally selective surfaces of Co-pigmented anodic Al2O3
Authors: Blain J. , LeBel C. , Saint-Jacques R. G. , Rheault F.
Published: July 2002

The multilayer model of Al anodized selective surfaces has been revised by taking into account surface defects and incident angle of of illumination. This theory has been applied to Co-pigmented surfaces. Emphasis was put on extended experimental determination of all parameters used in the theory. With a detailed scanning and transmission electron microscope study of the structure, the size of the pores and their aerial density have been determined. Moreover, the surface roughness has been measured. This has permitted the calculation of the dielectric permeability for each layer. The permeabilities have then been used to compute spectral reflectance curves using the Bruggeman theory. Computer calculated reflectance curves based solely on experimental data agree well with experimental results for λ≥2 μm. At shorter wavelengths, interference peaks that were predicted, but not observed, were minimized by considering surface roughness.
Electron backscattering from bulk materials
Authors: Antolak A. J. , Williamson W.
Published: July 2002

Monte Carlo calculations to determine the backscattering coefficient for electrons incident on bulk materials have been carried out on a Cray I using the electron/photon transport computer code sandyl. The elements Al, Cu, Ag, and Au have been studied over an energy range from 10 keV to 1 MeV, and the results are compared with some experimental data.
Theory of deep level trap effects on generation-recombination noise in HgCdTe photoconductors
Authors: Iverson A. Evan , Smith D. L.
Published: July 2002

We present a theory of the effect of deep level centers on the generation-recombination (g-r) noise and responsivity of an intrinsic photoconductor. The deep level centers can influence the g-r noise and responsivity in three main ways: (i) they can shorten the bulk carrier lifetime by Shockley–Read–Hall recombination; (ii) for some values of the capture cross sections, deep level densities, and temperature, the deep levels can trap a significant fraction of the photogenerated minority carriers. This trapping reduces the effective minority carrier mobility and diffusivity and thus reduces the effect of carrier sweep out on both g-r noise and responsivity; (iii) the deep level centers add a new thermal noise source, which results from fluctuations between bound and free carriers. The strength of this new noise source decreases with decreasing temperature at a slower rate than band-to-band thermal g-r noise. Calculations have been performed for a X=0.21, n-type Hg1−xCdxTe photoconductor using the parameters of a commonly occurring deep level center in this material. We find that for typical operating conditions photoconductive detector performance begins to degrade as the deep level density begins to exceed 1016 cm−3.
Double injection in Si:In devices
Authors: Hurm V. , Hornung J. C. R. , Manck O.
Published: July 2002

The current-voltage characteristics of Si:In double-injection devices were measured up to breakdown in the temperature range 20–80 K. To vary the amount of optical carrier generation the devices were either exposed to a 50 K cold shield or a 300 K background. The breakdown voltages were found to be strongly dependent on device temperature and irradiation intensity. By using simple analytical expressions it is shown that the unexpected low values at high temperatures or at high irradiation levels are due to large densities of thermally or optically generated holes. To obtain a satisfactory agreement between theory and experiment the regional approximation method is employed. The analysis extends previous treatments by taking into account field-dependent mobilities and capture coefficients. The description of the prebreakdown characteristics includes also the lowering of the ionization energies of the acceptor centers at high field strengths.