bluuebunny/crossref_metadata_2025 huggingface dataset:
A multicomponent, multitemperature model for high density plasma processing reactors
Authors: Meyyappan M. , Govindan T. R.
Published: July 2002

We present a coupled model for neutral transport and charged species dynamics in high density plasma processing reactors. The model consists of conservation equations for mass, momentum, and energy within a multicomponent, multitemperature framework. The radially averaged one-dimensional model is applied to an electron cyclotron resonance CF4 discharge and results are presented for various pressures and flow rates. The pressure drop in the reactor is found to be significant compared to the pressure itself in high density, low pressure reactors which affects the plasma, and flow characteristics significantly. The nature of the viscous pressure drop in the reactor is also confirmed by two-dimensional fluid dynamics simulations of only the gas flow.
Photothermal characterization of vertical and slanted thermal barriers: A quantitative comparison of mirage, thermoreflectance, and infrared radiometry
Authors: Ocariz A. , Sanchez-Lavega A. , Salazar A. , Fournier D. , Boccara A. C.
Published: July 2002

We present a quantitative and comparative study of three different photothermal techniques based on the signal produced on vertical/slanted thermal barriers under a variety of barrier/sample conditions. Models based on integral methods are developed to calculate the amplitude and phase of the sample surface temperature and mirage deflection in surrounding air. The geometries studied include: vertical, tilted, buried, and finite size barriers separating identical or different media. The models incorporate the probe and pump beam sizes, the thermal resistance of the barrier and the optothermal characteristics of the sample. Experimental measurements are performed on a variety of fabricated barriers with three modulated photothermal techniques: the thermoreflectance, infrared radiometry, and mirage detection. We discuss in a comparative way the limits, drawbacks and the applicability of each technique. Model fits to the experimental results allow characterization of the thermal barrier (spatial localization, geometry, orientation, and size) and provide an accurate determination of its thermal resistance.
Terahertz ballistic current oscillations for carriers with negative effective mass
Authors: Gribnikov Z. S. , Korshak A. N. , Vagidov N. Z.
Published: July 2002

It is shown that the stationary distribution of ballistic current carriers moving across a thin doped base is unstable if there exists a negative effective mass (NEM) part in the carrier dispersion law. Under such a condition, a regime with a quasistationary current oscillations is established for a wide range of voltages across ballistic diode. The oscillation frequency and amplitude depend on the base length, doping concentration, and applied voltage. The current oscillations take place in a short-circuit regime (in absence of an external resonator). We consider asymmetric double quantum wells and/or composite ΓX quantum wells as possible structures allowing for the required dispersion relation with NEM part. Carrier dynamics in these structures are described quasiclassically and the validity of such a treatment is discussed.
Optical and structural properties of ZnCdSe/ZnSSe/ZnMgSSe separate confinement heterostructures
Authors: Oh Eunsoon , Lee S. D. , Jung H. D. , Kim J. R. , Kim M. D. , Kim B. J. , Ji J. K. , Park H. S. , Kim T. I. , Ivanov S. V. , Toropov A. A. , Shubina T. V.
Published: July 2002

We have grown ZnCdSe/ZnSSe/ZnMgSSe separate confinement heterostructures by molecular-beam epitaxy. Strain on the ZnSSe layer is calculated from x-ray and photoluminescence data. The temperature dependence of band-gap energy and the photoluminescence intensity in the Cl-doped ZnCdSe active layers is compared with that of undoped ones.
Ultrahigh time-resolution vibrational spectroscopy of shocked molecular solids
Authors: Hambir Selezion A. , Franken Jens , Hare David E. , Chronister Eric L. , Baer Bruce J. , Dlott Dana D.
Published: July 2002

A method is described for obtaining ultrahigh time-resolution vibrational spectra of shocked polycrystalline materials. A microfabricated shock target array assembly is used, consisting of a polymer shock generation layer, a polymer buffer layer, and a thin sample layer. A near-IR pump pulse launches the shock. A pair of delayed visible probe pulses generate a coherent anti-Stokes Raman (CARS) spectrum of the sample. High-resolution Raman spectra of shocked crystalline anthracene are obtained. From the Raman shock shift, the shock pressure is determined to be 2.6 GPa. The rise time of shock loading is 400 ps. This rise time is limited by hydrodynamics of the shock generation layer. The shock velocity in the buffer layer is found to be 3.7 (±0.5) km/s, consistent with the observed shock pressure. As the shock propagates through a few μm of buffer material, the rise time and pressure can be monitored. The rise time decreases from ∼800 to ∼400 ps over the first 6 μm of travel, and the pressure begins to decline after about 12 μm of travel. The high-resolution CARS method permits detailed analysis of the vibrational line shape. Simulations of the CARS spectra show that when the shock front is in the crystal layer the spectral linewidths are inhomogeneously broadened by the distribution of pressures in the layers. When the crystal layer is behind the front, the spectral linewidth can be used to estimate the temperature. The increase of the spectral width from the ambient 4 to ∼6.5 cm−1 is consistent with the expected temperature increase of ∼200°.
Structural properties of ZnSe layers grown on (001) GaAs substrates tilted toward [110] and [010]
Authors: Kim Jin-Sang , Suh Sang-Hee , Kim Chang-Hoon , Chung Su-Jin
Published: July 2002

We have investigated the structural properties of ZnSe epilayers that were molecular beam epitaxially grown on (001) GaAs substrates with different tilt angles and tilt directions. We measured the properties of the epilayers by x-ray diffraction, transmission electron microscopy, and etch pit density analysis. Tilting the (001) GaAs substrate toward [010] was very effective in reducing the surface defect density of the ZnSe layers, while tilting toward the [110] direction was of no use. We could observe the increasingly two-dimensional nature of the initial growth mode in the (001) GaAs substrate tilted toward [010]. Growth of a 1.8-μm-thick ZnSe layer on (001) GaAs tilted 4° toward [010] resulted in a very low surface defect density of 1×104 cm−2. Such a low defect density has seldom been obtained in ZnSe, without growing a GaAs buffer layer below the ZnSe layer.
The reorientation transition in Co/Au(111)
Authors: Oepen H. P. , Millev Y. T. , Kirschner J.
Published: July 2002

The spin reorientation transition in as-grown wedge-shaped Co/Au(111) films has been analyzed. Two critical thicknesses have been detected just like in the annealed case. Here, these are shifted to smaller values. The behavior of the system can be explained on the basis of the thickness-driven trajectory in the anisotropy space of the system. Both the first and second anisotropy constants have been determined: K1s=0.66 mJ/m2, K2s=−0.12 mJ/m2. They are both smaller by modulus than their counterparts from the annealed case. The results provide quantitative evidence for the increase of surface anisotropy after annealing.
Effect of corrosion on magnetic properties for FeMn and NiO spin valves
Authors: Burkett S. L. , Kora S. , Bresowar J. L. , Lusth J. C. , Pirkle B. H. , Parker M. R.
Published: July 2002

Spin-valve multilayer structures are promising candidates for next generation read heads in high-density magnetic recording applications. Two commonly used antiferromagnetic layers that exhibit effective pinning for spin valves are FeMn and NiO. Previously, the only corrosion studied of the two materials with respect to magnetic recording are concerned with immersing thin films into acidic and basic solutions. In a realistic corrosion study of spin valves constructed with these pinning materials, we find a high humidity environment is catastrophic to the FeMn spin valves, even with protective Ta capping layers. Scanning electron microscopy along with magnetic measurements on edge protected samples gives convincing evidence that edge effects seem to dominate. Protection of the edges with an epoxy film merely slows down the degradation. In contrast, NiO spin valves show remarkable resistance to corrosion. While magnetoresistance ratio decreases for FeMn spin valves with increased corrosion, coercivity remains relatively constant and pinning field actually increases for both material systems.
Determination of exchange anisotropy by means of ac susceptometry in Co/CoO bilayers
Authors: Ström Valter , Jönsson B. J. , Rao K. V. , Dahlberg Dan
Published: July 2002

The strength, or stiffness Kud, of the magnetic unidirectional anisotropy in Co (90–300 Å)/CoO bilayers has been studied with ac susceptometry. We develop a model to describe the ac susceptibility which indicates that the stiffness Kud decreases linearly with temperature as (1−T/Tcrit). As the temperature increases and Kud decreases, a rotation of the magnetization to a uniaxial easy direction is observed. The values of Kud determined by this small amplitude field oscillation technique are found to be larger than the values obtained when evaluated by the usual hysteresis loop technique. We observe that the exchange field, Hex, could be greatly enhanced and its deterioration after repeated magnetization reversals significantly reduced by partially capping the Co surface prior to oxygen exposure.
Magnetic coupling between grains in CoCrPt/Cr thin film improved by decrease of the deposition temperature and post-annealing
Authors: Mukai R. , Yamanaka K. , Oshiki M.
Published: July 2002

A technology for decreasing the magnetic coupling between grains in CoCrPt/Cr thin-film system has been investigated, whereby a formation technology for a magnetic thin film is developed for high-performance longitudinal recording media. An increase of coercivity and the decrease of magnetic coupling between grains can be achieved. Since the decrease of magnetic coupling between grains results in an increase of coercivity and a decrease of media noise, the value of Hc/Hkgrain must increase to the maximum value of 0.5 in the case of media produced on a nontextured disk. The increase of Hc/Hkgrain can be realized by segregating nonmagnetic elements at the grain boundaries of a Co-based alloy. The effect of post-annealing on the segregation has been investigated. In the Co-based alloy/Cr structure case, Cr as nonmagnetic element is diffused from the Cr underlayer into the Co-based alloy magnetic layer during this post-annealing, resulting in segregation at the grain boundaries. It has been found that the remarkable increase of the maximum value of coercivity and the decrease of the annealing temperature at which the maximum value is obtained is created by the decrease of deposition temperature. In the case of 20-nm-thick CoCrPt/50-nm-thick Cr system deposited at room temperature, a maximum value of coercivity of 4571 Oe was obtained after post-annealing at 460 °C. This annealing was realized by rapid thermal annealing at 1.5 kW for 20 s. A maximum value of Hc/Hkgrain of 0.46 was indicated in this case.
Effect of near-interfacial nitrogen on the oxidation behavior of ultrathin silicon oxynitrides
Authors: Lu H. C. , Gusev E. P. , Gustafsson T. , Garfunkel E.
Published: July 2002

Medium energy ion scattering has been used to study the role of nitrogen in the thermal oxidation kinetics of ultrathin silicon oxynitrides. Oxynitride films with different amounts of nitrogen near the SiOxNy/Si interface and pure (control) SiO2/Si films were reoxidized in dry O218 under equivalent conditions. The spatial distribution of O18 incorporated into the films was analyzed by high-resolution depth profiling methods. Analogous to the pure SiO2 case, we observed two distinct regions where oxygen incorporation into the oxynitride films occurs: at/near the interface and near the outer oxide surface. The (near) interface oxide growth reaction is found to be significantly retarded by the presence of near-interfacial nitrogen (with a higher degree of the retardation for higher concentrations of nitrogen). The presence of nitrogen near the interface does not affect the surface exchange reaction.
Temperature dependence of the fundamental absorption edge in CuInTe2
Authors: Marı́n G. , Rincón C. , Wasim S. M. , Power Ch. , Sánchez Pérez G.
Published: July 2002

The temperature dependence of the energy gap EG and the binding energy Rx of free excitons in single crystals of CuInTe2 have been calculated using Elliot’s model. The samples were prepared by the method of tellurization of stoichiometric Cu and In in liquid phase and the vertical Bridgman technique. The value of Rx around 4 meV agrees quite well with that deduced from the effective mass approximation. The variation of EG with temperature is compared with the empirical model proposed by A. Mannogian and J. C. Woolley [Can. J. Phys. 62, 285 (1984)]. The estimated value of the Debye temperature is in agreement with ΘD=191.4 K reported from specific heat measurements.
Population inversion in optically pumped asymmetric quantum well terahertz lasers
Authors: Harrison P. , Kelsall R. W.
Published: July 2002

Intersubband carrier lifetimes and population ratios are calculated for three- and four-level optically pumped terahertz laser structures. Laser operation is based on intersubband transitions between the conduction band states of asymmetric GaAs-Ga1−xAlxAs quantum wells. It is shown that the carrier lifetimes in three-level systems fulfill the necessary conditions for stimulated emission only at temperatures below 200 K. The addition of a fourth level, however, enables fast depopulation of the lower laser level by resonant longitudinal optical phonon emission and thus offers potential for room temperature laser operation.
Dynamic relaxation of the elastic properties of hard carbon films
Authors: Hirvonen J.-P. , Koskinen J. , Kaukonen M. , Nieminen R. , Scheibe H.-J.
Published: July 2002

The effect of enhanced atomic mobility on the growth of hard carbon films was examined. Tetrahedrally bonded amorphous carbon films were deposited by condensing energetic carbon ions using an arc-discharge deposition method. The deposition temperature varied between 50 and 400 °C. The dependence of elastic properties on deposition temperature was examined by determining the frequency-dependent propagation velocity of ultrasonic surface acoustic waves induced by a laser. A remarkable decrease in elastic coefficient was revealed above the deposition temperature of 300 °C and complete relaxation was obtained at 400 °C. This observation was analyzed by using a simple model which was in turn supported by molecular dynamics simulations. The relaxation turns out to be a thermally activated, dynamic process with an activation energy of 0.57 eV. Possible relaxation mechanisms associated with the migration of atoms or defects on a growing surface are discussed.
Diffusion of near surface defects during the thermal oxidation of silicon
Authors: Ganem J.-J. , Trimaille I. , André P. , Rigo S. , Stedile F. C. , Baumvol I. J. R.
Published: July 2002

The diffusion of defects during the thermal growth of SiO2 film on Si(100) in dry O2 was investigated using sequential treatments in natural oxygen (16O2) and in heavy oxygen (18O2) in a Joule effect furnace. The O18 depth profiles were measured with a depth resolution better than 1 nm, using the nuclear reaction narrow resonance O18(p,α)15N (ER=151 keV, ΓR=100 eV). From these profiles, we confirmed that just below the surface an exchange between the oxygen atoms from the gas phase and those from the silica occurs, even for silica films thicker than 20 nm. This fact is not predicted by the Deal and Grove model. A diffusion of oxygen related defects takes place in the near surface region, with an apparent diffusion coefficient D*=4.33×10−19 cm2/s for an oxidation temperature of T=930 °C and for an oxygen pressure of P=100 mbar.
Determination of the local microstructure of epitaxial AlN by x-ray absorption
Authors: Katsikini M. , Paloura E. C. , Cheng T. S. , Foxon C. T.
Published: July 2002

Hexagonal AlN, epitaxially grown on GaAs, is studied using x-ray absorption measurements at the N-, O-, and Al-K edges. The measured distances of the nitrogen nearest neighbors (nn) are found shorter than expected by 0.04–0.13 Å for the first to third nn shells, respectively. Nitrogen atoms are fourfold coordinated with Al as first nearest neighbors (nn), while Al atoms are fourfold coordinated with N and O atoms. The Al–N distance is 1.85 Å, i.e., it is smaller by 0.04 Å than expected. A reduction in the nn distances is also observed in the second and third nn shells where the N–N and the N–Al distances are found 0.07 and 0.13 Å shorter than expected, respectively. The reduction in the nn distances is attributed to the presence of oxygen contamination. The Al–O distance is only 0.18 Å smaller than the Al–N distance, i.e., O is a substitutional impurity in the N sublattice. The characteristic angular dependence of the N-K edge NEXAFS spectra verifies the hexagonal structure of the AlN film. Moreover, from the dependence of the areas under the NEXAFS resonances versus the angle of incidence ϑ, the directions of maximum electron charge densities are determined. Finally, the p-partial density of states in the conduction band is discussed.
Influence of complex phonon spectra on intersubband optical gain
Authors: Kisin Mikhail V. , Gorfinkel Vera B. , Stroscio Michael A. , Belenky Gregory , Luryi Serge
Published: July 2002

Electron-phonon scattering rates and intersubband optical gain spectra were calculated, including the optical phonon confinement effect in AlGaAs/GaAs/AlGaAs quantum well heterostructures. Comparison of the calculated gain spectra with those calculated using the bulk phonon approximation shows that details of the phonon spectrum have a strong influence on the intersubband optical gain.
Analysis of the thermally stimulated discharge current around glass-rubber transition temperature in polyethylene terephthalate
Authors: Neagu Eugen R. , Marat-Mendes Jose N. , Das-Gupta Dilip K. , Neagu Rodica M. , Igreja Rui
Published: July 2002

The nature of the thermally stimulated discharge current (TSDC) for polyethylene terephthalate samples in the temperature range from room temperature to above glass-rubber transition temperature of the amorphous phase is analyzed. The well conditioning of the sample is strictly necessary in order to have a good reproducibility and accuracy of results. A main peak was observed whose maximum temperature moves towards a lower value with the decreasing of the amount of charge that flows through the sample during polarization. The peak position changes as well, if the sample is polarized in air or in oxygen and the nature of change is more important in the case of oxygen. The shape of the peak is complex and at least four shoulders have been identified around 85, 90, 105, and 125 °C using the cleaning technique. The activation energy tends to increase with repetition of the TSDC runs, in the glass-rubber transition temperature range, in the case when the cleaning technique is used for the peaks separation. For the conditioned samples, there is a good agreement between the experimental results and the analytical expression of the current, particularly in the region where it reaches a maximum, and so relevant values for the characteristic parameters of the peak are determined. The time interval of the short circuiting of the sample, at room temperature, before the TSDC measurement, strongly influences the initial rise of the current and consequently the parameters of the peak. A possible redistribution of the internal field arising from the injected charge, the heterocharge, and the existing charge in the sample as received, has been put forward to account for the experimental evidences. The conclusion is that the current is mainly determined by the space-charge released from the traps that are likely continuously distributed in energy. For the stated polarization conditions, the charge is released from the shallow traps with an activation energy in the range 0.23–0.32 eV and a concentration of ∼1018/m3. The dipolar charge is of little importance.
Kinetics of growth of AlAs oxide in selectively oxidized vertical cavity surface emitting lasers
Authors: Koley Bikash , Dagenais M. , Jin R. , Pham J. , Simonis G. , McLane G. , Stone Dennis
Published: July 2002

The wet oxidation kinetics of AlAs layers of interest in vertical cavity surface emitting laser (VCSEL) fabrication are investigated in detail. The process is modeled as a diffusion-reaction process. For oxidation over a long time interval, variation of the oxidation rate with the variation of the radius of the etched mesa of the VCSEL is observed. A theory has been developed to obtain the rate equation of the oxidation process and the dependence of the oxidation rate on the size of the VCSEL is explained.
The activation energy for GaAs/AlGaAs interdiffusion
Authors: Wee S. F. , Chai M. K. , Homewood K. P. , Gillin W. P.
Published: July 2002

We present data of the interdiffusion coefficient of AlGaAs/GaAs over the temperature range 750–1150 °C, and obtain EA and D0 values of 3.6±0.2 eV and 0.2 (with an uncertainty from 0.04 to 1.1) cm2/s, respectively. These data are compared with those from the literature taken under a wide range of experimental conditions. We show that despite the range of activation energies quoted in the literature all the data can be described using a single activation energy. Using this value of EA to fit the published data and then determining D0 for each data point we find that the published data fall into two clusters. One, for samples annealed under a gallium rich overpressure and a second for As rich or capped anneals. This result can be explained by the diffusion in all cases being governed by a single mechanism, vacancy-controlled second-nearest-neighbor hopping.
Two local vibrational modes related to hydrogen in GaN
Authors: Duan J. Q. , Zhang B. R. , Zhang Y. X. , Wang L. P. , Qin G. G. , Zhang G. Y. , Tong Y. Z. , Jin S. X. , Yang Z. J. , Zhang X. , Xu Z. H.
Published: July 2002

We have observed two absorption bands located at around 1730 and 2960 cm−1 in the infrared (IR) absorption spectra from undoped GaN samples which are grown using low pressure metalorganic vapor phase epitaxy and irradiated by gamma ray and then exposed to a radio frequency hydrogen plasma. Proton implantation followed by gamma-ray irradiation of the GaN samples can also activate the IR band at around 1730 cm−1. Based on the experimental results, we tentatively ascribe the 1730 cm−1 band to the local vibrational modes of Ga–H complexes in the vicinity of N vacancies and the 2960 cm−1 band to those of either N–H complexes in the vicinity of Ga vacancies or C–H complexes.
Interferometric quantum wire switch
Authors: Flory Curt A.
Published: July 2002

A device topology is proposed and analyzed which is based upon quantum wire components. The device controls the conductance between an input line and a pair of output lines by varying the phase shift around a quantum wire ring connecting the external nodes. The phase shift is controlled using a simple electron stub tuner. Switching characteristics with efficiencies greater than 95% for certain geometries have been calculated.
Surface photovoltage spectroscopy of an InGaAs/GaAs/AlGaAs single quantum well laser structure
Authors: Ashkenasy N. , Leibovitch M. , Shapira Yoram , Pollak Fred H. , Burnham G. T. , Wang X.
Published: July 2002

An InGaAs/GaAs/AlGaAs single quantum well graded-index-of-refraction separate-confinement hetero-structure laser has been analyzed using surface photovoltage spectroscopy (SPS) in a contactless, nondestructive way at room temperature. Numerical simulation of the resulting spectrum made it possible to extract growth parameters, such as the InGaAs well width, the well and cladding compositions, as well as important electro-optic structure data of this device, including the lasing wavelength and built-in electric field. The results highlight the power of SPS in obtaining performance parameters of actual laser devices, containing two-dimensional structures, in a contactless, nondestructive way.
Studies on surface damage induced by ion bombardment
Authors: Wang Yugang , Kang Yixiu , Zhao Weijiang , Yan Sha , Zhai Pengji , Tang Xiaowei
Published: July 2002

Highly oriented pyrolitic graphite (HOPG) samples were bombarded by different kinds of ions, including H, He, B, C, and Au, at an energy range from 530 keV to 4.5 MeV. After bombardment, the sample surfaces were observed with scanning tunneling microscopy. All these experimental results show that the energetic ions could cause observable protrusionlike damage on the HOPG surfaces. The ratio of the areal density of protrusion to the ion dose increases with the nuclear energy loss and is in the range of 10−5 to 2. The possible mechanism of these phenomena is also discussed.
Influence of the addition of Co and Ni on the formation of epitaxial semiconducting β-FeSi2: Comparison of different evaporation methods
Authors: Mangelinck D. , Wang L. , Lin C. , Gas P. , Grahn J. , Östling M.
Published: July 2002

β- FeSi 2 films containing 4–25 at. % of Co or Ni have been grown on (111) Si using three different evaporation methods: deposition of the metal film at room temperature followed by solid state reaction (solid phase epitaxy), deposition of the metal on a heated wafer [reactive deposition epitaxy: (RDE)] codeposition of metal and Si in the stoichiometric proportions [molecular beam epitaxy: (MBE)]. The films have been analysed with Rutherford backscattering spectrometry, x-ray diffraction, secondary ion mass spectroscopy, and scanning electron microscopy. We show that β-FeSi2 can be obtained with the three methods, however the quality, the epitaxial character and the morphology of the films differ. By far, the best results are obtained by MBE. In that case the codeposition of a Fe(Ni) alloy and Si at 550 °C leads to a large, epitaxial, mirror like β-Fe(Ni)Si2 layer with a homogeneous Ni concentration. Detailed analysis of the Fe(Ni) and Fe(Co)/Si reaction and comparison with the Fe/Si one shows that: (i) Ni and Co do not modify the temperature of formation and the stability of the different Fe silicides providing the solubility limits in the different phases are not exceeded (e.g., 6 and 12 at. % in β-FeSi2), (ii) the first stages of the reaction are characterized by the formation of a nonhomogeneous layer of FeSi. We did not observe the formation of a Si solid solution in Fe or of the ordered Fe3Si phase, (iii) the transformation from FeSi to β-FeSi2 induces a degradation of the β-FeSi2 layer morphology. This explains why the processes (RDE and MBE) bypassing the formation of FeSi give better epitaxial layers.
Modeling and analysis of photomodulated reflectance and double crystal x-ray diffraction measurements of tensilely strained InGaAs/InGaAsP quantum well structures
Authors: Rowland G. , Hosea T. J. C.
Published: July 2002

Room temperature photomodulated reflectance (PR) and double crystal x-ray diffraction (DCXRD) measurements have been performed on a series of tensilely strained InxGa1−xAs multiple quantum well (QW) laser structures, with In0.80Ga0.20As0.43P0.57 barriers, which are lattice-matched to an InP substrate. Seven samples are studied, with nominal QW In composition varying between x=0.533 and 0.316, corresponding to biaxial tensile strains between 0% and 1.5%, respectively. The DCXRD measurements provide accurate information on composition, strain and layer thickness, while the PR yields the energies of both allowed and forbidden critical point interband QW transitions, and how these vary with strain, particularly the transitions between the ground-state conduction band and heavy/light hole valence band levels. A three-band effective mass formalism is used to model the QW transitions and very good agreement with the PR measurements is obtained once excitonic binding energies, and the quantum confined Stark effect are taken into account.
Relative atomic chlorine density in inductively coupled plasmas containing chlorine and boron trichloride
Authors: Hebner G. A. , Fleddermann C. B.
Published: July 2002

Two photon allowed laser induced fluorescence has been used to measure the relative atomic chlorine density in inductively driven radio frequency discharges containing mixtures of chlorine, boron trichloride, argon and nitrogen. In contrast with previous measurements in pure chlorine discharges, the atomic chlorine density increased with rf power in pure BCl3 discharges. In mixtures of Cl2 and BCl3, the Cl density was constant with rf power and increased with pressure, similar to pure Cl2 discharges. In addition, the Cl density varied linearly with Cl2/BCl3 ratio, and was a factor of three higher in pure Cl2 than in pure BCl3. The addition of argon or nitrogen to BCl3/Cl2 mixtures had no effect on the relative Cl density. Finally, measurements of the Cl density as a function of spatial location showed that the Cl density was uniform in the discharge region. Several gas phase chemical mechanisms in Cl2/BCl3 plasmas are hypothesized based on the atomic chlorine measurements presented in this work with previous measurements of other gas phase plasma species in this reactor geometry.
Electroluminescence of silicon nanocrystallites prepared by pulsed laser ablation in reduced pressure inert gas
Authors: Yoshida Takehito , Yamada Yuka , Orii Takaaki
Published: July 2002

We report on an electroluminescent (EL) diode with novel active layers of silicon (Si) nanocrystallites. The Si nanocrystallite active layer was prepared by pulsed laser ablation in an ambient of reduced pressure inert gas. The structure of the EL diodes was semitransparent platinum (Pt) electrode/Si nanocrystallite layer/p-type Si/Pt electrode. We have observed visible spectra of not only photoluminescence around 2.07 eV, but also EL around 1.66 eV at room temperature. The EL diodes showed a rectifying behavior caused by a Schottky-like junction. Furthermore, we have found that the EL diodes showed strong nonlinear dependence of EL intensity on current density. A possible mechanism of the EL diode emission is impact ionization by minority hot carriers injected through the surface oxide layers and the successive radiative recombination.
Influence of current density on the magnetization process in active spin-valve elements
Authors: Portier X. , Petford-Long A. K. , Anthony T. C. , Brug J. A.
Published: July 2002

Simultaneous magnetoresistance measurements and observation of magnetic domain structures have been performed on active spin-valve elements by means of in situ experiments in a Lorentz transmission electron microscope. Two different spin-valve structures with NiFe and NiFe/Co sense layers have been studied with two sizes of rectangular elements. The effect of different applied current values has been analyzed and the addition of a Co layer in the sense layer has a large influence on the spin-valve behavior and on the domain structure. Also, two different processes for magnetic domain growth and motion have been observed for low or high applied current densities.
Temperature dependence of magnetoimpedance effect in amorphous Co66Fe4NiB14Si15 ribbon
Authors: Kim Y. K. , Cho W. S. , Kim T. K. , Kim C. O. , Lee Heebok
Published: July 2002

The temperature dependence of the magnetoimpedance (MI) effect is important both for scientific study and for thermal stability of MI sensors. We have performed the measurement of MI effect in amorphous Co66 Fe4 NiB14 Si15 (Metglas 2714A) ribbon from a cryogenic chamber where the temperature of the sample can vary from 10 to 300 K. The ac current was fixed at 10 mA for all measured frequencies ranging from 100 kHz to 10 MHz. The magnetoimpedance ratio (MIR) was revealed the drastic increment as a function of MIR(T)=MIR(0)exp(cT2), where c is a constant. The measured MIR values at room temperature are usually 2–3 times larger than the data measured at 10 K for all measured frequencies. However, the shapes of the MIR curves are remained. This result shows the potential application of the MI effect for a temperature sensor.
Suppression of superconductivity by injection of spin-polarized current
Authors: Koller Daniel , Osofsky M. S. , Chrisey D. B. , Horwitz J. S. , Soulen R. J. , Stroud R. M. , Eddy C. R. , Kim J. , Auyeung R. C. Y. , Byers J. M. , Woodfield B. F. , Daly G. M. , Clinton T. W. , Johnson Mark
Published: July 2002

A spin polarized current has been injected into high Tc superconductors resulting in a significant reduction in the superconductor’s critical current. Such injection may serve as the basis of a new class of superconducting devices for control, switching and amplification. Preliminary results using both Permalloy and CMR materials as injectors are presented.
Magnetostriction and field induced transitions in La1−xSrxMnO3 in pulsed magnetic fields
Authors: Popov Yu. F. , Kadomtseva A. M. , Vorob’ev G. P. , Ivanov V. Yu. , Mukhin A. A. , Zvezdin A. K. , Balbashov A. M.
Published: July 2002

Magnetostriction λ∥(H) and field-induced phase transitions were studied in the single crystal of La1−xSrxMnO3 (x=0, 0.05, 0.1, and 0.175) in the pulsed magnetic fields up to 230 kOe. Anomalies in the λ∥(H) curves were revealed at 200 kOe in the LaMnO3, which were identified with the spin-reorientation AyFz→AzFy in the magnetic field H∥b axis. A complicated magnetostriction behavior was observed in La0.875Sr0.175MnO3, related to the field-induced transition between orthorhombic and rhombohedral crystal structures.
Induction mapping of magnetostrictive materials
Authors: Dooley Jennifer , De Graef Marc , McHenry Michael E.
Published: July 2002

An energy-filtered magnetic induction mapping technique has been implemented on a JEOL 4000EX equipped with a Gatan imaging filter. A study of the magnetic domain structure in Terfenol-D, a magnetostrictive actuator material, is presented as an example application of the technique. The method is equivalent to differential phase contrast microscopy by the reciprocity theorem. Image simulations of all stages of the induction mapping process are shown to support these observations.
Polarization dependence of crystalline colloidal array diffraction
Authors: Pan Guisheng , Sood Ajay K. , Asher Sanford A.
Published: July 2002

We measured the polarization dependence of the Bragg diffraction efficiency of a crystalline colloidal array and compared the experimental results to that predicted by theory. The diffraction efficiency for π polarized light decreases to zero for an incidence angle of 45° to the diffracting planes. Our experimental diffraction and transmission results quantitatively agree with the predictions of dynamical diffraction theory.
Modeling of charging damage during interlevel oxide deposition in high-density plasmas
Authors: Hwang Gyeong S. , Giapis Konstantinos P.
Published: July 2002

Monte Carlo simulations of pattern-dependent charging during interlevel dielectric (ILD) deposition in high-density plasmas reveal that the initial conformality of the ILD film plays a crucial role in metal line charging up and the subsequent degradation to the buried gate oxide to which the metal line is connected. Line charging occurs when the top dielectric is thick enough to prevent tunneling currents while the sidewall dielectric thickness still allows tunneling currents to flow to the metal line; the differential charging of the sidewalls, which induces the latter currents, is caused by electron shading. The results suggest that charging can be reduced by depositing a more conformal ILD film around the metal line and/or by increasing the ability of the film surface to dissipate charge.
Carrier lifetime measurements using free carrier absorption transients. II. Lifetime mapping and effects of surface recombination
Authors: Linnros Jan
Published: July 2002

A novel noncontact technique for semiconductor wafer mapping of the charge carrier lifetime is reviewed. The principle is based upon measurements of free carrier absorption transients by an infrared probe beam following electron-hole pair excitation by a pulsed laser beam. The technique is demonstrated here for Si wafer lifetime mapping, both for homogenous wafers as well as for wafers having pn junctions, and the performance and limitations are addressed. In a companion article J. Appl. Phys. 84, 275 (1998), (part I), the injection dependence is treated in more detail. We demonstrate the broad range of accessible injections, allowing on-wafer lifetime mapping both of the minority carrier lifetime and of the high injection lifetime as well as of Auger recombination effects. Furthermore, problems of surface recombination for bare Si surfaces are elucidated while pn junctions or other barriers are shown to suppress diffusion of carriers to surfaces. Also, a scheme for low temperature surface passivation is demonstrated and the resulting surface recombination velocity is derived. Finally, a few examples of characteristic lifetime maps from processed samples are discussed. We conclude that the technique is one of the few available for monitoring of the carrier lifetime during a full device process sequence.
Electrical properties of CdS and CdSe films deposited on vibrating substrates
Authors: Mohanchandra K. P. , Uchil J.
Published: July 2002

Polycrystalline cadmium sulphide (CdS) and cadmium selenide (CdSe) films are deposited on glass substrates kept at room temperature using the method of resistive heating. In this article, the influence of substrate vibrations at ultrasonic frequency during deposition on the electrical properties of the films is discussed. The resistivity of the films has been studied as a function of temperature, and the activation energies have been determined for the films deposited on a vibrating substrate and on a static substrate. It is found that the carrier concentration is less in the case of the films deposited on vibrating substrate although the activation energy remains unaltered. This result is in agreement with the carrier concentration determined from Hall effect measurements on these films. The vibration of the substrate leads to better stoichiometry and crystallinity in the films as confirmed by x-ray diffraction studies.
Transient currents in pulsed metal–oxide–semiconductor tunnel diodes
Authors: Vercik A. , Faigón A.
Published: July 2002

The effect of tunneling currents on the transient from deep depletion towards equilibrium in thin oxide metal–oxide–semiconductor capacitors was experimentally investigated. Very thin oxide samples exhibit similar transients for both p- and n-type substrates. This symmetry breaks down for oxide thicknesses of more than 3.5 nm. Three qualitatively different behavior patterns, depending on the oxide thickness, can be identified by the current transient curves for the n-type substrate samples. From an analysis of the associated currents, the three patterns correspond to dominance by the minority carrier tunneling, dominance by the majority carrier tunneling, and enhanced generation through impact ionization.
Carrier localization effects in energy up conversion at ordered (Al0.5Ga0.5)0.5In0.5P/GaAs heterointerface
Authors: Yamashita Kenichi , Kita Takashi , Nishino Taneo
Published: July 2002

We investigated up-converted photoluminescence (UPL) in long-range ordered (Al0.5Ga0.5)0.5In0.5P grown on GaAs (115) A and GaAs (001). A multidomain structure of the ordered epitaxial film, each domain having its own order parameter, causes a band gap fluctuation. This enhances a localization of excited carriers from the GaAs layer. The UPL intensity excited at 1.83 eV depends nonlinearly on the excitation-laser power. It was found that an excitation-power dependence of the normal PL intensity excited by an above-gap light (2.54 eV) agrees well with those of the UPL at 11 K. However, at elevated temperatures, the excitation-power dependence of the normal PL intensity becomes linear. These results suggest that the nonlinear dependencies of the UPL intensity at low temperature closely relate to localization properties of photoexcited carriers. Furthermore, we observed band-filling effects on UPL under an irradiation of the above-gap light.
7Li and 31P nuclear magnetic resonance studies of Li1−3xMgFexPO4
Authors: Goñi A. , Bonagamba T. J. , Silva M. A. , Panepucci H. , Rojo T. , Barberis G. E.
Published: July 2002

We report a 7Li and 31P nuclear magnetic resonance (NMR) study in the Li1−3xMgFexPO4 phases between 150 and 410 K. This study, complementary to those made using Mössbauer and magnetic neutron diffraction experiments, confirms that the Fe ions enter as Fe(III) in the lattice, and that they enter substituting Li ions. Ionic conductivity measurements, together with the NMR behavior of the 7Li and 31P NMR spectra show that no Li mobility occurs in the temperature range studied even with the addition of the Fe impurity.
Electron nuclear double resonance of a nearly axial Rh2+ center in solution-grown NaCl crystals
Authors: Callens F. , Vrielinck H. , Matthys P. , Zdravkova M. , Vercammen H. , Schoemaker D.
Published: July 2002

Rh 3+ -doped NaCl single crystals grown from aqueous solution were studied with electron paramagnetic resonance and electron nuclear double resonance after irradiation at liquid nitrogen temperature. [RhCl6]4− complexes with two next-nearest neighbor charge compensating vacancies have been detected. The two vacancy-Rh2+ axes make an angle of 900 to each other and are perpendicular to the center symmetry axis. After warming the sample, this center with C2v symmetry decays consecutively into two other [RhCl6]4− centers reported earlier in Rh3+-doped NaCl and AgCl Bridgman crystals on the one hand, and/or in solution-grown NaCl:Rh3+ crystals irradiated at room temperature on the other hand.
A comparative Raman study of ferroelectric PbTiO3 single crystal and thin film prepared on MgO substrate
Authors: Yuzyuk Yu. I. , Farhi R. , Lorman V. L. , Rabkin L. M. , Sapozhnikov L. A. , Sviridov E. V. , Zakharchenko I. N.
Published: July 2002

A Raman study of a highly oriented PbTiO3 thin film deposited on a MgO single crystal has been performed as a function of the temperature. The results have been compared with those obtained from a single crystal prepared from the same batch and those reported in the literature for polycrystalline thin films and single crystals. A shift in the transition temperature is observed from the soft mode behavior, together with more usual lower values of its frequency, which are both related to effective hydrostatic pressure due to the clamping of grains by their neighbors in the distorted tetragonal structure. The large soft mode linewidth and its integrated intensity, which do not vanish at the ferroelectric to paraelectric transition temperature, have been interpreted in terms of the coupling of this mode (and more generally of all polar phonons) with the static strain fields originating from the clamping effect and the epitaxial conditions.
Optical characterization of molecular beam epitaxially grown InAsSb nearly lattice matched to GaSb
Authors: Marciniak M. A. , Hengehold R. L. , Yeo Y. K. , Turner G. W.
Published: July 2002

Molecular beam epitaxially (MBE)-grown InAsSb nearly lattice matched to (001) GaSb substrates has been studied by infrared absorption, photoluminescence (PL), and double crystal x-ray diffraction (DCXRD). The absorption measurements, made at temperatures of 6–295 K, resulted in determinations of the temperature and compositional dependencies of the energy gap and the absorption coefficients for InAs1−xSbx (0⩽x⩽0.192). Temperature- and laser excitation power-dependent PL measurements showed only a single band edge peak for the ternary samples (Δa/a⩽+0.623%). Both low temperature PL linewidths (as narrow as 4.3 meV) and observations of LO-phonon replicas indicate the good quality of this material. However, careful analysis of the PL data indicates that even this good material may have a tendency for phase separation resulting in compositional inhomogeneity as reported previously for MBE-grown InAsSb. (004) DCXRD measurements resulted in lattice mismatches between −0.629%⩽Δa/a⩽+0.708% for these samples, while (115) DCXRD measurements indicated that tensile strain persisted in the epilayers, even for thicknesses up to 1.4 μm.
Strain dependent optical phonon frequencies of cubic ZnS
Authors: Siakavellas M. , Kontos A. G. , Anastassakis E.
Published: July 2002

Bulk ZnS crystals have been examined by Raman spectroscopy at room temperature under uniaxial stress. Both transverse optical and longitudinal optical frequencies exhibit shifts which are linear in the stress. From the observed slopes we obtain the complete set of phonon deformation potentials which, in turn, are used to predict the LO phonon frequency shifts in strained ZnTe/ZnS and ZnSe/ZnS superlattices as a function of the layer thickness. The results are in agreement with previously reported values obtained from Raman measurements in such superlattices.
Optical loss in InAs-based long-wavelength lasers
Authors: Gun’ko N. A. , Khalfin V. B. , Sokolova Z. N. , Zegrya G. G.
Published: July 2002

A microscopic quantum-mechanical analysis of the intervalence band absorption of radiation (IVA) with hole transition into the spin-orbit split-off band has been made. It was found that IVA can heavily influence the threshold characteristics and quantum efficiency of heterolasers based on InAs. A detailed study of the threshold characteristics as functions of temperature and heterostructure parameters has been analyzed taking into account IVA.
Modeling topology formation during laser ablation
Authors: Hodapp T. W. , Fleming P. R.
Published: July 2002

Micromachining high aspect-ratio structures can be accomplished through ablation of surfaces with high-powered lasers. Industrial manufacturers now use these methods to form complex and regular surfaces at the 10–1000 μm feature size range. Despite its increasingly wide acceptance on the manufacturing floor, the underlying photochemistry of the ablation mechanism, and hence the dynamics of the machining process, is still a question of considerable debate. We have constructed a computer model to investigate and predict the topological formation of ablated structures. Qualitative as well as quantitative agreement with excimer-laser machined polyimide substrates has been demonstrated. This model provides insights into the drilling process for high-aspect-ratio holes.
Evaluation of mechanical damage by high resolution x-ray diffraction and minority carrier recombination lifetime in silicon wafer
Authors: Choi Chi-Young , Lee Joon-Hyung , Cho Sang-Hee , Lee Dong-Kun , Kim Chang-Soo
Published: July 2002

In Czochralski silicon wafers, the effect of mechanical back side damage was systematically analyzed by x-ray diffuse scattering and minority carrier recombination lifetime measurements. X-ray section topography and wet oxidation/preferential etch methods were also employed. A liquid honing method was used to induce mechanical damage, and the damage grade was varied by controlling process parameters. A high resolution x-ray analysis of the samples was carried out before and after heat treatment at 1100 °C for 60 min. The magnitude of diffuse scattering was analyzed quantitatively by integrating the excess intensity of diffuse scattering into a reciprocal space map and its correlation with the mechanical damage was examined. As the grade of mechanical damage increased, the degree of diffuse scattering increases and minority carrier recombination lifetime decreases, suggesting the generation of more defects. We discuss other experimental results from the viewpoint of the structure–property relationship.