bluuebunny/crossref_metadata_2025 huggingface dataset:
Frequency resolved admittance spectroscopy measurements on In0.52Al0.48As/InxGa1−xAs/In0.52Al0.48As single quantum well structures
Authors: Marsal L. F. , López-Villegas J. M. , Bosh J. , Morante J. R.
Published: July 2002

In this work a new admittance spectroscopy technique is proposed to determine the conduction band offset in single quantum well structures (SQW). The proposed technique is based on the study of the capacitance derivative versus the frequency logarithm. This method is found to be less sensitive to parasitic effects, such as leakage current and series resistance, than the classical conductance analysis. Using this technique, we have determined the conduction band offset in In0.52Al0.48As/InxGa1−xAs/In0.52Al0.48As SQW structures. Two different well compositions, x=0.53, which corresponds to the lattice-matched case and x=0.60, which corresponds to a strained case, and two well widths (5 and 25 nm) have been considered. The average results are ΔEc=0.49±0.04 eV for x=0.53 and ΔEc=0.51±0.04 eV for x=0.6, which are in good agreement with previous reported data.
Magnetic and structural studies of sputtered Co/Cu multilayer films
Authors: Kim J. D. , Petford-Long Amanda K. , Jakubovics J. P. , Evetts J. E. , Somekh R.
Published: July 2002

The structure and magnetic properties of sputtered Co/Cu multilayer films with various layer thicknesses have been studied. X-ray diffractometry and high resolution electron microscopy show the films to be polycrystalline with a fcc structure and strong [111] texture in the growth direction. The magnetoresistance (MR) of the films depends critically on Cu layer thickness (tCu), with maximum values for films with tCu around 1 nm. Large differences in saturating field are seen for films with tCu and tCo differing by a nominal 0.1 nm. The magnetic domain structure, studied using Lorentz microscopy, shows strong dependence on tCu. High MR-value films showed evidence of antiphase magnetic domain boundaries. The high MR samples show antiferromagnetic coupling, with higher saturating fields than seen in the ferromagnetically coupled films.
Determination of Si self-interstitial diffusivities from the oxidation-enhanced diffusion in B doping-superlattices: The influence of the marker layers
Authors: Gossmann H.-J. , Gilmer G. H. , Rafferty C. S. , Unterwald F. C. , Boone T. , Poate J. M. , Luftman H. S. , Frank W.
Published: July 2002

Si self-interstitial diffusivities can be extracted from the diffusive behavior of certain metals (e.g., Au) in an inert annealing ambient or from the diffusion of dopant markers (typically B) under oxidizing conditions. Each type of experiment yields fairly consistent results; however, interstitial diffusivities obtained in these two ways differ greatly. The marker layer experiments rely on the assumption that the presence of the dopant does not disturb the diffusion of the interstitials, and the validity of this assumption is explored. A model of interstitial diffusivity in the presence of B is developed, two extreme cases of the B-atom–interstitial interaction strength are considered, and the predictions of the model are compared with experiments of oxidation-enhanced diffusion in B doping-superlattices. From this comparison it is concluded that trapping of interstitials by B atoms in the markers cannot be responsible for the different values of the Si interstitial diffusivity reported in the literature. Further, it is shown that the presence of the dopant does not perturb the behavior of the Si self-interstitials in the doping-superlattices, i.e., the markers are ‘‘unobtrusive’’ probes of interstitial behavior.
Unified particle simulation technique for the plasma bulk and the cathode sheath of a dc glow discharge
Authors: Meyer Peter , Wunner Günter , Schmitt Wolfgang , Ruder Hanns
Published: July 2002

The unified particle simulation of the entire glow discharge including plasma bulk and electrode sheaths suffers from the bad representation of particles in the cathode fall and/or from expensive computing time. To improve the efficiency and reliability of such simulations we develop a splitting procedure for the simulation particles that increases the sampling rate in critical phase space regions. The technique is demonstrated with the help of a simplified model of a dc glow discharge. Simulation particles representing ions and electrons are traced from electrode to electrode by moving the particles in self-consistent fields. For comparison, the same model of the discharge is analyzed in the framework of transport equations. To improve the spatial density profiles of the macroscopic equations, we accounted for nonlocal effects by adjusting the Townsend ionization coefficient with the help of the particle simulation.
On the two-state microstructure of nanocrystalline chromium
Authors: Eastman J. A. , Fitzsimmons M. R.
Published: July 2002

High-angle neutron powder diffraction was used to investigate the grain size dependence of the Debye–Waller parameter (DWP) of nanocrystalline and coarse-grained chromium samples. The DWP measured at 20 K depends linearly on inverse grain size and is consistent with a two-state model in which defects with short-ranged displacement fields are present in differing concentrations in two distinct microstructural regions within individual grains. One possible model microstructure consists of grain boundary and free surface regions with significantly larger concentrations of point defects than in grain interiors. Evidence is also seen for an enhancement of the temperature-dependent component of the DWP of chromium with decreasing grain size, indicating different behavior than seen previously for nanocrystalline palladium.
Thermal behavior of deep levels correlated with iron in silicon metal-oxide-semiconductor structure
Authors: Kishino S. , Iwamoto S. , Yoshida H. , Niu H. , Matsuda T.
Published: July 2002

Thermal behavior of deep levels correlated with iron in Si MOS (metal-oxide-semiconductor) structure has been studied by isothermal capacitance transient spectroscopy. As a result, it is shown that interstitial iron scarcely affects the interface trap (Nt) of MOS structure. This is made clear by measuring Nt of Si MOS diodes containing iron impurity, the interstitial component of which is controlled by low temperature annealings. In addition, the low temperature (400 °C) annealing decreases interstitial iron concentration as well as interface trap density. This phenomenon is very lucky for Si MOS devices.
Persistent photoconductivity and DX centers in Cd0.8Zn0.2Te:Cl
Authors: Bennett J. W. , Thio Tineke , Kabakoff S. E. , Chadi D. J. , Linke R. A. , Becla P.
Published: July 2002

Transport measurements on large single crystals of Cd0.8Zn0.2Te:Cl indicate that Cl donors form DX centers in CdZnTe. We have observed persistent photoconductivity (PPC) with an annealing temperature Ta≊130 K. Hall-effect experiments indicate that the PPC arises from a persistent increase in the density of charge carriers; the saturation density is Nsat=6×1016 cm−3. The deep binding energy of the DX center is Ed=0.22 eV.
Modeling electromigration-induced stress evolution in confined metal lines
Authors: Clement J. J. , Thompson C. V.
Published: July 2002

A model for stress evolution in confined metal interconnects due to electromigration was proposed recently by M. A. Korhonen, P. Borgesen, K. N. Tu, and C.-Y. Li [J. Appl. Phys. 73, 3790 (1993)], in which interconnect failure is associated with the buildup of stress to a critical level. We show that the analytic solution for a semi-infinite line with a blocking boundary given by Korhonen et al. is a good approximation only when the stress buildup is small. This is not usually the case for narrow, encapsulated interconnect lines in which the electromigration-induced stress can be quite high prior to failure. A complete model description and a more accurate analytic solution to the differential equations describing the electromigration-induced stress buildup at a blocking boundary is presented.
Electron capture time measurements in GaAs/AlGaAs quantum-well infrared photodetectors: Photoresponse saturation by a free-electron laser
Authors: Duboz J. Y. , Costard E. , Nagle J. , Berset J. M. , Ortega J. M. , Gérard J. M.
Published: July 2002

The intersubband photoresponse in GaAs/AlGaAs quantum-well detectors has been measured with a free-electron laser delivering picosecond pulses. The saturation of the detector photocurrent with increasing power was observed. A model is presented that takes the absorption saturation and transport properties into account and allows the electron lifetime determination from the photocurrent saturation. The electron lifetime is found to increase with the electric field applied in the detector from 1 ps at low field up to 10 ps or more at high field (15 kV/cm). Effects of doping and well asymmetry are discussed.
The effects of polymeric coatings on the low-temperature microbending losses in initially curved double-coated optical fibers
Authors: Shiue Sham-Tsong
Published: July 2002

The thermally induced microbending losses in initially curved double-coated optical fibers at low temperature are investigated. The deflections in an initially curved fiber increase gradually with an increase in the thermally induced compressive axial force. The increase of deflection in an optical fiber results in an increase of microbending loss. In order to minimize such a microbending loss, the Young’s modulus and Poisson’s ratio of the primary coating should be increased. This means that a best selection of the Poisson’s ratio of the primary coating is 0.5. On the other hand, the effective thermal expansion coefficient of the primary coating, and the thickness, Young’s modulus, and effective thermal expansion coefficient of the secondary coating should be decreased. However, there exists an optimum value for the thickness of the primary coating. The thermally induced lateral pressure on the glass fiber can also produce microbending loss. Both effects of the axial force and lateral pressure on the microbending losses must be considered, so there exist optimum values for the Young’s moduli and effective thermal expansion coefficients of the primary coatings. An easy rule for the selection of the polymeric materials and their thicknesses to minimize the low-temperature microbending losses are also proposed.
Model for the fine structure of zero field steps in long Josephson tunnel junctions and its comparison with experiment
Authors: Barbara P. , Monaco R. , Ustinov A. V.
Published: July 2002

The single fluxon dynamics in the resonant regime has been investigated on high-quality low-loss Nb/Al–AlOx/Nb window Josephson tunnel junctions. A new model accounting for the fine structure of zero field steps in linear junctions is proposed. Depending on the fluxon velocity and on the junction losses, resonances may occur between the fluxon and the plasma waves corresponding to different wave numbers. This mechanism relies on a single proposition that the fluxon experiences an acceleration approaching the nonideal boundaries of the junction. We find good agreement between theory, numerical simulations, and experiments. The presence of the idle region has been proved to play a determinant role for the occurrence of the fine structure.
Dynamics of cavitation bubble induced by 193 nm ArF excimer laser in concentrated sodium chloride solutions
Authors: Turovets Igor , Palanker Daniel , Kokotov Yu. , Hemo Itzhak , Lewis Aaron
Published: July 2002

Cavitation bubbles were generated by the 193 nm argon fluoride excimer laser delivered with a specially designed tip into absorbing NaCl solution. The dynamics of bubble formation and collapse have been studied using fast flash photomicrography. The bubble dimensions were measured at different time delays as a function of the tip exit diameter, the energy fluence of the laser, and the NaCl concentration. The dynamics of the cavitation bubble created on the tip is compared with the well-studied dynamics of bubbles resulting from dielectric breakdown near a boundary.
Vacuum arc plasma jet propagation in a toroidal duct
Authors: Alterkop B. , Gidalevich E. , Goldsmith S. , Boxman R. L.
Published: July 2002

A two fluid magneto-hydrodynamic theory of vacuum arc plasma jet propagation in a magnetized toroidal duct is developed. The physical mechanisms of jet transverse displacement and plasma losses are analyzed and the centrifugal force on the ions is shown to play the principle role in these processes. Optimal conditions for jet propagation occur when the centrifugal force is balanced by the electrical force on the ions. An analytical solution of the nonlinear problem of plasma beam transport through a toroidal duct is obtained for the two cases where ions are magnetized or not magnetized. The ion mass current decreases with the azimuthal distance along the torus as (1+φ/φ0)−1 where φ0 is a characteristic angular distance, for the case when ions are magnetized, and exponentially when the ions are not magnetized. Numerical calculations show that the decrease of plasma density leads to a longitudinal electric field and current. This current, together with the current due to the centrifugal drift, form a current loop which is closed through the plasma and structures outside the torus. Moreover if there are optimal conditions for jet propagation at the torus entrance, they are approximately conserved along the length of the torus.
Picosecond time-resolved magnetization dynamics of thin-film heads
Authors: Freeman M. R. , Smyth J. F.
Published: July 2002

The application of picosecond magneto-optic sampling techniques to studies of the magnetization dynamics of thin-film recording heads is described. Time-resolved magnetization measurements are performed using picosecond stroboscopic scanning Kerr microscopy. A Faraday probe is used to monitor the coil excitation current with the same optical setup, yielding a direct measure of the magnetic propagation delay through the head. This delay is found to have a marked spatial dependence across the face of the pole tips. As an aid to visualization of the spatial dependence, scanned images of the polar Kerr rotation at fixed time delays are acquired.
Transition from in-plane to perpendicular magnetization in MSR magneto-optical disks
Authors: Nishimura Naoki , Hiroki Tomoyuki , Okada Takeshi , Tsunashima Shigeru
Published: July 2002

Transition from in-plane to perpendicular magnetization caused by temperature changes have been investigated for double-layer (GdFeCo/TbFeCo) and triple-layer (GdFeCo/GdFe/TbFeCo) magneto-optical recording films. The transition in the GdFeCo layer occurs mainly as a result of change in the demagnetizing energy of the GdFeCo layer having compensation temperature. Such transition occurs more rapidly in the triple-layer film than that in the double-layer film. Micromagnetic calculation showed that in the double-layer film the interface wall penetrates deeply into the GdFeCo readout layer, while in the triple-layer film the wall is almost completely confined within the GdFe intermediate layer having a large Ms and a low Tc. The triple-layer film is found to improve the characteristics of magnetically induced super resolution (MSR).
Low temperature luminescence studies of Ca1−xErxF2+x thin films epitaxially grown on silicon substrates
Authors: Barrière A. S. , Césaire T. , Hirsch L. , Raoux S. , Lambert B.
Published: July 2002

Room temperature photoluminescence studies of Ca1−xErxF2+x thin films epitaxially grown on silicon substrates exhibit strong light emissions in both the visible range and the infrared domain. With an Ar+-ion laser as an excitation source, the maximum of the 4I13/2→4I15/2 infrared (1530 nm) luminescence of Er3+ (4f11) ions was found for x=0.16. It is assumed that a particular Er3+ ion environment exists in the layers to explain why the quenching phenomena do not dominate at these very high erbium concentrations. To describe this environment, a photoluminescence study at low temperature (2 K) has been performed which shows that only one Er3+ ion site (having C4v symmetry) predominates for an erbium substitution rate x≤0.02. At higher Er3+ concentrations, however, a clustering process of erbium ions is observed. In thin films, however the clustering appears only at concentrations two orders of magnitude higher than in bulk single cystals.
Breakdown and defect generation in ultrathin gate oxide
Authors: Depas M. , Vermeire B. , Heyns M. M.
Published: July 2002

In this work the dielectric reliability of thermally grown ultrathin 3 nm SiO2 layers in poly-Si/SiO2/Si structures is examined. This is compared with a study of the defect generation in the 3 nm gate oxide during tunnel injection of electrons. In these ultrathin SiO2 layers, direct tunneling of electrons becomes very important. An increase of the direct tunnel and Fowler–Nordheim tunnel current during high-field stressing was observed and is explained by the creation of a positive charge in the oxide associated with slow interface traps. It is demonstrated that a higher current instability corresponds with a lower charge to breakdown value (QBD) of the oxide. From these results we conclude that the creation of slow interface traps is an important precursor effect for the 3 nm gate oxide breakdown.
Formation of extended defects in silicon by high energy implantation of B and P
Authors: Cheng J. Y. , Eaglesham D. J. , Jacobson D. C. , Stolk P. A. , Benton J. L. , Poate J. M.
Published: July 2002

The extended defects induced in silicon by high energy implantation (1.5 MeV B and 2.6 MeV P) have been investigated by plan-view and cross-sectional transmission electron microscopy studies and defect etching measurements. The threading dislocations were identified to be long dislocation dipoles generated in the region of the ion projected range which grew up to the surface. The formation of threading dislocations is shown to have a strong dependence on the implantation dose and O concentration. After 900 °C annealing, a high density of threading dislocations was formed for B and P implants in a dose range of 5×1013–2×1014 cm−2 and 5×1013–3×1014 cm−2, respectively. The threading dislocation density in B-implanted Czochralski Si substrates was found to be much higher than that in B-implanted epitaxial Si substrates. This difference is attributed to the strong pinning effect of oxygen immobilizing dislocations in Czochralski substrates. Because P impurities are also efficient at pinning dislocation motion in Si, a high density of threading dislocations was observed even in epitaxial Si substrates with P implantation. Two-step annealing with a first step at 700 °C (to precipitate oxygen) and a second step at 900 °C was found to be very effective at eliminating the formation of threading dislocations.
Giant magnetoresistance of perpendicular magnetic Co/Au multilayers
Authors: Honda S. , Fujimoto T. , Nawate M.
Published: July 2002

Co/Au multilayers have been prepared on glass substrates by electron-beam evaporation techniques. The perpendicular anisotropy is induced when the Co layer thickness is less than 12 Å and its origin is discussed phenomenologically. In the perpendicular magnetic multilayers, large giant magnetoresistance appears and it consists of hysteretic and nonhysteretic components. The occurrence mechanism of these components has been discussed and it is suggested that the former arises from antiparallel spin alignment between adjacent Co layers due to the random wall position layer by layer, and the later is related to the granular-type giant magnetoresistance.
Pumping-beam-induced photovoltaic effect on the photoreflectance of a δ-doped GaAs film
Authors: Wang D. P. , Chen C. C. , Shen T. L. , Hsu T. M. , Lee W. C.
Published: July 2002

The photoreflectance (PR) spectroscopy of a δ-doped GaAs film has been measured at 300 K. Results reveal many Franz–Keldysh oscillations (FKOs) above the band-gap energy, which will enable the electric-field strength to be determined from the periods of FKOs. Since the photovoltaic effect cannot be neglected in PR measurements when using light as both the pumping and probing beams, it is generally assumed that the modulation field δF is much smaller than the built-in field F so that the periods of the FKOs will not be affected by the pumping beam. However, the induced photovoltage can be over 2/3 of Fermi level at low temperatures and cannot be neglected even at room temperature. Hence, the finite value of δF needs to be taken into consideration. The effect of δF on the shapes of PR is discussed, and it is shown that the FKOs of PR oscillate at a frequency corresponding to F−δF/2.
Enhancement of conduction-band effective mass in III–V semiconductor alloys induced by chemical disorder
Authors: Fan J. C. , Chen Y. F.
Published: July 2002

The conduction-band effective masses in InxGa1−xAs with a complete range of composition, and InAlGaAs and InGaAsP alloys covering the complete range of lattice matched to InP have been determined by far-infrared optically detected cyclotron resonance and magnetophotoconductivity measurements. It is found that the measured effective masses as a function of alloy composition are heavier than the values predicted from the five-band k⋅p theory. We show that this discrepancy can be resolved by including the effect of disorder-induced potential fluctuations that causes the wave function mixing between conduction and valence bands. We find that the strength of the potential fluctuations can be well described in terms of the Phillips electronegativity difference related to chemical disorder.
Physical basis and limitation of universal mobility behavior in fully depleted silicon-on-insulator Si inversion layers
Authors: Shoji Masanari , Omura Yasuhisa , Tomizawa Masaaki
Published: July 2002

The physical basis and the limitation for the universal mobility behavior of fully depleted silicon-on-insulator (SOI) metal–oxide–semiconductor Si inversion layers are shown by means of an analysis of the electronic states (potential profile, subband structure, and electron density distribution). As long as the top Si layer thickness is larger than the inversion layer thickness and the electron density is much higher than the impurity concentration in the inversion region, it is proved that the electronic states of an SOI Si inversion region are equivalent to those of a certain bulk Si inversion region. In this context, the definition of the effective vertical electric field Eeff for SOI inversion layers is derived and it ensures the identical mobility dependence on Eeff for SOI and bulk Si inversion layers. The effective carrier mobility μeff behavior in SOI Si inversion layers is universal, irrespective of structural parameters or back gate voltages, over the Eeff range where the mobility is essentially limited by phonon scattering and/or surface roughness scattering at the upper interface. On the other hand, when the electron density distribution of the inversion region reaches the lower surface of the top Si layer sufficiently, it is predicted that the universal mobility behavior is not maintained, but there exists another kind of mobility behavior which is dependent on the top Si layer thickness. Moreover, self-consistent calculations for the electronic states clarify the range where the equivalence of the electronic states for SOI and bulk Si inversion regions holds as function of the effective field Eeff, the top Si layer thickness, and the top Si layer impurity concentration. The phonon-limited mobility is also evaluated to confirm the equality of the mobility for SOI and bulk Si inversion regions.
Submicron spin valve magnetoresistive random access memory cell
Authors: Chen E. Y. , Tehrani S. , Zhu T. , Durlam M. , Goronkin H.
Published: July 2002

Spin valve magnetoresistive random access memory cells with widths varying from 1.5 to 0.25 μm and an aspect ratio of length/width more than 10 were fabricated and tested. In general, the switching field of the free magnetic layer was found to be inversely proportional to the width of the cell. Adequate pinning was shown for cell width down to 0.75 μm. For 0.5 and 0.25 μm wide cells, the switching field of the free magnetic layer is comparable to the pinning field of the other magnetic layer. So the pinned magnetic layer rotates with the free magnetic layer. The giant magnetoresistive ratio of the cell drops dramatically. Potentially, this may be a fundamental problem for this memory mode. Solutions are proposed.
Auger carrier relaxation in self-assembled quantum dots by collisions with two-dimensional carriers
Authors: Uskov A. V. , Adler F. , Schweizer H. , Pilkuhn M. H.
Published: July 2002

Carrier relaxation in self-assembled quantum dots due to Coulomb interaction with two dimensional (2D) carriers is studied theoretically. Auger coefficients for carrier relaxation rates are calculated in the dipole approximation for Coulomb interaction. The dipole approximation allows one to derive selection rules for Auger relaxation in a cylindrical quantum dot, and to describe a general picture of Auger relaxation via energy levels in self-assembled quantum dots. A numerical example for InAs/GaAs self-assembled quantum dots demonstrates that the Auger effect may lead to relaxation times in the order of 1–10 ps at 2D carrier densities of 1011–1012 cm−2. This result demonstrates the possibility of fast carrier relaxation in quantum dots if the carrier density in the surrounding barrier is sufficiently high. Analytical formulas for Auger coefficients are derived for moderate temperatures of the 2D carriers.
Electron-trapping-triggered anneal of defect states in silicon-rich hydrogenated amorphous silicon nitride
Authors: Oversluizen G. , Lodders W. H. M. , Johnson M. T. , van der Put A. A.
Published: July 2002

The dc-current stress behavior of Mo/a-SiNxHy/Mo thin-film diodes is discussed for several a-SiNxHy-plasma-deposition conditions. Current transport is governed by thermionic field emission of electrons over a reverse biased Schottky barrier. The barrier height is determined by the a-SiNxHy-plasma-deposition conditions. Therefore these back-to-back Schottky devices provide an elegant way to perform dc-current stressing at several well defined carrier densities for similar stress fields. It is shown that such experiments allow assessment of defect-state creation/anneal mechanisms in a-SiNxHy. An electron-trapping-triggered anneal mechanism accounts for the observed dependence of the defect density at the electrode injecting contact (cathode) on the hole-barrier height at the anode. Also a new microscopically detailed anneal reaction scheme is proposed. The defect-state creation/anneal mechanism is expected to be generally applicable for all silicon-rich hydrogenated amorphous silicon alloys.
Elastic scattering cross sections for the p+He system in the energy region of 1.4–24 MeV
Authors: Nurmela A. , Rauhala E. , Räisänen J.
Published: July 2002

The elastic scattering cross sections for proton scattering from He4 were determined in the proton energy region of 1.4–6.0 MeV. The measurements were performed at laboratory angles of 110°–170° for proton energies of 1.4–2.7 MeV and at angles of 140° and 170° for proton energies of 2.7–6.0 MeV. The scattering cross sections for H1 recoils by He4 ion bombardment for helium energies of 5.6–24 MeV at recoil angles of 4°–28° were calculated by kinematically reversing the reaction. The helium targets were prepared by implanting 60 keV He4 ions into thin tantalum foils. The helium concentration was determined by transmission elastic recoil detection analysis employing 10 MeV Si28 ions. The obtained cross section data are compared with the available literature values. Differences up to 10% are found in the values at the cross section curve maximum in comparison to earlier data.
Tip artifacts in atomic force microscope imaging of ion bombarded nanostructures on germanium surfaces
Authors: Chen Y. J. , Wilson I. H. , Lee C. S. , Xu J. B. , Yu M. L.
Published: July 2002

In this communication, we present a study of tip artifacts in atomic force microscope images of nanometer-scale cellular structures created on germanium surfaces by ion bombardment. It is demonstrated that the appearance of a columnar/granular morphology is due to severe image distortion when the tip size is comparable with the mean cell/hole diameter. These tip artifacts can often be deconvoluted by inverting the image and the lateral extension of the cell/hole can be reproduced with reasonable accuracy.
Effects of H coverage on Ge segregation during Si1−xGex gas-source molecular beam epitaxy
Authors: Kim H. , Taylor N. , Abelson J. R. , Greene J. E.
Published: July 2002

The effects of H coverage θH on Ge segregation during Si1−xGex gas-source molecular beam epitaxy (GS-MBE) were investigated using D2 temperature programmed desorption (TPD). Si1−xGex films with x=0.01–0.30 were grown from Si2H6/Ge2H6 mixtures at Ts=450–800 °C, held at the growth temperature for 30 s, cooled to <200 °C, and then exposed to atomic deuterium until saturation coverage. D2 TPD spectra were fit using four peaks corresponding, in order of decreasing activation energy, to desorption from Si monodeuteride, Ge–Si mixed-dimer monodeuterides, Si dideuteride, and Ge monodeuteride. Steady-state Ge surface coverages were determined from the TPD data as a function of Ts and x. In contrast to solid-source MBE films grown in this temperature regime, Ge segregation during GS-MBE decreases with decreasing Ts due to the increasing H coverage. The results were well described by a model accounting for the Si/Ge site exchange and θH. The Ge segregation enthalpy varies from −0.28 eV at Ts⩾800 °C, where the steady-state hydrogen coverage θH approaches zero, to −0.10 eV at Ts⩽450 °C, where θH is nearly saturated.
Photoluminescence study of defects in Si+ ion implanted thermal SiO2 films
Authors: Zhang Jia-Yu , Bao Xi-Mao , Li Neng-Sheng , Song Hai-Zhi
Published: July 2002

Point defects and structure damages in Si-implanted thermal SiO2 films were examined by photoluminescence (PL) spectra, electron spin resonance spectra, and infrared absorption spectra. Under ∼5 eV excitation, the as-implanted film had two PL bands peaked at 4.3 and 2.4 eV, respectively. After thermal annealing, the peak energy of the low-energy band shifted from 2.4 to 2.7 eV with the increase of the annealing temperature to 1100 °C, and its intensity and width, and the relative ratio between the intensities of the two PL bands changed also. The change of the ratio, and the width and peak position of the low-energy band via annealing temperature was consistent with the recovery of the implantation-induced structure damage such as densification and distortion of silicon tetrahedra. We propose that the two PL bands are due to neutral oxygen vacancies (NOVs), and the PL characteristics of the NOV defects are related to the structure damage of the SiO2 network.
Diffusional creep as a stress relaxation mechanism in electromigration
Authors: Glickman E. , Osipov N. , Ivanov A. , Nathan M.
Published: July 2002

The classical Blech description of the electromigration—stress interplay in interconnects treats the maximum electromigration compressive stress as a material constant (the yield stress). Systematic drift velocity and hillock topography observations in bare Al, anodized Al, and Cu conductors show this description to be valid only for relatively low current densities j. With increasing j, the actual stress surpasses this threshold stress and increases progressively, i.e., the stress is shown to adjust to j. The explanation of this adjustment evolves naturally from the attribution of the stress relief mechanism to creep (time-dependent plastic flow). A diffusional creep mode is the one most likely to explain the data. Coble creep is ruled out as the diffusional creep mechanism, while Nabarro-Herring creep may be a good candidate. The thresholds for electromigration and for the egress of excess atoms diffusing to the hillock surface are addressed in terms of linear tensions of dislocations and surface ledges.
Comment on “A model of hole trapping in SiO2 films on silicon” [J. Appl. Phys. 81, 6822 (1997)]
Authors: Devine R. A. B. , Warren W. L. , Karna S.
Published: July 2002

Recent measurements of oxygen-vacancy creation in Si/SiO2/Si structures during high temperature annealing which suggest an activation energy of 1.5 eV for the process have been interpreted in terms of a simple thermodynamic model. We demonstrate that this model is inconsistent with thermochemical calculations which indicate that the energy for this process is 4.5 eV [K. P. Huber and G. Hertz, Molecular Structure and Molecular Structure IV, Constants of Diatomic Molecules (Van Nostrand Reinhold, New York, 1979), p. 490]. Another process involving thermally induced oxygen out-diffusion at the SiO2/Si interface has an effective activation energy for oxygen-vacancy creation ∼2.0 eV, this is more consistent with the experimental data.
Magneto-chromatic effects of tunable magnetic fluid grating
Authors: Hong Chin-Yih , Horng H. E. , Jang I. J. , Wu J. M. , Lee S. L. , Yeung Wai Bong , Yang H. C.
Published: July 2002

The ordered structures in Fe3O4 kerosene-based magnetic fluid films were discovered and the magneto-chromatic effects were also observed under various magnetic fields. In this report, we studied the relationship between the ordered structures and the magneto-chromatic effects theoretically and experimentally. The nearly perfect hexagonal structures with the distance between two columns d in μm range for our magnetic fluid thin films offer a two-dimensional tunable magnetic fluid grating in the visible light region. By using a grating model, the diffraction patterns for visible lights at certain incident angle θ, wavelength λ, and column distance d, were calculated. Experimentally, it was found that the conditions of the observed light around the direction perpendicular to the plane of film coincide with the calculated results. Therefore, the magneto-chromatic effects resulting from the ordered structures of the tunable magnetic fluid grating were confined.
First-principles exchange interactions between ferromagnetic and antiferromagnetic films: Co on NiMn, a case study
Authors: Schulthess T. C. , Butler W. H.
Published: July 2002

Heisenberg exchange parameters at the interface of antiferromagnetic NiMn with ferromagnetic Co are calculated from first principles. We use a layer version of the Korringa–Kohn–Rostocker multiple-scattering approach and an expression, which is based on the expansion of the band energy, to calculate the exchange parameters from the underlying electronic structure. For bulk systems, the parameter sets yield Curie temperatures that are in good agreement with experimental values. In the interface region, the interlayer interactions in NiMn change significantly compared to the bulk while the intralayer interactions are almost unchanged.
An effect of nitrogen on magnetic properties and microstructure of Fe–Nb–B–N nanocrystalline thin films
Authors: Park J. Y. , Suh S. J. , Noh T. H. , Kim K. Y. , Kim H. J.
Published: July 2002

Fe–Nb–B–N films with good soft magnetic properties were fabricated by Ar+N2 reactive sputtering. The quaternary films have better soft magnetic properties than that of Fe–Nb–B films. The best magnetic properties are saturation magnetization of 16.5 kG, coercivity of 0.13 Oe and effective permeability of about 5000 up to 10 MHz. It was observed by transmission electron microscopy that the Fe–Nb–B–N thin film annealed at 590 °C consisted of three phases: a fine α-Fe phase whose grain size is around 7 nm, a Nb–B rich amorphous phase and NbN precipitates with the size of less than 3 nm. The fine grained α-Fe structure, together with finely dispersed NbN precipitates and the amorphous boundary phase are considered to be a main factor for the good magnetic properties.
Semi-insulating GaAs as a relaxation semiconductor
Authors: Santana J. , Jones B. K.
Published: July 2002

It is shown that semi-insulating GaAs diodes exhibit all the qualitative electrical properties expected from a relaxation semiconductor. The degree of ideality increases after irradiation by neutrons for liquid encapsulated Czochralski and liquid phase epitaxy (LPE) material although LPE material is almost lifetimelike directly from manufacture. Experimental results are shown for current–voltage and capacitance–voltage frequency over a range of temperatures for samples in the low- and high-space charge limit conditions. The implications for commercial GaAs and other compound semiconductor devices are discussed.
Geometrical field effects in voltage pulse fabrication of nanostructures using scanning tunneling microscopy
Authors: Campbell P. A. , Farnan G. A. , Walmsley D. G.
Published: July 2002

Voltage pulsed modification of surfaces in air with a scanning tunneling microscope has been studied with a view to understanding the physical processes involved. Incremented negative pulses have been applied to a tungsten tip to determine the threshold for feature writing on gold. The primary event observed with virgin tips is pit formation, which is interpreted as due to the transfer of gold cations from sample to tip. Subsequent pulsing establishes a threshold for a secondary process in which hillocks form on the gold surface and which are thought to be the result of gold anion retransfer from tip to sample. The thresholds are 4.16 and 3.92 V, respectively, for the two processes. For one particular tip, which gave rise to a Y-shaped pit, a three-dimensional profile was subsequently obtained by crashing it at a remote site on the surface and imaging the crater formed. The geometrical parameters of the tip, so elaborated, allowed a model of the electrostatic potential between tip and sample during pulsing to be numerically evaluated by solution of Laplace’s equation and the field pattern over the surface to be determined. For the blunt pyramid involved, there is substantial anisotropy though modest field reduction at positions some nm from the projection of the tip on the surface. It is then a straightforward matter to understand the Y shape of the pit formed on the surface by the initial pulse. Field evaporation is thereby confirmed as the operative process. Reference experiments using gold tips showed no threshold difference between primary and secondary modification, a result consistent with the field evaporation mechanism.
Hydrogenation and annealing effects in p-type ZnSe thin films grown on GaAs (100) substrates
Authors: Kim M. D. , Park H. S. , Kim T. W.
Published: July 2002

Photoluminescence (PL) and Raman scattering measurements have been carried out to investigate the hydrogenation and annealing effects in p-type ZnSe epilayers grown on n-type GaAs (100) substrates by molecular beam epitaxy. After hydrogenation, the PL spectra showed that the deep acceptor-bound exciton peak disappeared and that the peak position of the donor–acceptor pair peak shifted to a higher energy. When the hydrogenated ZnSe/GaAs heterostructure was annealed at 300 °, a bound exciton due to neutral acceptors appeared. The Raman intensity of the plasma longitudinal optical-phonon-coupling mode increased after hydrogenation. These results indicate that the crystallinity of the p-type ZnSe epilayers grown on n-type GaAs substrates is improved by hydrogenation and that hydrogenated and annealed ZnSe films grown on GaAs substrates hold promise for potential application as buffer layers for the growth of Zn1−xMgxSySe1−y active layers.
Diffusion lengths of carriers in n- and p-type ZnMgSSe cladding layers of green laser diodes
Authors: Snoeks E. , Marshall T. , Petruzzello J. , Pashley M. D. , Chao L.-L. , Cargill G. S.
Published: July 2002

We have used cross sectional cathodoluminescence microscopy as a fast and nondestructive tool to characterize II–VI based green laser diodes. We find evidence for carrier mediated excitation of semiconductor layers that are not directly irradiated by the focused electron beam, from which diffusion lengths of lower mobility carriers (presumably holes) can be estimated. We find that N-doped (p-type) ZnMgSSe exhibits a very low (near) band edge luminescence efficiency. The diffusion length of minority carriers in p-type ZnMgSSe:N [(1–2)×1017 cm−3 net acceptor concentration] was found to be lower than for n-type ZnMgSSe:Cl with roughly equal dopant concentration. The diffusion length of minority carriers in n-type ZnMgSSe:Cl decreases from 0.21 μm for a doping level of (1–2)×1017 cm−3 to <0.05 μm when the n-type doping is increased to (2–4)×1018 cm−3. This decrease in diffusion length is accompanied by an increase of a broad luminescence band around 550 nm, which is attributed to Cl-related defects in the gap. The effective probe size in our cross sectional CL is close to the waist diameter of the focused electron beam. This phenomenon is discussed with regard to the sample geometry and its implication for the determination of carrier diffusion lengths.
Limits on quality factors of localized defect modes in photonic crystals due to dielectric loss
Authors: Ueta Tsuyoshi , Ohtaka Kazuo , Kawai Noriko , Sakoda Kazuaki
Published: July 2002

The spectral widths of defect modes localized at line defects formed in a two-dimensional photonic crystal composed of a square lattice of dielectric cylinders were analyzed theoretically. The transmission spectra calculated by the layer-doubling method based on the vector–cylindrical–wave expansion of the internal field showed a rapid decrease of the spectral width with increasing number of the lattice layers when the dielectric loss is absent. Quality factors larger than 107 were predicted for the total lattice layers of 18. However, the numerical evaluation of the decay constant of the defect modes due to the imaginary part of the dielectric constant showed that the actual quality factor is limited by the dielectric loss. The calculated widths agreed qualitatively with the experimental observations by Lin et al. [Appl. Phys. Lett. 68, 3233 (1996)].
Optical properties of poly(disilanyleneoligothienylene)s and their doping characteristics
Authors: Yoshino K. , Fujii A. , Nakayama H. , Lee S. , Naka A. , Ishikawa M.
Published: July 2002

Optical absorption spectra, photoluminescence (PL), Stokes shift, and electroluminescence (EL) in poly(disilanyleneoligothienylene)s have been found to be dependent on the length of oligothienylene units. The color of EL changes from green to red with increasing length of oligothienylene from three to seven thiophene rings. Their stability is much higher than polysilanylene and increases with increasing length of oligothienylene and by C60 doping. Photoconductivity is strongly enhanced and PL is remarkably quenched upon C60 doping, which were discussed by the photo-induced electron transfer between aromatic units in these polymers and C60.
Oscillation period of the interlayer coupling for epitaxial Fe/Cr1−xVx(100) and (211) superlattices
Authors: You Chun-Yeol , Sowers C. H. , Inomata A. , Jiang J. S. , Bader S. D. , Koelling D. D.
Published: July 2002

The microscopic origin of the 18 Å period in the oscillatory interlayer exchange coupling of Fe/Cr(100) and (211) superlattices is investigated by alloying the Cr spacer with V to alter its Fermi surface. The addition of V increases or decreases in size the various Fermi surface calipers that are candidates for governing the oscillation period, such as those that span the ellipse, lens, octahedron, and nested sheets. Epitaxial sputtered superlattices of (100) and (211) orientation were grown and characterized via magnetoresistance measurements as a function of spacer layer thickness for different V-doping levels. A small decrease of the oscillation period is found experimentally which strongly implicates the N-centered ellipse as the origin of the 18 Å period in Fe/Cr superlattices.
Structural modifications in ion-implanted silicate glasses
Authors: Battaglin G. , Arnold G. W. , Mattei G. , Mazzoldi P. , Dran J.-C.
Published: July 2002

The structural modifications induced in fused silica and soda-lime glasses by implantation (argon, nitrogen) have been studied using step-height profilometry, Rutherford backscattering spectrometry, transmission electron microscopy, and scanning electron microscopy. The step-height measurements indicated a transformation in structure (−ΔL to +ΔL) at energy depositions on the order of 1023 keV/cm3 for both fused silica and soda-lime glasses. This change modifies the three-membered ring structure in fused silica initiated by the lower deposition energy of 1–2×1020 keV/cm3. The Rutherford backscattering spectrometry measurements show the initiation of the new structure by changes in the argon peak and a spreading of the argon to greater depths. The scanning and transmission electron microscopy measurements are complementary to these changes. The data presented can be understood in terms of ion-implantation induced stress.
Optical properties of GaN layers grown on C-, A-, R-, and M-plane sapphire substrates by gas source molecular beam epitaxy
Authors: Tripathy S. , Soni R. K. , Asahi H. , Iwata K. , Kuroiwa R. , Asami K. , Gonda S.
Published: July 2002

GaN layers were grown on C-, A-, R-, and M-plane sapphire substrates by the electron cyclotron resonance–molecular beam epitaxy technique. We addressed a combined utilization of Raman spectroscopy, photoluminescence (PL) and reflectance measurements to investigate the optical properties of these high-quality GaN layers. First order optical phonons of A1, E1, and E2 symmetries were observed in the Raman spectra and the peaks are indicative of the wurtzite crystal structure. All three intrinsic exciton transitions arising from A, B, and C interband transitions were observed in reflectance measurements. The PL spectra were dominated by A and B free exciton transitions and the recombination of an exciton bound to a neutral donor. The experimental data clearly revealed a thickness-dependent change of the biaxial strain in the GaN layers grown on (0001) C-plane sapphire. The residual strain induced in these layers was found to have a strong influence in determining the energies of the excitonic transitions. Resonant Raman scattering measurements were performed by temperature tuning of fundamental gap in 1.0 μm GaN on C-plane sapphire. The influence of epitaxial strain in free exciton properties of GaN layers grown on various orientations of sapphire has been discussed based on the PL and reflectance results. The exciton binding energies were estimated in the GaN layers grown on C-, A-, and M-plane sapphire substrates. Polarized Raman measurements were performed on GaN layers grown on various orientations of sapphire and we observed quasipolar modes of both E1 and A1 symmetries. An additional broad photoluminescence band centered around 2.74 eV was observed in the GaN layers grown on R- and M-plane sapphire substrates. The defect induced Raman scattering in resonance with this band shows strong Raman scattering peaks resulting from the transition between energy levels of donor species or defect states.
Compensation defects in annealed undoped liquid encapsulated Czochralski InP
Authors: Fung S. , Zhao Y. W. , Xu X. L. , Chen X. D. , Sun N. F. , Sun T. N. , Zhang R. G. , Liu S. L. , Yang G. Y. , Guo X. B. , Sun Y. Z. , Yan R. Y. , Hua Q. H.
Published: July 2002

As-grown undoped n-type semiconducting and annealed undoped semi-insulating (SI) liquid encapsulated Czochralski (LEC) InP has been studied by temperature dependent Hall measurement, photoluminescence spectroscopy, infrared absorption, and photocurrent spectroscopy. P-type conduction SI InP can frequently be obtained by annealing undoped LEC InP. This is caused by a high concentration of thermally induced native acceptor defects. In some cases, it can be shown that the thermally induced n-type SI property of undoped LEC InP is caused by a midgap donor compensating for the net shallow acceptors. The midgap donor is proposed to be a phosphorus antisite related defect. Traps in annealed SI InP have been detected by photocurrent spectroscopy and have been compared with reported results. The mechanisms of defect formation are discussed.