bluuebunny/crossref_metadata_2025 huggingface dataset:
Low frequency and microwave characterization of submicron-gate In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As heterojunction metal-semiconductor field-effect transistors grown by molecular-beam epitaxy
Authors: Kuang J. B. , Tasker P. J. , Ratanaphanyarat S. , Schaff W. J. , Eastman L. F. , Wang G. W. , Chen Y. K. , Aina O. A. , Hier H. , Fathimulla A.
Published: July 2002

Doped-channel i-In0.52Al0.48As/n+-In0.53Ga0.47 As/i-In0.52Al0.48As heterojunction metal-semiconductor field-effect transistors lattice matched to the InP substrates with gate lengths in the submicron range have been fabricated and characterized. The dc and microwave performance of the devices are presented in this paper. Drain current anomalities, or the kink effects, were observed at room temperatures as well as at 77 K in the dc measurements. The kinks are associated with the deep-level electron trapping, and are not present at microwave frequencies. The dc and microwave bias points for achieving maximum transconductance are different. Normal microwave characteristics are exhibited. A compression of transconductance gm is observed in the dc measurement, while such gm degradation phenomenon does not appear at microwave frequencies. At 10 GHz, an extrinsic gm of 507 mS/mm, a current-gain-cutoff frequency ft of 49.5 GHz, and a power-gain-cutoff frequency (fmax) of 70.5 GHz were observed for a 0.25-μm-gate device. For a 0.3-μm-gate device, a gm of 545 mS/mm, an ft of 42 GHz, and an fmax of 114 GHz were measured. Output conductance as low as 7.7 mS/mm was measured. A voltage gain (gm/gds) as high as 64 was observed. The voltage gain for measured devices is well above 20 for a wide range of bias conditions. Fabricated devices show their potential for high-frequency operations. Further investigation of the origin of traps should result in improved low-frequency device characteristics.
Two-dimensional quantum corrections to the magnetoconductance of InSe at low temperatures owing to weak localization
Authors: El-Khatouri D. , Khater A. , Balkanski M. , Tuchendler J.
Published: July 2002

Experimental results for the magnetoconductance of the layered semiconductor InSe at low temperatures are presented for both H∥c and H⊥c configuration in externally applied magnetic fields. They are well represented by the theoretical results of weak localization for two-dimensional magnetoconductance, for a system the thickness of which is ∼15 nm, which is the average distance between stacking faults along the c axis. These results confirm the anisotropic character of electrical transport, and signal the effects of weak disorder, in this material.
Microstructure-image enhancement by scanning photoacoustic microscopy
Authors: Sasaki Akira , Fukaya Jisuke
Published: July 2002

Enhancement of the piezoelectric-photoacoustic signal from surface microstructures is achieved by the contact with silicone oil.
Effect of mechanical strain on electrical characteristics of hydrogenated amorphous silicon junctions
Authors: Utsunomiya Michito , Yoshida Akira
Published: July 2002

We have investigated the effect of mechanical strain on the current-voltage characteristics of hydrogenated amorphous silicon p-i-n junctions. When strain was applied parallel to the junction plane, the forward and reverse currents changed by 8% under the strain of 7.5×10−4. The strain sensitivity of the forward current decreased with increasing applied voltage, but the reverse current remained constant. We have explained the strain effect with the voltage dependence of strain sensitivity in the change of the ratio of the recombination current to diffusion current flowing through the amorphous junctions and the changes of the carrier concentrations in the two currents.
Characterization of YBa2Cu3O7−x bulk samples prepared by citrate synthesis and solid-state reaction
Authors: Yang Y. M. , Out P. , Zhao B. R. , Zhao Y. Y. , Li L. , Ran Q. Z. , Jin R. Y.
Published: July 2002

YBa2Cu3O7−x bulk samples made by citrate synthesis and pyrolysis are characterized and compared with samples made by solid-state reaction. Calcination at 830 °C followed by sintering at 950 °C of samples made of pyrolyzed powder gives pellets with quite good superconducting properties. They are very dense (6.06 g/cm3) and have a specific heat jump of 4 J/mol K at 91 K. X-ray diffraction shows a strong c-axis orientation, scanning electron microscope, and energy dispersive x-ray spectroscopy show a homogeneous structure and composition for these kinds of samples.
Deposition of nickel microstructures by CO2 laser-assisted decomposition of nickel tetracarbonyl
Authors: Tonneau D. , Auvert G. , Pauleau Y.
Published: July 2002

Nickel microstructures were produced from decomposition of Ni(CO)4 on quartz plates locally heated with a focused cw CO2 laser beam operating at 10.59 μm. The profile and deposition rate of Ni dots were determined as functions of irradiation time, reactant pressure, laser power, and laser-induced surface temperature. The kinetic data were found to be in good agreement with those of the visible laser-induced chemical vapor deposition (CVD) of Ni dots and CVD of Ni films in furnace-type CVD reactors. The decomposition of Ni(CO)4 molecules irradiated with the infrared laser light occurred via a purely thermal process.
Diffuse discharges at high-current density
Authors: Byszewski W. W.
Published: July 2002

Diffuse discharges were studied in an impedance-matched experimental system. A traveling-wave transmission line system was used to produce a high-voltage pulse (up to 40 kV), with a rise time of approximately 2 ns and a total pulse width of approximately 100 ns. Gas mixtures of C3F8 and c-C4F8 with He in a pressure range between 100 and 600 Torr were investigated. Plane parallel electrodes with 10-cm diameter and electrode spacings from 0.25 to 1.5 cm provided uniform field conditions in the discharge region. UV radiation produced by a flashboard placed behind a perforated anode surface provided the volumetric preionization necessary for maintenance of the diffuse discharge. A low ionization potential seedant was used to assure a uniform preionization. High-current-density diffuse discharges were maintained for approximately 100 ns. At low-current density, the diffuse discharge in an electronegative gas mixture operated under balanced electron growth conditions with constant voltage. At high-current densities (above 100 A/cm2), the discharge operating voltage decreased and was found to be as much as two times lower than the low-current glow-discharge voltage. The operating voltage also decreased with time during individual discharge under such conditions.
The dependence of photovoltaic characteristics of metal-insulator-semiconductor solar cells on dislocation density
Authors: Divigalpitiya W. M. R. , Morrison S. R.
Published: July 2002

Experimentally determined solar cell parameters of a large number of metal-insulator-semiconductor cells on damaged p-type silicon are compared with the dislocation conductivity model [J. Appl. Phys. 60, 406 (1986)]. Cell behavior is explained in terms of conducting dislocations. The variation of major cell parameters with the density of dislocations is calculated using the model. It is predicted that silicon with mild surface damage where dislocation density is less than about 105 cm−2 can produce solar cells of almost equal quality as dislocation-free Si.
High-resolution resonant refractive index lithography and applications
Authors: Rauschenbach K. , Lee C. A.
Published: July 2002

We describe resonant refractive index lithography (RRIL), a new technique to enhance the resolution of optical lithography. RRIL utilizes a highly refractive layer between the mask and the photosensitive layer to increase optical resolution. The refractive index of this layer is enhanced by a resonant absorption near the wavelength of the exposing radiation. In this work GaAs, which has a large resonant refractive index increase conveniently centered around the mercury spectral g line, is used as the refractive layer. It is shown that the large reduction in wavelength, which is more than a factor of 5 at 431 nm, enables this technique to increase resolution by as much as 226%. In addition, the absorption associated with the increased refractive index significantly attenuates the diffracted light and virtually eliminates standing waves that would be produced by reflections between the mask and the substrate. Furthermore, the refractive medium enhances the collimation of the exposing radiation. We demonstrate the RRIL technique by fabricating an opposed gate-source transistor with a sub-quarter-micrometer source electrode. The dimensions and alignment precision achieved were less than one-half the wavelength of the incident radiation. In this paper RRIL is introduced, experimental results are presented and compared with a model of the diffraction effects, and finally the RRIL technique is applied to planar lithography and microscopy.
Inhibition of aqueous degradation of Y1Ba2Cu3O7−x high-T
c superconductor by nitrogen ion implantation
Authors: Chaudhari S. M. , Viswanathan R. , Bendre S. T. , Nawale P. P. , Kanetkar S. M. , Ogale S. B.
Published: July 2002

The influence of 60-keV N+2 ion implantation on the aqueous degradation of the Y1Ba2Cu3O7−x high-Tc superconductor is studied by the small-angle x-ray diffraction technique. Structural depth profiling is performed by registering the x-ray data at several small angles of incidence between 0.3° and 10.0° within Seeman–Bohlin geometry. Examination of samples implanted at a dose value of 3×1017 ions/cm2 and subjected to different aqueous treatments reveals that implantation arrests the degradation process and imparts structural stability to the superconductor. Resistivity temperature data are also provided for specific cases of interest.
Calculation of superconducting granular bridges as networks of Josephson junctions
Authors: Kuhlemann T. , Hinken J. H.
Published: July 2002

In order to understand the mechanisms which determine the I-V characteristics of granular bridges, a model was established treating the granular bridge as a network of Josephson junctions. Calculations of many diverse configurations of such networks show that only certain superpositions of voltages of single junctions lead to Shapiro steps in the overall I-V curves of the network. These steps can be obtained when the granular bridge consists of a few grains only and when the ac current is applied with not too high a frequency. Then, characteristics of single junctions determine the behavior of the network, and Shapiro steps probably will appear.
Transient heat transport in solids
Authors: Claro F. , Mahan G. D.
Published: July 2002

It is shown that heat flow is severely decreased in transient phenomena, due to nonlocal effects. The case of phonon transport in a steep temperature gradient is discussed in detail for semiconductors. Fixed end temperatures and an initial heat pulse propagating in a homogeneous sample are considered as boundary conditions. The temperature profile evolves in all cases significantly slower than local theories predict.
Optical behavior near the fundamental absorption edge of sputter-deposited microcrystalline aluminum nitride
Authors: Aita C. R. , Kubiak C. J. G. , Shih F. Y. H.
Published: July 2002

The optical behavior near the fundamental absorption edge (4.1–6.6 eV) of sputter-deposited microcrystalline aluminum nitride grown on unheated fused silica substrates is studied here. The absorption coefficient α shows three types of behavior with incident photon energy E: (1) a high-energy region (>6.06 eV) in which α slowly varies with E, (2) a middle-energy region (∼5.6–6.06 eV) in which α varies directly with exp E, and (3) a low-energy shoulder. High- and medium-energy absorption is modeled in terms of a disordered semiconductor, using a coherent potential approximation with Gaussian site disorder in the valence and conduction bands. α is expressed in terms of three interrelated energy parameters: the energy-band gap of the virtual crystal (6.18 eV), the energy gap of the disordered crystal (5.50–5.64 eV), and the inverse slope of the exponential dependence of α on E (0.24–0.29 eV). Enhancement of α at low energy is explained in terms of a discrete absorption band whose strength is ∼6×1020/cm3.
On entropy generation in phase-change heat conduction
Authors: Charach Ch. , Rubinstein I. L.
Published: July 2002

This paper addresses the entropy production in heat conduction, accompanied by melting/solidification. The expressions for the time derivative of the entropy and the excess entropy production in selected Stefan problems are derived. These physical quantities are shown to be meaningful evolution characteristics for several phase-change processes that evolve towards equilibrium or self-similar asymptotic attractors. Prigogine’s theorem of minimal steady-state entropy production is shown to be invalid for the phase-change heat conduction.
Asymptotic behavior and Lorentz factor for small-angle elastic scattering profiles from preferentially oriented asymmetric bodies
Authors: Shibayama Mitsuhiro , Nomura Shunji , Hashimoto Takeji , Thomas Edwin L.
Published: July 2002

The small-angle scattered intensity functions I(h) were analyzed for asymmetric bodies of thin disks (TD; R≫2L), narrow rods (NR; 2L≫R), and prolate (PE; va≫a) and oblate ellipsoids of revolution (OE; va≪a). h, R, and 2L, 2a, and 2av are the magnitude of scattering vectors defined as h=(4π/λ)sin θ, with 2θ and λ being the scattering angle and wavelength of the radiation in the medium, respectively, the radius and length of the disk (or rod), and the lengths of two major axes of the ellipsoid of revolution, respectively. The functions I(h) scale as h−γ (γ=0,1,2,4) and show crossovers between different exponents γ, which depend on the aspect ratio (L/R or v) and the orientation distribution function W(α). When the aspect ratio is much larger or much smaller than unity, the relationship between the intensities at a given direction Ir(h) and that perpendicular to the longest axis of the particle Ip(h) was found to be related by Ir(h)∼h−γL Ip(h), for h≫1/max(R,L) or 1/max (va,v), where h−γL is the so-called Lorentz factor or Lorentz correction factor. The criteria for this relationship to be valid were discussed in terms of the aspect ratio and W(α) of the particle.
As-grown Y-Ba-Cu-O thin films by reactive coevaporation with oxygen plasma cooling
Authors: Matsumoto M. , Akoh H. , Takada S.
Published: July 2002

We have developed a new fabrication process of as-grown Y-Ba-Cu-O thin films using a reactive coevaporation method specially with the rf-plasma cooling in the low oxygen pressure of 0.4 mTorr. By this O2 plasma cooling process, the transition temperature Tc is improved from 40 to 81 K for the film with a thickness of 1000 Å. The x-ray diffraction analysis shows that the activated oxygen species generated by the rf plasma make Y-Ba-Cu-O films oxidize sufficiently even in the low pressure of oxygen. In addition, we have studied the thickness dependence of Tc for as-grown films with various thicknesses of 60–2000 Å.
X-ray excited luminescence spectroscopy of barium fluorohalides
Authors: Crawford M. K. , Brixner L. H. , Somaiah K.
Published: July 2002

Photostimulated luminescence (PSL) phosphors, such as BaFBr:Eu, are currently used in x-ray screens for digital medical imaging. There is, however, little known about the mechanistic details responsible for the luminescence process in these materials. This paper describes a study of the emission mechanism in the host lattice BaFX(X=Cl, Br). Electron-hole recombination luminescence produced by x-ray irradiation has been observed. The recombination luminescence intensity is temperature dependent and yields information concerning the ionization process in these crystal lattices. This information is fundamental to the PSL process.
On the correlation between high-order bands and some photoluminescence lines in neutron-irradiated FZ silicon
Authors: Zhong Lei , Wang Zhanguo , Wan Shouke , Lin Lanying
Published: July 2002

The defects in float-zone silicon irradiated by fast neutron with fluences up to 4.0×1018 n/cm2, followed by various heat treatments, have been studied by low-temperature photoluminescence (PL) and infrared absorption measurement with emphasis upon the high-order band (HOB) and its relationship with the commonly observed PL-lines such as I1 (1.018 eV) and I3(1.039 eV). It has been shown that band 1124 cm−1, unlike the other higher-order bands, is considerably broader for the sample annealed at low temperature (for example, 385 °C) with FWHM as large as 3 meV and is apparently narrowed as the anneal temperature was increased. We have obtained the I3 line and its phonon replicas in the near-infrared absorption measurement, further proving the transition involved in the I3 defect center to be electronic in nature. The combination of luminescence and absorption experiment results demonstrated that the HOB could be well developed after PL lines such as I1 and I3 disappeared completely, or vice versa. PL lines could be observed before the HOB emerged, therefore ruling out the possibility proposed by earlier authors that the HOB could be correlated with some PL lines.
I
n s
i
t
u transmission electron microscopy study on the epitaxial growth of CoSi2 on Si(111) at temperatures below 150 °C
Authors: Nieh C. W. , Lin T. L.
Published: July 2002

We report an in situ transmission electron microscopy study on the epitaxial growth of CoSi2 on Si(111) from a 10-nm-thick amorphous mixture of Co and Si in the ratio 1:2 which was formed by codeposition of Co and Si near room temperature. Nuclei of CoSi2 are observed in the as-deposited film. These nuclei are epitaxial and extend through the whole film thickness. Upon annealing, these columnar epitaxial CoSi2 grains grow laterally at temperatures as low as 50 °C. The kinetics of this lateral epitaxial growth was studied at temperatures between 50 and 150 °C. The activation energy of the growth process is 0.8±0.1 eV.
A cyclotron resonance mechanism for very-low-frequency whistler-mode sideband wave radiation. I. Introduction and description of external resonances
Authors: Sá L. A. D.
Published: July 2002

The first part of the paper introduces the reader to the physical and mathematical aspects of the problem of sideband formation associated with very-low-frequency whistler-mode waves propagating in ducts in the magnetosphere. It starts with an introduction to the general problem of charge distribution in the duct and looks at the effect of monochromatic electromagnetic waves acting on such distributions. It describes sidebands as due to wave-wave interactions occurring in the magnetosphere through electron cyclotron resonances, and concentrates on sideband radiation coming from resonances located outside the wave potential wells (external resonances). It also presents a general solution to the electron equation of motion, based on the Kolmogorov–Arnold–Moser theorem, that lists the possible sideband radiation frequencies. Both an analytical treatment, based on Lie transform perturbation theory, and a numerical treatment, based on phase plots, are used in the detailed part of the analysis. Effects of the inhomogeneity of the magnetic field of the Earth are mainly neglected in the first part of the paper.
Calculated potential and electric field distributions around an active nerve fiber
Authors: Heringa A. , Stegeman D. F. , de Weerd J. P. C.
Published: July 2002

Potential distributions around a model nerve fiber are computed by using analytical methods. The fiber is situated either in a homogeneous isotropic unbounded conductor or in a homogeneous isotropic cylinder. In the latter case the source is placed either centrically or eccentrically. The potential distributions are used to derive the precise electric field distribution. The results are presented in equipotential and field line maps. It is described how the inherent numerical problems in the calculations can be avoided. It is demonstrated that the boundaries of the volume conductor and the nature of the source (potential source, current source) can significantly influence the field, even at large distances from this source.
A simple physical principle for determining mode boundaries in superconducting loop circuits
Authors: Lee Gregory S.
Published: July 2002

A new physical principle is presented that immediately yields the auxiliary equation needed for the calculation of threshold or mode boundaries in superconducting loop circuits. We call this principle the loop inductance law, or L3 for short. The principle states that the determinant of the differential loop inductance matrix vanishes at threshold. L3 is equivalent to the resultant equation obtained by the method of Lagrange multipliers devised by Tsang and Van Duzer [J. Appl. Phys. 46, 4573 (1975)], but in contrast to that method, the auxiliary equation is much more quickly apparent. A number of examples are explicitly demonstrated.
Secondary emission 1/f noise revisited
Authors: van der Ziel A. , Fang P. , van Rheenen A. D.
Published: July 2002

Fang and van der Ziel’s analysis of secondary emission 1/f noise in secondary emission pentodes is extended to 16 individual data points. It is found that by proper choice of the secondary electron path length dda, good agreement between the experimental values of the Hooge parameter αH and the theoretical values predicted by Handel’s quantum 1/f noise theory is obtained for 14 data points. Handel’s equations for the Hooge parameter of the tubes thus seem to have heuristic validity. The values of the secondary electron path length dda differ somewhat from tube to tube and may also depend slightly on bias; these effects are attributed to the electron-optical system formed by screen grid, dynode, and anode.
Modeling of luminescence phase delay for nondestructive characterization of Si wafers
Authors: Guidotti D. , Batchelder J. S. , Finkel A. , Gerber P. D. , Van Vechten J. A.
Published: July 2002

We have modeled the generation, diffusion, and recombination of photoexcited electrons and holes for the case of Czochralski Si wafers having a defect-free-zone (DFZ) device layer of thickness d above a highly precipitated wafer core and having a finite surface recombination velocity, S. The incident photoexcitation source has a Gaussian power distribution and is focused to a small spot on the sample surface. When the source is sinusoidally modulated at frequency ν, the intrinsic band-edge photoluminescence (PL) emission displays modulations at the fundamental and first overtone of the modulation frequency. The PL signals at frequencies ν and 2ν are delayed in phase, with respect to the source modulation by angles φ2(ν) and φ2(2ν). We relate these phase angles to material properties such as d, S, the optical absorption coefficient α at the incident wavelength, and to the effective carrier lifetimes τ1 and τ2 in the DFZ and precipitated wafer core, respectively. We show that when τ1 and τ2 are independently measured and S≲100 cm/s, as is common for a Si surface passivated with a thermally grown oxide layer, it is possible to deduce d from a measurement of φ2(ν) or φ2(2ν).
Pin-on-disk tribology of thin-film magnetic recording disks
Authors: Karis T. E. , Novotny V. J.
Published: July 2002

Tribological studies of friction and wear were performed on carbon overcoated thin-film magnetic recording media with pin-on-disk tests. Scanning microellipsometry was employed to measure the wear of carbon overcoats on rigid magnetic media. Severe wear produced after the carbon film wore through was measured by mechanical profilometry. The wear rate of the carbon is three orders of magnitude lower than that of the underlying metallic layers and is nearly proportional to slider load. Micrographs of the wear tracks and the magnitude of the wear coefficient from the Archard wear equation indicate three-body abrasive wear.
Self-aligned TiN barrier formation by rapid thermal nitridation of TiSi2 in ammonia
Authors: Kamgar Avid , Baiocchi F. A. , Emerson A. B. , Sheng T. T. , Vasile M. J. , Haynes Richard W.
Published: July 2002

Partial or full nitridation of TiSi2 layers has been achieved by rapid thermal nitridation in pure ammonia. Several analytical techniques such as transmission electron microscopy, x-ray photoemission spectroscopy, and Rutherford backscattering, have been used to study the nitridation process. It was found that a 60-s anneal at 900 °C was sufficient to yield a 20–30 nm TiN layer on top of the TiSi2 layer, provided that the starting TiSi2 surface was free of Si or Ti oxides. Annealing at 1000 °C for 60 s, on the other hand, nitrided the entire 95-nm TiSi2 layer. Detailed structural and chemical analysis of the samples before and after nitridation showed that the nitridation process takes place by nitrogen atoms bonding to Ti atoms and displacing the Si atoms. The dissociated Si atoms diffuse towards the TiSi2/Si interface forming an epitaxial layer of nonuniform thickness on the Si substrate. The resulting TiN layer is substantially thinner than the starting TiSi2 layer. It has a somewhat rough top surface and a very nonuniform interface with the underlying TiSi2 or Si. A small amount of Si remains on the top surface mostly in the form of Si3N4.
Diffusion length and lifetime in highly Ga-doped PbSnTe layers grown by liquid-phase epitaxy
Authors: Shahar A. , Feit Z. , Zussman A.
Published: July 2002

Minority-carrier diffusion length of a highly Ga-doped Pb0.78Sn0.22Te (n=1.5×1019 cm−3) liquid-phase epitaxy grown layer was measured between 10–80 K using a light spot scanning technique on a beveled diode. The carrier lifetime, derived from the observed diffusion length, and the measured mobility is shown to be dominated by Auger recombination. The effect of Ga and In heavy doping on the spectral response of homostructure PbSnTe diodes is demonstrated. The advantage of Ga over In as an n-type dopant of the cladding layer of PbSnTe homostructure lasers is discussed.
Research on the characteristics of H2 Raman conversion pumping by a 1-J XeCl excimer laser
Authors: Lou Qihong
Published: July 2002

Detailed results are presented of a high-efficiency Raman conversion of a 1-J XeCl excimer laser with an unstable resonator. We had 90% photon conversion of 18-MW-power XeCl laser radiation with 39% photon efficiency to the third Stokes order at 499 nm. The effects of rare-gas concentration in a H2–rare-gas mixture on the Raman conversion characteristics were investigated. Finally, stimulated Raman scattering between the excited states of H2 at high gas pressure was observed, and conditions for generating these lines are discussed.
Modeling dust layer behavior in pulsed precipitation and comparison with bench scale experimental results
Authors: Salasoo Lembit , Nelson J. Keith , Tardos Gabriel I. , Snaddon Robert W. L. , Walsh Kevin A.
Published: July 2002

The effect of a collected flyash layer on electrostatic precipitator (ESP) behavior is investigated. Dust layer and back corona effects are combined with a previously developed model of pulse energized precipitation to simulate experimental measurements. To obtain reproducible results and size-specific efficiencies in the presence of a flyash layer required the use of entrained model particles and carefully controlled humidity. Differences between empirical model parameters obtained here and values derived from other experiments suggest that electrical sneakage is a significant mechanism; extension of the model to accommodate this sneakage is discussed. Physical explanations are given for the efficiency maxima and minima with pulse rate variation that are exhibited by the model, and the implications for pulser control are discussed. It is concluded that the model has been developed to such a stage as to permit its utilization for the design of pulsed ESP supplies and controllers.
Annealing studies of highly doped boron superlattices
Authors: Jackman T. E. , Houghton D. C. , Jackman J. A. , Denhoff M. W. , Kechang Song , McCaffrey J. , Rockett A.
Published: July 2002

Coevaporation of B2 O3 during silicon molecular-beam epitaxy at growth temperatures (TG ) varying from 540 to 800 °C has been used to prepare superlattice structures (pipi’s) of varying boron concentration (3×1018 –3×1020 B cm−3). The superlattices were subsequently subjected to various annealing procedures and the layers were examined by secondary ion mass spectrometry, electrochemical profiling, and cross-sectional transmission electron microscopy. A significant redistribution of boron was observed even before annealing for TG >700 °C and high boron concentrations. In addition, significant oxygen was incorporated for TG ≤700 °C, with a growth rate of 0.5 nm s−1 and a B2 O3 flux of 2×1013 cm−2 s−1. After annealing, the boron diffusion coefficients were determined for the layers and found to vary significantly with TG.
Two-dimensional conductivity in the layered semiconductor InSe at low temperatures owing to weak localization
Authors: El-Khatouri D. , Khater A. , Balkanski M. , Julien C. , Guesdon J. P.
Published: July 2002

Experimental results for the electrical conductivity of the layered semiconductor InSe are reported. At low temperatures they are well represented by weak localization theory for two-dimensional conductance which illustrates the weak disorder owing to the presence of large concentrations of stacking faults.
Thermal hysteresis during phase transition in Ag2Te thin films: Thickness effect
Authors: Das V. Damodara , Karunakaran D.
Published: July 2002

Electrical conductivity and thermoelectric power measurements as a function of temperature have been carried out on Ag2Te thin films of different thicknesses prepared on glass substrates at room temperature in a vacuum of 5×10−5 Torr. It is found that the phase transition temperatures (located by a steep change in resistance and thermoelectric power with temperature) during heating and cooling are different, thereby showing a thermal hysteresis during the phase transition. It is also found that the magnitude of the hysteresis is a function of thickness, increasing with decreasing thickness. This can be due to the large surface-to-volume ratio, small grain size, and a large density of dislocations in thin films.
Electrode breakdown in magnetohydrodynamic plasmas: Stability analysis
Authors: Kumar A. Satheesh , Gupta Bhumesh
Published: July 2002

Stability analysis has been carried out for current conduction in magnetohydrodynamic conditions using the perturbation approach. Conditions for the onset of instability at the electrode surface and the corresponding critical values of current density and electric field have been obtained. Experimental values of the critical cathode potential drop have been used to obtain the work function of the composite surface (formed due to the deposition of seed material at the electrode) as a function of the electrode temperature.
The role of point defects in anomalous diffusion of implanted boron in silicon
Authors: Bao Xi-mao , Guo Qiang , Hu Mei-sheng , Feng Duan
Published: July 2002

The influence of implantation damage on the anomalous diffusion has been observed by varying the relative positions of the boron profile and damage distribution produced by silicon preimplantation at different energies. It is shown that the anomalous diffusion of implanted boron is caused by the implantation damage rather than the fast diffusing interstitial boron. During annealing, the extended defects acting as sinks for point defects retard the anomalous diffusion in and near the defected band, however, for prolonged annealing they begin dissolving and emitting point defects which support the anomalous diffusion.
Ion-beam direct-write mechanisms in palladium acetate films
Authors: Gross M. E. , Brown W. L. , Harriott L. R. , Cummings K. D. , Linnros J. , Funsten H.
Published: July 2002

Pd features have been fabricated by high-energy ion irradiation (2-MeV He+, 2-MeV Ne+, and 20-keV Ga+ ions) of thin palladium acetate films. 2-MeV He+ irradiation produces smooth metallic-looking features that contain up to 30% of the original carbon and 5% of the original oxygen content of the film. Films irradiated with 2-MeV Ne+ ions contain slightly lower amounts of carbon and oxygen residues, but the films’ appearance varied with thickness. Exposures made with a 20-keV Ga+ ion beam, focused to a 0.2-μm spot, produce features with carbon and oxygen contents higher than those found with He+ and Ne+ exposures. Heating the ion-beam-defined palladium features in a hydrogen ambient reduces the carbon and oxygen contents and improves the electrical conductivity. Decomposition mechanisms and comparisons with laser direct writing are discussed.
Phase identification of chemically etched InP by x-ray diffraction techniques
Authors: Hsieh H. F. , Shih H. C.
Published: July 2002

Traditionally, the chemical composition of surfaces prepared by various chemical, thermal, and plasma oxidation are analyzed by x-ray photoelectron spectroscopy. In this work, both x-ray wide-angle and glancing angle diffraction techniques were used, not only to investigate chemical composition, but also to characterize the structural features of the chemical oxide grown on an InP (100) surface in both HCl and HNO3 etches. These oxides all showed different degrees of preferred orientation with respect to the substrate. In 1M–8M HCl etches, the gradient composition, identified as crystalline hydrous InPO4, was the predominant phase and the rest was mainly composed of hydrous InPO4-based oxides. Coherent hydrated layers, also identified as hydrous InPO4, were obtained in HNO3 etches. In addition, the observation that InI -InIII mixed valence and InI chloro compounds are produced helped clarify the understanding of the dissolution mechanism of InP.
Development of a photorefractive grating via temporally modulated photoconductivity and a correlated ac bias
Authors: Montgomery R. M. , Lange M. R.
Published: July 2002

A process is described which utilizes an alternating electric bias field to develop a photorefractive grating. The bias field is applied synchronously with an optically modulated photoconductivity. The key to the technique is correlation between the applied ac bias and the time varying intensity field. This differs from previous work in which an uncorrelated ac bias was applied to enhance photorefraction. A theoretical development of this process is presented along with the experimental confirmation of this effect. The ac bias utilized in the experiment consists of an electric field produced by a bulk acoustic wave (via piezoelectricity). This is applied in the presence of a modulated optical field to produce the photorefractive grating. Over 30 dB of dynamic range of the grating deflected signal is observed by this approach.
Dissociation and product formation in NF3 radio-frequency glow discharges
Authors: Hargis P. J. , Greenberg K. E.
Published: July 2002

Laser Raman spectroscopy was used to measure NF3 dissociation and N2 formation in the active volume of 13.56-MHz NF3 radio-frequency (rf) discharges. Gating the rf discharge suppressed optical emission, allowing NF3 and N2 Raman measurements at rf powers where N2 production was expected to be significant. Greater than 90% dissociation of the NF3 was observed in a 750 mTorr discharge at rf power densities on the order of 1 W/cm2 , yet less than 50 mTorr of N2 was produced. NF was the only other nitrogen containing species detected in the active volume of the discharge.
A new solid-state cesium ion source
Authors: Kim S. I. , Seidl M.
Published: July 2002

A novel Cs+ion source combining the advantages of porous metal ionizers with those of zeolite emitters has been developed. Cesium ions are chemically stored in a cesium-mordenite solid electrolyte (Cs-M SE) pellet whose emitting surface is coated with a porous tungsten thin film. Cesium supply to the emitting surface is controlled by a voltage applied across the solid electrolyte pellet. Cs+ ion emission takes place on the surface of the porous tungsten electrode by surface ionization. The ionic conductivity of Cs+ ion in the Cs-M SE is of order of 10−5 Ω cm−1 at 1000 °C. The interface properties between electrolyte and electrodes play a major role in the cesium ion source. The cathode electrode interface (emitting electrode) determines the stability of the supply current density to the emitting surface. The lifetime of the source is found to depend on the anode interface. In a steady-state operation, an ion-emission current density of the order of 20 mA/cm2 has been extracted for 30 h at a total ion-emission current of 100 μA at 1000 °C. This corresponds to 10 C of extracted charge.
Fundamental magneto-optics
Authors: Zak J. , Moog E. R. , Liu C. , Bader S. D.
Published: July 2002

The reflection-transmission problem is considered for light from a boundary between two magnetic media with arbitrary direction of the magnetization within each medium. Explicit formulas are derived for the magneto-optic coefficients.
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u investigation of InAs metalorganic chemical vapor deposition growth using reflectance anisotropy
Authors: Koch Stephanie M. , Acher Olivier , Omnes Franck , Defour Martin , Razeghi Manijeh , Drévillon B.
Published: July 2002

Using reflectance anisotropy, we have investigated InAs metalorganic chemical vapor deposition under optimal growth conditions. The measured optical anisotropy of the growing surface is significantly different from that of the nongrowing, AsH3-stabilized surface. This difference δ becomes more pronounced at low V/III gas flow ratios and low temperatures. The value of δ also depends on the light energy, reaching a maximum in the range of 2.30–2.38 eV. In addition, we show that it is possible to monitor effects of the reactor on the growth, namely transient flow perturbations on the growing surface due to the switching of gas flows.
Diffusion barrier properties of Ti/TiN investigated by transmission electron microscopy
Authors: Mändl M. , Hoffmann H. , Kücher P.
Published: July 2002

Detailed analytical transmission electron microscopy investigations were performed on a well-known diffusion barrier system for very-large-scale integration metallization. It will be demonstrated that interfacial reactions are of great importance for the barrier mechanism. Both Ti and TiN act as diffusion barrier for the semiconductor and the metallization, respectively. For an aluminum-based metallization, TiN has a ‘‘spongelike’’ function due to its ability to absorb several amounts of aluminum at elevated temperatures and therefore inhibits diffusion towards the substrate. Ti acts for silicon as a compound forming barrier according to Nicolet’s classification [in Tungsten and Other Refractory Metals for Very Large Scale Integration Applications II, edited by E. K. Broadbent (Materials Research Society, Pittsburgh, 1987); pp. 19–26].
Large subband spacings in δ-doped quantum wires
Authors: Snider G. L. , Tan I.-H. , Hu E. L.
Published: July 2002

Quantum wire subband separations of 15 meV have been calculated in delta-doped structures using self-consistent, two-dimensional, solutions of the Poisson and Schrödinger equations. δ-doped layers are used to provide the high charge concentrations needed to obtain lateral confinement, while avoiding parasitic conduction paths.
Analysis of calorimetric measurements of grain growth
Authors: Chen L. C. , Spaepen F.
Published: July 2002

A method for extracting the parameters describing the process of grain growth from calorimetric data is presented. Both isothermal and scanning experiments are considered. It is demonstrated that the Kissinger method used for determining the activation enthalpy of a nucleation-and-growth process can be used for a grain growth process as well. Characteristic differences between the signals, both scanning and isothermal, from nucleation-and-growth and grain growth are pointed out. These are useful for distinguishing truly amorphous structures from microcrystalline ones by their transformation behavior. As an example, the method is applied to a study of grain growth in microquasicrystalline Al-Mn thin films.
Observation of nonbolometric responses to microwave irradiation on YBaCuO films
Authors: Chang K. , Yong G. , Wenger L. E. , Chen J. T.
Published: July 2002

Nonbolometric response to 8.3-GHz microwave radiation in the resistive transition region of electron-beam-deposited YBaCuO thin films is distinguished from the bolometric response by their different applied microwave power dependence with the nonbolometric effect dominating the voltage response below the boiling temperature of liquid nitrogen. In the presence of a dc magnetic field, the microwave-induced dc voltage in unbiased films shows an oscillatory behavior as a function of microwave power as well as a polarity reversal depending upon the direction of the dc magnetic field. This behavior is consistent with the electromagnetic response arising from the Josephson vortex motion in the junction regions within these granular films.
Modeling the behavior of the magnetic force microscope
Authors: Bryant Paul , Schultz S. , Fredkin D. R.
Published: July 2002

Results of some numerical simulations are presented that model the behavior of the magnetic force microscope under various probe/sample configurations. Analysis is carried out under the assumption of uniform magnetization of an axially symmetric probe of various types including: sphere, cylinder, conical tip, and rounded magnetically coated conical tip. In these cases the analysis can be made by studying the effective magnetic surface charge on the probe. We also consider the case of a spherical probe with magnetization that can rotate in response to the local field. The sample configurations studied are also of the axially symmetric type, which can be used to model the fields generated by arrays of cylindrical samples, e.g., alumite.
Soft-magnetic properties of compositionally modulated Fe/Al films
Authors: Haeiwa T. , Negoro H. , Matsumoto M.
Published: July 2002

Soft-magnetic properties of Fe/Al compositionally modulated multilayer films prepared in the low argon pressure of 2 mTorr with double target dc magnetron sputtering have been studied. Characteristic x-ray diffraction peaks corresponding to artificial structure on [Fe(4–50 Å)/Al(8 Å)]150 multilayer films were observed. Maintaining a constant Al layer thickness of 8 Å, the coercivity in the hard axis rapidly decreases from 50 Oe to <1 Oe as the Fe layer thickness increases from 4 to 24 Å. When the Fe/Al thickness ratio is around 3, minimum coercivity was obtained. In the region of bilayer thickness ratio δFe/δAl < 3.0, the Ms per Fe unit volume decreases with decreasing δFe/δAl. The higher resistivity was obtained in the films of δFe/δAl < 3.0, and resistivity decreases as δFe/δAl increases. The internal film stress also decreases as δFe/δAl increases. The [Fe(20 Å)/Al(8 Å)]150 multilayer film exhibited a low coercivity 0.5 Oe, a high saturation magnetization 1210 emu/cm3, and a high resistivity 119 μΩ cm.
A model for heterogeneous growth of Si1−xGex films from hydrides
Authors: Robbins D. J. , Glasper J. L. , Cullis A. G. , Leong W. Y.
Published: July 2002

Growth rates for Si1−xGex films (0≤x≤0.19) have been measured between 610–750 °C using low pressure H2/SiH4/GeH4 mixtures and at different temperatures these rates show different dependencies on composition x. A model attributes this complex behavior to competition between an increasing rate for desorption of surface hydrogen and a decreasing sticking probability for the reactive hydrides as x increases. The latter effect is explicitly reported for the first time. GeH4 is found to be ∼4.7 times more reactive than SiH4, and relative surface hydrogen coverages on Si and Si0.87Ge0.13 films measured by secondary ion mass spectroscopy are compared with the model.
The evidence for interaction of the N-N pair with oxygen in Czochralski silicon
Authors: Qi M. W. , Tan S. S. , Zhu B. , Cai P. X. , Gu W. F. , Xu X. M. , Shi T. S. , Que D. L. , Li L. B.
Published: July 2002

Evidence for interaction between the N-N pair and interstitial O in N-doped Czochralski silicon has been presented by studying the annealing behavior of the corresponding IR absorption bands.
Microwave detection using granular Bi-Sr-Ca-Cu-O thin films
Authors: Boone B. G. , Sova R. M. , Moorjani K. , Green W. J. , Grabow B. E.
Published: July 2002

We report here results of our investigations of the nonbolometric mode of detection in granular Bi-Sr-Ca-Cu-O thin films. We find that both bolometric and nonbolometric modes appear in the same sample under mutually exclusive conditions: bolometric with light (633 nm) and nonbolometric with microwaves (9 GHz). Our measurements indicate that the nonbolometric mode of detection is more sensitive than the bolometric mode in our samples, a result which offers promise for application to microwave power measurement. Possible mechanisms for the nonbolometric mode are reviewed, and the concept of using a broadband spiral antenna directly coupled to the superconducting detector for microwave power sensing is briefly described.
Response of photodiodes in the vacuum ultraviolet
Authors: Husk D. E. , Tarrio C. , Benitez E. L. , Schnatterly S. E.
Published: July 2002

We have measured the responses of four commercial photodiodes in the vacuum ultraviolet from 20 to 600 eV and have also measured the inelastic-electron-scattering spectra of the materials contained in the diodes from 0 to 260 eV. Three of the diodes are silicon: an enhanced channel device, an x-ray-stabilized silicon diode, and a p-i-n diode. The fourth is a gallium arsenide phosphide Schottky diode. The diode response has been modeled by considering absorption through the surface layer and inelastic surface recombination. The model produces an excellent description of the measured responses. From our analysis we have obtained reasonable values for the number of electrons produced per eV of incident radiation, the thicknesses of the surface layers, the surface recombination velocities, and the average diffusion lengths of the minority carriers. The highest efficiency is obtained for a silicon x-ray-stabilized diode followed by the gallium arsenide phosphide diode. We find that both of these diodes make excellent, stable soft-x-ray detectors.
Molecular-dynamics simulations of bulk and surface damage production in low-energy Cu→Cu bombardment
Authors: Karetta Frank , Urbassek Herbert M.
Published: July 2002

Molecular-dynamics simulations are employed to study in detail the effects of low-energy (≤100 eV) bombardment of a Cu (001) surface by Cu atoms. By following the simulation up to 4 ps in real time, the end configuration of defects in the target can be observed. We present results on the vacancy and interstitial distribution in the target, the spontaneous defect recombination, the number of surface vacancies and adatoms produced, and the mixing of target atoms induced by the bombardment. Furthermore, the fate of the projectile atom−backscattering and implantation−and the sputtering behavior are investigated. The relevance of the results on the modelling of ion-beam (assisted) deposition is discussed.
The effect of low-thermal-budget anneals and furnace ramps on the electrical activation of arsenic
Authors: Orlowski Marius , Subrahmanyan Ravi , Huffman Gary
Published: July 2002

The electrical activation of arsenic under low-thermal-budget anneals has been studied by annealing high-dose (7 × 1015 cm−2) arsenic implants under various conditions. It is shown that detailed consideration of the initial electrical activation immediately after damage annealing, as well as the ramp-up and -down conditions, is necessary in order to model the diffusion and electrical activation of the arsenic. The various stages of the annealing process are described, and the cumulative effect of each stage in the cycle on the final degree of electrical activation is discussed in the context of experimental results and dynamics of arsenic clustering and declustering.