bluuebunny/crossref_metadata_2025 huggingface dataset:
Excitonic transition and electronic subband studies in CdxZn1−xTe/ZnTe asymmetric step quantum wells
Authors: Kim T. W. , Kim D. S. , Park H. L.
Published: July 2002

Photoluminescence (PL) and photoluminescence excitation (PLE) measurements were carried out to investigate the interband transitions in CdxZn1−xTe/ZnTe asymmetric step quantum wells which consist of a deep Cd0.1Zn0.9Te well and a shallow Cd0.18Zn0.82Te well bound by two thick ZnTe barriers. The results for the PL data at 20 K showed clearly the excitonic transition from the first electronic state to the first heavy-hole state (E1–HH1), and the PLE data showed the excitonic transition from the second electronic state to the first heavy-hole state (E2–HH1), which in this case is forbidden by the selection rules in contrast to the square-quantum-well case, together with the (E1–HH1) transition. The electronic subband energies and the wave functions in the step quantum wells were calculated, taking into account the strain effects by an envelope-function approximation and the calculated values of the interband transitions were in reasonable agreement with those obtained from the PL and the PLE measurements. These results indicate that CdxZn1−xTe/ZnTe step quantum wells hold promise for potential applications such as new types of modulators and quantum-well infrared photodetectors in the blue-green region of the spectrum.
Nucleation of domain walls in iron garnet single crystals grown from liquid phase epitaxy
Authors: Shirai Kazushi , Ishikura Kenji , Takeda Norio
Published: July 2002

When bismuth-substituted iron garnet (RBi)IG single crystals grown from liquid-phase-epitaxy (LPE) are magnetized, the magnetic domain structure gradually evolves. However the domain-wall nucleation that occurs during the demagnetization is not yet understood clearly. This phenomenon is important, because the working of some optical devices that utilize (RBi)IG single crystals depends directly on the formation of domains of opposite direction. In this paper, the authors present a theoretical description of domain-wall nucleation in LPE-grown (RBi)IG single crystals. It was found that the nucleation field is determined by the strength of the microscopic domain-wall which is fixed on the surface of the crystal. Furthermore, the nucleation field is modified by the addition of a magnetic field.
Generalized formula for the stability and instability criteria of current-voltage characteristics measurements in the negative differential conductance region of a resonant tunneling diode
Authors: Huang Chih Yuan , Morris James E. , Su Yan Kuin
Published: July 2002

A formula in terms of the equivalent circuit parameters of a resonant tunneling diode (RTD) and its loading for three different equivalent circuit models of RTD’s is derived to describe the apparent change, occurring in the presence of unstable oscillation, in the negative differential conductance (NDC) region of dc current-voltage (I-V) characteristics measurements. The measured experimental I-V data and the related parameters of RTD’s from several fabricated devices are applied to the formula in terms of the stability and instability criteria to do the numerical verification. It has shown good agreement between the derived formula and the experimental I-V data of RTD. Simulated program with integrated circuits emphases (SPICE) simulation shows the flattened and the broken sections, which represent the occurrence of the unstable oscillation, appearing in the NDC region of I-V curve, which also validates the applicability of the derived formula.
Analysis of the responsivity of silicon p-i-n photodiodes to Nd:YAG laser pulses
Authors: Glaenzer R. , Aceves M.
Published: July 2002

The carrier transport equations for a silicon p-i-n photodiode have been linearized, and analytic solutions of the responsivity have been obtained for a step function of weakly absorbed radiation. These solutions have been used to calculate the responsivity to Q-switched pulses (tens of nanoseconds) from a Nd:YAG laser. Examples of the tradeoff between responsivity and electrical pulsewidth are given. Finally, the use of p-i-n photodiodes to detect mode locked (tens of picoseconds) pulses by taking advantage of the long period between pulses is shown to be feasible if the pulse shape does not have to be resolved.
Monte Carlo study of shot noise suppression
Authors: Reklaitis A. , Reggiani L.
Published: July 2002

We present a Monte Carlo study of shot noise suppression in double barrier nonresonant heterostructure GaAs/AlGaAs diodes. Substantial suppression up to a factor 0.5 is found in agreement with a formula of de Jong and Beenakker [Phys. Rev. B 51, 16 867 (1995)] obtained within Langevin–Boltzmann theory. The spectrum of current noise exhibits two resonant peaks before the cutoff region. These peaks are associated with certain features of the carrier motion due to reflections from the first barrier and oscillations inside the GaAs well, respectively.
Magnetotransport, magneto-optical, and electronic subband studies in InxGa1−xAs/InyAl1−xAs modulation-doped strained double quantum wells
Authors: Kim T. W. , Jung M. , Lee D. U. , Kim J. H. , Yoo K. H. , Lee J. Y. , Ryu S. Y.
Published: July 2002

Magnetotransport and magneto-optical measurements on InxGa1−xAs/InyAl1−yAs modulation-doped strained double quantum wells with a 100 Å In0.8Ga0.2As well and a 100 Å In0.53Ga0.47As quantum wells separated by a 35 Å In0.25Ga0.75As potential barrier were carried out to investigate the electrical and the optical properties of the electron gas in the quantum wells. The Shubnikov-de Haas measurements at 1.5 K demonstrated clearly the occupation of three subbands in the quantum wells by a two-dimensional electron gas. The electron effective masses determined from the slopes of the cyclotron resonance peak energies as a function of the magnetic field were 0.06171 and 0.05228me. The electronic subband energies, the subband energy wavefunctions, and the Fermi energy in the quantum wells were self-consistently calculated a transfer matrix method taking into account the exchange-correlation effect, the strain effect, and the nonparabolicity effect, and the results of the cyclotron resonance measurements qualitatively show the nonparabolicity effect in the strained double quantum well.
Magnetization and flux creep in thin YBa2Cu3O7−δ films of various thickness
Authors: Sheriff E. , Prozorov R. , Yeshurun Y. , Shaulov A. , Koren G. , Chabaud-Villard C.
Published: July 2002

We report on the thickness dependence of the irreversible magnetization in superconducting Y1Ba2Cu3O7−δ films of thickness 350–3000 Å. Our results reveal a nonmonotonous dependence of the persistent current density j on the film thickness, which is interpreted in terms of surface pinning and variations in the surface microstructure. Measurements of the time dependence of j show that under certain conditions relaxation curves of samples of different thickness cross each other, i.e., the sample with initially larger j exhibits after some time a lower j. The crossing point is shifted to shorter times as the temperature is increased. We propose a simple explanation to this effect and discuss its practical implications. Low dose heavy ion irradiation of the films has a modest effect on j and on the rate of its relaxation.
Brillouin light-scattering study of TbFeCo thin films
Authors: Boyle J. W. , Cowen J. A. , Yasseen K. M. , Booth J. G. , Boardman A. D. , Booth K. M. , Lord D. G.
Published: July 2002

Spin-wave excitations have been observed, using Brillouin light scattering, in thin films of TbFeCo, grown by sputtering on silicon substrates, with thicknesses in the range 4.5–250 nm. The variations of spin-wave frequency with applied in-plane magnetic-field H (100 Oe⩽H⩽4.5 kOe) and in-plane magnon wave-number k (4.24×104⩽k⩽2.41×105 cm−1) were obtained. For these films, oxidation during the deposition process produces a bulk film, which is very weakly ferrimagnetic and, therefore, largely magnetically dead. However, further oxidation, at the film surface after deposition, due to exposure to air, increases the magnetization to produce a magnetically active surface layer. The results were modeled as a Damon–Eshbach surface mode, and the TbFeCo films considered as a magnetic film on a nonmagnetic layer, the thicknesses of which were both unknown. The frequency versus field measurements enabled values for the saturation magnetization and gyromagnetic ratio to be determined. The measurements of the frequency versus wave number showed evidence that, for the thicker films, the magnetically active layer was only a small fraction of the total thickness, and the active layer thicknesses were determined. The values of magnetizations are compared with those obtained from vibrating sample magnetometry measurements.
4f
-shell configuration of Yb in InP studied by electron spin resonance
Authors: Ishiyama T. , Murakami K. , Takahei K. , Taguchi A.
Published: July 2002

We have performed electron spin resonance (ESR) measurements on Yb-doped n-type and p-type InP layers epitaxially grown by metalorganic chemical vapor deposition. ESR spectra of Yb3+(4f13) were observed in both n-type and p-type samples. However, the ESR intensity of Yb3+(4f13) for n-type samples was found to be much lower than that for p-type samples. This suggests that most Yb ions in Yb-doped n-type InP are in the Yb2+(4f14) state rather than in the Yb3+(4f13) state. Thus an electron captured by the trap level formed by Yb in the band gap of InP is not located outside the Yb 4f shell as reported previously, but accommodated in the Yb 4f shell.
Relaxation of water proton spins by paramagnetic spin-label molecules in porous glass
Authors: Choi C. , Bharatam J. , Geilikman M. , Dusseault M. B. , Pintar M. M.
Published: July 2002

A water proton spin-lattice relaxation study of the spin-label molecules 2,2,6,6- tetramethyl-4-acetamido-piperidine-1-oxyl (TMAPO) solution in glass pores of 127 nm diam reveals that when the porous glass is hydrated with a 1 mM TMAPO solution, the TMAPO concentration in pore water is maintained constant during dehydration. However, it was observed that if the pore diameter is 49.1 nm or smaller, the Langmuir isotherm is not applicable, although the surface-to-volume ratio is larger. The observed proton relaxation’s dependence on pore volume-to-water volume ratio V0/V, is in excellent accord with the results of the electron paramagnetic resonance experiments and supports a model based on the fast exchange of water between nonequivalent environments.
A low temperature gate oxide process for n-channel SiGe modulation doped field effect transistors
Authors: Bozon B. , Zijlstra T. , Glück M. , Hersener J. , van der Drift E. , König U.
Published: July 2002

The implementation of a novel low temperature gate oxide to a n-channel SiGe modulation doped field effect transistor (MODFET) fabrication process is investigated. The approach is based on the thermal oxidation rate of sputtered a-Si being twice as high compared to c-Si, thus enabling self-aligned nm control in oxide growth at reduced temperatures (600 °C). The electrical characterization of metal-oxide-semiconductor (MOS)-gated MODFETs was used to check the device quality of the silicondioxide. The transconductance varies with the oxide thickness according to the expectations. Device modeling studies show how drawbacks (e.g., of a negative threshold voltage) can be eliminated to yield a practical high-performance MOS-gated SiGe MODFET with a largely improved gate swing.
Current increase in thin gate-oxide (3.5–7.0 nm) metal–oxide–silicon structures with the boron-doped polycrystalline-silicon gates biased negatively
Authors: Itsumi Manabu , Sato Yoshiyuki , Nakayama Satoshi , Muramoto Susumu
Published: July 2002

We have investigated gate-current instability in boron-doped polycrystalline-silicon gate metal–oxide–silicon structures. Gate-current increase is observed only for oxide thicknesses of 3.5–7.0 nm and for negative gate voltage. The current-increase characteristics are reversible for positive and negative bias cycles. When the gate is negatively or positively biased, the flatband voltage remains constant, suggesting that there is no positive charge buildup at the Si–SiO2 interface. The experimental results suggest that a positive charge buildup or the formation of a conductive region at the gate–SiO2 interface is involved in the current increase. A model for this current instability is presented.
Dependence of the emission characteristics of magnetized surface-wave plasmas on the azimuthal configuration of the wave field
Authors: Pérès I. , Dallaire A. , Jones P. , Margot J.
Published: July 2002

A 1D plasma-wave model initially developed for describing a plasma sustained by a surface wave in the azimuthally symmetric configuration (m=0) was modified for simulating surface waves in the dipolar mode (m=1). Using this model, it is shown that the maintenance limit for unmagnetized plasmas in the symmetric mode, which, as was previously determined, requires that the product of the wave frequency and the plasma radius be smaller than 2 GHz cm, is no longer valid for magnetized plasmas. Comparison of calculated and measured radial distributions of argon atoms in a radiative excited state shows that changes observed in this distribution when varying some of the operating conditions can be explained by a switching of the discharge from one mode to the other. Conditions for selection of the mode are derived from considerations on wave propagation and power dissipation along the plasma column.
Field effect-induced quasi-one-dimensional electron transport in GaAs/AlxGa1−xAsheterostructures
Authors: Herfort J. , Austing D. G. , Hirayama Y.
Published: July 2002

We describe an approach to realize quasi-one-dimensional electron gases using an undoped GaAs/AlxGa1−xAsheterostructure. It is demonstrated that with a combination of ion implanted ohmic regions and a narrow top gate, a quasi-one-dimensional electron gas with a very high electron density can be formed. The width of the narrow top gate is varied between 0.4 and 1.0 μm. The wires are characterized by low temperature magnetotransport experiments. The effective wire width is found to be comparable to the gate width. The high mobility of about 95 m2/V s is only 5%–10% less than that obtained in a two-dimensional electron gas of the same material and is maintained at low temperatures.
Spatial and temporal characteristics of a vacuum-arc rail-gun plasma
Authors: Roychowdhury P. , Vijayan T. , Iyengar S. T.
Published: July 2002

The dynamics of a vacuum-arc operated rail-gun plasma were numerically simulated for the undercritically damped regime and confirmed in experiments. Analytical solutions of arc current, its velocity, and position also showed good agreement with the results. The spatial development of the arc is shown here to follow a linear behavior, even though the propulsion velocity followed an exponential-step function due to the sinusoidal nature of the arc current. Peak arc current ∼100 kA, 15 μs period was propelled to ∼106 cm/s as indicated in time-of-flight measurements and simulations. The voltage signal induced on a B-dot probe by the dynamic sinusoidal arc was simulated, which compared well with the measured probe signal. A Gaussian current distribution inside the measured arc length ∼1–2 cm, was established by unfolding the B-dot probe signal. A peak magnetic field of the order 1–5 kG was also interpreted inside the arc. The emerging plasma contained ion current over tens of amperes in the pulse duration encompassing the arc envelope.
Kinetics of Cu3Ge formation and reaction with Al
Authors: Huang J. S. , Huang S. S. , Tu K. N. , Deng F. , Lau S. S. , Cheng S. L. , Chen L. J.
Published: July 2002

Cu 3 Ge films have been found to have a low resistivity, good adhesion on SiO2, good thermal stability on Si, and good oxidation resistance. It has the potential as an ideal adhesion/barrier/passivation layer for Cu ultralarge scale integration metallization. The kinetics of Cu3Ge formation and the thermal stability of Cu3Ge against Al were studied by in situ resistivity measurement, Rutherford backscattering spectrometry, and transmission electron microscopy. We found that Cu reacted with Ge in the temperature range of 100–200 °C. The activation energy of the Cu–Ge compound formation was found to be 1.1±0.1 eV. The Cu–Ge compound was identified as ε-Cu3Ge from transmission electron microscope diffraction patterns. Upon annealing the ε-Cu3Ge became unstable on Al at the temperature range of 300–350 °C. In the reaction between Al and Cu3Ge, Cu preferentially reacted with Al to form an ε-Al2Cu3 compound. The activation energy of formation of the Al–Cu compound was found to be 2.1±0.1 eV.
Characterization of unicompositional GaInP2 ordering heterostructures grown by variation of V/III ratio
Authors: Inglefield C. E. , DeLong M. C. , Taylor P. C. , Chun Y. S. , Ho I. H. , Stringfellow G. B. , Kim J. H. , Seong T. Y.
Published: July 2002

Photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies are employed to investigate single heterostructures based on two GaInP2 layers that have the same composition but different degrees of order on the cation sublattice. Four sample configurations are studied: two complementary single heterostructures, a more ordered layer grown on a less ordered layer and vice versa, and two single layers nominally equivalent to the constituent layers of the heterostructures. The degree of order of the two layers was controlled via the V/III ratio used during organometallic vapor phase epitaxial growth. From our measurements, the difference between the band gaps of the two layers is 20–30 meV. The PLE spectra show clearly that the emission comes from both layers of the heterostructures and that the PL is excited by direct absorption of the exciting light into each layer as well as the injection of carriers from the less ordered (higher band gap) layer into the more ordered (lower band gap) layer. The data clearly show that the heterostructures contain two layers, each very similar to the corresponding single layer sample.
Multilambda Rabi cavities in atomic beam frequency standards
Authors: De Marchi A. , Tavella P. , Bava E.
Published: July 2002

Multilambda Rabi cavities have been shown to be a viable solution for the reduction of cavity phase shift and other Doppler related effects in atomic beam frequency standards. For this reason they may be advisable to use in devices in which operations that are apt to measure or correct cavity phase shift are impossible or undesirable. These include short sealed (commercial) tubes, possibly some primary standards with vertical beam (because it is not easy to operate an atomic beam directed vertically down), and microgravity clocks. Analytical and numerical results are reported on particular cavity examples. They support the idea that a Ramsey cavity is not always the only solution for guiding microwaves in a beam standard. A comparison of line shapes between experimental results obtained with an atomic beam and numerical calculations is also reported.
Dislocation model of a subsurface crack
Authors: Yang Fuqian , Li J. C. M.
Published: July 2002

A dislocation model of a subsurface crack parallel to the surface is presented. For tensile loading, the results agree with those of previous workers except that we studied the crack very close to the surface and found that KII (mode II stress intensity factor) approaches KI (mode I stress intensity factor) to within about 22% (KII=0.78KI). (Note that KII is zero when the crack is far away from the surface). Using bending theory for such situations, it is found that both stress intensity factors are inversely proportional to the 3/2 power of the distance between the subsurface crack and the free surface. For shear loading, the crack faces overlap each other for the free traction condition. This indicates the failure of the model. However, there was no overlap for tensile loading even though the stresses in front of the crack oscillate somewhat when the crack is very close to the surface.
Time-resolved study of coherent and incoherent transport in an InGaAsP/InGaAsP superlattice electro-optic modulator
Authors: Cho G. C. , Ziebell A. , Dekorsy T. , Bakker H. J. , Opitz B. , Kohl A. , Kurz H.
Published: July 2002

Coherent and incoherent transport processes of charge carriers in an InGaAsP/InGaAsP superlattice embedded in a p-i-n diode are investigated by time-resolved differential electroabsorption spectroscopy. The initial stages of the current evolution in the first picosecond after excitation with a femtosecond optical pump pulse are resolved. Coherent current oscillations within the superlattice layer are observed with a frequency depending on the electric field applied to the superlattice. These current oscillations are due to Bloch oscillations performed by excited carriers. We compare contributions of electroabsorption and excitonic bleaching to the time-resolved signal. A strong influence of incoherent carrier dynamics such as sub-picosecond field screening and carrier sweep-out on the dephasing and frequency of Bloch oscillations is observed.
Thermal composition of DyF-, HoF-, and TmF-based gases
Authors: Kaledin Leonid A. , Holbrook Robert T. , Kunc Joseph A.
Published: July 2002

The partition functions are calculated for gases consisting of Ln and F atoms, Ln+ ions, LnF and F2 molecules, and LnF+ molecular ions (Ln≡Dy, Ho, Tm) and are subsequently used in determining the local thermal equilibrium compositions of such gases.
Translational vibrations of domain structure in ferroelectrics
Authors: Sidorkin A. S.
Published: July 2002

The collective vibrations of domain boundaries connected with a local change of a domain width in ferroelectrics with the 180° domain structure are investigated. It is shown that there exist two branches of such vibrations: of quasiacoustic and quasioptic type. The influence of the piezoelectric effect on the change of the dispersion law of these vibrations was investigated. The influence of the spectrum of translational vibrations of domain boundaries on the frequency dispersion of dielectric permeability of ferroelectrics was also determined.
Laser-induced chemical vapor deposition of nanostructured silicon carbonitride thin films
Authors: Besling W. F. A. , Goossens A. , Meester B. , Schoonman J.
Published: July 2002

Laser-induced chemical vapor deposition of silicon carbonitride thin films has been investigated using a continuous wave CO2 laser in parallel configuration with the substrate. The reactant gases in this process, hexamethyl disilazane and ammonia, are rapidly heated by CO2 laser radiation due to their absorption of the laser energy. Polymerlike silicon carbonitride films or agglomerated nanosized particles are formed depending on process conditions. Dense, smooth films or nanostructured deposits have been synthesized at low substrate temperatures (Ts<300 °C) on quartz, copper, and silicon and can be obtained with controlled microstructures. Surface morphology, composition, and type of chemical bonding have been studied with electron microscopy and spectroscopic analysis and are correlated to the most important laser process parameters. X-ray photoelectron spectroscopy and reflectance Fourier transform infrared spectroscopy show that the deposits consist of Si–N, Si–C, and Si–O bonds, linked together in a x-ray amorphous, polymerlike structure. The nitrogen content is about 40% and can be varied by adding ammonia to the reactant gas flow. The layers are readily contaminated with oxygen after exposure to air, caused by hydrolysis and/or oxidation.
Mechanical properties and quality of diamond films synthesized on Ti–6Al–4V alloy using the microwave plasmas of CH4/H2 and CO/H2 systems
Authors: Catledge Shane A. , Vohra Yogesh K.
Published: July 2002

Microwave plasma-enhanced chemical vapor deposition was used to grow diamond films on Ti–6Al–4V alloy using various gas phase precursors. The results of four types of experiments with different gas mixtures are compared: (1) 2% CH4 in H2; (2) initial saturation of 5% CH4 in H2 followed by 2% CH4 in H2; (3) a CO-rich mixture with a CO:H2 ratio of 8; and (4) a hybrid mixture of 2% CH4 in H2 followed by a CO:H2 ratio of 8. The substrate temperature during deposition with CH4/H2 mixtures was between 715 and 810 °C, and was between 550 and 600 °C when CO/H2 mixtures were used. Optical emission spectroscopy was used to monitor the excited gas-phase species in the plasma. The films were characterized by micro-Raman spectroscopy, glancing-angle x-ray diffraction, and nanoindentation. The films grown with the type (1) mixture often exhibited good quality with high hardness (70 GPa) but suffered from poor adhesion to the substrate. The films grown with the type (2) mixture were of slightly lower quality and hardness (58 GPa) but exhibited better adhesion. The films produced from the type (3) mixture were adhered, but exhibited very low growth rates and low hardness (18 GPa). Finally, the films produced from the hybrid type (4) mixture were of poor quality and suffered from poor adhesion to the substrate. The differences in interfacial phases and mechanical properties for each film are discussed and the usefulness of each gas mixture for the diamond growth is evaluated.
Multi-photon pumping in a large band gap semiconductor laser
Authors: Liu C. S. , Tripathi V. K.
Published: July 2002

Population inversion in a large band gap semiconductor, e.g., ZnSe or ZnS, could be achieved by irradiating it with a picosecond Nd: glass laser of power density exceeding 30 GW/cm2. The laser field induces valence band electrons to tunnel to the conduction band, creating electron-hole plasma. The electron-hole recombination produces coherent radiation at ultraviolet wavelength. Nonlocal effects have a significant influence over the gain.
Theoretical investigation on quantum well lasers with extremely low vertical beam divergence and low threshold current
Authors: Yang G. W. , Xu J. Y. , Xu Z. T. , Zhang J. M. , Chen L. H. , Wang Q. M.
Published: July 2002

A specially designed quantum well laser for achieving extremely low vertical beam divergence was reported and theoretically investigated. The laser structure was characterized by two low index layers inserted between the waveguide layers and the cladding layers. The additional layers were intended to achieve wide optical spread in the cladding layers and strong confinement in the active region. This enabled significant reduction of beam divergence with no sacrifice in threshold current density. The numerical results showed that lasers with extremely low vertical beam divergence from 20° down to 11° and threshold current density of less than 131 A/cm2 can be easily achieved by optimization of the structure parameters. Influences of individual key structure parameters on beam divergence and threshold current density are analyzed. Attention is also paid to the minimum cladding layer thicknesses needed to maintain low threshold current densities and low internal loss. The near and far field patterns are given and discussed.
Spatial distribution of collisionless ions confined in an electron cyclotron resonance ion source
Authors: Batygin Yuri K.
Published: July 2002

Numerical calculations were done to study spatial distribution of ions in a minimum B magnetic mirror configuration of an electron cyclotron resonance ion source and to estimate the fraction of extracted ions from the electron cyclotron resonance (ECR) plasma. Due to the large value of required computer time, simulations were performed for one ion component (Ar+5) in collisionless approximation without particle Coulomb interaction. In the adopted model, plasma had a stationary six-fold profile. The shape and value of beam emittance are mostly defined by magnetic field topology. A portion of extracted ions from the ECR plasma observed in simulations was 0.5%.
Linear analysis of electromigration-induced void instability in Al-based interconnects
Authors: Hao T.-H. , Li Q.-M.
Published: July 2002

Void shape changes induced by electromigration pose reliability problems in Al-based interconnects. Recent observations have shown that a rounded void sometimes collapses to a transverse slit in an interconnect with bamboo-like grain structure. This article provides a linear stability analysis for a circular void that is only partially conductive in an otherwise infinite conductive medium. The relation between the inner conductivity (i.e., the conductivity of the medium in the void) and the critical remote electric field intensity, Ecr, for the linear stability of the void is established. It is proven that when the inner conductivity becomes zero, Ecr goes to infinity, and we can look upon the inner conductivity of a vacuum void as zero. That is why the vacuum circular void is linearly stable. It is also shown that when the inner conductivity is very small, the stability of a void is sensitive to it. From the computational results, we know that if the inner conductivity is 0.1% of that outside the void, the Ecr is only twenty times of that for the dislocation loop case.
Analysis of grating light valves with partial surface electrodes
Authors: Furlani E. P. , Lee E. H. , Luo H.
Published: July 2002

The grating light valve (GLV) is a micro-electromechanical reflection phase grating that operates on the electrostatic deflection of microbeams. In a conventional GLV, each beam is coated with a surface electrode that spans its length. In this paper, a GLV with partial electrode coverage is studied. An analysis is presented of the deflection profile and switching voltage for a series of electrode lengths. These results are compared with the performance of a conventional GLV.
Constant-resistance deep-level transient spectroscopy in submicron metal-oxide-semiconductor field-effect transistors
Authors: Kolev Plamen V. , Deen M. J.
Published: July 2002

This article describes a new variation of a deep-level transient spectroscopy (DLTS) technique convenient for the measurement of submicron field-effect transistors where standard capacitance DLTS cannot be used. Constant-resistance (CR) DLTS is similar to the conductance DLTS, but it is more sensitive and it does not require simultaneous measurement of the transconductance gm or surface mobility μ for calculation of the trap concentrations. In addition, the DLTS signal is largely independent of the transistor size, thus allowing measurements of very small-size transistors. The proposed technique is not restricted to metal-oxide-semiconductor field-effect transistors, but can be used also to study other field-effect transistors.
Observation of neutron guided waves from the open end of a thin film waveguide and a waveguide interferometry
Authors: Pogossian S. P. , Menelle A. , Le Gall H. , Ben-Youssef J. , Desvignes J. M.
Published: July 2002

Neutrons guided wave propagation were observed at the open end of a thin film waveguide. A low-index-leaky waveguide coupler is used for coupling the incident beam into the thin guiding film. After guided propagation over a distance of a few millimeters, the neutrons are diffracted at the open end of the guide giving a Fraunhofer diffraction pattern. The diffracted neutron intensity distribution is in fairly good agreement with the theory. An interferometer based on the splitting of the far-field pattern on two separate peaks is proposed.
Double quantum well segments in ballistic diode bases
Authors: Gribnikov Z. S. , Korshak A. N. , Mitin V. V.
Published: July 2002

We consider space charge limited ballistic electron transport in short current-conducting channels formed by single and double quantum well segments. Independent contacts to the bottom-well and the top-well forming the double quantum well segment is stipulated. Three different structures are simulated: a resonant overlap structure, a resonant cover structure, and a coupler structure. It is shown that anode currents in these structures oscillate with increasing voltage across the structure, resulting in repeatedly N-shaped current–voltage (I–V) characteristics. A modulation level of the current oscillations is close to 100%. The shape of these oscillations is substantially asymmetric both for the overlap and the cover structures. The asymmetry is due to a very strong nonlinear space charge modulation, and N-shaped parts of I–V characteristics can become Z-shaped when a strong tunnel connection in the double quantum well segment takes place. In the coupler structure the modulation of partial anode currents flowing out through each of two anodes, which are independently contacted to the bottom-well and the top-well, occurs only. The space charge increases monotonously with the voltage. Justification criteria of the classic approach used in our calculations are discussed in detail.
Extrinsic origins of electrical transport anomalies near the superconducting transition in mesoscopic aluminum lines
Authors: Burk B. , Chien C.-J. , Chandrasekhar V. , Strunk C. , Bruyndoncx V. , Van Haesendonck C. , Moshchalkov V. V. , Bruynseraede Y.
Published: July 2002

We investigate whether inadvertent noise currents may induce the previously reported resistive peak and negative differential resistance (dV/dI) anomalies near the superconducting transition in quasi-one-dimensional aluminum lines. Although our samples show no intrinsic anomalies, low frequency current deliberately applied to the sample in addition to the ordinary measuring current induces the anomalies. In our work the resistive peak results from simple mixing, but the negative dV/dI feature arises from a more complex effect.
Observation of quantized conductance in split-gate In0.53Ga0.47As/In0.77Ga0.23As/InP point contacts using Cr/Au p-InP Schottky barriers
Authors: Schäpers Th. , Appenzeller J. , Hardtdegen H. , Lüth H.
Published: July 2002

We report on the observation of quantized conductance in split-gate In0.53Ga0.43As/Ga0.77In0.23As/InP point contacts. For the Schottky gates Au/Cr in combination with p-InP was used. As a result our split-gate point contacts show low pinch-off voltages and no measurable leakage current through the gates. Up to five conductance steps were observed at a temperature of 1.4 K. Our approach to fabricate split-gate Schottky contacts can be used for quantum point contacts operating at higher temperatures as well as for superconductive quantum point contacts.
Energy state of Nd3+ doped in barium sodium niobate crystals
Authors: Xia H. R. , Hu L. J. , Wang C. J. , Li L. X. , Yue S. B. , Meng X. L. , Zhu L. , Yang Z. H. , Wang J. Y.
Published: July 2002

Nd-doped barium sodium niobate (Ba2Na)1−xNdxNb5O15 (BNN:Nd), with x=0.025 and a Curie temperature of 537±2 °C, crystallizes with a filled tungsten bronze-type structure in the tetragonal system. The lattice constants are a=b=1.2446(1) and c=0.3991(1) nm at room temperature. There are two formulas per unit cell. The five typical deep energy levels, formed by the Nd3+ ions doped in the A1 and A2 sites, are 2.36, 2.12, 1.68, 1.55, and 1.43 eV. Investigating the green and yellow second-harmonic generation shows that the BNN:Nd crystal can be expected as a useful material for the green, especially for the yellow laser radiation at room temperature.
Magneto-optical properties of nanocomposite films obtained by partial reduction of (Ni,Mg)O and (Co,Mg)O solid solutions
Authors: Smith J. A. , Limthongkul P. , Hartsuyker L. , Kim S. Y. , Sass S. L.
Published: July 2002

Metal-ceramic nanocomposite films consisting of either Ni or Co particles embedded in a MgO matrix were produced by two techniques involving the partial reduction of a mixed oxide solid solution. Transmission electron microscopy, Rutherford backscattering spectrometry, x-ray diffraction, and magneto-optical Faraday and Kerr rotation measurements were used to characterize the films. The metallic particles were well dispersed in the films, resistant to subsequent re-oxidation, with their size controlled by choice of processing conditions. The coercive field of the samples is influenced by the residual strain arising from the coefficient of thermal expansion difference between the film and the substrate upon which it is deposited. Large magneto-optical Faraday and Kerr rotations are achieved for relatively thick nanocomposite samples as compared to pure metallic films.
Ellipsometric measurements of the polarizability anisotropies of push–pull molecules in solution
Authors: Fort A. , Muller J. , Cregut O. , Mager L. , Vola J. P. , Barzoukas M.
Published: July 2002

We have developed an experimental setup for the measurement of the polarizability anisotropy of push–pull molecules in solution. We have used this technique to investigate prototype push–pull molecules that have been incorporated as doping chromophores in low glass transition temperature photorefractive polymers. Results obtained evidence for these compounds that the refractive index modulation is dominated by the orientational birefringence contribution while the electro-optic contribution remains small.
Experimental and computational study of copper–gadolinium alloy evaporation
Authors: Chatain S. , Gonella C. , Roblin P.
Published: July 2002

We report an experimental study of the expansion of a gadolinium–copper atomic vapor mixture in vacuum and the comparison with a test-particle Monte Carlo simulation. This simulation gives a description of collision relaxation in the binary case, taking account of excited metastable levels. The metal alloy was evaporated by a focused electron gun. We measured the net mass flow rate, radial velocities, and angular flux profiles. These data show the occurrence of aerodynamic phenomena in these mixtures: the velocity increase and the narrowing of the angular flux profile of a heavy element with a light element present, the decrease in the velocity, and broadening of the angular flux profile of the light element with a heavy element present. There is good agreement between the experimental results and the computations.
Calculation of the electron-optical characteristics of electron beams transmitted into vacuum from a sharp tip-thin foil junction
Authors: van Bakel G. P. E. M. , Borgonjen E. G. , Hagen C. W. , Kruit P.
Published: July 2002

The electron-optical characteristics of a novel electron source consisting of a sharp tip-thin foil tunnel junction are calculated, taking into account the tunnel junction, electron transport through the freestanding metal foil, and transmission across the opposing vacuum emission surface. A tunable high-pass energy filter is obtained, via adjustment of the tunnel bias voltage, enabling monochromatization of the electron beam. The dependence of the vacuum emission current, energy spread, reduced brightness, and virtual source size on the tunnel bias voltage are evaluated for a constant tunnel junction current of 10 nA and a foil thickness of 5 nm. Because the dimensions of the tunnel junction are comparable to the electron wavelength, diffraction plays an important role. As a result, the reduced brightness and vacuum emission current are related via the expression B=Iemission (2 me/h2). First, the source may be operated at a tunnel bias voltage for which the energy spread approaches the value for a room-temperature field-emission source (0.2 eV), with a vacuum emission current of 1 nA and a reduced brightness of 7×108 A m−2 sr−1 V−1. By careful adjustment of the tunnel bias voltage to the foil work function value it is possible, in principle, to contain 50% of the beam current within an energy spread of 100 meV at a total vacuum emission current of 0.1 nA and a reduced brightness of 7×107 A m−2 sr−1 V−1. The virtual source size in this case is approximately 1.4 nm. The energy spread may be decreased even further, down to the room-temperature thermionic limit, at the expense of vacuum emission current and, consequently, reduced brightness.
Band bending and field penetration on surfaces of ultrawide band gap semiconductors: Diamond and aluminum nitride
Authors: Lin L.-T. Steven , Liou Yung
Published: July 2002

Theoretical calculations were performed to study band bending and field penetration on surfaces of ultrawide band gap semiconductors in a negative field. The band bending was most prominent in the p-type materials with the surface potential of −4.85 eV for diamond and −5.53 eV for AlN at −20 V/μm and 400 K. The space charge region was terminated within a few microns in diamond and a few tens of microns in AlN. An appreciable penetrating field existed in the space charge region of p-type materials with a field strength of 2 to 3 V/μm for diamond and 0.2 to 0.3 V/μm for AlN. For the intrinsic and n-type (N doped) cases, the potential dropped very slowly from the surface to the bulk region while the field dropped very quickly within 0.1 μm. It was also found that the effective electron affinity was negative for p-type materials and positive for n-type materials. The characteristics of field emission from ultrawide band gap semiconductors according to our calculated results were also discussed.
Oscillation of polar Kerr rotation in PtCu/Co multilayers
Authors: Li J. , Ma P. P. , Wang Y. J. , Guo Z. H. , Chen J. C. , Chen L. Y. , Zhang R. J.
Published: July 2002

The effect of Cu doped into Pt spacer layers on magneto-optical properties for sputtered Pt/Co multilayers has been investigated. The polar Kerr rotation θk oscillates with the content of Cu in Pt spacer layers, and an obvious enhancement of θk at the first and second peaks on its oscillation curve can be seen. The numerical calculation indicates that the components of conductivity tensor in PtCu layers make a simultaneous oscillation with the polar Kerr rotation. These behaviors may result from the spin polarization in PtCu layers.
Interplay of capillary and elastic driving forces during microstructural evolution: Applications of a digital image model
Authors: Bullard Jeffrey W. , Garboczi Edward J. , Carter W. Craig
Published: July 2002

A recently developed model of curvature-driven, two-dimensional microstructure evolution is modified to include elastic strain energy at solid-fluid interfaces as an additional driving force for mass transport. Local phase distributions within a digital image of the microstructure are used to interpolate an isopotential contour that represents the equivalent sharp surface, along which local properties such as curvature are calculated. To determine the strain energy distribution, a finite element method is employed, using the pixel grid as the mesh. Interface-reaction-controlled mass transport is simulated using a finite difference approach along the interface. Calculations of the strain energy density and chemical potential distributions within simple systems show reasonable agreement with analytical results, and the predicted stability and evolution of such systems also agree with the predictions of other investigators. The model is also applied to a more complex system for which neither analytical nor other numerical methods can be readily used, and useful quantitative information is obtained on the energetics and structural changes.
Numerical analysis of a thin microcrystalline p layer in p-i-n a-Si:H solar cells
Authors: Topic Marko , Smole Franc , Furlan Jože
Published: July 2002

We have used our numerical simulator to examine the function of a thin microcrystalline p(μc-Si:H) layer in a p-i-n hydrogenated amorphous silicon (a-Si:H) based solar cell. In the analysis of a p(μc-Si:H)-i-n structure, three parameter sets were chosen for the purpose of verifying the validity of the reported measured p(μc-Si:H) material parameters. The results revealed that the correct setting of the p(μc-Si:H) work function is of prime importance. Analysis of a double window layer with an inserted p(a-SiC:H) layer and an accompanying i(a-SiC:H) buffer layer in the p(μc-Si:H)-i-n structure showed that the i(a-SiC:H) buffer layer beneficially affects the JSC and fill factor and furthermore, the insertion of a few nanometers thick p(a-SiC:H) layer between the p(μc-Si:H) layer and i(a-SiC:H) buffer layer additionally improves the solar cell performance.
Thermal stability of copper silicide passivation layers in copper-based multilevel interconnects
Authors: Hymes S. , Kumar K. S. , Murarka S. P. , Ding P. J. , Wang W. , Lanford W. A.
Published: July 2002

Copper thin films were exposed to a dilute silane mixture at temperatures in the range of 190–363 °C. The resulting silicide surface layers were characterized by four-point probe, Rutherford backscattering spectrometry, and x-ray diffraction. A definitive stability regime is observed in which progressively higher copper content phases exist with increasing temperature. Cu3Si, formed in silane, on annealing converts to Cu5Si and eventually to no silicide layer by a silicon diffusion reaction that in an inert ambient drives silicon into underlying copper to form a solid solution. In oxidizing ambients, a similar phenomenon occurs but now silicon also diffuses to surfaces where it oxidizes to form a self-passivating SiO2 layer on surface. These results have important implications governing integration of copper silicide as a passivation layer and silicon hydride based dielectric deposition in copper-based multilevel interconnect in ultralarge scale integration.
Influence of the implanted K-cluster size distribution on the shift of W work function
Authors: Girardeau-Montaut Jean-Pierre , Girardeau-Montaut Claire
Published: July 2002

The shift of the work function up to 2 eV, at the surface of polycrystalline tungsten, due to implantation by 30–110 keV K+ ions, can be explained by the simple assumption of small K-clusters formation inside the metal surface layer. An improved model is proposed which takes into account most of the characteristic parameters for the implantation process and the alkali-cluster formation inside the surface. In particular, the cluster size distribution being one of the most critical parameter, it is essential to derive its influence on the shift of the work function at the metallic surface, and also on the other related parameters. Taking into account the previous experimental data, it is then possible to determine the most probable K-cluster size distribution, and also to estimate the limits of variation ranges of the characteristic parameters.
1.3 μm InGaAsP/InP capped mesa buried heterostructure laser with an undoped cladding layer in base epitaxial growth
Authors: Swaminathan V. , Reynolds C. L. , Geva M.
Published: July 2002

A study of Zn diffusion behavior in capped mesa buried heterostructure lasers reveals the Zn profile in the base epitaxial region of InGaAsP/InP heterostructures to be dominated by diffusion during regrowth. This diffusion behavior has enabled us to fabricate a laser without any Zn doping in the p clad during base growth. The lasing characteristics at 25 °C are comparable to those of normally Zn-doped structures. The Zn diffusion into the undoped cladding layer, and thus, the temperature performance of these lasers are dependent on the level of Zn doping in third growth.