bluuebunny/crossref_metadata_2025 huggingface dataset:
Residual stresses in evaporated silicon dioxide thin films: Correlation with deposition parameters and aging behavior
Authors: Leplan H. , Geenen B. , Robic J. Y. , Pauleau Y.
Published: July 2002

Silicon dioxide thin films have been prepared by electron-gun evaporation under various deposition conditions. The residual stresses in SiO2 films were determined by measurements of the radius of curvature of Si and Ge substrates. The composition and density of films were deduced from Rutherford backscattering spectroscopy and elastic recoil detection analyses. The films were found to be stoichiometric (Si/O=1/2) under the deposition conditions investigated. The compressive residual stresses in films deposited at the base pressure (2×10−5 mbar) varied from −20 to −550 MPa as the substrate temperature increased from 20 to 285 °C. At a substrate temperature of 200 °C, the residual stresses varied from +70 to −180 MPa with decreasing oxygen pressure in the deposition chamber. The contribution of three types of stresses, namely thermal, intrinsic, and water-induced stresses, can be distinguished. The stress component resulting from the absorption of water molecules in porous SiO2 films was obtained from variation of residual stresses caused by the changeover of samples from air to vacuum. The level of this stress component was dependent on the density of films. An evolution of residual stresses from compressive to tensile with time of sample storage in a conventional clean-room environment was measured for all evaporated SiO2 films investigated in this study. In addition, the hydrogen content in films increased progressively with increasing aging time in air. The kinetics of this stress evolution was considerably reduced when the films were stored in vacuum. The origin of residual stresses and the stress aging mechanism are discussed.
Mechanisms for highly ionized magnetron sputtering
Authors: Hopwood J. , Qian F.
Published: July 2002

A simple model for ionization of sputtered metals by a high-density plasma is presented. Experimentally, ion flux fractions of greater than 80% can be obtained by sputtering aluminum into a region of dense plasma (ne∼1012 cm−3). Such a process has important applications in the filling of high-aspect-ratio features encountered in microelectronics fabrication. Both electron-impact and Penning ionization mechanisms are considered in this model. Under conditions of low electron density (ne≪1011 cm−3), Penning ionization is found to be the dominant ionization path. This is consistent with the accepted ionization mechanism for conventional diode sputtering. When high electron densities are generated, however, electron-impact ionization plays a significant ionization role. Langmuir probe measurements of the inductively coupled plasma indicate that the electron density lies between 2×1011 and 2×1012 cm−3. The model, in combination with measured plasma density, is used to calculate ion fractions. Modeled and experimentally measured aluminum ion fractions compare favorably. The effects of chamber dimensions, argon pressure, and sputtered metal density are investigated and shown to be important in optimizing the ionization fraction.
Observation of excitonic polariton and broadening of room-temperature exciton in strained InGaAs/GaAs quantum wells
Authors: Shen W. Z. , Shen S. C. , Tang W. G. , Wang S. M. , Andersson T. G.
Published: July 2002

Photoluminescence and absorption spectra of strained InGaAs/GaAs single quantum well (SQW) and multiple quantum well (MQW) structures as a function of well width have been investigated in detail. It has been demonstrated that the strength of the exciton-LO phonon coupling is quite stronger in InGaAs/GaAs SQW structures than that of InGaAs/GaAs MQW structures by aid of the temperature-dependent linewidth analysis. The critical temperature for the excitonic polariton-mechanical exciton transition in InGaAs/GaAs quantum well structures is found to be ∼35 K.
Chemical vapor deposition of B-doped polycrystalline diamond films: Growth rate and incorporation efficiency of dopants
Authors: Gonon P. , Deneuville A. , Fontaine F. , Gheeraert E. , Campargue A. , Chenevier M. , Rodolphe S.
Published: July 2002

The growth rate and the incorporation efficiency of dopants have been studied in the case of chemical vapor deposition of B-doped polycrystalline diamond films. The deposition rate is found to decrease with the addition of diborane in the gas phase. This is correlated with a modification of the plasma chemistry as observed by emission spectroscopy (decrease in the H/H2, CH/H, and C2/H ratios with the addition of diborane). The concentration of boron incorporated in the films is observed to vary with the square of the boron concentration in the gas phase.
High density plasma processing of diamond films on titanium: Residual stress and adhesion measurements
Authors: Catledge Shane A. , Vohra Yogesh K.
Published: July 2002

High density plasma processing of diamond films on titanium was carried out by microwave plasma chemical vapor deposition. The deposited films were characterized by Raman spectroscopy and thin film x-ray diffraction. We measure a residual compressive stress of 3.5±1.0 GPa which is lower than that obtained in previous studies. A measure of the film adherence to the titanium substrates was obtained by examining micro-Raman spectra near Brale C indentations. Using a model for biaxially stressed polycrystalline diamond films, it is determined that as much as 7.8 GPa can be sustained in the film before delamination occurs. Our experimental results are compared to earlier adhesion data of diamond on titanium.
Study of the mechanical nanocrystallization process of amorphous Fe78B13Si9 alloy using the pair function method
Authors: Grigoriew H. , Jachimowicz M.
Published: July 2002

An amorphous Fe78B13Si9 alloy was subjected to high-energy ball milling. Studies were performed for several increasing milling times by means of differential scanning calorimetry and x-ray diffraction. The initial alloy and the milled samples were studied using the pair function method. The analysis of the results has shown that in an amorphous phase defects are created during the first stage of milling, leading to a modified crystallization mechanism. Bulk nucleation is the next stage. The process of the nucleus growth is very limited.
A technology oriented model for transient diffusion and activation of boron in silicon
Authors: Höfler A. , Feudel Th. , Strecker N. , Fichtner W. , Stegemann K.-H. , Syhre H. , Dallmann G.
Published: July 2002

We propose a model for point-defect-assisted transient diffusion and activation of high-dose boron implants in silicon. To model transient diffusion, a nonlinear equilibrium clustering model for point defects is used. The activation of boron is modeled as a Fermi-level-dependent transformation of inactive dopant clusters to substitutional atoms. Comparison with experimental data shows that this approach can provide a description of both rapid thermal annealing and long-time furnace annealing steps, with an excellent predictive capability for both chemical and electrically active profiles.
Optical admittance studies of vanadium donor level in high-resistivity p-type 6H-SiC
Authors: Evwaraye A. O. , Smith S. R. , Mitchel W. C.
Published: July 2002

The vanadium donor level in high-resistivity p-type 6H-SiC has been studied using optical admittance spectroscopy. Besides the conductance peak due to the band to band transitions, there are three conductance peaks in the spectra of most of the samples. These peaks correspond to photoexcitation of electrons from the valence band to the defect levels. The conductance peak due to the vanadium donor [V4+(3d1)] level at Ev+1.55 eV is identified. The build up of the photoconductance at this peak was studied and it was found that the conductance transients are completely described by a sum of two exponential expressions. The relevant parameters, α1, α2, Gmax(1) and Gmax(2), were determined as functions of temperature. The persistent photoconductance (PPC) due to this defect was also studied. The decay kinetics of the PPC follow the stretched exponential form. The potential barrier against recapture of carriers was determined to be 220 meV for the vanadium donor level.
Structural properties of carbon nitride films prepared by high dose nitrogen implantation into carbon thin films
Authors: Xin Huoping , Lin Chenglu , Xu W-ping , Wang Lianwei , Zou Shichang , Wu Xinglong , Shi Xiaohong , Zhu Hong
Published: July 2002

Carbon nitride films were successfully prepared by ion beam synthesis method. 100 keV N+ ions at a dosage of 1.2×1018 cm−2 were implanted into carbon thin films at different temperatures. The samples were evaluated by x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, cross-sectional transmission electron microscopy (XTEM), Rutherford backscattering spectroscopy (RBS), x-ray diffraction analysis (XRD), and Vickers microhardness measurement. XPS results show that most of the implanted nitrogen atoms are free state. Most of the carbon atoms have C–C bonding and a little of them form a C–N bond. It also can be clearly seen that the content of the C–N covalent bonding state in the samples is increased by raising the implanting temperature of the samples. Raman spectrum indicates that there is a Raman band near 2300 cm−1 corresponding to carbon-nitrogen stretching. XTEM and RBS studies show that there is a buried layer of carbon nitride. XRD and TEM analyses reveal that the buried carbon nitride is predominantly amorphous with a small volume fraction of nanocrystallites. The sample has a higher hardness than that of a carbon thin film.
Effect of thermal annealing on the dielectric properties of KTiOPO4 single crystals
Authors: Satyanarayan M. N. , Bhat H. L. , Srinivasan M. R.
Published: July 2002

Dielectric properties of potassium titanyl phosphate have been investigated as a function of thickness and frequency, as well as annealing treatment under various atmospheres. The low frequency dielectric constant of KTP crystals is shown to depend upon the sample thickness, and this feature is attributed to the existence of surface layers. The frequency-dependent dielectric response of KTP exhibits a non-Debye type relaxation, with a distribution of relaxation times. The dielectric behavior of KTP samples annealed in various atmospheres shows that the low frequency dielectric constant is influenced by the contribution from the space charge layers. Prolonged annealing of the samples leads to a surface degradation, resulting in the formation of a surface layer of lower dielectric constant. This surface degradation is least when annealed in the presence of dry oxygen. From the analysis of the dielectric data using complex electric modulus, αm has been evaluated for the virgin and annealed samples.
The exciton transition in extremely shallow quantum well structures: Strong coupling between the distributions in the quantized and in-plane directions
Authors: Park S. , Kwon O’D.
Published: July 2002

The planar radius and the binding energy of excitons in extremely shallow quantum well (ESQW) structures are calculated theoretically. As the strength of an applied electric field increases, the exciton planar radius increases and the binding energy decreases rapidly compared with a conventional quantum well, which explains the rapid peak quench in ESQW structures. We also calculate the energy difference between heavy hole and light hole exciton transitions in quantum wells with various barrier heights. Due to the small energy difference in ESQW structures, the light hole peak is not clearly resolved from heavy hole peak by room-temperature photocurrent experiments.
A unified description of two voltage-varying methods for evaluating surface recombination velocity from electron-beam-induced current: Application to normal- and planar-collector configurations
Authors: Luke Keung L.
Published: July 2002

Ever since their respective appearance in the literature, the Watanable–Actor–Gatos (WAG) and Berz–Kuiken (BK) methods—two voltage-varying methods for determining the ratio of surface recombination velocity over diffusion coefficient (sT/D) from electron-beam-induced current (EBIC) data measured as a function of beam voltage—have coexisted as separate, independent methods. Judged by the frequency of its citations in the literature and endorsements in review articles, the WAG method appears to be the method of choice. In this article it is shown that these two methods have a common origin and that in fact they are identical when the EBIC is linearly related to the effective beam penetration depth. Unifying these methods leads to the development of a more general method, named here as the slope-extrapolated-intercepts or SEIs method. To demonstrate its generality, the SEIs method is used to investigate a variety of situations: normal- and planar-collector geometries, Gaussian and point sources, and a wide range of values of material parameters and effective beam penetration depth. It is found that the SEIs method, or the simpler but less general and less accurate BK method, and not the WAG method, should be the method of choice to evaluate sT/D from voltage-varying EBIC data.
Micro-probe Raman spectroscopy for detection of inhomogeneities in YVO4 single crystals
Authors: Erdei S. , Jin B. , Ainger F. W. , Bhalla A. S. , Keszei B. , Vandlik J. , Süveges A.
Published: July 2002

Several near quasicongruent undoped YVO4 single crystals grown by the Czochralski (CZ) technique as well as near stoichiometric YVO4 single crystals grown by the top-seeded solution growth technique, were investigated by micro-probe Raman spectroscopy using unpolarized argon–ion laser light. The line broadening effects of the Raman active mode at 379 cm−1 indicate that all CZ grown crystals possess wider peak widths than near stoichiometric YVO4. In the latter case a value of 9.23 cm−1 was measured for full width at half-maximum. Although the annealing process in O2 can improve the oxygen stoichiometry in the originally slightly oxygen deficient CZ grown YVO4 crystals, certain remaining peak broadening effects demonstrate a Y–V related stoichiometry problem by both lower (external) and higher frequency (internal) modes. Radial inhomogeneous distributions were observed in CZ specimens by the shift of external Raman modes at 157 and 162 cm−1 frequencies. In addition, nonassigned low intensity extra Raman peaks appeared over 1000 cm−1 frequencies in all CZ grown samples. The above detected changes in Y–V–O stoichiometry demonstrate a complex phase system around the homogeneity region of quasicongruent YVO4 specimens and enable a more realistic and unified interpretation of the segregated defects and stoichiometry changes in CZ grown YVO4 single crystals than previously available.
Piezoelectrically forced thickness-shear and flexural vibrations of contoured quartz resonators
Authors: Lee P. C. Y. , Wang J.
Published: July 2002

In a previous article a set of first-order equations of motion is obtained for contoured crystal plates and for frequencies up to and including those of the fundamental thickness-shear modes. In the present article the governing equations of contoured plates are extended to include the electric potential which is coupled to the mechanical fields by the piezoelectric effect. These equations are, then, employed for the study of piezoelectrically forced thickness-shear and flexural vibrations of beveled AT-cut quartz plate, i.e., the plate with a portion of uniform thickness between the two wings of the double wedge. Analytical solutions are obtained by Frobenius method. Displacements, stresses, and electric potential are derivable from six independent functions which are in the form of infinite power series. In addition to the calculations of resonance frequencies and mode shapes, the effects of the contouring on the forced mechanical displacements, electric potential, surface charge, and capacitance ratio are examined.
Junction sharpness in field-induced transistor structures in CuxAg1−xInSe2
Authors: McAlpine N. S. , McConville P. , Haneman D. , Chernyak L. , Cahen D.
Published: July 2002

We have measured the widths of the transition regions at p-n-p junctions that are formed on CuxAg1−xInSe2 by high electric field at room temperature, by using a scanning tunneling microscope with capacity for measuring current–voltage curves on physical contact. We find marked transition regions of low conductivity with widths in the range of 1.3–5 μm. This shows that the junction created by the electromigration mechanism in this material, while diffuse by the standards of those produced by high-temperature or high-energy methods, are remarkably sharp by solid-state ionic measures.
Raman scattering probe of ion-implanted and pulse laser annealed GaAs
Authors: Verma Prabhat , Jain K. P. , Abbi S. C.
Published: July 2002

We report Raman scattering studies of phosphorus-ion-implanted and subsequently pulse laser annealed (PLA) GaAs. The threshold value of implantation fluence for the disappearance of one-phonon modes in the Raman spectrum of ion-implanted GaAs sample is found to be greater than that for the two-phonon modes by an order of magnitude. The phonon correlation length decreases with increasing disorder. The lattice reconstruction process during PLA creates microcrystallites for incomplete annealing, whose sizes can be given by the phonon correlation lengths, and are found to increase with the annealing power density. The intensity ratio of the Raman spectra corresponding to the allowed longitudinal-optical (LO)-phonon mode to the forbidden transverse-optical (TO)-phonon mode, ILO/ITO, is used as a quantitative measure of crystallinity in the implantation and PLA processes. The threshold annealing power density is estimated to be 20 MW/cm2 for 70 keV phosphorus-ion-implanted GaAs at a fluence of 5×1015 ions/cm2. The localized vibrational mode of phosphorus is observed in PLA samples for fluences above 1×1015 ions/cm2.
Temperature and field-induced magnetization flips in amorphous Er–Fe alloys evidenced by x-ray magnetic circular dichroism
Authors: Garcia L. M. , Pizzini S. , Rueff J. P. , Vogel J. , Galéra R. M. , Fontaine A. , Kappler J. P. , Krill G. , Goedkoop J.
Published: July 2002

Magnetic properties of amorphous Er1−xFex alloys with x≊0.7 have been studied. Macroscopic characterization has been performed by measuring temperature- and field-dependent magnetization. Applying a magnetic field the compensation temperature first decreases, but increases again at larger fields. This ‘‘exotic’’ behavior has been interpreted in terms of the sperimagnetic character of both subnetworks. The suggested scheme has been checked by measuring x-ray circular magnetic dichroism at the Er M5-edge. Using this atom-sensitive technique we have been able to detect temperature-induced as well as field-induced flips of the Er-subnetwork with respect to the direction of the applied field.
High-power-use Mn–Zn ferrites with monodomain structure prepared by low-temperature sintering
Authors: Liu C. S. , Wu J. M. , Nan Lin I. , Chen C. J.
Published: July 2002

Densely sintered Mn–Zn ferrites with grain size varying between 1 and 6 μm were obtained. Then the effect of grain size was investigated in detail by power loss analysis and scanning electron microscopy examination of microstructure. It is found that the power loss is seen to be lowered from 260 to 120 kW/m3 at 500 kHz, 50 m T and 90 °C with grain size decreased in the order of 3 μm. It is assumed that the residual loss from domain wall resonance is a dominant factor of power loss from 500 kHz to 1 MHz. Therefore we conclude that Mn–Zn ferrite display a grain size dependent power loss with transition at grain size about 3 μm due to the absence of intragranular domain wall and these fine core materials can be prepared by low sintering temperature and the optimum control of atmosphere containing 0.5% O2.
(100)-textured 3% silicon steel sheets by manganese removal and decarburization
Authors: Tomida Toshiro
Published: July 2002

Texture development in 3% Si steel sheets by the manganese removal and decarburization process has been investigated. The 3% Si steel sheets that contain Mn and C were first annealed in vacuum at α-ferrite (α)/austenite (γ) duplex or γ phase temperatures, and then decarburized. During the vacuum annealing a manganese removal induced phase transformation to α occurs in a thin layer near the sheet surface. Pronounced (100) textures with a variety of in-plane anisotropies develop in the layer. The subsequent decarburization promotes the growth of the surface grains into the interior, providing the entire sheet with the same texture. The resultant materials exhibit excellent soft-magnetic properties.
First-order velocity shift and reflection coefficient for surface acoustic wave propagation
Authors: Thoma C. , Hahn Y.
Published: July 2002

Design of surface acoustic wave (SAW) devices requires accurate values of velocity shift q and reflection coefficient r associated with finger overlays placed on the substrate material. In previous treatments variational and perturbative approaches have been developed for calculating first-order reflection coefficients and velocity shifts; however, the anisotropic substrate materials have until now been modeled by an effective isotropic substrate. We extend the variational and perturbative calculations of the first-order quantities to fully anisotropic crystals for several standard SAW substrate and overlay materials. Moreover, we report results obtained with both electrically free and shorted trial functions, and suggest optimum parametrizations of q and r, to first order in h/λ, where h is the finger thickness and λ is the Rayleigh wavelength.
Effect of Al interlayers on growth and magneto-optic properties of MnBi thin films
Authors: Rüdiger U. , Fumagalli P. , Berndt H. , Schirmeisen A. , Güntherodt G. , Holländer B.
Published: July 2002

Bi/Mn/Al/Bi/Mn multilayers with different Al-interlayer thickness have been deposited on glass substrates at room temperature. The multilayers are not protected by a passivating layer, such as SiOx, in order to investigate the interplay between Al-interlayer thickness and homogeneity, granularity, and topography before and after annealing. Due to the Al interlayer, the diffusion across the Bi/Mn/Al/Bi/Mn stack was reduced as demonstrated by x-ray analysis, scanning electron microscopy, and Rutherford backscattering spectrometry. During annealing, two (MnxBi100−x)100−yAly layers are formed which are separated by an Al interlayer. After annealing, polar Kerr hysteresis loops as measured from the front side of the films show a superposition of two hysteresis loops, opposite in sign, with different coercive fields. The presence of different coercive fields is explained by different granularity of the top and bottom (MnxBi100−x)100−yAly layer. The coercive field of the top (MnxBi100−x)100−yAly layer reaches values up to 1.25 T, while the bottom layer shows a constant value of 0.3 T independent of the Al-interlayer thickness. The opposite sign of the two contributions to the Kerr loops is explained by the different relative index of refraction at the air/(MnxBi100−x)100−yAly and the Al/(MnxBi100−x)100−yAly interface.
Electrical properties of heteroepitaxial grown tin-doped indium oxide films
Authors: Taga Naoaki , Odaka Hidefumi , Shigesato Yuzo , Yasui Itaru , Kamei Masayuki , Haynes T. E.
Published: July 2002

Oriented thin-film tin-doped indium oxide (ITO) was heteroepitaxially grown on optically polished (100) or (111) planes of single-crystalline yttria-stabilized zirconia (YSZ) substrates using e-beam evaporation or dc magnetron sputtering techniques. Pole figure x-ray diffraction analyses revealed that the heteroepitaxial relations were (001)ITO∥(001)YSZ, [100]ITO∥[100]YSZ, and (111)ITO∥(111)YSZ, [110]ITO∥[110]YSZ, respectively. X-ray rocking curve analyses and Rutherford backscattering spectrometry revealed that the e-beam evaporated heteroepitaxial ITO films had much higher crystallinity than the one deposited by dc magnetron sputtering. Both carrier density and Hall mobility of the e-beam evaporated heteroepitaxial films showed steady increases in a wide temperature range, which could be interpreted in terms of the increasing Sn-doping efficiency caused by the improvement of the crystallinity of In2O3 host lattice, and hence the decreasing Sn-based neutral scattering centers.
Modeling neutral dynamics in pulsed helium short-gap spark discharges
Authors: Eichwald O. , Jugroot M. , Bayle P. , Yousfi Dr. M.
Published: July 2002

A numerical analysis of the neutral dynamics is performed in the case of helium short-gap spark discharges to show the energy memory effect of recurring discharges. The millimetric (4 mm) and submillimetric (0.3 mm) discharges are studied at atmospheric pressure and ambient temperature (293 K). This corresponds to a neutral density of 2.5×1025 m−3. The maximum injected power is either 50 or 3 W with a duration of 1 μs, the relaxation time between the two successive injections is 5 μs. The evolution of the neutral gas is described with the classical transport equations written in a two-dimensional cylindrical geometry with plane electrodes and solved with powerful numerical schemes. The effect of the discharge on the neutral gas is represented by energy and momentum transfers. The neutral gas is no longer considered as an infinite sink dissipating the energy of the electrons and ions acquired from the field. It is shown that the energy and momentum transfer effects initiate and control the variations of temperature, pressure, and neutral population. Concerning the recurring aspect, the neutral memory effect persists during the time lapse between two successive discharges and directly influences the gas dynamics of the following discharge. The specific behavior of the gas dynamics for the shorter gap (0.3 mm) is also discussed in terms of boundary effects. In particular, the influence of the latter on the velocity field is studied.
Thermodynamic analysis of two-dimensional crystal growth in nucleated isotactic polypropylene
Authors: Pieruccini M. , Marco G. Di , Lanza M.
Published: July 2002

A thermodynamic model is used to describe the two-dimensional crystallization kinetics (as observed by means of a calorimeter) of polypropylene nucleated with small amounts of indigo. The customary expression of the free enthalpy associated to secondary nucleation is initially used to analyze the experimental data. A significant dependence of the apparent surface tension (either basal or lateral) of the nuclei on the concentration of indigo is pointed out. To account for this effect, a phenomenological correction to the free enthalpy of nucleation is considered afterwards, which is connected with an entropy contribution arising from the formation of the crystal–melt interface. A more detailed data analysis is then carried out in light of this model.
Analysis of magnetic field dependent Hall data in narrow bandgap Hg1−xCdxTe grown by molecular beam epitaxy
Authors: Antoszewski J. , Faraone L.
Published: July 2002

The analysis of magnetic field dependent Hall data is presented for three representative Hg1−xCdxTe layers grown by Molecular Beam Epitaxy with x in the range 0.193 to 0.244. These samples exhibit ‘‘anomalous’’ Hall characteristics which are analyzed using a hybrid approach consisting of mobility spectrum (MS) analysis followed by a multi-carrier fitting (MCF) procedure. This hybrid approach is able to readily separate contributions to the total conductivity arising from extrinsic carriers, thermally activated intrinsic electrons, and two-dimensional electron layers. The extracted transport parameters for thermally activated intrinsic electrons are shown to be in excellent agreement with established physical models for narrow bandgap HgCdTe. The two-dimensional electron layers are found to be only weekly temperature dependent with an electron mobility in the range of 2 to 4×104 cm2/V s and a sheet density in the range of 1011 to 1012 cm−2. Of particular interest, is the fact that the ‘‘anomalous’’ Hall characteristics exhibited by all three samples are shown not to be indicative of poor-quality material. This anomalous behavior is found to be due to comparable contributions to the total conductivity from either bulk majority carrier holes and intrinsic minority electrons, or bulk majority carriers and a two-dimensional electron population. The practical aspects of implementing the MS+MCF procedure are discussed, with particular emphasis on the range of magnetic fields required for unambiguous and accurate parameter extraction.
The electronic structure of InGaAs/InP quantum wells measured by Fourier transform photoluminescence excitation spectroscopy
Authors: Dalfors J. , Lundström T. , Holtz P. O. , Radamson H. H. , Monemar B. , Wallin J. , Landgren G.
Published: July 2002

We report on novel results from a systematic study of excitonic transitions in high quality metalorganic vapor phase epitaxy grown InxGa1−xAs/InP quantum wells (QWs). The electronic structure of the QWs has been studied as a function of QW width as well as the built-in strain. The characterization has been performed by means of a combined Fourier transform photoluminescence (FTPL) and FTPL excitation study of the InxGa1−xAs/InP QWs. Detailed information on the energy positions for the excitons associated with various subbands (for the electrons, heavy and light holes) up to n=5 have been obtained. The experimentally determined energy positions have been compared with theoretical predictions based on an effective mass model and bulk deformation potential theory.
Photoacoustic spectroscopy of diluted magnetic semiconductors
Authors: Felici A. C. , Lama F. , Piacentini M. , Papa T. , Debowska D. , Kisiel A. , Rodzik A.
Published: July 2002

The absorption coefficient of several diluted magnetic semiconductors was measured below the fundamental absorption edge of the pure host compound at room temperature using the photoacoustic technique. Several absorption bands have been detected and assigned to electronic transitions between the crystal field split 3d levels of the transition metal ion. In addition, weak absorption thresholds have been observed and assigned to the ionization of the transition metal d states. An energy level diagram of the d states has been discussed.
Stress-induced alignment of NL8 thermal donors in silicon: Energetics and kinetics
Authors: Trombetta J. M. , Watkins G. D. , Hage J. , Wagner P.
Published: July 2002

Preferential alignment is produced for the NL8 thermal double donors (TDDs) when uniaxial stress is applied during their formation at ∼450 °C. The recovery kinetics reveal that they can reorient readily on the time scale of their lifetime and their individual alignments therefore reflect the strain fields that each introduces into the lattice. Analysis reveals that each of the donor cores produces large compressional strain along its C2v [001]′ axis, the magnitude of which decreases monotonically with increase in the TDD species series, suggesting strain relief as the mechanism for nearby oxygen accumulation. The rate and activation energy for the reorientation suggests that the process is limited by the diffusion motion of the nearby interstitial oxygen atoms, with ∼5 jumps being required for TDD3, the third in the series, and progressively more for the subsequent ones.
X-ray standing wave study of CdTe/MnTe/CdTe(001) heterointerfaces
Authors: Boulliard J. C. , Capelle B. , Gualandris S. , Lifchitz A. , Cibert J. , Tatarenko S.
Published: July 2002

The x-ray standing wave method is used to investigate some crystallographic features of the first stages of growth of ultrathin pseudomorphic MnTe(001) strained layers buried in CdTe on CdTe(001) substrates. Experiments with 004 and 113 reflecting planes show evidence of the presence of both MnTe clusters and diluted CdMnTe alloy.
Effects of strain, substrate misorientation, and excitonic transition on the optical polarization of ordered zinc-blende semiconductor alloys
Authors: Zhang Yong , Mascarenhas A. , Ernst P. , Driessen F. A. J. M. , Friedman D. J. , Bertness K. A. , Olson J. M. , Geng C. , Scholz F. , Schweizer H.
Published: July 2002

Optical polarization in ordered GaInP2 alloys has been studied by low-temperature photoluminescence. A perturbative theory that includes the effects of lattice mismatch, substrate misorientation, and excitonic transitions has been developed for making quantitative comparisons between experimental results and theoretical predictions. We show that to obtain quantitative information about ordering from the polarization of near-band-gap transitions, all of the above-mentioned effects should be taken into account. This study demonstrates that the electronic and optical properties of a monolayer superlattice formed by partial ordering in the GaInP2 alloy can be well described by a simple perturbative Hamiltonian, i.e., a quasicubic model.
Surface spin disorder in ferrite nanoparticles (invited)
Authors: Kodama R. H. , Berkowitz A. E. , McNiff E. J. , Foner S.
Published: July 2002

Anomalous magnetic properties of organic coated NiFe2O4 nanoparticles have been reported previously (Berkowitz et al.).5 These properties included low magnetization with a large differential susceptibility at high fields and shifted hysteresis loops after field cooling, while Mössbauer spectra indicated that all of the material was magnetically ordered. In the present study, we find that the lack of saturation in high fields is accompanied by irreversibility (i.e., hysteresis loops are open) up to 160 kOe. In addition, the particles exhibit time dependent magnetization in 70 kOe applied field. The high field irreversibility and the loop shift both vanish above 50 K. We propose a model of the magnetization within these particles consisting of ferrimagnetically aligned core spins and a spin- glass-like surface layer. We find that qualitative features of this model are reproduced by a numerical calculation of the spin distribution. The implications of this model for possible macroscopic quantum tunneling in these materials are discussed.
Influences of temperature and transport properties on the birefringence of CdGeAs2
Authors: Fischer D. W. , Ohmer M. C. , McCrae J. E.
Published: July 2002

We have directly measured the birefringence Δn of CdGeAs2 using polarized light interference spectra obtained in transmittance from 2.4 to 18 μm over a temperature range of 14–450 K. Four different samples, exhibiting a wide range of free carrier concentrations, were studied. It was found that free carriers can have a significant effect on the room-temperature birefringence. At 14 K, however, the data from all samples were virtually identical. The temperature dependence of Δn was obtained from a sample with low carrier concentration (≈1015/cm3) and high resistivity (9 Ω cm). Its temperature derivative d(Δn)/dT was determined at 50 K increments over the entire 14–450 K temperature range, and was found to vary from 2.6×10−5/K at 100 K to 5.1×10−5/K at 400 K. A least-squares fit to the data yielded a temperature coefficient for Δn of 8.2×10−8/K. Hall-effect measurements indicate that the resistivity, mobility, and carrier concentration all exhibit a significant temperature dependence. The resistivity for one sample increased by a factor of 108 when cooled from room temperature to 14 K. Our results suggest that previously published Δn values were probably obtained from samples with relatively high carrier concentrations, and that our results more accurately describe the true intrinsic birefringence of the material. The value of Δn decreases by 0.0004 per 1016 carriers a factor of 10 less than suggested by theory but still significantly large. The heavy to light hole effective mass ratio in the uppermost valence band was found to be 7.1.
An analysis of iron-iron interatomic distances in several rare earth transition metal intermetallics
Authors: Marasinghe G. K. , Ezekwenna Peter C. , James W. J. , Hu Z. , Yelon W. B.
Published: July 2002

As a part of a systematic study of the dependence of iron-iron exchange interactions on near neighbor iron-iron distances in rare earth transition metal magnetic materials, we have conducted a statistical analysis of interatomic distances in Nd2Fe17, Nd2Fe17N3, and Nd2Fe14B. Results, in general, support the notion that larger near neighbor iron-iron distances promote higher Curie temperatures. In this work, special attention has been paid to the expansion of the Nd2Fe17 lattice due to interstitial nitrogenation and the accompanying increase in the Curie temperature. Within the unit cell, the expansion of the Nd2Fe17 lattice due to nitrogenation is highly nonuniform. When nitrided, the distance between near neighbor 6c iron sites in Nd2Fe17 increases only slightly, by 0.021 Å. However, the distances between other near neighbor iron pairs separated by less than 2.45 Å increases by about 0.04 Å. The nitrogenation of Nd2Fe17 effectively reduces the number of near neighbor iron pairs separated by less than 2.45 Å by 92%. However, near neighbor interatomic distances involving the 18h sites are the most affected by nitrogenation. Consequently, the 18h site may play a major role in the enhancement of the Curie temperature due to nitrogenation.
Recombination kinetics of excess carriers in semiconductor quantum wells
Authors: Jin Shirong , Li Aizhen
Published: July 2002

A theoretical investigation of radiative and nonradiative recombination of excess carriers in a semiconductor quantum well (QW), which takes into account the exciton screening effect, is presented. The analytical formula of photoluminescence (PL) lifetime and efficiency of a QW are obtained. Calculations for the case of GaAs/AlGaAs quantum wells show that the variation of PL lifetime and efficiency with temperature is strongly related to material characteristics as well as the detailed growth techniques. When the ratio of the radiative recombination rate to the nonradiative recombination rate is less than unity, there is no characteristic temperature. In the regime of low excitation intensity, the increase of the majority carrier density is helpful to enhance the formation of the electron-hole pairs into excitons. Under higher excitations, the exciton population factor and the PL efficiency increases with increasing excitation intensity. The exciton screening effect depends, in addition to excitation intensity, upon background carrier density.
Model for the quasineutral region capacitance of p/n junction devices
Authors: Liou J. J. , Xue J. , Cao X. , Zhou W.
Published: July 2002

The capacitance associated with free-carrier charge storage in the quasineutral region is a primary factor in limiting the switching speed of p/n junction devices. This capacitance has been conventionally modeled using assumptions such as low-level injection, nondegeneracy, complete impurity ionization, and no space-charge region thickness modulation. These assumptions can give rise to a large error in device modeling, particularly for modern devices with very small geometry and high bias conditions. In this article, a comprehensive quasineutral region capacitance model including relevant device physics is developed. Comparisons between the present and conventional models are made, and the effects of using these two different models on the total capacitance of junction diode are also investigated.
Scanning magnetoresistance microscopy (SMRM): Imaging with a MR head
Authors: Yamamoto S. Y. , Schultz S.
Published: July 2002

We have developed a new scanning magnetic microscopy that uses commercial magnetoresistive (MR) record/playback heads as sense probes. A high-resolution, linearized positioning stage is used to raster scan a magnetic sample with respect to the MR head while the head is in physical contact with the sample. An upper bound on the spatial resolution of the scanning magnetoresistance microscope (SMRM) is 100 nm in the “downtrack” direction and 1–2 μm in the “crosstrack” direction of the head. Magnetic force microscopy has better spatial resolution than SMRM, but SMRM gives a more quantifiable signal since the MR head response can be calibrated in a uniform external field. Furthermore, SMRM has the unique ability to apply localized fields to the sample via the inductive write element.
Intrinsic microstrains and normal-phase flicker noise in YBa2Cu3O7 epitaxial films grown on various substrates
Authors: Bobyl A. V. , Gaevski M. E. , Karmanenko S. F. , Kutt R. N. , Suris R. A. , Khrebtov I. A. , Tkachenko A. D. , Morosov A. I.
Published: July 2002

Local measurements of structural characteristics such as intrinsic microstrain along the c axis of the lattice ε=δc/c and its mean square fluctuation 〈ε〉, oxygen deficiency x, cation composition, etc. were performed on epitaxial YBa2Cu3O7 films grown on various substrates (MgO, BaSrTiO3/MgO, SrTiO3, LaAlO3, ZrO2/Si, Al2O3). A number of film microstrips were fabricated and the normalized flicker noise intensity (Hooge parameter α) and the resistivity ρ at 300 K were measured at each characterized point. A theoretical model was developed that explains the observed first growth of α with 〈ε〉 and the well-known high level of the normal-phase flicker noise in various high temperature superconducting compounds. Comparison of the experimental and simulated dependence of α on 〈ε〉, frequency, and temperature permits one to determine numerically the theoretical parameters of the double-well potential with minima located at the chain (O1) and empty (O5) oxygen lattice positions of the CuO plane.
Nonlinear microwave properties of Nb3Sn sputtered superconducting films
Authors: Andreone A. , Cassinese A. , Di Chiara A. , Iavarone M. , Palomba F. , Ruosi A. , Vaglio R.
Published: July 2002

We report on microwave measurements of the surface impedance Zs=Rs+iXs of Nb3Sn superconducting films deposited by planar magnetron sputtering on sapphire substrates. The samples show the A15 structure with maximum Tc(R=0) of 17.4 K and residual resistivity ratios up to β≈3. The measurements are performed by a microstrip resonator technique using a meander line geometry. The power dependence of Zs is studied at different temperatures and frequencies in the range of 1–10 GHz using the fundamental and higher order modes of the resonator. The effect of a dc magnetic field applied with different orientations is also studied. The data are analyzed in the context of a simple model able to describe most of the reported loss mechanisms.
Surface hardening of Al by high current Fe-ion implantation
Authors: Gao K. Y. , Liu B. X.
Published: July 2002

Surface modification of Al was studied by high current Fe-ion implantation using a metal vapor vacuum arc ion source. In the implantation process, two parameters were adjusted, that is, current density and ion dose, corresponding to varying the temperature and time for growing surface Fe-aluminide compound. The major hardening phase was identified to be Al13Fe4 and its depth profile was found to depend on the current density and dose. At a fixed dose of 3×1017 Fe/cm2, implanting with a low current density from 25 to 51 μA/cm2, the Al13Fe4 compound penetrated into a depth between 2500 and 4000 Å. Whereas implanting with a high current density up to 101 μA/cm2, the Al13Fe4 compound not only be situated in a 1000 Å surface layer, but also extended into a deep region when the dose was increased to 1×1018 Fe/cm2. Another dual implantation was conducted with two different current densities and it resulted in a modified region of 4500 Å thick with a high concentrated Al13Fe4 compound in a 1000 Å surface layer. Accordingly, the microhardness of the implantation treated Al films was considerably increased. The formation of the hardening phase of Al13Fe4 compound was responsible for the improvement of the surface mechanical property and was discussed in terms of temperature rise, irradiation time, and radiation-enhanced diffusion in the process of implantation.
Compensation implants in 6H–SiC
Authors: Edwards Andrew , Dwight Deborah N. , Rao Mulpuri V. , Ridgway M. C. , Kelner G. , Papanicolaou N.
Published: July 2002

In this work, we have performed Si and C isoelectronic implantations in n-type and vanadium (V) implantations in p-type 6H–SiC to obtain highly resistive regions. The compensation is achieved by the lattice damage created by the Si and C implantations and the chemically active nature of the V implant. For the Si and C implantations, the as-implanted resistivity initially increased with increasing implant fluence due to the introduction of compensating levels caused by the lattice damage, then decreased at higher fluences due to hopping conduction of the trapped carriers. The resistivity of the Si and C implanted material has been measured after isochronal heat treatments over the temperature range of 400–1000 °C. The maximum resistivity values measured for Si and C implanted and heat treated material were ∼1012 Ω cm. For the 700 °C V implantation in p-type SiC, resistivities of >1012 Ω cm were measured after 1500 or 1600 °C annealing to activate the V implant. Redistribution of the V implant is observed after annealing.
Dependence of carbon incorporation on crystallographic orientation of GaAs and AlGaAs grown by metalorganic chemical vapor deposition using CBr4
Authors: Son Chang-Sik , Kim Seong-Il , Kim Yong , Park Young K. , Kim Eun Kyu , Min Suk-Ki , Choi In-Hoon
Published: July 2002

The electrical properties of CBr4-doped GaAs and Al0.3 Ga0.7As epilayers grown on GaAs substrates with various surface crystallographic orientations from (100) toward (111)A were investigated. Carbon incorporation into GaAs and AlGaAs epilayers was performed by atmospheric pressure metalorganic chemical vapor deposition using CBr4. The electrical properties of the epilayers showed a strong crystallographic orientation dependence. With an increase of the surface offset angle, the hole concentration of CBr4-doped GaAs and AlGaAs epilayers rapidly decreased showing a hump at (311)A. The trend of the hole concentration dependence on the offset angle was not changed with growth temperatures in the range of 550–650 °C. Carbon incorporation is much higher in AlGaAs than in GaAs.
Electron emission from a laser ablated and laser annealed BN thin film emitter
Authors: Busta H. H. , Pryor R. W.
Published: July 2002

Electron emission from a ∼100-nm-thick, laser ablated and laser annealed, carbon-doped BN film deposited on polycrystalline diamond was measured at room temperature and at pressures of about 1×10−8 Torr. For a 500-μm-diam extraction electrode, currents of several mA were obtained which corresponds to current densities of >1 A/cm2. At low currents, the current–voltage characteristics follow the classical Fowler–Nordheim behavior. At higher currents, deviations occur which are correlated to a nonlinear BN film resistance which ranges from 3×106 Ω to 5×104 Ω. For comparison, similar measurements were performed for the polycrystalline diamond film. Current densities of only 1 mA/cm2 were obtained which is attributed to a much higher sample resistance of about 1×109 Ω.