bluuebunny/crossref_metadata_2025 huggingface dataset:
High-resistance regions produced in an
Authors: Tell B. , Chang T. Y. , Brown-Goebeler K. F. , Kuo J. M. , Sauer N. J.
Published: July 2002

The sheet resistance, Hall mobility, and carrier concentration as a function of He ion dose have been measured across the In1−x−yGaxAlyAs system. Starting with heavily doped n-type epitaxial layers (n∼1018 cm−3), except for the lowest band-gap constituent In0.53Ga0.47As, the sheet resistance can be increased more than five orders of magnitude for He doses above 2.5×1013 cm−2. For the other constituents, the sheet resistance can be made high enough and sufficiently thermally stable to be potentially useful for device applications.
Finite element analysis of thermal stresses in optical storage media
Authors: Evans K. E. , Nkansah M. A. , Abbott S. J.
Published: July 2002

Finite element techniques are used to calculate the thermal stresses generated in single-layer, optical storage thin films. The calculations predict that the thermal stresses generated by laser heating may reach values well beyond the strength of the media in times much less than that for pit formation by melting. Both dye-polymer and metal-based systems are considered with either air or substrate incident laser sources.
On the choice of a magnetostrictive transducer for interferometric magnetometry
Authors: Brugel D. , Gibbs M. R. J. , Squire P. T.
Published: July 2002

We report a study of the ac-induced magnetostriction of METGLAS 2605SC metallic glass ribbons, showing that transverse-field-annealed samples are extremely sensitive to small tensile stresses, and that under such conditions superior results can be obtained by annealing to produce a small volume fraction of surface crystallites.
Fluorine redistribution in a chemical vapor deposited tungsten/polycrystalline silicon gate structure during heat treatment
Authors: Eriksson Th. , Carlsson J.-O. , Keinonen J. , Petersson C. S.
Published: July 2002

Fluorine redistribution during heat treatment of chemical vapor deposited tungsten/polycrystalline silicon gate structures was analyzed by the nuclear resonance broadening technique. The tungsten layer was deposited from a hydrogen/tungsten hexafluoride gas mixture. Upon heat treatment in the temperature range 1020–1325-K tungsten disilicide formation was observed using Rutherford backscattering spectrometry. In the as-deposited sample, the fluorine was accumulated at the tungsten/polycrystalline silicon interface. After silicide formation the fluorine was observed at the tungsten disilicide/polycrystalline silicon interface. At temperatures above 1120 K fluorine starts to diffuse through the polycrystalline silicon layer. A variation in the total fluorine content between the samples was also observed. The origin of the fluorine redistribution as well as the variation in the total fluorine content is discussed in connection to conceivable mechanisms.
Compression of a single electromagnetic pulse in a spatially modulated nonlinear dielectric
Authors: Ikezi H.
Published: July 2002

Single electromagnetic pulses propagating in a spatially modulated nonlinear dielectric are compressed temporally. The system discussed may generate very short, high-power electromagnetic pulses.
Trapping of hydrogen implanted into titanium
Authors: Takeuchi Y. , Imanishi N. , Toyoda K. , Uchino T. , Iwasaki M.
Published: July 2002

Depth profiles and annealing behaviors of hydrogen implanted into titanium samples at an energy of 10 keV per nucleon were measured in the implantation temperature and fluence ranges of 77–400 K and of 6.3×1016–3.3×1018 H/cm2, respectively. Trapping enthalpies are deduced from the annealing curves. It was found that the trapping mechanism of hydrogen implanted into Ti depends on both the temperature and the fluence at the implantation. When implanted at a temperature sufficiently higher than 273 K, hydrogen moves from the surface layer to an underlying bulk and precipitates as hydride irrespective of fluence. On the other hand, at a temperature around or below 273 K, the implanted hydrogen atoms are trapped by the vacancies at a low concentration of hydrogen. However, hydride formation is realized where the local atomic ratio of H/Ti becomes close to the stoichiometric value of TiH2.
Comment on ‘‘Clockwise C-V hysteresis phenomena of metal–tantalum-oxide–silicon-oxide–silicon (P) capacitors due to leakage current through tantalum oxide’’ [J. Appl. Phys. 62, 4277 (1987)]
Authors: Voorthuyzen J. A.
Published: July 2002

Questions are raised concerning the ac conductance measured by J.-G. Hwu et al. [J. Appl. Phys. 62, 4277 (1987)] and its lack of frequency dependence.
Novel InSb/photochemical native oxide interface
Authors: Kepten A. , Shacham-Diamand Y. , Schacham S. E.
Published: July 2002

A novel interface to InSb based on photochemical native oxide (PNOX), which improves conventional ultraviolet (UV) enhanced deposition, is reported. Prior to the deposition of SiO2, an additional stage of growing a native oxide by exposing the semiconductor to N2O and Hg vapors at low pressure under UV illumination is introduced. Composition and electrical properties of the interface are discussed. Compositional analysis was performed by Auger electron spectroscopy. Electrical properties were characterized using metal-insulator semiconductor (MIS) capacitors and photodiodes implemented with UV enhanced chemical vapor deposition (CVD) oxide/PNOX/InSb. Interface state densities of 2–4×1011 cm−2 eV−1 are obtained with good uniformity and stability. The hysteresis of the MIS structure with 1000 Å photoinduced CVD oxide on PNOX is very small, about 0.32 V for a ±20 V span measured at 77 K.
Localized epitaxial growth of CrGe on (111) and (001) germanium
Authors: Hsieh Y. F. , Chen L. J.
Published: July 2002

Epitaxial CrGe was grown locally on both (111) and (001) Ge by a solid-phase epitaxy scheme. Both plan-view and cross-sectional transmission electron microscopy were applied to determine the orientation relationships between epitaxial CrGe and germanium substrates, and to characterize the microstructural features of epitaxial regions and CrGe/Ge interfaces. The best CrGe epitaxy was obtained in (111) samples annealed first at 250 °C for 1 h followed by heat treatment at 600 °C for 1 h. Epitaxial regions as large as 20 μm in size were observed. CrGe was the first refractory germanide grown epitaxially on germanium. The quality of epitaxy is also unsurpassed by any metal germanide epitaxy achieved to date. The growth of a number of epitaxial germanides on germanium with regular atomic arrangements at the interfaces may facilitate the basic understanding of metal-semiconductor interactions as well as enhance the performance of various semiconductor-based devices.
Electric-field-induced absorption effect in LPE-grown InGaAsP/InP multi-quantum-well waveguides
Authors: Ishino Masato , Matsui Yasushi , Sasai Yoichi , Ogura Mototsugu
Published: July 2002

Multi-quantum-well (MQW) strip-loaded waveguides, which are composed of liquid-phase-epitaxy-grown InGaAsP/InP systems, have been characterized in detail. Several MQW waveguides with well depths (Lz) ranging from 100 to 240 Å have been compared with bulk ones about the electric-field-induced absorption effect, considering the zero-bias propagation loss and the optical confinement factor in the region in which absorption occurs. It has been confirmed that the MQW (Lz∼100 Å) waveguides have an absorption change under the electric field more than five times larger than the bulk ones with the same zero-bias propagation loss.
Enhancements in the output energy of a KrF oscillator
Authors: McCown A. W. , Godard J. A. B.
Published: July 2002

Enhancements of up to 45% in the output energy of a KrF excimer laser have been observed following optical pumping of the resonator with as little as 1 mJ of 248-nm radiation from an external source. Polarization of the input beam leads to enhancement and partial polarization of the output pulse for time delays between the 2 pulses of up to 100 ns. Enhancement is not seen in seeding experiments performed on a KrF amplifier, indicating that the oscillator energy enhancement is due to optical seeding of the resonator cavity, resulting in a shorter amount of time required for the laser to reach threshold.
Effect of annealing on the electrical and structural properties of rf-sputtered TaSi2 Schottky contacts to GaAs
Authors: Whipple G. H. , Thompson M. G. , Kulkarni A. K.
Published: July 2002

TaSi2/GaAs Schottky contacts were fabricated, capped with SiO2, and annealed in flowing N2 at temperatures ranging from 400 to 900 °C. The electrical characteristics of the contacts were investigated through the use of current-voltage (I-V) and capacitance-voltage (C-V) techniques. The structure of the TaSi2/GaAs interface was studied by Auger electron spectroscopy. After annealing at temperatures up to 600 °C the electrical characteristics of the contacts improved. Degradation of the electrical characteristics was observed after annealing at temperatures above 600 °C. Some correlation was observed between the electrical characteristics and the structure of the GaAs/TaSi2 interface. The degradation is believed to be related to increased amounts of carbon and oxygen at the interface and an increased amount of oxygen in the TaSi2 film.
Photochromic film of 6-nitro-1′, 3′,3′-trimethylspiro-[2H-1-benzopyran -2, 2′-indoline] prepared by plasma polymerization
Authors: Matsui Kazunori , Yoshida Shuuji
Published: July 2002

Polymeric film of 6-nitro-1′, 3′, 3′-trimethylspiro-[2H-1-benzopyran-2, 2′-indoline](SP) was prepared by a plasma polymerization process and showed good surface morphology. It was found by ultraviolet-visible and infrared absorption studies that the molecular structure of SP after polymerization revealed a structure almost identical to that of the original compound. The film showed reversible photoisomerization and, accordingly, photochromism. These photochromic properties were much better in the polymerized film than for film prepared by the evaporation process.
Plasma scrape-off effect in a magnetized hollow-cathode arc discharge
Authors: Byszewski W. W. , Hummernbrum F. , Jauernik P. , Kempkens H. , Uhlenbusch J.
Published: July 2002

Simultaneous measure of Thomson and Rayleigh light scattering were performed in order to determine electron density, electron temperature, and neutral density distributions in a hollow-cathode arc. These measurements were performed in argon, nitrogen, helium, and hydrogen at approximately 1 Pa. The hollow-cathode arc has also been studied in nitrogen and argon at high pressures ranging from 1–550 Pa. In this paper we present only high-pressure data for nitrogen, although comparison with some results obtained in argon is provided. A plasma scrape-off effect leads to a reduction in electron density in front of the anode and consequently to an enhancement of the anode fall. This enhancement was detected through an increase in electron temperature.
Charge loss from a high-velocity ballistic probe in a high-pressure, low-density plasma
Authors: MacLatchy C. S.
Published: July 2002

An experiment has been performed to study the loss of charge from a high velocity probe as it passes through a high-pressure, low-density plasma generated by a flame. Charged projectiles are fired through the flame and the loss of charge is measured as a function of the flame density and the projectile speed. Expressions are derived for the charge loss based on the thin sheath, thick sheath, and the field-limited/sheath convection models normally used to describe the behavior of Langmuir probes. For a low-density flame plasma, the sheath conduction turns out to be field limited and the exponential function describing the charge loss has been verified experimentally. The charge loss from the ballistic probe is used to compute the electron density profile of the flame. At the sound velocity in air, the residual charge after passing through the flame suddenly drops to near zero, suggesting that the sheath conduction mechanism changes radically as the velocity passes through the transonic region. This result may have far-reaching implications for the use of Langmuir probes at transonic and supersonic speeds.
The tilted waveguide semiconductor laser amplifier
Authors: Salzman Joseph , Hawkins Raymond J. , Zah C. E. , Menocal Serafin , Lee T. P.
Published: July 2002

The performance of a tilted waveguide semiconductor laser amplifier is shown to be affected by tilt-induced intermode coupling at the mirrors of the device. We find that, for some device parameters, higher-order gain-guided modes can dominate the output field pattern of the amplifier even when the gain of the fundamental mode is greater than that of the higher-order modes. A simple coupled-mode analysis is presented to explain these observations, and the observed far-field intensity distribution of a laser amplifier is compared with the calculated results.
Characterization of GaAs implanted with molecular ions
Authors: Tamura Akiyoshi , Onuma Takeshi
Published: July 2002

We have investigated fundamental electrical and optical characteristics of GaAs implanted with SiFx and SFx (x=1, 2, and 3) molecular ions at energies which give the same dopant atom (Si or S) ion ranges. Three kinds of annealing methods were compared. Characterization of these implanted GaAs layers was carried out by the Hall effect, capacitance-voltage, secondary ion mass spectrometry, and 77-K photoluminescence measurements.
Ion implantation and rapid thermal annealing of Mg, Cd, and Si in AlxGa1−xAs grown by molecular-beam epitaxy
Authors: Lam Christine S. , Fonstad Clifton G.
Published: July 2002

Ion implantation and rapid thermal annealing of Mg, Cd, and Si in AlxGa1−xAs are reported. The dependence of activation on various Al compositions (x=0.15–0.35) and annealing temperatures was investigated. Activations of over 60% were achieved for both Mg and Cd. However, for the same annealing cycle, the activation efficiency of the Mg implants was found to be generally higher than that of Cd implants. No particular dependence of the activation efficiency on Al composition was observed for either ion. For Si29 implants, poor activation was observed in samples with x above 0.2, while for x=0.2 a maximum activation of 80% was achieved with a 1000 °C, 5 s annealing cycle.
A critique of contact charge spectroscopy
Authors: Lowell J. , Rose-Innes A. C. , El-Kazzaz A. M.
Published: July 2002

We describe further experiments to determine whether the charge transfer to a polymer from a series of metals is additive. We conclude that charge transfer is not additive if all the metals contact the same region. This conclusion remains valid over a wide range of sample preparation methods, and shows that the concept of a charge transfer window and the associated technique of ‘‘contact charge spectroscopy’’ may be invalid.
Heating of a dense plasma using a relativistic electron beam
Authors: Benage J. F. , Jones L. A. , Kania D. R. , Begay F.
Published: July 2002

We have carried out an experiment to measure the heating of a dense carbon plasma, ne∼1018–1019 cm−3, by a relativistic electron beam. Using spectroscopic methods, the temperature of the plasma was measured. By taking into consideration the heat loss mechanisms in the plasma, the amount of energy deposited into the plasma by the beam was determined. The results are consistent with theoretical predictions.
Comparison of the aperture and chromatic aberrations of magnetic round lenses with those of quadrupole doublets
Authors: Ling K. M. , Moses R. W.
Published: July 2002

The paraxial equation for rotationally symmetric magnetic lenses is integrated numerically by using the Numerov method. The normalized third-order aperture and second-order chromatic aberration coefficients (C3N and CcN) are calculated. A Fourier representation of the lens field is used, and a search for minimum C3N is carried out by varying the Fourier coefficients. Comparisons with comparable quadrupole doublets, and calculations of C3N and CcN for actual coil systems are presented. The main conclusion is that magnetic round lenses are about a factor of 2 better than comparable magnetic quadrupole doublets as far as the third-order aperture aberration is concerned, but the chromatic aberrations in both systems are comparable.
A submicrometer Nb/AlOx/Nb Josephson junction
Authors: Imamura Takeshi , Hasuo Shinya
Published: July 2002

High-quality, submicrometer Nb/AlOx /Nb Josephson junctions were fabricated. The junction area was defined by anodizing an upper Nb electrode using a thin SiO2 mask. By utilizing the anodized Nb as an etch stop during the reactive ion etching of the contact hole in an SiO2 insulator, we could make a junction smaller than the contact hole size. Using stress-free Nb for the junction electrodes was crucial in achieving good current-voltage characteristics. High-quality Nb/AlOx /Nb junctions as small as 0.7 μm square were produced. The quality parameter Vm was greater than 30 mV for a jc of 6800 A/cm2.
Reply to ‘‘Comment on ‘A new model of the rapid initial oxidation of silicon’ ’’
Authors: Schafer S. A. , Lyon S. A.
Published: July 2002

The inconsistencies with experiment claimed by Y. Z. Lu and Y. C. Cheng, J. Appl. Phys. 64, 1607 (1988), are only apparent.
Collisional-induced absorption in calcium rare-gas collisions
Authors: Coutts J. , Peck S. K. , Cooper J.
Published: July 2002

We have investigated the collisionally induced line shapes corresponding to the 1S0→1D2 4575-Å electric quadropole transition in neutral calcium for a variety of rare-gas perturber species. We interpret our results in terms of molecular potentials.
Preparation and electrical properties of polymeric TCNQ and TCNE films by plasma polymerization
Authors: Osada Y. , Yu Q. S. , Yasunaga H. , Wang F. S. , Chen J.
Published: July 2002

The plasma polymerization of TCNQ (tetracyanoquinodimethane) and TCNE (tetracyanoethylene) was carried out at 13.56 MHz from the gas phase and semiconductive polymeric films were obtained. The electrical conductivities of the films obtained ranged from 10−10 to 10−6 S cm−1 and the Al/polymer/ITO (indium tin oxide) sandwich cells made from the films showed rectifying behavior and photovoltaic response. Photoconductivity was also observed in the films. Infrared spectroscopy, ultraviolet spectroscopy, and x-ray photoelectron spectroscopy were utilized to characterize the structure, and these results as well as those from electrical measurements confirmed that a certain conjugation structure when the π electrons delocalized have been formed in the films. The influence of plasma polymerization conditions on the structure and electrical properties of films is also discussed.
Thermal stability of aluminum-tin-oxide thin-film interface
Authors: Eser E. , Ramos F. , Grez J.
Published: July 2002

Thermal stability of an Al/SnO2 contact was investigated in the temperature range of 120–166 °C. Contact resistance measurements showed that the degradation in a neutral ambient or in clean and dry air follows two different regime. At early stages contact resistance increases exponentially with the square root of time, possibly indicating the presence of a tunneling type of current flow through the interface. Activation energy for this process was found to be 0.91 eV. At later stages the contact resistance increases proportionally to the square root of time. In humid air catastrophic failure of the contact was observed. The degradation in this case was found to be more than two orders of magnitude higher compared to the degradation in dry or neutral ambient. In all cases, a 100-Å Ti barrier layer was found to virtually stop the degradation under the circumstances investigated in the present work. Auger electron spectroscopy analysis showed that the degradation of the contact is due to the diffusion of Al into the SnO2 film and the subsequent reduction of SnO2, resulting in the formation of Al2O3/metallic Sn mixture at the interface. The Ti barrier layer prevents the degradation process by acting as a diffusion barrier for Al.
Magnetic anisotropy in Ni/Fe artificial lattice film
Authors: Nagai Yasuhiro , Yanagisawa Keiichi , Senda Masakatsu
Published: July 2002

This paper presents an experimental investigation on the magnetic anisotropy and heat stability in Ni/Fe artificial lattice films. Magnetic anisotropy is found to increase as the lattice period and the Fe layer thickness decrease. The annealing of Ni/Fe films is shown to decrease hard-axis coercivity to 0.3 Oe. However, annealing at temperatures above 400 °C causes an increase in coercivity, perfect alloying of the Ni/Fe film, and recovery of the crystallinity of the Fe layer sandwiched between Ni layers. In the Ni/Fe (2/10 nm) film, very small magnetostriction and large saturation magnetization are maintained up to 350°C. A prototype thin-film head with a Ni/Fe yoke shows stable conventionally reproduced signals for small write currents, superior overwrite properties, and good heat stability at annealing temperatures below 300 °C.
A study of layer composition of InGaAs/InP multiquantum wells grown by metalorganic chemical vapor deposition using double-crystal x-ray diffraction theory and experiment
Authors: Barnett S. J. , Brown G. T. , Courtney S. J. , Bass S. J. , Taylor L. L.
Published: July 2002

InGaAs/InP multiquantum wells grown by metalorganic chemical vapor deposition have been studied by fitting computer simulated theoretical double-crystal x-ray rocking curves to experimental data. It is shown that the technique can identify the carry over of As into the InP barriers and the concentration and distribution of As are determined. The highest concentration of As observed was 21%, which was confined to the first 50 Å of the barrier and fell to 2% towards the following interface. Both the maximum and minimum concentration of As was found to decrease as a function of the pause time between growth of the InGaAs quantum well and the InP barrier layers. These observations were confirmed by secondary ion mass spectrometry (SIMS) and other experimental data on the same material is shown to support the results.
Light-induced degradation in undoped hydrogenated amorphous silicon films studied by the surface photovoltage technique: A comparison of lifetime versus space-charge effects
Authors: Hegedus Steven S. , Lin Hong-sheng , Moore A. R.
Published: July 2002

The calculation of the space-charge density under illumination from surface photovoltage measurements has been adapted to analyze light-soaking experiments in intrinsic hydrogenated amorphous silicon (a-Si:H). We find that the positive space-charge densities increase and the space-charge widths decrease with light exposure while very little change occurs in the hole diffusion length. These results indicate that changes in electric field distribution with light soaking are important causes of degradation of amorphous silicon solar cells, rather than changes which may ocur in the hole diffusion length. We also review and discuss results of others regarding application of the surface photovoltage (SPV) to study light-induced phenomena, evidence of two different types of light-induced defects, and potential limitations of SPV in a-Si:H.
Temperature stability of AlxGa1−xAs (0≤x≤1) thermal oxide masks for selective-area epitaxy
Authors: Jones Stephen H. , Lau Kei May , Pouch John J.
Published: July 2002

The use of thermal oxides of AlxGa1−xAs (0≤x≤1) as masking materials for selective-area epitaxy by organometallic chemical-vapor deposition has been investigated. It was found that the thermal oxide of GaAs is only applicable for low growth temperatures (≤600 °C), and the addition of aluminum significantly improves the thermal stability of the oxide. The oxide of Al0.4Ga0.6As is suitable for high-temperature deposition, but there are criteria for the thickness and oxidation temperature. Thin layers of AlAs oxidized at 475 °C are excellent masks and allow precise thickness control. Promising results of selective-area deposition using these aluminum oxide masks have been obtained. High-quality single crystal grew in mask openings uniformly surrounded by dense and fine-grain polycrystalline deposits, producing a planar duplication of the original pattern.
Comment on ‘‘Carrier concentration and activation energy in heavily donor-doped silicon’’ [J. Appl. Phys. 6
1, 591 (1987)]
Authors: Neumark G. F.
Published: July 2002

The present comment discusses some aspects of a recent analysis by Schechter of relative agreement between two theories and data in the heavy doping range. It is pointed out that this analysis uses an earlier theory of mine beyond its validity range, and that within its validity range the agreement given by my theory is fully as good as that of the other one (by Lee and McGill). It is pointed out that to select the better of the two theories, an examination of the respective physical assumptions seems called for. A comparison which summarizes differences in these assumptions is given, and highlights the necessity for further detailed work for a determination of the best set of assumptions.
Emission spectra of single quantum well lasers with inhomogeneous current injection
Authors: Tokuda Yasunori , Abe Yuji , Matsui Teruhito , Kanamoto Kyozo , Tsukada Noriaki , Nakayama Takashi
Published: July 2002

Emission spectra of a tandem-type GaAs single quantum well laser diode were investigated under pulsed operating conditions. By controlling the two injection current levels, we could force the device to operate not only at the lowest (n=1) quantized state transition but also at the second (n=2) transition. Anomalous pulse responses, moreover, were found for the two lasing modes which were simultaneously observed in time-integrated spectra. The dynamic emission behavior was utilized to achieve a variety of intensity combinations of the two radiation modes at the widely different wavelengths.
Generalized semiclassical quantum 1/f noise theory. I. Acceleration 1/f noise in semiconductors
Authors: van der Ziel Aldert
Published: July 2002

A generalized derivation of van der Ziel’s semiclassical 1/f noise theory is given. It includes 1/f noise in collision-free devices and collision 1/f noise in collision-dominated devices, but also acceleration 1/f noise in the latter devices; this is a new noise source. In all cases the Hooge parameter αH can be expressed in a similar form. The Hooge parameter of the third noise source varies as the square of the device length d as long as d is not too large. For very large d the Hooge parameter may saturate and this saturated value may correspond to Handel’s coherent state 1/f noise. For very large drift times τd deviations from the 1/f spectrum may occur.
An electron channeling study of polycrystalline YBa2Cu3Ox
Authors: Verhoeven J. D. , Gibson E. D. , Chumbley L. S. , McCallum R. W. , Baker H. H.
Published: July 2002

An electron channeling study has been done on large grained YBa2Cu3Ox samples. Selected area channeling patterns (SACP) were used to examine several dozen grains on electropolished surfaces and it was demonstrated that (a) the twin planes observed in polarized optical light microscopy lie parallel to {110} crystal planes, and (b) the long flat sides of high aspect ratio grains are formed by basal planes, and the shorter sides are formed by either (010), (100), or {110} planes. A majority of the large grains examined were found to contain subgrains, misaligned by 0.5°–1° and ranging in size from less than 3 to 20 μm. The origin of the subgrains is not understood.
Raman spectroscopic study of residual acceptors in semi-insulating bulk GaAs
Authors: Wagner J. , Ramsteiner M. , Seelewind H. , Clark J.
Published: July 2002

Electronic Raman scattering (ERS) has been used to study residual shallow acceptors in undoped semi-insulating (SI) GaAs grown by the liquid-encapsulated Czochralski technique. The dispersion of the cross section for ERS of shallow acceptors, as well as its absolute value, has been measured. It is shown that ERS allows a quantitative analysis of residual shallow acceptors in SI GaAs. Calibration factors for C and Zn acceptors are given. The detection limit of ERS is determined to ∼5×1014 cm−3 for 500-μm-thick standard wafers. Spatially resolved measurements show a systematic variation of the residual acceptor concentration across 2-in. GaAs wafers.
Laser etching of LiNbO3 in a Cl2 atmosphere
Authors: Beeson K. W. , Houlding V. H. , Beach R. , Osgood R. M.
Published: July 2002

Single-crystal LiNbO3 is etched in an atmosphere of 500-Torr Cl2 by focusing a 257-nm, frequency-doubled CW argon-ion laser beam onto the surface. The observed laser intensity threshold for etching is consistent with a process involving surface melting of the crystal. A single laser scan forms a shallow depression with marked ripples transverse to the direction of laser polarization, while repeated scans give a groove with a nearly triangular cross section. During laser etching, reacted material is redeposited on the crystal surface. This material is subsequently analyzed for chemical composition. The LiNbO3 surface is partially depleted of Li and O both at the etched grooves and at significant distances away from the grooves. Studies at low light intensities suggest that photochemical generation of gas-phase Cl radicals is responsible for the O depletion and part of the Li depletion. In addition, a dark reaction between Cl2 and LiNbO3 depletes only Li.
Simultaneous evaluation of viscosity and retardation time in glassy polymers by a parallel-plate technique
Authors: Macho E. , Alegría A. , Colmenero J.
Published: July 2002

In this work we describe a new experimental procedure for parallel-plate rheometry of glassy polymers above the glass-transition temperature range. This method has been used with an automated setup built by us which is linked to a HP-86 desk computer. Both our experimental procedure and experimental setup allow us not only to determine the Newtonian viscosity in the wide 104–109 Pa s range, but also the evaluation of a kind of retardation time. This is related to the time that the sample needs to reach the viscous behavior. Moreover, this time can be identified with the retardation time corresponding to the effects of the entanglements in the polymer melt, at least for the two polymers investigated here: polycarbonate and polysulfone.
Low-temperature homoepitaxial film growth of Si by reactive ion beam deposition
Authors: Yamada Hiroshi , Torii Yasuhiro
Published: July 2002

Homoepitaxial film growth maintaining primary surface structures of Si substrates was investigated by using the reactive ion beam deposition method proposed recently. This method uses ionized species of reactive SiH4 gas controlled in the low-energy region of less than 500 eV. At 100–150 eV, homoepitaxial film growth on Si(111) and Si(100) maintaining their primary 7×7 and two-domain 2×1 surface structures, respectively, can be achieved at the low temperatures of 650 and 600 °C, respectively. In addition, oxygen impurities on substrate surfaces, due to imperfect substrate cleaning and recontamination caused by residual gases in a growth chamber before film growth, were successfully reduced at 600 °C by irradiating the 100-eV controlled ionized species onto them.
The high-temperature stability of chemically vapor-deposited tungsten-silicon couples rapid thermal annealed in ammonia and argon
Authors: Broadbent E. K. , Morgan A. E. , Flanner J. M. , Coulman B. , Sadana D. K. , Burrow B. J. , Ellwanger R. C.
Published: July 2002

A rapid thermal anneal (RTA) in an NH3 ambient has been found to increase the thermal stability of W films chemically vapor deposited (CVD) on Si. W films deposited onto single-crystal Si by low-pressure CVD were rapid thermal annealed at temperatures between 500 and 1100 °C in NH3 and Ar ambients. The reactions were studied using Rutherford backscattering spectrometry, x-ray diffraction, Auger electron spectroscopy, transmission electron microscopy, and four-point resistivity probe. High-temperature (≥1000 °C) RTA in Ar completely converted W into the low resistivity (31 μΩ cm) tetragonal WSi2 phase. In contrast, after a prior 900 °C RTA in NH3, N inclusion within the W film and at the W/Si interface almost completely suppressed the W-Si reaction. Detailed examination, however, revealed some patches of WSi2 formed at the interface accompanied by long tunnels extending into the substrate, and some crystalline precipitates in the substrate close to the interface. The associated interfacial contact resistance was only slightly altered by the 900 °C NH3 anneal. The NH3-treated W film acted as a diffusion barrier in an Al/W/Si contact metallurgy up to at least 550 °C, at which point some increase in contact resistance was measured.
Characterization of layer-tilted state in ferroelectric liquid-crystal cells by electro-optical switchings
Authors: Chieu T. C. , Yang K. H. , Lien A.
Published: July 2002

Using an electro-optical method, we have determined the director tilt angle, the layer-tilt angle, and the quiescent-state azimuthal angles of a surface-stabilized ferroelectric liquid-crystal (SSFLC) cell as a function of temperature in the smectic C phase. The method is based on a collective switching of the director’s conical motion due to the interaction of the external field with the spontaneous polarization and the dielectric anisotropy of the liquid-crystal medium, together with a one-elastic constant free-energy model. Using the equation of total free energy, we have proved that only splayed states could be stabilized in layer-tilted geometry, but bistable cells could still be obtained. When the surface interactions at both substrate surfaces are nonidentical, the SSFLC cell will exhibit two distinct quiescent states: one stable and the other quasistable. The twist angles of the director from top to bottom substrates at quiescent states and the ratio of the surface polar to nonpolar interaction are deduced. The experimental observation and calculation on an overshoot in the rising part of the optical response upon bipolar switching are also presented.
An investigation of magnesium in indium phosphide grown by molecular-beam epitaxy
Authors: Cheng T. S. , Airaksinen V. M. , Stanley C. R.
Published: July 2002

The role of magnesium as a p-type dopant in the growth of InP by molecular-beam epitaxy (MBE) has been investigated. The growth was performed at substrate temperatures of ≊500 °C under conditions which produced high-quality unintentionally doped InP with 77 K residual electron concentrations of ND−NA ≊2×1015 cm−3 and mobilities up to 42 500 cm2 V−1 s−1. InP grown in an elemental Mg flux under such ‘‘optimum’’ conditions has electrical properties which are comparable to those of the undoped material. Using low-temperature photoluminescence, the presence of electrically active shallow acceptors due to Mg and C has been detected in the ‘‘Mg-doped’’ samples, with Mg being the dominant impurity. Mg is also found to be the principal, electrically active shallow acceptor in undoped InP. The activation energies for Mg and C are 40.9 and 44.4±0.3 meV, respectively, in excellent agreement with previously published data for low-dose ion-implanted InP. Secondary electron microscopy studies on the Mg-doped InP show that the concentration of morphological defects increases as the Mg flux is increased, suggesting Mg is responsible for assisting the formation of defects. However, the increase in defect density does not appear to affect either the electrical or the optical properties of the semiconductor. The small concentration of Mg incorporated into InP from an elemental source makes it unsuitable as a p-type dopant in MBE growth under the condition discussed here.
Energy-gap lowering through mechanical stress on metal-nitride-oxide-silicon structures
Authors: Kournettas P. , Bensch W.
Published: July 2002

Metal-nitride-oxide-silicon structures with various nitride thicknesses deposited on a 50–nm silicon dioxide layer prepared by a thermochemical reaction of tetraethylorthosilicate (TEOS) have been prepared. Capacitance-voltage (C-V) measurements have been performed after applying a voltage for a fixed time to determine the amount of accumulated interface charge. Infrared measurements have been carried out to obtain qualitative information about the internal stress in the TEOS layer. The accumulated charge and internal stress in TEOS increases with increasing nitride thickness. This observation indicates a lowering of the energy gap of TEOS.
Threshold characteristics of epitaxial Al(Ga,As) surface-emitting lasers with integrated quarter-wave high reflectors
Authors: Gourley P. L. , Drummond T. J. , Zipperian T. E. , Reno J. L. , Plut T. A.
Published: July 2002

We report a study of threshold characteristics of as-grown surface-emitting lasers fabricated with molecular-beam epitaxy by the monolithic integration of two quarter-wave high reflectors (mirrors) of AlAs/Al0.4Ga0.6As surrounding an active spacer layer. The spacer was either a multiple quantum well of GaAs/Al0.4Ga0.6As (100 Å/200 Å) or GaAs. Several structures were grown corresponding to different mirror reflectance and different spacer thicknesses from ultrashort 0.9 to 10 μm. One of the structures was chemically etched to form a two-dimensional array of microlasers. All of the structures were photopumped at room temperature, and the lasing threshold was determined. Without any lateral confinement, the threshold irradiance was as low as 2×105 W/cm2. Near-field images of the light emitted slightly above threshold reveal several competing filaments. This competition broadens the lasing linewidth, but can be controlled by lateral confinement schemes.
Effects of stress on threshold, wavelength, and polarization of the output of InGaAsP semiconductor diode lasers
Authors: Adams Charles S. , Cassidy Daniel T.
Published: July 2002

The effects of tension and compression applied to unbonded InGaAsP semiconductor diode lasers have been studied. The observed dependence of threshold, wavelength, and polarization of the laser output on the applied stress is explained in terms of the strain dependence of the valence-band wave functions. The polarization behavior is found to be related to thermal stress and the structure of the device. A technique has been developed to measure the thermal stress induced by current heating at the 105-dyn/cm2 level.
A cylindrical waveguide with periodic step changes in the radius: Interaction between two transverse magnetic modes
Authors: Schill Robert A. , Seshadri S. R.
Published: July 2002

The propagation of the modal voltages and currents is investigated for the transverse magnetic modes having azimuthal variation in a cylindrical waveguide with periodic step changes in the radius. The transfer coefficients are evaluated explicitly for small relative changes in the radius. The theory is applied to treat the selective and coherent coupling between two forward traveling modes.
Evidence for band-gap narrowing effects in Be-doped, p-p+ GaAs homojunction barriers
Authors: Chuang H. L. , DeMoulin P. D. , Klausmeier-Brown M. E. , Melloch M. R. , Lundstrom M. S.
Published: July 2002

The electrical performance of Be-doped, p-p+ GaAs homojunction barriers is characterized and analyzed. The results of the analysis show that minority-carrier electrons, at 300 K, have a mobility of 4760 cm2/V s at a hole concentration of 2.3×1016 cm−3, and that the effective recombination velocity for these homojunction barriers is about 6×104 cm/s. We present evidence that this unexpectedly high recombination velocity is a consequence of an effective reduction in band gap due to the heavy impurity doping. The effective band-gap shrinkage in this Be-doped material grown by molecular-beam epitaxy appears to be comparable to that already observed for Zn-doped GaAs grown by metalorganic chemical vapor deposition. This work demonstrates that so-called band-gap narrowing effects significantly influence the electrical performance of GaAs devices.
Spin-wave properties in multilayered structures including interface anisotropies and exchange (abstract)
Authors: Hillebrands Burkard
Published: July 2002

Results are presented of new theoretical investigations in which spin waves in multilayered structures are calculated, properly including both magnetic interface anisotropies and exchange.1 The work is an extension of a recently introduced theory for the calculation of single-layer spin-wave frequencies by Rado and Hicken, including interface anisotropies and exchange.2 The calculations were carried out for two different types of multilayered structures, i.e., for multilayers consisting of alternating magnetic and nonmagnetic multilayers, and for all-magnetic multilayers. In both cases all layers were of the same thickness. The solutions were obtained by solving for

the Maxwell equations and the Landau–Lifshitz torque equation. The boundary conditions consist of the Maxwell boundary conditions, and the Rado–Weertman boundary condition3 in the case of magnetic/nonmagnetic multilayers. In the case of all-magnetic multilayers, modified Rado–Weertman boundary conditions were used.4,5 In the case of magnetic/nonmagnetic multilayers, both dipolar-type (Damon–Eshbach-type) modes and exchange-dominated modes are obtained. The dipolar modes are frequency split as a result of the dipolar coupling of single-layer spin waves across the nonmagnetic spacer layers. The

exchange modes show no frequency splitting apart from the crossing regimes with the dipolar modes. In the regime of small layer thicknesses, where the dipolar modes are well frequency separated from the exchange modes, the calculations reproduce results obtained by neglecting exchange contributions.6 In the limit of very small layer thicknesses (<40 Å), the influence of interface anisotropies manifests itself for the dipolar modes in a frequency increase, as well as in a reduced coupling across the nonmagnetic layers. In the crossing regimes of dipolar modes and exchange modes, the modes exchange their mode characteristics, leading to a pronounced frequency gap. The width of the gap is

mostly determined by the amount of interface anisotropy. The calculation of an all-magnetic multilayered structure, consisting of three Fe layers with interleaving Ni layers, was carried in the limit of maximum exchange coupling across the interfaces.1 The results show frequency splittings both for dipolar modes and for exchange modes. In the limit of an infinite number of layers, the exchange modes will eventually form a band of exchange-dominated collective spin waves reminiscent of the band of collective dipolar spin waves in magnetic/nonmagnetic multilayers. The crossing regimes of dipolar modes with the

exchange modes show frequency gaps close to those observed for magnetic/nonmagnetic multilayers.
Amorphous Tb20Fe80/Al2O3 multilayers (abstract)
Authors: Krishnan R. , Porte M. , Tessier M. , Vitton J. P. , Lecars Y.
Published: July 2002

We have prepared amorphous Tb20Fe80/Al2O3 multilayer films by rf sputtering onto water-cooled glass substrates using 100-W rf power and argon pressure of 6 mT. The thickness of the Al2O3 layer was kept constant at 4 nm and that of Tb-Fe (denoted as d) was varied from 4 to 10 nm. The total number of bilayers was in the range 10–15. A single layer of Tb-Fe of 200 nm was also prepared to serve as a reference. All the films were given a protective Al2O3 layer of about 15 nm thick. Magnetization (M) and a hysteresis loop were obtained using a VSM. Uniaxial anisotropy (Ku) and M were measured with a torque meter. Polar Kerr loops were taken with a HeNe laser. For d>6 nm M remains the same but increases sharply for d<6 nm. This is attributed to preferential oxidation of Tb in very thin layers. Ku increases from 0.6 to 1.2×106 ergs cm−3 when d increases from 4 to 7 nm and remains so for thicker films. Though Ku appears even for thinner layers, the coercivity remains low (0.2–0.6 kOe) but attains a value of 2 kOe only for d>8 nm. This would indicate that the microscopic mechanisms for these two properties are not the same. Finally, only samples with d>8 nm show all the characteristics of the thick single layer. Detailed analysis of the torque curves will be presented.
III-V semiconductor thin-film optics: Optical modulator and filter arrays
Authors: Kemeny Peter C.
Published: July 2002

The application of optical thin-film interference structures, consisting of epitaxial III-V alloy layers, to the fabrication of optoelectronic devices operating in the 1–10-μm wavelength range which are suitable for two-dimensional array integration and relevant to optical communications and computing is discussed. This paper deals with surface geometry narrow band filters and current injection modulators. Closely related surface lasers will be described in a subsequent publication. An environmentally stable filter consisting of GaAs and AlAs epitaxial layers with a passband width of 1.2 nm at a wavelength of 1.6 μm is demonstrated. Such filters are found to be tunable by tilting. A proposed design for a surface current injection modulator operating at a wavelength of 1.3 μm is given with a modulation ratio of 10:1 anticipated for an operating current of 5 mA. The significant advantages of compound semiconductor expitaxial layers over polycrystalline coatings for general thin-film optics applications are outlined briefly.
A partially passive magnetic suspension for a discoidal wheel
Authors: LeMarquand Guy , Yonnet Jean-Paul
Published: July 2002

For discoidal or annular rotors, a magnetic suspension made only with one passive axial bearing and one active radial bearing is very well adapted. This suspension is relatively simple, and can operate without any additional damping system. A flywheel prototype has been built to test this magnetic suspension. The rotor is a 300-mm-diam aluminum disk (7.3 kg weight) rotating at 9000 rpm. In operation, the crossing of the different critical frequencies occurs without any problem, because the only one excited mode (cylindrical motion) is actively controlled, and the others which are passively stabilized (axial and conical modes) are not excited.
A new concept of magnetic thin-film heads with superconductors
Authors: Chen Y. X. , Yan D. R. , Xie Y. , Zhang M. L.
Published: July 2002

A new concept of the thin-film heads for magnetic recording introduced in this paper is to use the superconductive film as a perfect diamagnet to be the gap medium between the two magnetic poles of a thin-film ring head for the longitudinal magnetic recording. By using the finite-element method, the magnetic field and its distribution for the new designed ring head with a single-layer superconductive film or multilayer structure as the medium between the magnetic poles is calculated. The results show that the diamagnetic film in the gap not only increases the amplitude of the magnetic field in front of the magnetic poles, but also makes the distribution of the magnetic field much sharper, and the amplitude of the field is less influenced by the throat height of the pole tip as well.