bluuebunny/crossref_metadata_2025 huggingface dataset:
Reduction of thermal damage in ultrathin gate oxides after intrinsic dielectric breakdown
Authors: Lombardo S. , La Magna A. , Crupi I. , Gerardi C. , Crupi F.
Published: July 2002

We have compared the thermal damage in ultrathin gate SiO2 layers of 5.6 and 3 nm thickness after intrinsic dielectric breakdown due to constant voltage Fowler–Nordheim stress. The power dissipated through the metal–oxide–semiconductor capacitor during the breakdown transient, measured with high time resolution, strongly decreases with oxide thickness. This is reflected in a noticeable reduction of the thermal damage found in the structure after breakdown. The effect can be explained as the consequence of the lower amount of defects present in the oxide at the breakdown instant and of the occurrence of a softer breakdown in the initial spot. The present data allow us to estimate the power threshold at the boundary between soft and hard breakdown, and they are compared to numerical simulations of heat flow.
Si/SiGe modulation-doped heterostructures grown on silicon-on-insulator substrates for high-mobility two-dimensional electron gases
Authors: Di Gaspare L. , Alfaramawi K. , Evangelisti F. , Palange E. , Barucca G. , Majni G.
Published: July 2002

The growth of high-mobility modulation-doped Si/SiGe heterostructures on silicon-on-insulator substrates is demonstrated. The structural and electrical properties of the samples are reported to be comparable with those of similar samples grown on standard Si substrates. Electron mobilities as high as 2900 cm2/Vs at room temperature and 8.2×104 cm2/Vs at 4.2 K were obtained.
Radial-pattern formation in the polycarbonate substratum of recordable compact disks
Authors: Tanimura M. , Ishikawa I. , Tachibana M. , Shinozaki K. , Kojima K.
Published: July 2002

A radial pattern is found to form in the polycarbonate (PC) substratum of a recordable compact disk. Characteristic features of the pattern are that it is composed of about 80 needle-like regions, the shape of which closely resembles a thin film. In addition, white light is found to scatter at the needle-like region/matrix boundaries. This suggests that the PC substratum may have inferior transparency due to the formation of this pattern. Thus, it is important to understand the bifurcation of the radial-pattern formation from the viewpoint of materials science and engineering. Based on the mechanics of the PC viscous fluid, it has been found that the bifurcation of the pattern formation has a Reynolds number of about 10−3.
Self-organized carbon nanotips
Authors: Jang Jin , Chung Suk Jae , Kim Hong Sik , Lim Sung Hoon , Lee Choong Hun
Published: July 2002

We have developed a carbon nanostructure, which is comprised of high-density carbon nanotips on a graphite layer. These carbon nanotips, with tip diameters of ∼10 nm, are grown by high-density plasma chemical vapor deposition onto Ni-coated Si using an inductively coupled plasma. The Ni on Si changes into NiSi2 by substrate heating. First, a carbon buffer layer and then a graphene sheet are formed on the NiSi2. Then, the carbon nanotips are grown by a C2H2/H2 plasma on the graphene sheet. The carbon nanotips show good adhesion to the substrate and are almost aligned, with an average length of 110 nm. They exhibit a turn-on field of 0.1 V/μm, a field amplification factor of ∼13 000, a current density of 2 mA/cm2 at a field of 2 V/μm, and uniform electron emission.
Modified Airy function method for modeling of direct tunneling current in metal–oxide–semiconductor structures
Authors: Wang Jing , Ma Yutao , Tian Lilin , Li Zhijian
Published: July 2002

Using a modified Airy function (MAF) to solve the Schrödinger equation in the whole metal–oxide–semiconductor structure, a fully quantum-mechanical model of direct tunneling current from an inverted p-Si substrate through ultrathin oxides is presented. The effects of tunneling on the electrostatic potential and the distribution of electrons are also included when self-consistently solving the Schrödinger and Poisson equations in silicon. Due to the semianalytical nature of the MAF method, the model has high efficiency. Model results are compared with experimental data and show excellent agreement. Moreover, an approximately linear relationship between the logarithm of the direct tunneling current and oxide thickness is found out.
Importance of quadrupolar ordering in antiferroelectric liquid crystal devices
Authors: Parry-Jones L. A. , Elston S. J.
Published: July 2002

A model of switching in antiferroelectric liquid crystals is presented which predicts both helix unwinding in the pretransitional regime and a field induced transition to the ferroelectric state. When the ratio of the coefficients of the quadrupolar and dipolar ordering terms in the bulk free energy expression exceeds a critical value, the latter transition becomes first order, in agreement with experimental observation. We have determined these coefficients in the commercial mixture CS4001. The ratios of the coefficients imply that all three states (antiferroelectric and two ferroelectric) are stable in the ground state, i.e., antiferroelectric liquid crystals are truly tristable.
Measurement of quantum efficiency in Pr3+-doped CaAl4O7 and SrAl4O7 crystals
Authors: Wang Xiao-jun , Huang Shihua , Lu Lizhu , Yen William M. , Srivastava A. M. , Setlur A. A.
Published: July 2002

We demonstrated a method for measuring the quantum efficiency of deep UV emission using the two-step excitation and the difference of the integrated spectral intensities in Pr3+-doped CaAl4O7 and SrAl4O7 crystals. The quantum efficiencies of the emission from the lowest 4f5d state in the two systems have been estimated to be less than 10% at room temperature. The effect of excited-state absorption of the lowest 4f5d state is analyzed for the quantum efficiency measurement. The actual efficiency may be higher when this effect is taken into account, especially under the condition of strong excitation.
Selective Si epitaxial growth technique employing atomic hydrogen and substrate temperature modulation
Authors: Schroeder T. W. , Ma P. F. , Lam A. M. , Zheng Y.-J. , Engstrom J. R.
Published: July 2002

We present here a low-temperature (Ts<630 °C) process for the selective epitaxial growth of Si that employs atomic hydrogen. Modulation of both the substrate temperature and the flux of atomic hydrogen gives alternating growth and suppression/etching cycles, resulting in a significant increase in selectivity. Epitaxial thin-film quality is essentially unaffected, as verified by in situ analysis via low-energy electron diffraction, and ex situ analysis via scanning electron and atomic-force microscopy.
Treatment of organic polymer surfaces by CF4 plasmas: Etching by fluorine atoms and influence of vacuum ultraviolet radiation
Authors: Schwarzenbach W. , Derouard J. , Sadeghi N.
Published: July 2002

Previous works have shown that atomic fluorine is the main etching agent of organic polymer surfaces subjected to fluorinated plasma treatments. In this work the etching probability per F atom impinging on a polymer-like material (hexatriacontane C36H74, a model molecule for high density polyethylene) has been estimated from direct measurements of the etching rate using a quartz crystal microbalance and from the absolute F atom concentration using threshold mass spectrometry. This etching probability has roughly the same value as the sticking probability of F atoms on this surface, which is in the range of 1%–3%. It has been pointed out that the reactivity of the surface with respect to F atoms is enhanced when the polymer surface is seen by the plasma. This could be due to either ions or vacuum ultraviolet (VUV) radiation. To more fully understand this point, we have built an external independent VUV source to irradiate the sample and we have used threshold ionization mass spectrometry to monitor the F atoms kinetics. The simultaneous irradiation of the substrate by VUV increases by a factor of 2 the reactivity of the substrate with respect to F atoms.
Improved superconducting quantum interference devices by resistance asymmetry
Authors: Testa G. , Pagano S. , Sarnelli E. , Calidonna C. R. , Furnari M. Mango
Published: July 2002

Direct current superconducting quantum interference devices made by Josephson junctions with asymmetric shunt resistances have been numerically investigated in the low temperature regime. When combined with a damping resistance, the asymmetry leads to a flux to voltage transfer coefficient several times larger than the one typical of symmetric devices, together with a lower magnetic flux noise. These results show that this type of asymmetric device may replace the standard ones in a large number of magnetometric applications, improving the sensitivity performance. The large transfer coefficient may also simplify the readout electronics allowing a direct coupling of asymmetric devices to an external preamplifier, without the need of an impedance matching flux transformer.
Ion acoustic shock waves in a collisional dusty plasma
Authors: Ghosh Samiran , Sarkar Susmita , Khan Manoranjan , Gupta M. R.
Published: July 2002

The effect of ion–dust collisions on small amplitude nonlinear dust ion acoustic waves has been investigated. Analytical investigation shows that propagation of the small amplitude wave is governed by Korteweg–de Vries (KdV) Burger equation. It is found that the coefficient of the Burger term is proportional to the ion viscosity, which arises through ion–dust collisions and depends on the temperatures and number densities of the electrons, ions and also on the number density of dust grains, as seen in a recent experiment (Nakamura et al.). Numerical investigations on the basis of that experimental data show that the dust–ion acoustic wave exhibits both oscillatory and monotonic shocks depending on the number density of dust particles, as observed in that experiment [Nakamura et al., Phys. Rev. Lett. 83, 1602 (1999)].
Method for repairing Mo/Si multilayer thin film phase defects in reticles for extreme ultraviolet lithography
Authors: Mirkarimi P. B. , Stearns D. G. , Baker S. L. , Elmer J. W. , Sweeney D. W. , Gullikson E. M.
Published: July 2002

The development of a nearly defect-free reticle blank is an important challenge facing extreme ultraviolet lithography (EUVL). The core element of an EUVL reticle blank is the reflective Mo/Si multilayer film, and deposition of Mo/Si on very small substrate defects can result in critical Mo/Si phase defects. In this article we present a method for repairing Mo/Si multilayer film phase defects in EUVL reticle blanks. An electron beam is used to deposit energy in the immediate vicinity of the defect, producing a small local contraction of the layer thicknesses due to silicide formation at the Mo/Si interfaces. We show in simulations that this contraction can significantly reduce the original structural deformation. We also present experimental results showing that it is possible to use an electron beam to controllably produce depressions in Mo/Si with nanometer-scale depths, and that this can be achieved without significantly impairing the reflective properties of the Mo/Si multilayer films.
Correlation between nucleation layer structure, dislocation density, and electrical resistivity for GaN films grown on a-plane sapphire by metalorganic vapor phase epitaxy
Authors: Twigg M. E. , Koleske D. D. , Wickenden A. E. , Henry R. L. , Binari S. C.
Published: July 2002

Transmission electron microscopy has been used to study AlN nucleation layers (NLs) grown using metalorganic vapor phase epitaxy, in order to link the resistivity of unintentionally doped GaN films to NL microstructure. We observed that high-resistivity (HR) GaN films grew on large-grained NLs, which, in turn, grew on smooth sapphire surfaces. These HR films had a higher density of edge dislocations than screw and mixed dislocations. Low-resistivity GaN films were found to grow on fine-grained NLs that grew on rougher sapphire surfaces. These LR films had a density of edge dislocations close to the combined density of screw and mixed dislocations. The LR films in this study were also found to have a buried conductive layer that is detectable using capacitance–voltage measurements.
Effect of composition inhomogeneity on the photoluminescence of InGaN/GaN multiple quantum wells upon thermal annealing
Authors: Chuo Chang-Cheng , Chang Mao Nan , Pan Fu-Ming , Lee Chia-Ming , Chyi Jen-Inn
Published: July 2002

The optical properties of thermally annealed InGaN/GaN multiple quantum wells were investigated by low-temperature photoluminescence measurements. It is found that the photoluminescence peak exhibits a redshift followed by a blueshift as the annealing time is increased. In contrast, the assigned photoluminescence peak from an In-rich dot-like structure shows a monotonic blueshift with more annealing time. Transmission electron microscopic observation confirms that the density of dot-like structures is reduced after thermal annealing, indicating that phase separation does not take place in these samples. Instead, in-plane and out-plane outdiffusion of dot-like structures is proposed to account for the spectral shift with more annealing time. Based on this diffusion model, a quantized state transition in the quantum well along with the composition inhomogeneity and piezoelectric field is considered to be the dominant luminescence mechanism.
Effect of chirp in diffraction of short electromagnetic pulses through subwavelength apertures
Authors: Mitrofanov Oleg , Lee Mark , Pfeiffer L. N. , West K. W.
Published: July 2002

Short electromagnetic pulses experience significant spectral and temporal deformation when diffracted on subwavelength apertures. Temporal delay/advancement is one of the effects that occurs when a pulse passes through the aperture. In this study, it is demonstrated that the intrinsic negative chirp of terahertz pulses is the origin of the temporal advancement in the limit that the aperture is much smaller than the wavelength of the pulse. The advancement is shown to disappear for unchirped terahertz pulses. The chirp effect is general for any system where the diffracted or scattered field is wavelength dependent.
Self-doping of cadmium stannate in the inverse spinel structure
Authors: Zhang S. B. , Wei Su-Huai
Published: July 2002

Using first-principles total energy calculations, we have studied self-doping in the ternary transparent conducting oxide, Cd2SnO4. Formation of the CdO and SnO2 binaries limits the inverse spinel Cd2SnO4 phase into a narrow region in the atomic chemical potential (μ) space. This suggests that μSn is not independent of μCd, so a Cd-rich growth or annealing condition also implies Sn-rich, and vice versa. We found that the widely accepted intrinsic donors such as oxygen vacancy and cadmium interstitial are not responsible for the observed conductivity in Cd2SnO4: both require too much energy to form. In addition, the oxygen vacancy is rather deep. We show instead that the Sn-on-Cd antisite defect is the most probable donor responsible for the n typeness under Cd-rich conditions.
Two-photon absorption photocurrent enhancement in bulk AlGaAs semiconductor microcavities
Authors: Folliot H. , Lynch M. , Bradley A. L. , Dunbar L. A. , Hegarty J. , Donegan J. F. , Barry L. P. , Roberts J. S. , Hill G.
Published: July 2002

We report on two-photon absorption (TPA) photocurrent in semiconductor microcavities. We experimentally show a substantial increase in the TPA photocurrent generated, at resonance, in a GaAlAs/GaAs microcavity designed for TPA operation at ∼890 nm. An enhancement factor of ∼12 000 of the photocurrent is obtained via the microcavity effect, which could have an important impact on the use of TPA devices for high speed switching and sampling applications. Our results also show the implications of the cavity photon lifetime on autocorrelation traces measured using TPA in semiconductor microcavities.
Dielectric barrier microdischarges: Mechanism for the charging of cellular piezoelectric polymers
Authors: Lindner Michael , Bauer-Gogonea Simona , Bauer Siegfried , Paajanen Mika , Raukola Jaakko
Published: July 2002

Charged closed-cell polymer foams have been found to be highly sensitive piezoelectric materials. Charging is shown to arise from dielectric barrier microdischarges within the voids of the cellular polymer. Above the threshold voltage for breakdown in the voids, the microdischarges are evidenced by light emission from the polymer, as well as by displacement-voltage hysteresis loops. Monitoring light emission during breakdown is shown to provide a quick check for the suitability of foams for piezoelectric applications. Additionally it allows for the visualization of micropores in foams in a nondestructive way. The piezoelectric response of the foam can be switched by applying dc-voltage pulses of alternating polarity above the breakdown threshold, thereby showing the feasibility of patterning the piezoelectric properties within the film plane. Although piezoelectric foams are nonferroelectric, the experiments prove similarities to ferroelectric materials with respect to hysteresis behavior, as well as a threshold (coercive) field for switching of the polarization and piezoelectricity.
Enhancement of the light emissions from zinc oxide films by controlling the post-treatment ambient
Authors: Shi W. S. , Agyeman O. , Xu C. N.
Published: July 2002

Highly-oriented zinc oxide (ZnO) films were grown on quartz glass substrates by radio frequency magnetron sputtering method. The temperature dependence of the photoluminescence spectra of the ZnO films annealed in argon, argon mixed with 5% hydrogen (H2/Ar) and oxygen ambient, respectively, was investigated from −190 to 600 °C. Results shown that UV light emission was greatly enhanced by annealing the as-grown ZnO film in H2/Ar ambient. Meanwhile, strong visible light emission was observed from the ZnO film annealed in oxygen ambient, and intense emissions in both UV and visible region were obtained from the ZnO films annealed in argon ambient. The UV emission from the ZnO films showed a high thermal stability that can be clearly observed up to 400 °C. The effect of the annealing ambient and the photoluminescence temperature dependence are discussed with the relations to the structural defects.
Polarization charges at spontaneously ordered (In, Ga)P/GaAs interfaces
Authors: Krispin P. , Knauer A. , Gramlich S.
Published: July 2002

The depth-resolved electrical characteristics of n- and p-type GaAs/(In, Ga)P/GaAs heterojunctions are examined by capacitance–voltage measurements. Different epitaxial growth conditions are chosen to produce heterointerfaces with (In, Ga)P layers of various degrees of order. Irrespective of the conduction type of the heterojunction studied, we find positive [negative] sheet charges at the (In, Ga)P-on-GaAs [GaAs-on-(In, Ga)P] interfaces. The density of both interfacial charges increases with increasing degree of (In, Ga)P order. The experimental results can be completely explained by taking into account the spontaneous polarization of ordered (In, Ga)P. The polarization difference between ordered (In, Ga)P and GaAs (no polarization) results in opposite sheet charges at the two complementary interfaces with GaAs, in accordance with theoretical predictions.
Fabrication and low-temperature transport properties of selectively grown dual-gated single-electron transistors
Authors: Motohisa J. , Nakajima F. , Fukui T. , van der Wiel W. G. , Elzerman J. M. , De Franceschi S. , Kouwenhoven L. P.
Published: July 2002

We report on the fabrication of a dual-gated single-electron transistor (SET) based on a quantum dot (QD) formed by selective area growth of metalorganic vapor-phase epitaxy, and its low-temperature transport properties. We observe clear Coulomb oscillations in a SET fabricated in combination with direct growth of nanostructures and lithographically defined metal gates. The magnetic field dependence of the Coulomb oscillations as well as the Coulomb diamonds suggest strong carrier confinement in our QD.
Periodic orbit quantization of the anisotropic Kepler problem
Authors: Christiansen Freddy , Cvitanović Predrag
Published: July 2002

The periodic orbit quantization on the anisotropic Kepler problem is tested. By computing the stability and action of some 2000 of the shortest periodic orbits, the eigenvalue spectrum of the anisotropic Kepler problem is calculated. The aim is to test the following claims for calculating the quantum spectrum of classically chaotic systems: (1) Curvature expansions of quantum mechanical zeta functions offer the best semiclassical estimates; (2) the real part of the cycle expansions of quantum mechanical zeta functions cut at appropriate cycle length offer the best estimates; (3) cycle expansions are superfluous; and (4) only a small subset of cycles (irreducible cycles) suffices for good estimates for the eigenvalues. No evidence is found to support any of the four claims.
Cycles homoclinic to chaotic sets; robustness and resonance
Authors: Ashwin Peter
Published: July 2002

For dynamical systems possessing invariant subspaces one can have a robust homoclinic cycle to a chaotic set. If such a cycle is stable, it manifests itself as long periods of quiescent chaotic behaviour interrupted by sudden transient ‘bursts’. The time between the transients increases as the trajectory approaches the cycle. This behavior for a cycle connecting symmetrically related chaotic sets has been called ‘cycling chaos’ by Dellnitz et al. [IEEE Trans. Circ. Sys. I 42, 821–823 (1995)]. We characterise such cycles and their stability by means of normal Lyapunov exponents. We find persistence of states that are not Lyapunov stable but still attracting, and also states that are approximately periodic. For systems possessing a skew-product structure (such as naturally arises in chaotically forced systems) we show that the asymptotic stability and the attractivity of the cycle depends in a crucial way on what we call the footprint of the cycle. This is the spectrum of Lyapunov exponents of the chaotic invariant set in the expanding and contracting directions of the cycle. Numerical simulations and calculations for an example system of a homoclinic cycle parametrically forced by a Rössler attractor are presented; here we observe the creation of nearby chaotic attractors at resonance of transverse Lyapunov exponents.
Ring wave solutions of a n+1-dimensional Sine–Gordon model
Authors: Di Garbo A. , Fronzoni L. , Chillemi S.
Published: July 2002

The dynamical properties of the ring wave solutions of the model ψtt−∇n2ψ+sin ψ+ε sin (ψ/2)+αψt=0 (0⩽ε≪1,0⩽α≪1) are studied analytically and numerically for spatial dimension (n=2,3). The model is obtained as a continuum approximation of a multidimensional Frenkel–Kontorowa lattice. We will show that in the case ε>0, α=0 (or α>0) the return effect of the ring wave does not occur only for well defined values of ε. It will be shown numerically that the dissipative perturbation αψt (α>0) stabilizes both the velocity and the wave profile of the ring wave when the return effect does not occur.
Synchronized family dynamics in globally coupled maps
Authors: Balmforth N. J. , Jacobson A. , Provenzale A.
Published: July 2002

The dynamics of a globally coupled, logistic map lattice is explored over a parameter plane consisting of the coupling strength, ε, and the map parameter, a. By considering simple periodic orbits of relatively small lattices, and then an extensive set of initial-value calculations, the phenomenology of solutions over the parameter plane is broadly classified. The lattice possesses many stable solutions, except for sufficiently large coupling strengths, where the lattice elements always synchronize, and for small map parameter, where only simple fixed points are found. For smaller ε and larger a, there is a portion of the parameter plane in which chaotic, asynchronous lattices are found. Over much of the parameter plane, lattices converge to states in which the maps are partitioned into a number of synchronized families. The dynamics and stability of two-family states (solutions partitioned into two families) are explored in detail.
Phase space structure and anomalous diffusion in a rotational fluid experiment
Authors: Kovalyov S.
Published: July 2002

The transport of passive scalars is considered in a model of rotating annulus experiments. The system has a chain of vortices and a jet, separated by a stochastic layer. For special values of the control parameters, the boundary of the stochastic layer can contain self-similar structures of islands with regular trajectories. Two such values are identified, with the structure being on the jet boundary and on the vortex boundary, respectively. The transport properties for both cases were studied by high-precision direct numerical integration of the equations of motion. The presence of such structures is found to significantly affect the statistical properties of the trajectories and the transport exponent. The results of the computations are compared with various theoretical models of anomalous diffusion. The particle behavior was found to depend significantly on the time scale, with different theories being applicable on different time intervals. Some regimes do not match any of the existing theories.
Accurate, short series approximations to Fermi–Dirac integrals of order −1/2, 1/2, 1, 3/2, 2, 5/2, 3, and 7/2
Authors: Van Halen P. , Pulfrey D. L.
Published: July 2002

Short series approximations based on the classical series expansions of the Fermi-Dirac integrals Fj(x) are presented for the orders −1/2, 1/2, 1, 3/2, 2, 5/2, 3, and 7/2. The approximations are accurate to better than 1 part in 105 over the range − ∞ <x< ∞ .
A new equation of state for aluminum
Authors: Holian K. S.
Published: July 2002

A new equation of state (EOS) has been produced for aluminum, which accurately reproduces experimental data for both the liquid and solid states. It also has a melting transition that reproduces measurements of the temperature vs pressure along the melt line. The liquid part of the EOS was calculated with the soft-sphere model for liquid metals, and the solid EOS is based upon a Birch-equation cold curve and Grüneisen thermal contributions. The range of the table extends from room temperature to 1.6 eV and from densities of 10−3–103 g/cm3.
Effect of order of stress and field application on the measured flux density in 1% Mn pipeline steel
Authors: Atherton David L. , Sudersena Rao T.
Published: July 2002

Experiments involving different orders of field and stress application on the measured flux density in 1% Mn pipeline steel samples were performed in order to examine the validity of LeChatelier’s principle. In the low-field regions the flux density in the sample was found to be strongly dependent on the order of applied stress and field, as stated by Bozorth. The results obtained for stress-induced magnetization changes were in accordance with the Jiles–Atherton theory.
Computer simulation of damage processes during ion implantation
Authors: Kang H. J. , Shimizu R. , Saito T. , Yamakawa H.
Published: July 2002

A new version for the marlowe code, which enables dynamic simulation of damage processes during ion implantation to be performed, has been developed. This simulation code is based on uses of the Ziegler–Biersack–Littmark potential [in Proceedings of the International Engineering Congress on Ion Sources and Ion-Assisted Technology, edited by T. Takagi (Ionic Co., Tokyo, 1983), p. 1861] for elastic scattering and Firsov’s equation [O. B. Firsov, Sov. Phys. JETP 61, 1453 (1971)] for electron stopping. By introducing a damage function  f(z)=l−exp[−ΔE(z)/Ecrit], where ΔE(z) is the deposition energy due to nuclear stopping per unit volume at depth z and Ecrit is the critical energy assessed from the experiment, the present code allows us to simulate how the crystalline structure at depth z transforms to the disordered structure, resulting in the marked change in the penetration of implanted ions as ion implantation proceeds. To examine the applicability of the present simulation code for practical ion implantation, we have performed dynamic simulations of the depth profile of implanted ions considering the changes in the crystalline structure due to disordering during ion implantations, and the results are compared with the experimental results of Mayer et al. [Can. J. Phys. 46, 664 (1968)]. The agreement between theoretical and experimental results has been found to be very good. A prediction on the dose dependence of lattice disorder for practical low-dose implantation in GaAs is also presented.
Coaxial plasma accelerator in the snowplow mode: Analytical solution in the weak coupling limit
Authors: Dietz David
Published: July 2002

The analytical solution of the system of coupled ordinary differential equations which describes the time evolution of an ideal coaxial plasma gun operating in the snowplow mode is obtained in the weak coupling limit, i.e., when the gun is fully influenced by the driving circuit but the circuit is negligibly influenced by the gun. Criteria are derived for the validity of this limit, and numerical examples are presented. Finally, sample applications to calculating maximum plasma speed and gun efficiency are presented.
Effect of object potentials on the wake of a flowing plasma
Authors: Katz I. , Mandell M. J. , Parks D. E. , Wright K. , Stone N. H. , Samir U.
Published: July 2002

Measurements and calculations have been carried out to determine the structure of electric potential and ion density in the near wake created by the flow of a high-Mach-number plasma past a conducting plate biased with respect to the undisturbed plasma. Results are obtained for a molecular nitrogen plasma with ambient electron densities N of the order of 105 cm−3, ion temperatures of θi≂0.025 eV, electron temperatures of θ∼0.3 eV, and plasma flow velocities of V0≂106 cm/s, corresponding to V0/(θ/M)1/2≂11. For high-Mach-number flow past an unbiased object, the wake structure is very nearly that predicted for the expansion of an initially uniform plasma half-space into vacuum; in this case there is a sharply defined ion front moving under the influence of an electric field produced by charge separation between ions and electrons near the front. With bias potential φp such that qφp/θ is in the range −1 to −10, a well-defined ion front still exists, but its motion is strongly affected by the imposed potential. This effect can be explained in terms of the impulse received by those ions passing through the sheath region near the plate edge. Two-dimensional simulations of the laboratory experiments were performed by using a multiple waterbag technique. The results for both zero and finite ion temperatures are almost noise-free and support the approximate analytical model. The calculated density for 10 θ negative bias on the plate is compared with the measured profile.
Formation of large metal clusters by surface nucleation
Authors: Knauer W.
Published: July 2002

The formation of metal clusters with hundreds of atoms in and near vapor ejection nozzles is analyzed. A previously discussed model, cluster generation by homogeneous nucleation and collisional growth in the vapor phase, is found to be untenable because it cannot account for the large number of collisions required to remove the latent heat of condensation, freed during cluster growth. An alternative mechanism that involves heterogeneous nucleation (i.e., cluster formation on surfaces) is proposed and evaluated. To determine the applicability of this mechanism, the following process steps are considered: formation of an adequate supply of critical embryos on nozzle and adjacent crucible walls, growth of embryos into large clusters, and cluster ejection into the surrounding vapor atmosphere. The conclusion is that, with nonwetting vapor and surface material combinations, substantial quantities of large clusters can be formed and ejected. Specifically, predictions for silver vapor at a few Torr pressure, passing through a graphite nozzle at about 1600 K, are cluster generation rates of 1013–1014 clusters/cm2 s, and cluster sizes up to about 600 atoms. Available experimental observations support these predictions qualitatively.
Effects of leakage current on isothermal capacitance transient spectroscopy signals for midgap levels in GaAs
Authors: Kim Eun Kyu , Cho Hoon Young , Min Suk-Ki , Choh Sung Ho , Namba Susumu
Published: July 2002

The leakage current effects for the midgap levels in the electron-beam-metallized (EBM) Al/GaAs junction were studied by isothermal capacitance transient spectroscopy. In this junction, a new electron deep level which might be due to the surface defects induced during the EBM process was detected. The observed thermal emission time constants of the new deep level and the EL2 level (Ec −0.81 eV) in EBM-Al/GaAs were increased during the low-temperature annealing up to 355 °C, while the leakage current density in this junction was decreased down about 4×10−7 A/cm2. We represent that these behaviors of the midgap levels could be well explained by the effect of the leakage current in the Al/GaAs Schottky junction.
Measurement of ion energy distributions at the powered rf electrode in a variable magnetic field
Authors: Kuypers A. D. , Hopman H. J.
Published: July 2002

High-resolution energy distributions of ions, accelerated by the sheath at the powered electrode of a low-pressure 13.56-MHz gas discharge, have been measured. The observed spectra are compared to existing models. Excellent agreement between measured and calculated spectra is obtained. Detailed information on rf sheath behavior is derived from the observed energy profiles and from the measured total ion current densities towards the electrode surface. Analogous to the case of dc discharges, a decrease of sheath thickness is observed when a homogeneous variable magnetic field (0≤B≤315 G) is applied. However, the product of magnetic-field strength B and sheath thickness d is found to be independent of sheath voltage. This leads to the conclusion that in rf discharges, sheath contraction under influence of a magnetic field proceeds by a different mechanism than in dc discharges. It is suggested that the value of the product Bd is determined by the (virtually constant) temperature of the plasma electrons, rather than by the energy of secondary electrons that have been liberated from the electrode surface by ion bombardment. The decrease of sheath thickness d with magnetic-field strength B leads to a changing capacitive-voltage division of the applied generator voltage over the discharge. When the magnetic-field strength is sufficiently high, this may result in a sign reversal of the electrode self-bias voltage.
The closing diamond anvil optical window in multimegabar research
Authors: Ruoff Arthur L. , Luo Huan , Vohra Yogesh K.
Published: July 2002

The tetragonal distortion of a diamond anvil supporting a sample pressure of over 4 Mbars is such that the cubic crystal becomes elastically distorted to a tetragonal crystal with c/a ■0.69. These large distortions in the anvil greatly change its optical properties. The decrease of the band gap of diamond with pressure is described in terms of a dielectric model and in terms of experimental data to 4.05 Mbars. It is shown how this band gap decrease makes it impossible to excite ruby fluorescence using argon or He-Cd lasers above about 250 GPa or so (depending on the wavelength). The radiation cannot get through the diamond anvil to the ruby. There is a very strong stress-induced luminescence in Type Ia diamond in the red at pressures above 2 Mbars and in infrared above 2.5 Mbar. This latter fluorescence, if assumed to be due to ruby R1 fluorescence (no ruby is present) suggests that the pressure is 5.6 Mbars.
Probe diagnostics of anisotropic plasma in a hollow cathode arc
Authors: Klagge S. , Lunk A.
Published: July 2002

Measuring the second derivatives of electron retarded current characteristics of a plane probe at different angle positions, the coefficients f*i(ε) of the velocity distribution function developed as a Legendre polynomial are determined for the anisotropic plasma of a hollow cathode arc discharge. The integral values deduced from this for the electron concentration ne and the mean electron energy ε̄, as well as the drift velocity vd, show only a limited dependence on the number of angle positions used for measurement. Even for measurements at a single angle position (Druyvesteyn method), the values obtained for ne, ε̄, and vd differ by less than 10% from the corresponding values measured with the multiposition method, so long as vdrift ≤ vthermal. On the contrary, the shape of f*i(ε), like the angle dependence f*(θ)ε=const, is clearly affected by the number of angle positions used. A Maxwell distribution superimposed by a group of directed fast electrons proves to be a sufficient model for the plasma investigated here.
Soft magnetic properties of Co-Fe-Al-N films
Authors: Iwasaki Hitoshi , Akashi Reiko , Ohsawa Yuichi
Published: July 2002

This article reports on the relations between the magnetic properties and crystal structure of Co-Fe-Al-N films prepared by rf magnetron sputtering in a mixed Ar and N2 gas atmosphere. Slightly substrate-biased 4 at. % Al films showed a low coercivity of less than 80 A/m, a low magnetostriction of less than 1×10 −6, and a high saturation magnetic flux density of 1.7 T. These features were maintained after annealing at up to more than 500 °C. The low Hc was related to the crystal structure of a face-centered-cubic phase with an about 10-nm grain size. No detectable AlN was observed by an x-ray diffractometry even after annealing. However, the lattice constant after annealing was nearly equal to that of a Co-Fe alloy and the Al content increased with the increase in sputtering N2-gas content, suggesting the binding of Al and N atoms.
Lattice position of Si in GaAs determined by x-ray standing wave measurements
Authors: Shih A. , Cowan P. L. , Southworth S. , Fotiadis L. , Hor C. , Karlin B. , Moore F. , Dobisz E. , Dietrich H.
Published: July 2002

The x-ray standing wave (XSW) technique was applied to determine the lattice location of Si impurity atoms in GaAs(100) crystals. The synchrotron radiation of X24A at the national synchrotron light source was utilized to set up backreflection XSW, an experimental geometry which drastically relaxes the otherwise stringent requirement on the lattice perfection. Specifically, the lattice sites were determined with respect to the [311] reflection planes which differentiate a Ga site from an As site. With the aid of an appropriate choice of the x-ray fluorescence filter, we were able to study GaAs(100) samples with very low levels of Si impurities. On a sample doped with 4×1018 cm−3 Si during the molecular-beam epitaxy growth, we found that the Si atoms predominantly occupied the Ga sites. On both an ion-implanted sample after annealing and a sample with Si impurities introduced by thermal diffusion, about 30% of the Si atoms occupied the Ga sites, and the rest occupied random sites. The As site occupation was less than 6%. Suggestions are made for further experiments with improved sensitivity.
In situ determination of optical constants of growing hydrogenated amorphous silicon film by p-polarized light reflectance measurement on the surface
Authors: Takano A. , Kawasaki M. , Koinuma H.
Published: July 2002

The reflection of p-polarized laser light was monitored in situ to elucidate the surface reaction process in plasma chemical vapor deposition of a-Si:H. The reflectance oscillated with the film growth. The deposition rate, refractive index, and absorption coefficient of the film were evaluated so that the detected reflectance oscillation could be best fitted with the pattern calculated by using the thickness and optical constants of the growing film as variable parameters. The deposition rate was unchanged by the variation of substrate temperature in the range between room temperature and 250 °C, whereas the refractive index and absorption coefficient increased with the substrate temperature in this range. The presence of a loosely packed layer as thick as 5 nm was clearly indicated by the analysis of time-dependent reflectance variation.
Demonstration of high peak-to-valley current ratio in an N-p-n AlGaAs/GaAs structure
Authors: Wang Y. H. , Wei H. C. , Houng M. P.
Published: July 2002

Using the combination of carrier injection modulation (bipolar mode) and channel blocking effect (junction field-effect transistor mode), we demonstrate a three-terminal voltage-controllable negative differential resistance device with a high room-temperature peak-to-valley current ratio in an N-AlGaAs/p+-GaAs/n-GaAs structure. The third terminal is formed through a self-aligned p-type diffused ohmic contact process to the n-GaAs layer instead of the p+-GaAs layer. The structure can be viewed as a modified integration circuit of a bipolar transistor and a junction field-effect transistor.
Reply to ‘‘Comment on ‘Current transport in Pd/n-InP diodes formed at room and low temperature’ ’’ [J. Appl. Phys. 72, 3803 (1992)]
Authors: Anderson W. A. , Lee H. J.
Published: July 2002

A further analysis of our previous data [Z. Q. Shi and W. A. Anderson, J. Appl. Phys. 72, 3803 (1993)] suggests conduction by thermionic field emission at low voltage for Au or Pd/n-InP Schottky diodes fabricated by cryogenic processing or low temperature (LT). Data at higher voltages follow the thermionic emission mechanism as described by R. T. Tung, J. Appl. Phys. 73, 4064 (1993). We do not feel that the inhomogeneity model of Tung should be applied to the LT diode due to the nature of thin film formation for metals deposited at low temperature.
Optical Kerr-effect measurement for a series of alcohols
Authors: Harrison Neil J. , Jennings Barry R.
Published: July 2002

Nanosecond optical Kerr-effect (OKE) measurements are reported using a modified apparatus, designed to enable rapid and precise data recording in pure liquids. Careful design of the apparatus enables measurements to be made at several inducing wavelengths without substantial apparatus modifications. The first measurement of the optical Kerr effect for benzene at an inducing wavelength of 532 nm is presented together with novel OKE data for the hitherto unstudied homologous alcohol series from methanol to 1-dodecanol. Analysis of the results indicates for this series the existence of a linear relationship between the carbon chain length and the optically induced Kerr constant somewhat similar to the behavior previously observed in the n-alkanes.
Transient flow of a Maxwell fluid on a rotating disk
Authors: Fong C. F. Chan Man , Kee D. De , Marcos B.
Published: July 2002

The unsteady flow of a thin layer of a Maxwell fluid is being considered. The radial speed and the thickness of the film are obtained analytically and numerically. The results obtained by both methods are in agreement.
Optically pumped laser action in double-heterostructure HgCdTe grown by metalorganic chemical vapor deposition on a CdTe substrate
Authors: Ravid A. , Cinader G. , Zussman A.
Published: July 2002

Photopumped laser action in a HgCdTe double-heterostructure grown by metalorganic chemical vapor deposition on a CdTe substrate containing (311)- and (211)-oriented grains was studied. The (311)-oriented device exhibited laser action around λ=4 μm with a threshold power increasing exponentially from 56 mW at T=12 K to 2.8 W at the highest lasing temperature of 90 K. The (211)-oriented laser device emitted around 2.5 μm. The threshold power of the (211) device was much higher than that of the (311) one (1.5 W at 12 K) and increased with temperature at a lower rate to 4.8 W at the highest lasing temperature of 110 K. Front illumination photoluminescence from both active and cladding layers of the (311)-oriented heterostructure was studied as a function of temperature.
Photoluminescence properties of N-implanted Al0.30Ga0.70As0.62P0.38 alloy grown on GaAs0.61P0.39 substrates
Authors: Chen Chyuan-Wei , Wu Meng-Chyi
Published: July 2002

Luminescence data are presented on nitrogen-implanted Al0.30Ga0.70As0.62P0.38 epitaxial layers, which are grown on GaAs0.61P0.39 substrates by liquid-phase epitaxy, with different annealing temperatures by the rapid thermal annealing technique. Except for the four emission peaks observed from undoped AlGaAsP layers, involving near-band-to-band, donor-to-valence-band, conduction-band-to-acceptor, and donor-acceptor-pair transitions, we also observe the recombinations from the NΓ, N′Γ, and Nx states associated with the nitrogen isoelectronic impurity in the N-implanted AlGaAsP layer. The existence of such states has been predicted by a theory of the N trap that includes both the long- and short-range characters of isoelectronic impurity potential in III-V alloys. The states NΓ and N′Γ are observed to lie below the Γ conduction-band minimum by 24 and 16 meV, respectively. The Nx state is associated with indirect emission and is below the Γ conduction-band minimum by 34 meV. This is a report on the luminescence study of N-implanted AlGaAsP alloy.
Beam breakup instability in an annular electron beam
Authors: Lau Y. Y. , Luginsland John W.
Published: July 2002

It is shown that an annular electron beam may carry six times as much current as a pencil beam for the same beam breakup (BBU) growth. This finding suggests that the rf magnetic field of the breakup mode is far more important than the rf electric field in the excitation of BBU. A proof-of-principle experiment is suggested, and the implications explored.
InP on Si substrates characterized by spectroscopic ellipsometry
Authors: Zwinge G. , Ziegenmeyer I. , Wehmann H.-H. , Tang G.-P. , Schlachetzki A.
Published: July 2002

We used spectroscopic ellipsometry to analyze the refractive index and the absorption coefficient of thin buffer layers of InP grown by metalorganic vapor phase epitaxy on Si substrates. We found a pronounced influence on the crystallographic properties of the subsequently grown InP main layer. The drastically increased optical absorption of the buffer layers is possibly caused by a high density in misfit dislocations or twins originating from the difference in lattice constants of InP and Si.
Comment on ‘‘Generalized study on angular dependence of induced second-order nonlinear optical polarizations and phase matching in biaxial crystals’’ [J. Appl. Phys. 46, 3992 (1975)]
Authors: Shi Jie , Jassemnejad Bahaeddin
Published: July 2002

Seventeen years ago, Ito, Naito, and Inaba [J. Appl. Phys. 46, 3992 (1975)] studied the general nature of induced second-order nonlinear optical polarizations and their phase matching in biaxial crystal. They derived the expressions of the effective nonlinear coefficients for both type I and type II phase matching. In recent research work, we found some errors in some of the expressions in that paper which were used by some papers published later.
Recombination model for heterostructure interfaces
Authors: Müllenborn M. , Haegel N. M.
Published: July 2002

Recombination and generation at slightly mismatched heterojunctions under optical excitation conditions are investigated with a model based on the ambipolar diffusion equation. This model is used to fit experimental photoluminescence power dependencies in order to analyze interface-related parameters as a function of lattice mismatch. Power dependencies are derived for photoluminescence of directly excited surface layers and photoluminescence generated indirectly by carrier diffusion or photon recycling through the interface region. Experimental results are presented for AlGaAs/GaAs and GaInP/GaAs heterostructures.
Effect of band-to-band (radiative) transitions in semiconductors
Authors: Khan W. I.
Published: July 2002

Efforts have been made to study the effect of the band-to-band radiative transitions in semiconductors. The computed results show the excess carrier density (Δn) to be nonuniform across the material. The variation in Δn has been computed. This result leads to a uniform carrier density in the material under certain conditions. Attempts are taken to study the variation of the coefficients b and c as a function of the constant α for the uniform carrier density conditions. Finally experimental result in an n-N GaAs-Al0.3-Ga0.7As heterojunction has been presented, which shows an agreement with the theoretical result so obtained.