bluuebunny/crossref_metadata_2025 huggingface dataset:
Microwave and ion beam studies of an Applied Bθ diode
Authors: Renk T. J. , Hammer D. A.
Published: July 2002

A parametric study of microwave radiation emitted from an ‘‘applied Bθ’’ magnetically insulated ion diode, covering frequencies between 0.3 and 85 GHz, indicates that collective mechanisms are responsible for the 1–10-MW peak output. These collective mechanisms may also be related to the degradation in ion beam quality seen by a scintillator/streak camera diagnostic. This degradation is most apparent when the microwave flux is at its maximum. A deformation of the plasma appears to be the most likely cause of the disturbances seen in the ion beam.
Kinetics of the silicon dioxide growth process in afterglows of microwave-induced plasmas
Authors: Vinckier C. , Coeckelberghs P. , Stevens G. , Heyns M. , De Jaegere S.
Published: July 2002

A fast flow reactor technique, by which thin silicon dioxide layers can be grown, is described in detail. Wafers 3 in. in diameter are treated in the afterglow of a microwave-induced plasma in oxygen/argon mixtures. This method allowed us to produce SiO2 layers of a uniform thickness up to 300 Å. It is shown that the oxide growth rate initially follows a parabolic dependence on the oxidation time while at thicknesses from about 170 Å on, a linear relationship is observed. Various physicochemical parameters affecting the oxidation rate are investigated, such as the flow velocity, the wafer position, the microwave power, and the temperature. It is also shown by chemical titration techniques that oxygen atoms in their electronic ground state are the major oxidizing species under the experimental conditions used.
Temperature dependence of the dynamic response of the photorefractive signal in Bi12SiO20
Authors: Arizmendi Luis , Powell Richard C.
Published: July 2002

The dynamic response of the photorefractive signal in Bi12SiO20 with no external electric field was studied as a function of temperature. At low temperatures, the response follows the predicted exponential behavior. At temperatures higher than 220 °C with the writing beams on, the signal increases to a peak intensity and decays with time, with a time constant that varies with temperature. When the write beams are turned off and no erasure beam is present, the signal exhibits a sharp decrease and then increases to a secondary maximum before the final decay occurs. When an erasure beam is present, the same general signal pattern is observed but the secondary peak can be significantly greater at high temperatures. The theory of Kukhtarev satisfactorily describes the signal patterns observed at low temperatures. The more complex signal patterns observed at high temperatures are explained by postulating the presence of mobile positive charges which compensate the electric fields established by the negative charges participating in the photorefractive response of the material.
Dielectric hysteresis behavior in form I poly(vinylidene fluoride)
Authors: Wang T. T. , Sondhi M. M. , von Seggern H. , Tasaka S.
Published: July 2002

The dielectric hysteresis behavior of polymer ferroelectrics has until now been described by an energy approach in which the redistribution of the crystal dipole orientation under an applied field is determined by the probability for the molecular dipoles to rotate about the long chain axes from one energetically stable position to the other. We propose an alternative approach in which the orientation of the dipole is determined by the equilibrium between the field-induced torque and the elastic restoring torque generated by the excursion of the dipoles from their initial stable positions. Measurements of hysteresis loops performed on both uniaxially and biaxially oriented films of form I poly(vinylidene fluoride) reveal that all the important features of the loops can be accounted for by our model. An added advantage of our model is that it allows for description of switching experiment where inertial effects become important.
Effect of cathode surface area and separately stabilized cathodes on high power glow discharges for CO2 laser excitation
Authors: Evans D. R. , Harry J. E.
Published: July 2002

Results are presented which indicate the importance of the cathode surface area and the advantage of using separately stabilized cathodes for the excitation of high power CO2 lasers. The results indicate that operation of a glow discharge with multiple cathodes of adequate surface area enables operation in the abnormal glow region at higher currents than with a single cathode of the same total surface area. Increase in the current at which the glow-to-arc transition occurs, improved stability, improved utilization of the laser cavity in the electrode region, and a wide range of variation of discharge current are also obtained using multiple cathodes. Large surface area multiple cathodes have been successfully demonstrated in a new high power fast axial flow CO2 laser using a single discharge tube operating at discharge currents of up to 1.8 A corresponding to laser output powers of up to 5 kW.
A study of detonation processes in heterogeneous high explosives
Authors: Tang Pier K.
Published: July 2002

A model of multiple processes is used to simulate the behavior of reaction in detonation of heterogeneous high explosives. The features of the model are (1) the partition of the explosive medium into hot spots and the region exclusive of hot spots and (2) the separation of the mechanical-thermal process and chemical process. For each process, a characteristic time is assigned and is defined by a phenomenological relation. With assumptions, some fast processes are ignored in the governing equations. This investigation indicates the necessity of including a slow process near the end of the reaction. Comparisons with experiments using a Fabry–Perot velocimeter are presented for triaminotrinitrobenzene.
Laser plasma x-ray sources for microlithography
Authors: Chaker M. , Pépin H. , Bareau V. , Lafontaine B. , Toubhans I. , Fabbro R. , Faral B.
Published: July 2002

A plasma produced by laser irradiation of solid targets is a promising candidate as an efficient x-ray lithography source. In order to design a practical laser created x-ray source, it is necessary to study the factors affecting the x-ray emission. For this purpose, we investigate both theoretically and experimentally the influence of the laser target parameters on the x-ray emission in different spectral ranges for two laser wavelengths (λ=1.06 μm, λ=0.26 μm). From these results and considering mask transmission, resist sensitivities, and wafer throughput, we establish the characteristics of the laser required as an x-ray lithography source with performance acceptable for industrial applications.
Distribution of atoms in mixed III-V compounds
Authors: Sela I. , Gridin V. V. , Beserman R. , Sarfaty R. , Fekete D. , Morkoç H.
Published: July 2002

In mixed III-V semiconductors, AB1−xCx, the atoms are supposed to be randomly distributed. Using resonant Raman scattering as a probe, we determined the departure from a random distribution inside small volumes of the order of V≂(50 Å)3. It has been shown that the frequency splitting of the vibrational modes in the allowed and forbidden configuration can be attributed to the deviation from the nominal composition x within the characteristic volume of the electron-phonon interaction.
rf SQUID detector for single-ion trapping experiments
Authors: Weisskoff R. M. , Lafyatis G. P. , Boyce K. R. , Cornell E. A. , Flanagan R. W. , Pritchard D. E.
Published: July 2002

We have designed and constructed a novel superconducting detector sensitive enough to detect the axial motion of a single, trapped ion. This detector employs a tuned, superconducting transformer matched to a rf SQUID (superconducting quantum interference device) to yield an effective current sensitivity of 2.7×10−15A/(Hz)1/2 at 160 kHz. To optimize the detection system, we have used existing small-signal equivalent circuit models, and thus have tested these models in a new regime. We include details of our superconducting circuitry and of the modifications required to stabilize the commerical SQUID controls at 160 kHz. Finally, we present typical detected signals from trapped ions.
Shallow and deep donors in n-type Ga1−xAlxAs:Sn grown by metalorganic vapor-phase epitaxy
Authors: El Jani B. , Köhler K. , N’Guessan K. , Bel Hadj A. , Gibart P.
Published: July 2002

The electronic properties of Sn, a well-known group IV n-type dopant in GaAs, were studied in Ga1−xAlxAs alloys for the whole compositional range. These Sn-doped Ga1−xAlxAs epitaxial layers were grown by metalorganic vapor-phase epitaxy; Hall measurements were carried out for values ranging from x=0 to 1, Hall data for 0<x<0.4 were interpreted assuming a shallow donor bound to the Γ band, and a deep donor with an ionization energy of about 100 meV. Photoluminescence spectra of selectivity excited donor acceptor pairs show the existence of a deep donor at 100 meV below the Γ minimum for x>0.2.
Integrated on-line instrumentation for simultaneous automated measurement of magnetic field, induction, Barkhausen effect, magnetoacoustic emission, and magnetostriction
Authors: Jiles D. C.
Published: July 2002

A microcomputer-controlled instrument for simultaneous measurement of magnetic hysteresis, magnetostriction, Barkhausen effect, and magnetoacoustic emission is described. It incorporates custom designed software for control of the magnetic field during operations such as demagnetization, field sweeping, and anhysteretic magnetization, and for data logging and analysis. Results are recorded using a 12-bit analog to digital converter and are then stored on floppy disk. The magnetic hysteresis data are converted into six important magnetic parameters: coercivity, remanence, hysteresis loss, initial permeability, maximum differential permeability, and anhysteretic permeability. These, together with the magnetostriction, Barkhausen, and magnetoacoustic emission, are then related to the microstructure of the material.
Light scattering from thermal magnons in thin metallic ferromagnetic films
Authors: Cochran J. F. , Dutcher J. R.
Published: July 2002

A computer program has been written with which the complex resonant frequency can be calculated for a thin ferromagnetic metal film sandwiched between a nonmagnetic metallic substrate and a nonmagnetic metallic overlayer. The calculation includes exchange and magnetic damping having the Gilbert form. The program has been used to investigate the sensitivity of thin-film resonant frequencies to the resistivities of the overlayer, the substrate, and the magnetic film. It is concluded that the presence of an overlayer and of a substrate are unimportant for the analysis of Brillouin scattering data from films less than 100 Å thick: uncertainties in the absolute value of the frequency shift of the scattered light—typically 1:200—are greater than, or comparable with, the frequency shifts caused by an overlayer or a substrate.
Magnetization decay in Co-Cr films
Authors: Webb Bucknell C. , Schultz S. , Oseroff S. B.
Published: July 2002

We have measured magnetization time decay in perpendicularly oriented Co-Cr films over seven time decades as a function of field and temperature. The anomalous Hall coefficient of the sample itself, which is proportional to the magnetization within the sample, is used to determine the magnetization. Magnetization time decay measurements made with this technique, for times>10 s, agree with vibrating-sample magnometer (VSM) data taken at 77 and 300 K, but can be made as soon as 2 ms after turning off the external magnetic field used to saturate the sample. The principle features of magnetization decay in Co-Cr are as follows: (1) The magnetization time decay in Co-Cr films is nearly independent of external field over a range of several kG, unlike particulate media, where the magnetization decay rate is sharply peaked around the coercive field. (2) At 300 K, the magnetization time decay deviates markedly from log t, with the decay per decade of time dropping by almost a factor of 2 between 10−3 and 104 s. (3) For zero field, the deviation from a linear log t decay decreases with decreasing temperature, with a nearly constant magnetization time decay observed in any decade of time between 15 and 200 K. (4) At negative fields and temperatures below 15 K, a second region of log t decay with a larger decay rate is seen for t<100 ms. (5) For temperatures between 200 and 10 K, decay rates decrease linearly with decreasing temperature, and then below 10 K decay rates decrease more rapidly, and appear to approach zero when extrapolated to zero temperature.
A contactless method for determination of carrier lifetime, surface recombination velocity, and diffusion constant in semiconductors
Authors: Waldmeyer Jürg
Published: July 2002

A new optical, contactless method to determine carrier recombination lifetime, surface recombination velocity, and diffusion constant at high-level injection is described. In a measurement, a sample of a few mm3 volume and a thickness above 1.5 diffusion lengths is homogeneously illuminated by a band-gap light pulse, and the subsequent decay of the generated carriers is monitored by infrared absorption. Since the data extracted from a measurement represent averages over the whole sample, the technique is especially attractive for vertical power devices or solar cells, or also for process control using test wafers. In silicon, lifetimes between 0.5 and 1000 μs and surface recombination velocities between a few and 105 cm/s can easily be determined. In the first part, the paper gives the one-dimensional solution of the carrier diffusion problem associated with the experiment. This solution is of wider use, however, e.g., for recessed gate structures and power devices in general. In the second part, results for silicon with various surface preparation procedures are given. For lapped samples, an ‘‘electrical penetration depth’’ of the damage is found to be about 1.5 times the lapping grain diameter. Sodium dichromate is found to reduce an otherwise infinite surface recombination velocity to 245 cm/s in p-type and to 2000 cm/s in n-type silicon.
A study of the leakage mechanisms of silicided n+/p junctions
Authors: Liu R. , Williams D. S. , Lynch W. T.
Published: July 2002

Leakage mechanisms for shallow, silicided, n+/p junctions have been investigated. This study consists of two parts: (a) the isolation of the processing steps that cause junction leakage, and (b) the study of the mechanism for a particular process that causes leakage. Reactive ion etching, improper junction, silicide formation procedures, ion mixing, and mechanical stress are found responsible for junction leakage, although through different mechanisms. Two mechanisms have been identified for junction leakage: (a) generation centers in the depletion region caused by deep levels from damage, or from impurities, and (b) Fowler–Nordheim tunneling caused by irregularities at the silicide/silicon interface at high reverse bias. Junction leakage can be avoided by carefully designing the details of silicide and junction formation and by carefully fine-tuning the processing steps to prevent damage of the Si substrate after forming the junction. The best junctions are made by implanting As into CoSi2 and by driving the As into Si from the silicide at 800 °C. The lower temperature drive is possible since all ion damage is contained within the silicide, leaving no damage in the Si substrate to anneal out. Very shallow, silicided, n+/p junctions can be fabricated reproducibly. These junctions demonstrate the same electrical characteristics as deeper, nonsilicided junctions, indicating that there is no fundamental barrier prohibiting fabrication of low-leakage, silicided junctions.
Effects of heavy boron doping upon oxygen precipitation in Czochralski silicon
Authors: Hahn S. , Ponce F. A. , Tiller W. A. , Stojanoff V. , Bulla D. A. P. , Castro W. E.
Published: July 2002

In this investigation, diffuse x-ray scattering, Bragg line profile, and transmission electron microscopy have been employed for the study of point defects and their interaction with oxygen impurities in heavily boron-doped Czochralski Si wafers during various thermal treatments between 450 and 1050 °C for time intervals from 2 to 128 h. Bragg line profile data show that (1) materials tend to become more perfect during the initial stages of thermal annealing regardless of anneal temperatures and (2) the integral width and full width at half-maximum both exhibit minima after a thermal treatment at 450 °C for 32 h while the opposite behavior is observed for a thermal treatment at 1050 °C. The diffuse x-ray scattering data have shown that (1) the nature of the predominant defects depends upon annealing temperature, time and ramping cycles; and (2) the mean cluster size ranges between 1.4 and 2.0×103 nm regardless of annealing temperature and time. Transmission electron microscopy results show (1) slower precipitation kinetics occur than in lightly doped materials, (2) virtually no precipitates have been observed, even after 128 h for annealing temperatures up to 650 °C, (3) amorphous precipitates with a {100} platelet morphology are observed after prolonged anneals at 800 °C, and (4) the appearance of complex precipitate structures have been observed at 1050 °C. These results indicate significantly different behavior from that of lightly doped silicon. Finally, using a thermodynamic and kinetic model, we attempt to explain these heavy boron doping effects on SiO2 precipitation in Czochralski Si.
Dislocation loops and precipitates associated with excess arsenic in GaAs
Authors: Lee B.-T. , Gronsky R. , Bourret E. D.
Published: July 2002

Dislocation loops and precipitates in an arsenic-rich GaAs crystal have been studied by transmission electron microscopy to investigate their formation mechanism and establish their relationship to point defects. The precipitates are identified to be hexagonal arsenic phases having a simple orientation relationship with the GaAs matrix. Detailed analyses of the loops indicate that they are composed of two separate defects lying on (111) planes: a faulted loop and a perfect loop. It is proposed that the loops are formed by condensation of excess arsenic interstitials followed by clustering of excess Ga vacancies and subsequent generation and movement of Shockley partial dislocation(s). The faulted loop is interpreted as an hcp arrangement of arsenic atoms. This model supports the hypothesis that arsenic interstitials and Ga vacancies coexist in GaAs at high temperatures although arsenic interstitials initiate the formation of arsenic-related dislocation loops. Implications concerning the formation process of the EL2 deep-level defect are also discussed.
Time-dependent diffusion of ion-implanted arsenic in thermally grown SiO2
Authors: Yamaji Tetsuo , Ichikawa Fumio
Published: July 2002

Arsenic implanted into thermally grown SiO2 was diffused in ambients of O2 and N2, and arsenic distributions in the SiO2 were analyzed with secondary ion mass spectrometry (SIMS). Arsenic was implanted at energies between 40 and 70 keV with a dose of 1×1015 cm−2 and diffused at temperatures between 1000 and 1100 °C. The profiles revealed retarded diffusion in the high-concentration region (>1×1019 cm−3) in both ambients. It was found that for N2 annealing the diffusion in the low-concentration region (<1×1019 cm−3) is highly enhanced in the early annealing stage and gradually reduced with annealing time, and that this time-dependent diffusion depends on the implantation energy and annealing temperature. Arsenic diffusivities and related parameters were extracted by fitting numerically calculated profiles to SIMS data. The time-dependent diffusion was attributed to the diffusion of interstitial arsenic and its reaction with the SiO2 network.
Antiphase domains in GaAs grown on a (001)-oriented Si substrate by molecular-beam epitaxy
Authors: Noge H. , Kano H. , Hashimoto M. , Igarashi I.
Published: July 2002

Antiphase domains (APDs) in the GaAs layer grown by molecular-beam epitaxy on a nominally (001)-oriented Si substrate were easily observed by molten potassium hydroxide etching or photoelectrochemical etching. The APD boundaries are almost parallel to {100} or {110} planes. The density of APDs decreases with the GaAs layer thickness in the 0.5–1.0-μm region from the GaAs/Si interface. The appearance of APDs depends on the preheating conditions of the substrate. Preheating at 950 °C for 30 min or at 1000 °C for 5 min was sufficient for the suppression of APDs. This may be due to the change of the Si surface structure and the following complete annihilation of APDs in the GaAs layer near the heterointerface.
Cluster size and temperature measurement in a pure vapor source expansion
Authors: Pruett J. G. , Windischmann H. , Nicholas M. L. , Lampard P. S.
Published: July 2002

Time-of-flight mass spectrometry was used to measure the cluster size and distribution in photo- and electron-impact ionized pure vapor expansions. In addition, fluorescence excitation spectroscopy measurements were made on the expansion of tellurium to determine the degree of cooling and identify the dominant cooling mode. Mass spectra were taken as a function of nozzle diameter, ranging from 0.2 to 13 mm, and source vapor pressure up to 400 Torr. Cluster size measurements were made on the following materials of moderately low and high melting point: Te, Zn, Se, Mg, Al, Ge, and Ag. Modeling of the dye laser excitation spectra of the Te dimer indicates that the vapor is rotationally cooled down to 150 K for a source pressure of 140 Torr, corresponding to a source temperature of 1073 K. Vibrational temperatures are significantly higher than rotational temperatures for all source conditions. All spectra obtained show only small clusters (<10 atoms per cluster) which are present in the source vapor before expansion. We conclude that a pure vapor source under the expansion conditions investigated does not produce measureable quantities of large clusters.
A basic analysis of pulsed photoacoustic signals using the finite elements method
Authors: Kasai Masanobu , Fukushima Sei , Gohshi Yohichi , Sawada Tsuguo , Ishioka Muneharu , Kaihara Mikio
Published: July 2002

A simulation of pulsed photoacoustic signals using the finite elements method is demonstrated, using a hypothetical cylindrical brass sample surrounded by air, and a weak energy density laser source to prevent the sample from being destroyed. Both the distribution of temperature and also the distribution of thermal deformation and thermal stress in the sample are discussed.
Exact thermal representation of multilayer rectangular structures by infinite plate structures using the method of images
Authors: Palisoc Arthur L. , Lee Chin C.
Published: July 2002

Using the method of images and the analytical temperature solution to the multilayer infinite plate structure, the thermal profile over finite rectangular multilayer integrated circuit devices can be calculated exactly. The advantage of using the image method lies in the enhanced capability of arriving at an analytical solution for structures where analytical solutions do not apparently exist, e.g., circular or arbitrarily oriented rectangular sources over multilayered rectangular structures. The new approach results in large savings in computer CPU time especially for small sources over large substrates. The method also finds very important applications to integrated circuit devices with heat dissipating elements close to the edge boundaries. Results from two examples indicate that the edge boundaries of a device may also be utilized to remove heat from it. This additional heat removing capability should have important applications in high power devices.
Characterization of residual carbon in semi-insulating GaAs
Authors: Boncek R. K. , Rode D. L.
Published: July 2002

We have found that undoped semi-insulating GaAs substrates convert from semi-insulating to strongly conducting p-type behavior following high-temperature annealing (830 and 885 °C) for long periods of time (22–60 h). Remarkably similar results have been obtained for both liquid-encapsulated Czochralski and horizontal Bridgman undoped semi-insulating GaAs synthesized by various manufacturers. Hole concentrations measured at room temperature are about p=9.1×1015 and 3.6×1016 cm−3 after 830 and 885 °C anneals, and p is uniform throughout the 380 to 510 μm substrate thickness for 885 °C anneals. Hall-effect measurements of carrier freeze-out indicate that residual carbon acceptors are the dominant shallow-acceptor species. Conversion to p type appears to arise from out-diffusion of EL2 deep donors and from formation of an additional acceptor-type native defect which also results from arsenic out-diffusion during annealing.
Finite size effects in a metallic spin glass (invited)
Authors: Cowen J. A. , Kenning G. G. , Bass Jack
Published: July 2002

We have observed finite size effects in thin films (20 Å<L<1000 Å) of CuMn with concentrations of 4%, 7%, and 13.5% Mn. In order to have measurable magnetization the samples are produced in the form of multilayers with silicon or copper interlayers. The interlayers are sufficiently thick (tSi =70 Å; tCu =300 Å) so that there are no observable interactions between the CuMn layers. The samples are characterized structurally by low-angle x-ray diffraction, imaging, and x-ray fluorescence using a scanning transmission electron microscope. The metallic films are also characterized by measuring the electrical resistivity of both multilayer and single-layer CuMn samples. The temperature Tg of the peak in the dc susceptibility shifts with film thickness L as (T0g−Tg)/T0g∼L−λ for all concentrations and for both Si and Cu interlayers. The results for 4% Mn will be discussed in detail and compared with previously published data on 7% Mn.
Energy transfer in monolayers with cyanine dye Sheibe aggregates
Authors: Möbius Dietmar , Kuhn Hans
Published: July 2002

A monolayer of an oxacyanine dye organized in Scheibe aggregates is doped with a thiacyanine dye (e.g., one molecule of the guest per 104 molecules of the host). Strong energy transfer from the excited host to the guest takes place at room temperature, the efficiency decreasing with lowering temperature T. The rate of energy transfer is proportional to T. A simple model of the excited state is discussed based on a coherent exciton extending over a certain domain. The exciton moves over the aggregate, occasionally reaching the vicinity of an acceptor molecule. The domain size of the exciton is inversely proportional to the absolute temperature T. As a consequence, the lifetime of the exciton is proportional to T, and therefore the energy transfer efficiency is proportional to T.
Internal fields of a spherical particle illuminated by a tightly focused laser beam: Focal point positioning effects at resonance
Authors: Barton J. P. , Alexander D. R. , Schaub S. A.
Published: July 2002

The spherical particle/arbitrary beam interaction theory developed in an earlier paper is used to investigate the dependence of structural resonance behavior on focal point positioning for a spherical particle illuminated by a tightly focused (beam diameter less than sphere diameter), linearly polarized, Gaussian-profiled laser beam. Calculations of absorption efficiency and distributions of normalized source function (electric field magnitude) are presented as a function of focal point positioning for a particle with a complex relative index of refraction of n̄=1.33+5.0×10−6i and a size parameter of α≊29.5 at both nonresonance and resonance conditions. The results of the calculations indicate that structural resonances are not excited during the on-center focal point positioning of such a tightly focused beam but structural resonances can be excited by proper on-edge focal point positioning. Electric wave resonances were found to be excited by moving the focal point from on-center towards the edge of the sphere parallel to the direction of the incident beam electric field polarization. Magnetic wave resonances were found to be excited by moving the focal point from on-center towards the edge of the sphere perpendicular to the direction of the incident beam electric field polarization.
Room-temperature observation of impurity states in bulk GaAs by photoreflectance
Authors: Pikhtin A. N. , Airaksinen V.-M. , Lipsanen H. , Tuomi T.
Published: July 2002

Photoreflectance (PR) experiments are performed on thick GaAs/GaAs epitaxial layers and on a nearly perfect GaAs single crystal. The first observations of PR spectra induced by impurities (shallow acceptors) in bulk semiconductors like gallium arsenide are reported.
Measurement of a high electrical quality factor in a niobium resonator for a gravitational radiation detector
Authors: Folkner W. M. , Moody M. V. , Richard J.-P.
Published: July 2002

The mechanical and electrical quality factors of a 10-g niobium resonator were measured at 4.4 K and were found to be 8.1×106, and 3.8×106, respectively. The value for the electrical quality factor is high enough for a system operating at 50 mK at a sensitivity level of one phonon. The resonator’s low damping properties make it suitable for use as a transducer for a cryogenic three-mode gravitational radiation detector. A practical design is given for the mounting of the resonator on a 2400-kg aluminum-bar detector. Projections are made for the sensitivity of a 2400-kg bar instrumented as a three-mode system with this resonator inductively coupled to a SQUID.
Gate dielectric and contact effects in hydrogenated amorphous silicon-silicon nitride thin-film transistors
Authors: Lustig Naftali , Kanicki Jerzy
Published: July 2002

The characteristics of glow-discharge hydrogenated amorphous silicon-silicon nitride (a-Si:H/a-SiNx:H) thin-film transistors (TFTs) are reported for various deposition conditions. TFTs incorporating a N-rich nitride gate dielectric, a-SiN1.6:H, are superior to a-Si:H TFTs with a Si-rich gate nitride, a-SiN1.2:H. In particular, the N-rich gate nitride TFTs show considerably less interface or near-interface charging during operation, improved stability, and a higher field-effect mobility. The average field-effect mobility μFE is found to be 0.27 and 0.41 cm2/V s for the Si- and N-rich gate nitride TFTs, respectively. A further improvement in mobility, μFE =0.61 cm2/V s, is achieved by increasing the N-rich gate nitride deposition temperature from 250 to 450 °C. These results suggest that N-rich a-SiNx:H, deposited at elevated temperatures, yields a more abrupt or ‘‘cleaner’’ a-SiNx:H/a-Si:H interface. We also show, for the first time, that using n+ μc-Si:H source-drain contacts in place of n+ a-Si:H improves device performance, yielding an average field-effect mobility of 0.84 cm2/V s, with an activation energy of 0.069 eV.
Accurate measurement of trivalent silicon interface trap density using small signal steady-state methods
Authors: Miller Jimmie A. , Blat Catherine , Nicollian Edward H.
Published: July 2002

The high–low-frequency capacitance method for determining the interface trap density is widely used in studying the effects of ionizing radiation on thermally grown SiO2, and in verifying the trivalent silicon interface traps first discovered in electron paramagnetic resonance studies. It is shown that the high–low-frequency capacitance method gives fictitious interface trap density peaks because of the departure of the 1-MHz high-frequency capacitance from the ideal high-frequency capacitance. This method gives accurate values of the interface trap density near the center of the silicon band gap, but for a given high frequency, the range of band-gap energy over which accurate values are obtained decreases with increasing interface trap density. Interface trap density is obtained over a band-gap energy range with an accuracy that is independent of interface trap density from a comparison of the measured and calculated slopes of gate bias versus equilibrium band-bending curves using the Q-C (charge-capacitance) method. The accuracy of this method is verified using the conductance method. This work shows that it is not likely that interface traps are trivalent silicon defects superimposed on a U-shaped background interface trap distribution of unknown identity.
Comparative study of photorefractive Bi12SiO20 crystals
Authors: Strohkendl F. P. , Tayebati P. , Hellwarth R. W.
Published: July 2002

We present the results of a comparative experimental study of optical and photorefractive properties at room temperature of four nominally undoped, single-crystal, commercially obtained, samples of cubic Bi12SiO20. We studied (1) the steady-state energy exchange between two overlapping 515-nm beams, (i.e., ‘‘beam coupling’’), (2) the decays of photorefractive (trapped-charge) gratings induced by uniform illumination, (i.e., ‘‘grating erasure’’), (3) spontaneous decay of photorefractive gratings in the dark (i.e., ‘‘dark decay’’), (4) photochromic damage, and (5) standard optical properties such as absorption coefficients and rotatory power. Fitting our results to a simple model of photoexcitation of both electrons and holes from a single species of deep traps, we obtained values for the effective density of deep traps, the diffusion lengths of both electrons and holes (i.e., mobility-lifetime products), quantum efficiencies (near unity), and the ratio of the electron and hole contributions to absorption at 515 nm. Although unexplained or anomalous grating decay characteristics were observed, the model gives an excellent overall account of photorefractive behavior, and suggests that this type of crystal would be suitable for making devices with predictable behavior.
Preparation of epitaxial ABO3 perovskite-type oxide thin films on a (100)MgAl2O4/Si substrate
Authors: Matsubara Shogo , Miura Sadahiko , Miyasaka Yoichi , Shohata Nobuaki
Published: July 2002

Epitaxial thin films of ABO3 perovskite-type oxides, including PbTiO3, (Pb0.90La0.10) (Zr0.65Ti0.35)0.975O3,BaTiO3, and SrTiO3, have been successfully obtained by rf magnetron sputtering on (100)Si substrate with an intermediate epitaxial layer of MgAl2O4. Only PbTiO3 grew in the tetragonal crystal structure and other materials grew in the cubic structure. The unit axis direction of the perovskite-type oxide films was coincident with that of the underlying MgAl2O4 films. The tetragonal PbTiO3 films were a mixture of c and a domain. The preferred orientation of the tetragonal PbTiO3 film, that is c to a domain volume ratio, could be controlled by the conditions of sample cooling after the deposition. Highly c-axis oriented films, which consisted of more than 90% c domains, were produced by cooling the sample at a high cooling rate, typically 30 °C/min, and by maintaining an rf plasma during cooling. The mechanism of the preferred orientation of PbTiO3 film has been explained by a balance of compressive stress due to a self-bias effect and tensile stress due to the lattice mismatch and due to the lattice anisotropy of tetragonal PbTiO3.
A deep-level transient spectroscopy study of high electron mobility transistors subjected to lifetime stress tests
Authors: Magno R. , Shelby R. , Anderson W. T.
Published: July 2002

Current and capacitance deep-level transient spectroscopy (DLTS) measurements have been used to examine the effect of accelerated lifetime stress tests on AlGaAs/GaAs high electron mobility transistor structures. The epilayers for these devices were grown by molecular beam epitaxy on semi-insulating GaAs substrates, and they were processed to have 0.7-μm long gates. The major defect detected by both the capacitance and current measurements on unstressed control devices is the DX center in the AlGaAs. The current DLTS tests on stressed samples reveal an additional defect, which is not found in capacitance DLTS measurements on the same devices. The new current DLTS line appears to be a minority-carrier trap, which is not expected as the trap filling pulse was not set to inject minority carriers. These features can be explained if the defect is associated with surface states located between the gate and either the source or the drain.
Low-temperature and selective growth of β-SiC using the SiH2Cl2/C3H8/H2/HCl gas system
Authors: Ohshita Y. , Ishitani A.
Published: July 2002

β-SiC is grown on a Si (100) substrate by the chemical vapor deposition method using the SiH2Cl2/C3H8/H2/HCl/ gas system. The addition of HCl to the SiH2Cl2/C3H8/H2 gas system makes it possible to grow stoichiometric β-SiC at the low temperature of 1000 °C. Moreover, β-SiC selective deposition on a Si (100) surface, with no nucelation on a SiO2 surface, is achieved in more than 1.5% HCl concentration. The mechanism of low-temperature selective β-SiC growth due to HCl addition is discussed.
An alternative proof of the generalized reciprocity theorem for charge collection
Authors: Donolato C.
Published: July 2002

An alternative proof is given of the generalized reciprocity theorem for charge collection discussed by Misiakos and Lindholm [J. Appl. Phys. 58, 4743 (1985)]. The present analysis directly yields an equation for the distribution of the charge collection probability in quasi-neutral regions of a semiconductor device and the associated boundary conditions.
Anatomy of a vertical metal halide discharge
Authors: Dakin James T. , Rautenberg Theodore H. , Goldfield Evelyn M.
Published: July 2002

Experimental measurements are compared with model calculations for a vertical metal halide discharge. The 400-W arctube has a gap of 4.3 cm, an inside diameter of 2.0 cm, and operates at about 5-atm Hg pressure with NaI and ScI3 additives. Emission spectroscopy is used to measure the discharge temperature and the densities of additive species. The model is based on the assumption of local thermodynamic equilibrium, and predicts the discharge behavior from first principles. Coupled equations describing the convective fluid flow, chemical equilibrium and diffusion, radiation transport, and discharge current flow are solved simultaneously so as to provide a self-consistent description of the discharge. Model results are compared with the experimental measurements. Discharge features such as the hot contraction regions near the electrode tips, and the depletion of additives from the upper parts of the discharge are discussed. Particular attention is paid to quantitative details of the Na diffusion.
Raman scattering study of lattice disorder in 1-MeV Si-implanted GaAs
Authors: Braunstein G. , Tuschel D. , Chen Samuel , Lee S.-Tong
Published: July 2002

We have used Raman scattering to study the lattice disorder created by the implantation of 1-MeV Si ions into GaAs. Using the change in the longitudinal optical (LO) phonon-line position as the signature for lattice damage, combined with chemical etching for controlled layer removal, we monitored the evolution of the disorder depth profile as a function of implantation dose. The shape of the depth profile of the disorder agrees with the theoretical simulation trim for doses of 1×1014 cm−2 or lower. For higher doses a saturation is observed in the amount of residual disorder. This saturation is a manifestation of dynamic annealing occurring during the high-energy implantations, which we attribute to enhanced defect mobility, induced by the transfer of energy to the lattice, in atomic collision cascade processes. In order to correlate the spectral features in the Raman spectra with structural changes in the ion-implanted samples, we characterized the implantation-induced lattice damage using ion-channeling and transmission electron microscopy (TEM) measurements. The residual defects in the MeV-implanted samples are found to consist of dislocation loops and discrete point defects dispersed in an otherwise perfect (although probably strained) crystalline lattice. An average distance between defects was estimated from the channeling and TEM studies, and compared with the coherence-length parameter L used in the ‘‘spatial correlation model,’’ which is commonly used to interpret quantitatively the Raman spectra of ion-implanted materials. Although the model gives a good fit to our data in terms of the position and linewidth of the LO phonon peak, no clear correlation could be established between L and the interdefect separations. We also observed the appearance of the broadbands at about 70, 180, and 245 cm−1, in the Raman spectra, which are commonly attributed to amorphous GaAs, although no trace of amorphous material was detected by the TEM analysis. Our results indicate that the quantitative interpretation of Raman spectra to determine crystalline properties of ion-implanted materials, as well as the assignment of Raman spectral features to particular defect structures, is not unambiguously established yet.
Current channel migration and magnetic field penetration in a perfectly conducting plasma with emitting, conducting boundaries
Authors: Grossmann J. M. , Ottinger P. F. , Mason R. J.
Published: July 2002

In collisionless simulations of the plasma erosion opening switch, a highly conductive plasma allows magnetic field penetration through the entire length of the plasma, to depths almost two orders of magnitude greater than the collisionless skin depth, c/ωpe. Field penetration is accomplished by a narrow (skin-depth-like) current channel that migrates through the plasma. The plasma behind the current channel is unable to shield the rising magnetic field from the body of the plasma and allows it to penetrate almost instantly and completely through the plasma up to the current channel. The migration of the channel and the penetration of the field appear to occur in the absence of both Coulomb collisions and instabilities. These unusual features are permitted by the electric field structure in the plasma behind the current channel and the presence of conducting boundaries that can emit electrons.
Simulation of the switching performance of an optically triggered pseudo-spark thyratron
Authors: Pak Hoyoung , Kushner Mark J.
Published: July 2002

The optically triggered pseudo-spark, also known as the back-lit thyratron, is a low-pressure plasma switch having an unheated metallic cathode, which has performance specifications competitive with conventional hot cathode thyratrons. In this paper a computer simulation of the BLT is presented. The simulation consists of a 2 1/2 -dimensional time-dependent continuum model for electron and ion transport using the local field approximation. The model includes an external circuit, and the user may specify the type of gas, pressure, geometry, and electrode materials. Predictions for the anode delay time are compared to experiment as a function of pressure (p), cathode-anode spacing (d), and trigger fluence. We find that switch closure depends critically on the formation of a virtual anode in front of the cathode hole by generation of positive space charge, and that the anode delay time decreases with increasing p, trigger fluence d, and cathode hole diameter. We also find switch performance is not well characterized by the pd product as in other plasma switches. Rather, we find these quantities depend separately on p and d in a manner which is a function of the geometry of the cathode.
Charge transfer in ZnS-type electroluminescence
Authors: Bringuier E.
Published: July 2002

In this paper, a simple model for the charge transfer in thin-film, ac-driven electroluminescent structures of doped ZnS type is proposed. We first review the minimal assumptions needed to account for the carrier emission under high-field conditions and its subsequent feedback on the field strength; it opens the way to a quantitative description of the field variation with time and the conduction current under arbitrary low-frequency drive conditions and without using any adjustable parameter. The charge-voltage relationships are also examined in detail. Conduction in the phosphor layer is assumed to originate from deep levels (traps) in the phosphor forbidden band gap, located at the insulator-phosphor interface. These levels act for charge storage, too. When a discrete trap level is considered, field clamping in the active layer is obtained; when a smooth interface-state energy density is assumed, deviations from the field clamping are possible and simply related to the interface parameters. Most of the work is analytical and the model is shown to exhibit the main qualitative features of nonmemory devices.
Magnetic properties of Fe-based diluted magnetic semiconductors (invited)
Authors: Twardowski A.
Published: July 2002

In recent years considerable interest was focused on diluted magnetic semiconductors (DMS), mainly Mn-based DMS. Mn++ ions in these materials possess only spin momentum (S=5/2), which is the source of the permanent magnetic moment localized on Mn ions. On the other hand, a new class of Fe-type DMS can serve as a much more general example, since Fe++ ions possess both spin and orbital momenta (S=2, L=2). Consequently the ground state of an Fe++ ion is a magnetically inactive singlet, and one is dealing only with field induced magnetic moments associated with Fe ions. This situation yields a substantially different magnetic behavior of Fe-based DMS with respect to Mn-type materials. In that respect, we review the magnetic properties of Fe-type DMS-like ZnFeSe, CdFeSe, HgCdFeSe, and HgFeSe. The influence of nonvanishing orbital momentum on specific heat, susceptibility, and magnetization is pointed out. We also show evidence of antiferromagnetic exchange interaction between Fe ions in these crystals. A possible (superexchange) mechanism of this interaction is discussed. A survey of exchange interaction parameters is presented.
Slow wave radiation fields of a slotted line antenna
Authors: Ganguli A. , Baskaran R.
Published: July 2002

The slow wave radiation fields of a slotted line antenna are calculated inside the antenna region. For this, a realistic magnetic current distribution, which takes into account the wave-slowing action of the antenna has been chosen. It is shown that the assumed distribution becomes accurate when the number of slots is large. The numerical results show that the radial component of the electric field is the dominant component, while the on-axis value of the axial component of the magnetic field decreases with increasing antenna radius. Relevance of the results to high density plasma production using such structures is pointed out.
Saturated laser-induced fluorescence in a high-pressure metal halide discharge
Authors: Kramer Jerry
Published: July 2002

Local measurements of the saturated laser-induced fluorescence (LIF) signal from pulsed laser excitation of the 6 3 P1 resonance state of Hg have been obtained in a high-pressure metal halide lamp. Hg atoms were excited at 436 nm (6 3P1 →7 3S1 ) and the laser-induced fluorescence was detected at 546 nm (7 3S1 →63P2 ). The LIF signals were obtained as a function of radial position and the ac phase angle. The LIF signals were corrected for the optical depth of the fluorescence. The LIF measurements were made under saturated conditions to minimize the spatial dependence of the fluorescence quantum efficiency in the discharge. The 6 3P1 density was a maximum at the arc center and monotonically decreased towards the wall. The relative 6 3 P1 profile was broader at the current zero crossing than at the current maximum. The 6 3 P1 density was undermodulated during the ac phase at the arc center compared to predictions based on the Hg 577-nm emission, suggesting a departure from local thermodynamic equilibrium. At a reduced radius of 0.62, the 6 3 P1 density was almost independent of phase angle. Estimates of the 6 3 P2 density were obtained from the optical depth. LIF measurements were also obtained by exciting the 6 3P2 level of Hg at 546 nm and detecting the fluorescence at 436 nm. The spatial and phase angle dependence of the LIF signals from a mercury discharge were very similar to the results from a metal halide lamp.