bluuebunny/crossref_metadata_2025 huggingface dataset:
Si delta-doped layers of GaAs by low pressure metalorganic vapor phase epitaxy
Authors: Li G. , Jagadish C. , Clark A. , Larsen C. A. , Hauser N.
Published: July 2002

Si delta-doped layers of GaAs were grown by low pressure metal organic vapor phase epitaxy (LP-MOVPE). The results showed that, in LP-MOVPE, growth rate plays a crucial role in confinement of dopants and growth temperature has only a secondary effect. Effects of purge time, doping temperature, and doping period on sheet carrier concentration of delta-doped layers were studied. The effect of growth rate on confinement of dopants was discussed.
Microwave properties of high-T
c Y1Ba2Cu3Oy superconducting bridges on Y2BaCuO5 substrates
Authors: Lee Kiejin , Park Gwangseo , Amatuni L. E. , Constantinian K. Y.
Published: July 2002

The microwave properties of high-Tc Y1Ba2Cu3Oy bridges have been measured at the frequency f=22 GHz at 4.2 K by means of a high sensitive radiometric probe method. The results, explained by the coherent hypervortex motion, show discontinuities in current-voltage characteristics, harmonic and subharmonic voltage steps under the external microwaves, and self-radiation peaks corresponding to the moving frequencies of hypervortices across the bridge.
Grain-growth process during crystallization of Fe80B20 amorphous alloys
Authors: Malizia F. , Ronconi F.
Published: July 2002

It is shown that the full isothermal crystallization analysis of Fe80B20 amorphous alloy must include not only a crystal nucleation-and-growth process but also a grain-growth process and that these two processes are separated in time during isothermal annealing. The parameters characterizing the grain-growth process have been found by the fitting calorimetrical signal with the one expected from the normal grain-growth theory. Transmission electron microscopy and selected area electron diffraction seem to confirm our results since they show that there is a good agreement between the average grain radius of crystallization products seen in the micrograph and the one calculated from the obtained parameters.
A theoretical investigation on the quantum field effect directional coupler
Authors: Xu Guangzhao , Yang Min , Jiang Ping
Published: July 2002

A theoretical investigation on the quantum field effect directional coupler is presented. The behavior of electrons in the device is studied by solving the Schrödinger equation directly. The complete transfer effect is revealed to be an intrinsic property of the parity symmetry of the system. Transfer length is precisely calculated by using the transfer matrix method. Two model transverse confinements have been used in the calculation. One is a symmetric double rectangular well; and the other is a symmetric double finite-parabolic potential. Conductance of the device is investigated by applying the Landauer formula. Conductance oscillations with Fermi energy and barrier height are obtained. One method of determining the transfer length from the curve of conductance vs barrier height is proposed. Special attention is paid to the multimodedness of the device. Correlation among the different modes is demonstrated to reduce the transfer effect of the device. Reflection at the interfaces between uncoupled and coupled waveguides is proved to be negligible.
Electrical activation of boron coimplanted with carbon in a silicon substrate
Authors: de Souza J. P. , Boudinov H.
Published: July 2002

It is demonstrated that the electrical activation in B+ (5.0×1014 cm−2 at 50 keV) implanted Si samples submitted to furnace annealing can be noticeably affected by a C+ coimplantation. It was found that a C+ dose ten times lower than that of B+ is not sufficient to influence the activation behavior of B. However, C+ implanted to a dose equal to or ten times higher than the B+ dose contributed, respectively, to the reduction or enhancement of the electrical activation of B after annealing in the temperature range of 450–700 °C. In addition, the reverse annealing of B is attenuated in the coimplanted samples and suppressed in samples where the C+ implantation damage was annealed prior to the B+ implantation. At temperatures ≳700 °C the electrical activation is not significantly affected by the C+ coimplantation. A model considering interaction between C and Si self-interstitial atoms during thermal annealing is proposed to account for the activation behavior of B in the dually implanted samples.
Characteristic length and time in electromigration
Authors: Shatzkes Morris , Huang Yusue
Published: July 2002

A characteristic length can be defined as the distance a vacancy moves under an electromigration force to do thermal work KT. The times for a vacancy to drift and diffuse this characteristic length are equal and thus define a characteristic time. The diffusion coefficient and the drift velocity are unity when these characteristic values are used as units of length and time. Therefore, when these units are used in the absence of vacancy sources and sinks, the vacancy continuity equation contains no parameters. These considerations are used to estimate the length current density threshold, the electromigration failure times, the edge-displacement velocity, and the incubation time. These estimates are consistent with published experimental results.
Magnetic exchange coupling for bilayered Ni81Fe19/NiO and trilayered Ni81Fe19/NiFeNb/NiO films
Authors: Soeya Susumu , Tadokoro Shigeru , Imagawa Takao , Fuyama Moriaki , Narishige Shinji
Published: July 2002

Exchange coupling between a ferromagnetic film and an antiferromagnetic NiO film was investigated. Bilayered ferromagnetic Ni81Fe19/antiferromagnetic NiO films had a large exchange coupling field and blocking temperature of about 200 °C. In trilayered Ni81Fe19/ferromagnetic (Ni81Fe19)100−xNbx/NiO films, a way could be developed to control the exchange coupling field at a small value by increasing the Nb of the intermediate film. The most important factor in the control seemed to be that the numbers of magnetic Fe and Ni atoms of (Ni81Fe19)100−xNbx, which contributed to the exchange coupling between (Ni81Fe19)100−xNbx and NiO, varied with the existence of nonmagnetic Nb at their interface. From experimental results with other trilayered Ni81Fe19/ferromagnetic (Ni100−xFex)93Nb7/NiO films, it was ascertained that the exchange coupling field seemed to be independent of the magnetic moment of the ferromagnetic film although unidirectional anisotropy constant was proportional to it. As for blocking temperature, it did not seem to be determined by the magnetism of the ferromagnetic material but the magnetism of the antiferromagnetic material.
The Hall effect in β-FeSi2 single crystals
Authors: Arushanov E. , Kloc Ch. , Hohl H. , Bucher E.
Published: July 2002

The results of the transport and magnetization measurements on β-FeSi2 single crystals are presented. The magnetic field dependence of the Hall coefficient in n-type β-FeSi2 was observed in the temperature range of 30–300 K and explained in the limits of a two-band model. The magnetization measurements were performed within the range 4.2–300 K. It was shown that the contribution of the anomalous Hall effect to the total Hall voltage is negligible. Parameters of charge carriers, taking part in conductivity were calculated and the separation between the bands was estimated.
Thermodynamic model of the compaction of powder materials by shock waves
Authors: Dijken D. K. , De Hosson J. Th. M.
Published: July 2002

For powder materials a model is proposed to predict the mean temperature behind the shock wave, the ratio between the increase of thermal energy and increase of total internal energy, as well as the mean final temperature after release of adiabatic pressure. Further, the change of pressure, specific volume, and the internal energy behind the shock wave are calculated together with the shock-wave velocity. All these variables are supposed to depend exclusively on flyer plate velocity, initial powder density, and initial powder temperature. The ratio between the increase of thermal energy and increase of total internal energy decreases rapidly upon decreasing initial powder density, resulting in a higher shock temperature and a lower shock pressure; therefore, a lower initial powder density results in a better bonding between the particles and fewer cracks after pressure release. Calculations are carried out for copper and agree fairly well with experiments.
Hall effect and impurity levels in lead doped indium selenide
Authors: Micocci G. , Tepore A. , Rella R. , Siciliano P.
Published: July 2002

Hall effect and deep hole level studies in indium selenide single crystal doped with lead are reported. The temperature dependence of the hole mobility can be interpreted by combining the homopolar optical phonon and the ionized impurity scatterings. Electrical properties above 180 K are dominated by an acceptor center at 0.48 eV from the valence band. Moreover, two hole traps of 0.49 and 0.63 eV depths have been evidenced by deep-level transient spectroscopy measurements. These centers are probably associated with defects or defect complexes due to lead atoms precipitated in the interlayers of the crystal.
Properties of Ca1−xSrxCuO2 infinite layer films grown by laser ablation deposition
Authors: Ma Q. Y. , Dosanjh P. , Entin I. , Liang R. , Carolan J. F. , Hardy W. N.
Published: July 2002

Films of the infinite layer compound Ca1−xSrxCuO2 have been grown on SrTiO3 substrates by pulsed laser ablation deposition. The properties of the films depend strongly on the processing temperature. Between 650–700 °C the films are epitaxial with the c axis oriented normal to the surface of the substrates. The surfaces of the films are smooth, as indicated by scanning electron microscopy. Films processed at temperatures above 740 or below 600 °C are polycrystalline. X-ray diffraction patterns show that the c-axis lattice constant varies from 3.23 Å for x=0.10, to 3.39 for x=0.66 and 3.43 Å for x=0.90. Electrical measurements show the films to have a semiconducting behavior; no diamagnetic transition was observed in these films.
Electron mobility in Hg0.78Cd0.22Te alloy
Authors: Krishnamurthy Srinivasan , Sher Arden
Published: July 2002

The electron mobility in Hg0.78Cd0.22Te is calculated by solving the Boltzmann transport equation with Fermi–Dirac statistics and a full band structure. The calculated values are in excellent agreement with experiments, and effects of various traditional approximations are discussed.
Structure and photoluminescence of AlP/GaP short-period superlattices grown by organometallic vapor phase epitaxy
Authors: Wang Xue-Lun , Wakahara Akihiro , Sasaki Akio
Published: July 2002

Short-period superlattices of (AlP)m/(GaP)n (m, n=4–11.5) are grown by atmospheric pressure organometallic vapor phase epitaxy using tertiarybutylphosphine as a phosphorus source. Structural and optical properties of the grown superlattices are characterized by double-crystal x-ray diffraction and photoluminescence (PL) measurements, respectively. By comparing the measured and the calculated full width at half-maximum of satellite peaks, we find that very high quality superlattices with atomically abrupt heterointerfaces are achieved. Strong emission of bound exciton is observed at low temperature. The exciton emission, however, disappears quickly as the temperature is increased, and only PL lines due to impurity recombination remain at high temperature (≳30 K). No evident phonon replica is observed in the PL spectra. From these results, a direct band-gap structure seems to be realized as expected from the zone-folding effect. However, the absence of band-to-band direct transition at high temperature suggests that the direct transition probability between the zone-folded conduction band and the valence band is not so large.
Infrared spectroscopy and secondary ion mass spectrometry of luminescent, nonluminescent, and metal quenched porous silicon
Authors: Hilliard J. , Andsager D. , Abu Hassan L. , Nayfeh Hasan M. , Nayfeh M. H.
Published: July 2002

Porous silicon with varying optical properties (luminescent, nonluminescent, and metal quenched) is investigated by transmission infrared (IR) spectroscopy and secondary ion mass spectrometry (SIMS). SIMS and transmission IR data are presented which show a lack of correlation between the optical properties of similarly prepared luminescent and nonluminescent porous silicon samples and the concentrations of the chemical elements and bonds detected therein. Similar results are obtained for a comparison of IR spectra before and after dissolving the topmost layers (∼2000 Å) of a luminescent sample in a KOH solution, exposing the nonluminescent porous material below. Finally, IR and SIMS results for luminescent porous silicon quenched by metal ion solutions show a large increase in oxygen after quenching, but it is argued that the increased oxygen is unlikely to be directly responsible for the quenching of luminescence.
Estimation of direct current bias and drift of Ti:LiNbO3 optical modulators
Authors: Nagata Hirotoshi , Kiuchi Kazumasa , Shimotsu Shinichi , Ogiwara Junichi , Minowa Junichiro
Published: July 2002

The dc drift data of Ti:LiNbO3 optical modulators are well fitted to an exponential equation, describing the relaxation phenomena of the dielectric materials. The relaxation time and the saturation voltage ratio, which are necessary to estimate the dc bias follow-up control, can be obtained from simple dc drift measurements.
Analytic model for the grain structures of near-bamboo interconnects
Authors: Joo Young-Chang , Thompson Carl V.
Published: July 2002

Scaling of electromigration test results for near-bamboo interconnects from accelerated test conditions to service conditions requires an understanding of the microstructural characteristics of the interconnects. An analytic model has been developed that allows prediction of the average polygranular cluster lengths and the number of clusters in a line, given the linewidth, the line length, and the characteristics of the grain size distribution of the original film. Grain-structure characteristics have also been measured for lines patterned from computer-generated thin-film microstructures. The large-cluster-length tail of the polygranular cluster-length distribution is well fit by an exponential distribution function, which can be accurately predicted using our new analytic model. Polycrystalline clusters shorter than a critical length Lcr cannot fail due to electromigration-induced grain-boundary diffusion alone, so that when all clusters in a line are shorter than Lcr, there is a transition in failure mechanisms. The model can be used to calculate the number of clusters longer than Lcr as a function of the line and grain-structure characteristics, as well as a function of the current density. The current-density dependence of the median time to failure due to polygranular failure mechanisms in near-bamboo lines, as well as the transition current density at which the transition in failure mechanisms occurs are predicted. This transition current density depends on the linewidth and the line length, as well as the grain size and grain size distribution of the film from which the line was patterned.
Constriction of the polarization by incoherent oxygen octahedral tilting in rhombohedral-structured lead zirconate titanate
Authors: Dai Xunhu , Xu Z. , Li Jie-Fang , Viehland Dwight
Published: July 2002

Double hysteresis loops have been observed in ferroelectric lead zirconate titanate ceramics with a Zr/Ti ratio of 65/35 (PZT 65/35). In addition, dielectric dispersion was found near 50 °C, corresponding to the high-temperature to low-temperature rhombohedral ferroelectric [FER(HT)-FER(LT)] transformation. Structurally this transformation is an oxygen octahedra tilting along the 〈111〉. It is proposed that an inability of the oxygen octahedra to coherently rotate within a rigid lattice generates random internal stresses which constrain the polarization. Small amounts of impurities on either the A site (La) or B site (Nb) were found to result in normal square-loop hysteresis behavior. It is believed that aliovalent impurities relax the lattice, resulting in increased coherent of the 〈111〉 oxygen rotations. Electron diffraction studies revealed a strong increase of the reflection intensity of 1/2〈111〉 superlattice spots after doping, supporting this possibility. In addition, thermal expansion measurements revealed a lattice contraction after La-modification, possibly reflecting enhanced octahedral tilting.
Field enhancement of the photoelectric and secondary electron emission from CsI
Authors: Buzulutskov A. , Breskin A. , Chechik R.
Published: July 2002

We have measured the electron emission from a CsI-coated multiwire cathode, induced by ultraviolet photons and electrons, in vacuum at high electric fields. We found an enhancement in quantum efficiency of a factor of 1.5 at 160 nm, 3 at 185 nm, and 25 above 200 nm, at a field of 500 kV/cm. At the short wavelengths the amplitude of the effect is a linear function of the square root of the field strength. The enhancement of the electron-induced secondary electron emission yield is dependent on the primary electron energy: for energies above 1 keV it varies by a factor of 2 to 10. A simple model of the field enhancement of the photoemission is suggested. Practical applications are discussed.
Investigation of thermomagnetic recording on MnBiAl films and observation of their recorded domains
Authors: Xu Y. , Zhang X. W. , Zhu W. K. , Yang H. S. , Wang Y. J.
Published: July 2002

Static thermomagnetic recording on MnBiAl films at 633 nm is reported. The intrinsic Kerr rotation of the sample investigated is 1.8° at 633 nm. A 14 mW pulsed laser was used to write stable domains with diameter of 1.2 μm under zero external applied magnetic field, and a 12 mW pulsed laser was utilized to erase the recorded domains using an external field 600 Oe. The direct observation of the homogeneously recorded domain arrays of 16×22 points on an area of approximately 0.01 mm2 shows that they possess a very good circular configuration, distinct margin, and a very high contrast between ‘‘0’’, ‘‘1’’ states due to large Kerr rotation θk and coercivity Hc. The number of write/erase cycles on MnBiAl is over 106 times, which is a significant improvement over the 103 times possible with MnBi. Measurements demonstrate that MnBiAl film is a promising magneto-optical recording medium.
Selective excitation of an associate donor-acceptor pair complex in iodine-doped CdTe
Authors: Lee Jaesun , Giles N. C. , Summers C. J.
Published: July 2002

Luminescence at 1.491 eV was detected at liquid-helium temperatures from CdTe epilayers heavily doped with iodine. The relatively sharp emission band (FWHM=4.4 meV) was observed under both above-band-gap and below-band-gap excitation. The intensity of the 1.491 eV emission was highly dependent on sample temperature and could only be detected below 45 K. Using the tunable output from a titanium:sapphire laser, selective excitation of this emission was performed to identify the recombination center. A localized mode of 36.5 meV, much larger than the 21.3 meV bulk CdTe mode, is associated with the defect center. We identify the defect as an associate donor-acceptor pair complex resulting from nearest neighbor cation (NaCd) and anion (ITe) point defects. The energy level associated with the (Na−Cd-I+Te) neutral associate pair is approximately 0.115 eV below the CdTe conduction band.
Electronic structures of Si1−xCx and Si1−x−yCxGey alloys
Authors: Xie Jianjun , Zhang Kaiming , Xie Xide
Published: July 2002

The linear-muffin-tin-orbital method with the atomic-sphere approximation is used to study the electronic structures of Si1−xCx and Si1−x−yCxGey alloys. The dependence of minimum band gap Eg, electronic density of states, and valence-band width on alloy composition is investigated. All inequivalent atomic configurations for each given alloy composition are considered. It is found that the electronic structures of Si1−xCx and Si1−x−yCxGey show an unexpected variation of band gap versus the carbon concentration: For small to moderate concentrations of C in Si1−xCx and Si1−x−0.125CxGe0.125, the band gap decreases from that of pure Si. The lattice relaxation does not change such character of Eg. The peak positions in density of states shift downward as the carbon concentration in Si1−xCx and Si1−x−0.125CxGe0.125 increases; meanwhile, the valence band is monotonically widened.
Spectroscopic characteristics of Pb0.95La0.05(Zr1−yTiy)0.9875O3 plasma and growth behavior of thin films by pulsed laser deposition
Authors: Cheng Hsiu-Fung
Published: July 2002

The characteristics of the spectra emitted from the species ejected by excimer laser were systematically analyzed using optical emission spectroscopy and Boltzmann plot approach. These characteristics were correlated with the growth behavior of Pb0.95La0.05(Zr1−yTiy)0.9875O3 films with y=1(PLT), or y=0.3(PLZT), synthesized by pulsed laser deposition technique. The increase in laser energy density moderately enhances the intensity of the spectral lines and insignificantly modifies the plasma temperature (Tp) of the Ti-species in the plume. The increase in oxygen pressure PO2, on the other hand, only slightly reduces the intensity of the spectral lines but tremendously lowers the Tp-values of the Ti-species. The plasma temperature is around TPLZTp=20 300 K and TPLTp=12 500 K for PO2<0.01 mbar and abruptly decreases to around TPLZTp=13 300 K and TPLTp=8000 K for PO2=0.1 mbar or 1 mbar. High plasma temperature of the PLZT plume, as compared with that of the PLT plume, is presumably the source which induces the formation of secondary phase in the PLZT films.
Reaction kinetics in synchrotron-radiation-excited Si epitaxy with disilane. II. Photochemical-vapor deposition
Authors: Akazawa Housei , Utsumi Yuichi
Published: July 2002

When a Si substrate in ambient disilane (Si2H6) is irradiated with synchrotron radiation (SR), three distinct species are excited simultaneously: irreversibly chemisorbed surface hydride, disilane gas, and disilane weakly trapped on the surface. The species-specific growth pathways in the SR-excited chemical-vapor deposition (SR-CVD) were investigated to clarify the reaction kinetics. Growth at pressure less than 10−5 Torr is due predominantly to the regeneration of new chemisorption sites by stimulated hydrogen desorption. With increasing pressure, the role of gas-phase photolysis becomes important. In the nonirradiated region, Eley–Rideal-type reactions of the decomposition products with the surface hydrides deposit Si adlayers in a layer-by-layer fashion. In the irradiated region, however, growth resulting from multilayer photolysis of weakly trapped disilane produces a hydrogenated Si network layer on the surface, and the layer converts to a uniform and epitaxial Si film.
Micron-scale thermal characterizations of interfaces parallel or perpendicular to the surface
Authors: Lepoutre F. , Balageas D. , Forge Ph. , Hirschi S. , Joulaud J. L. , Rochais D. , Chen F. C.
Published: July 2002

Theoretical and experimental possibilities are presented of a modulated photothermal method, laser-induced photoreflectance, for inspecting thermal diffusivities and quality of interfaces in composite materials with micron-scale spatial resolutions. The models are established for semi-infinite materials containing interfaces parallel or perpendicular to the sample surface. The applications concern thermal diffusivity measurements of anisotropic polycrystals and detection of thermal resistance in damaged materials and at interfaces between reinforcements and matrix in composites.
High-resolution x-ray diffractometry of ZnTe layers at elevated temperatures
Authors: Bochníček Z. , Holý V. , Wolf K. , Stanzl H. , Gebhardt W.
Published: July 2002

A high-temperature multicrystal x-ray diffractometer is used for measurement of elastic constants c11, c12 and the thermal-expansion coefficient of a heteroepitaxial ZnTe layer grown on a (001) oriented GaAs substrate. In addition to the standard double-crystal measurement, a new triple-crystal method is proposed. This method eliminates the angular instabilities of the high-temperature goniometer and bending of the substrate. The new method was used for determination of the thermal-expansion coefficient of a GaAs substrate. As a result of detailed discussion, the optimal experimental conditions are proposed for the limitation of the errors.
Visible photoluminescence from hydrogenated silicon particles suspended in a silane plasma
Authors: Courteille C. , Dorier J.-L. , Dutta J. , Hollenstein Ch. , Howling A. A. , Stoto T.
Published: July 2002

Visible photoluminescence at room temperature has been observed in amorphous hydrogenated silicon particulates during their formation in a silane radio-frequency plasma. Oxygen injection along with mass spectrometry measurements demonstrate that oxygen has no influence on the photoluminescence. The appearance of visible photoluminescence coincides with a particle agglomeration phase as shown by laser light scattering experiments, and electron microscopy shows silicon nanocrystals within these particulates. These observations of visible photoluminescence are consistent with the model of quantum confinement in the silicon nanocrystals.
Epitaxial growth and magnetoresistance of La1−xCaxMnO3−δ thin films on MgO(001) substrates
Authors: Gu J. Y. , Kim K. H. , Noh T. W. , Suh K.-S.
Published: July 2002

Perovskite La1−xCaxMnO3−δ thin films were deposited on MgO(001) substrates using pulsed laser deposition. Effects of deposition conditions, such as laser fluence, substrate temperature, and oxygen pressure, on growth behaviors of the films were investigated over a wide range. Epitaxial La0.7Ca0.3MnO3−δ /MgO thin films were able to be grown in situ under conditions such as 1.5–2.1 J/cm2 laser fluence, 650–750 °C substrate temperature, and 100–300 mTorr oxygen pressure. The oxygen pressure during the deposition is found to be closely related to crystalline orientations of the films. Rutherford backscattering spectroscopy measurements show that the epitaxial La1−xCaxMnO3−δ thin films have compositions similar to those of targets, demonstrating that pulsed laser deposition is a useful technique to get thin films with complicated chemical compositions. The magnetoresistance, −ΔR(6T)/R(0), of the La0.7Ca0.3MnO3−δ /MgO thin film was about −80%, which is smaller than the reported values (i.e., ∼−99.92%) of the La–Ca–Mn–O thin films on LaAlO3 substrates [S. Jin, T. H. Tiefel, M. McCormack, R. A. Fastnacht, R. Ramesh, and L. H. Chen, Science 264, 413 (1994)].
Electron-paramagnetic-resonance study of the Mn2+ luminescence center in ZnS:Mn powder and thin films
Authors: Yeom T. H. , Lee Y. H. , Hahn T. S. , Oh M. H. , Choh S. H.
Published: July 2002

The number of isolated Mn2+ ions and Mn2+ clusters in ZnS:Mn powder and thin films has been studied using Mn2+ spectra measured at room temperature with an X-band electron-paramagnetic-resonance spectrometer. While the concentration of the isolated Mn2+ ions decreases with increasing Mn concentration, the concentration of the clusters increases. At low Mn concentration, the Mn2+ ion substitutes for the Zn ion in ZnS:Mn in the cubic phase. At high Mn concentrations, where the ZnS powder has a dominant hexagonal phase, the Mn ion still prefers to substitute for Zn in ZnS:Mn at the cubic site rather than at the hexagonal site.
Nitrogen acceptors confined in CdZnTe quantum well structures
Authors: Zhao Q. X. , Baron T. , Saminadayar K. , Magnea N.
Published: July 2002

Nitrogen acceptors confined in a CdZnTe single quantum well, grown by molecular beam epitaxy, are investigated by different optical methods. The transitions related to nitrogen acceptors confined in the well are observed in the doping range between 1017 and 1018/cm3. The temperature and excitation intensity dependence of the nitrogen-related transitions in photoluminescence spectra indicates that these transitions correspond to the nitrogen acceptor bound excitons and to free electron to neutral nitrogen acceptor recombination. The binding energy of nitrogen acceptors confined in an 130-Å-wide Cd0.96Zn0.04Te/Cd0.86Zn0.12Te structure is deduced to be 51.7±0.5 meV from this study.
Interface characterization in electrodeposited Cu–Co multilayers
Authors: Nallet P. , Chassaing E. , Walls M. G. , Hÿtch M. J.
Published: July 2002

Multilayers of Cu–Co made by electrodeposition are characterized. The interface width and layer roughness are measured by the Fresnel technique in electron microscopy. It is shown that the quality of the interfaces is comparable to that of layers made by physical deposition techniques. By depositing the layers on a glass substrate, we also show that it is possible to measure the magnetoresistance of the multilayers without removing the substrate. The values obtained are discussed in relation to the roughness of the layers and the electrodeposition conditions.
Giant magnetoresistance in granular Fe–MgF2 films
Authors: Furubayashi T. , Nakatani I.
Published: July 2002

The giant magnetoresistance effect observed in granular Fe–MgF2 films, which consist of metallic particles embedded in an insulating medium, is reported. Large negative magnetoresistance (MR) with a magnitude up to 7.5% at 78 K was observed in semiconducting films with the Fe composition below the percolation threshold. Field dependence of the MR is well described by the form proportional to the square of the magnetization. The MR effect in this system seems to arise from the tunneling conductance between the Fe particles depending on the relative relation of the magnetization direction.
Barkhausen jumps during domain wall motion in thin magneto-optical films
Authors: Gadetsky S. , Mansuripur M.
Published: July 2002

A method with high spatial resolution is developed to study wall motion in thin magnetic films with perpendicular anisotropy. Barkhausen jumps during domain wall motion in amorphous TbFeCo films and polycrystalline Co/Pd multilayer films have been observed. The average distance between strong pinning sites in Co/Pd was found to be around 0.3–0.4 μm. Maximum pinning times as long as several seconds were observed. Magnitudes of major jumps in TbFeCo were around 0.7 μm.
Kinetics of oxidation on hydrogen-terminated Si(100) and (111) surfaces stored in air
Authors: Miura Taka-aki , Niwano Michio , Shoji Daisei , Miyamoto Nobuo
Published: July 2002

We have investigated the oxidation of hydrogen-terminated Si(111) and (100) surfaces stored in air, using synchrotron radiation photoemission spectroscopy and infrared absorption spectroscopy in the multiple internal reflection geometry. We demonstrate that water present in air is predominantly involved in the oxidation of surface Si–H bonds, and that native oxide starts to grow when the surface hydrogen coverage is decreased. In order to explain the latter phenomenon, we propose a kinetic model of oxidation which considers the manner in which native oxide formation preferentially occurs on those portions of the surface where the Si–H bonds are oxidized. We suggest that the oxidation of surface Si–H bonds, the rate of which is strongly dependent on the humidity of air, is a rate-limiting step in the native oxide formation on hydrogen-terminated Si surfaces.
Preparation of crystallized zinc oxide films on amorphous glass substrates by pulsed laser deposition
Authors: Hayamizu Shunichi , Tabata Hitoshi , Tanaka Hidekazu , Kawai Tomoji
Published: July 2002

Zinc oxide (ZnO) films with c-axis orientation have been prepared on glass substrates by pulsed laser deposition with an ArF excimer laser. The fluctuations of c-axis orientation of the ZnO films are evaluated by full width at half-maximum (FWHM) of the rocking curve of the x-ray diffraction. The ZnO films with a FWHM of 1.9° can be obtained on the optimum conditions (substrate temperature of 500–600 °C, O2 gas pressure of 2–6×10−4 Torr) even at a thickness of 200 nm. We have observed the crystallization of the ZnO during film formation by using in situ reflection high energy electron diffraction. It is confirmed that ZnO thin films with a thickness of up to about 50 nm have c-axis orientation on the glass substrates.
Spectral emissivities in the visible and infrared of liquid Zr, Ni, and nickel-based binary alloys
Authors: Krishnan Shankar , Nordine Paul C.
Published: July 2002

This article reports: (i) values of the spectral emissivities at λ=0.633 μm for liquid Zr, Ni, Ni–25% Sn, Ni–32.5% Sn, Ni–40% Nb, and Ni–75% Zr over a wide temperature range including undercooled and superheated conditions, (ii) experimentally determined infrared radiance temperatures (effective center wavelength about 2.0 μm) as functions of true temperature, and (iii) derived values of the spectral emissivity of these liquid materials in the infrared. Based on the thermal arrest, which occurs upon heating the solid at the melting point, we also report melting points for some of the alloys. For zirconium, temperature dependence of emissivity is reported at other wavelengths in the visible. For Ni–75% Zr, the emissivity dependence on wavelength was determined and compared with previously reported results for liquid zirconium and nickel. The spectral emissivity measurements were obtained using pulsed-dye laser ellipsometry on electromagnetically levitated liquid metals and the radiance temperatures of the specimens were recorded using three pyrometers. Two of these pyrometers had an operating wavelength near 650 nm. The third pyrometer had an operating wavelength range of 1–2.5 μm. Most of the materials studied exhibited moderate temperature dependence of the optical properties and emissivities. Only nickel and zirconium could be undercooled significantly in our apparatus. The infrared and 0.633 μm emissivities of the materials were consistent with the behavior of a typical metal showing emissivity variations with wavelength on the order of −0.07 μm−1.
Nonlinear response of quantum-confined electrons in nonparabolic subbands
Authors: Markelz A. G. , Gwinn E. G.
Published: July 2002

We show that quantum confinement can dramatically alter the density-dependence of the third-order susceptibility, χ(3)NP, that arises from band nonparabolicity. Our results predict an oscillatory dependence of the efficiencies for third-harmonic generation and four-wave mixing on the subband occupation of quantum wells, and for narrow wells with high charge densities predict an enhancement over the bulk susceptibility. We also make a simple estimate of the fields required to saturate this nonparabolicity contribution to χ(3). We discuss these results in light of recent experiments on third-harmonic generation from narrow-gap quantum wells at frequencies of ∼1 THz, and show that nonparabolicity may not be the only nonlinearity contributing to the large χ(3) observed.
Metastable chlorine ion temperature and drift velocity in an inductively coupled plasma
Authors: Hebner G. A.
Published: July 2002

Laser-induced fluorescence has been used to measure the temperature and radial drift velocity of metastable chlorine ions in inductively coupled Cl2 and Ar/Cl2 plasmas. In the center of the plasma, the Cl metastable ion temperature varied between 1500 and 3200 K for rf powers between 200 and 400 W and pressures between 7 and 30 mTorr. Increasing the chlorine fraction in an Ar/Cl2 gas mixture from 10% to 100% increased the Cl metastable ion temperature from approximately 1500 to 3200 K. Spatially resolved measurements of the ion temperature indicated that the ion temperature increased to between 4500 and 5500 K at the edge of the discharge and increased approximately 700 K moving from the rf source toward the lower electrode. Ion drift velocity in the radial direction was between 6×104 and 8×104 cm/s at the edge of the plasma. Implications of these measurements on the Ar/Cl2 chemistry and the energy transport in the plasma are discussed.
Misfit stress relaxation mechanism in CdTe(100) and CdTe/ZnTe(100) on a GaAs(100) highly mismatched heteroepitaxial layer
Authors: Nishino H. , Sugiyama I. , Nishijima Y.
Published: July 2002

We studied the misfit stress in CdTe(100)/GaAs(100). In general, this highly mismatched system initially forms a ‘‘coincidence interface,’’ where seven CdTe lattices match with eight GaAs lattices. In this system, the epilayer is elastically strained by the mismatch remaining between both groups of lattices. Afterward, the misfit stress is gradually relaxed with the generation of misfit dislocations. In this work, we derived a new model to describe this misfit relaxation mechanism and verified it with experimental observations. As introducing the effects of the interface modification, we found that the simple force balance between the substrate and epilayer governed the misfit stress. We assume that the relaxation process during growth is similar to that in CdTe/CdZnTe, since the residual misfit was fairly small. By extending the stress relaxation model of CdTe/GaAs, it is possible to explain the strain in CdTe/ZnTe/GaAs, which contains two highly mismatched interfaces. The threading dislocations in HgCdTe, derived from the CdTe buffer, decreased with increasing CdTe thickness. Assuming that the misfit dislocations are generated by bending threading dislocations, we could explain the dislocation reduction by utilizing the above misfit stress relaxation model. In spite of the extremely large mismatch, the structural quality of CdTe(100)/GaAs(100) was improved due to the relatively small strain remaining in the coincidence interface.
Formation of XeI(B) in low pressure inductive radio frequency electric discharges sustained in mixtures of Xe and I2
Authors: Barnes Paul N. , Kushner Mark J.
Published: July 2002

Low pressure excimer discharges (<1–5 Torr) are of interest for use as ultraviolet sources for lighting applications. XeI(B) is an attractive candidate for excimer lamps due to the low corrosive properties of iodine. The excimer is thought to be formed by either harpoon or ion-ion recombination reactions, the latter of which requires a third body. The formation of the excimer at low pressures is therefore problematic. To address this issue, an investigation was conducted to determine the kinetic processes which produce XeI(B) in a low pressure (0.5–5 Torr) inductive radio frequency discharge sustained in Xe and I2. The diagnostics applied in this study include laser-induced fluorescence, optical absorption spectroscopy, and optical emission spectroscopy. Our results indicate that for the experimental conditions, Xe+I2**→XeI(B)+I is a major reaction producing the excimer. This result differs from studies performed at higher pressures which concluded that the harpoon reaction between Xe* and I2 or ionic recombination between Xe+2 and I− are the major sources of XeI(B).
Effect of interposed Cr layer on the thermal stability of Cu/Ta/Si structure
Authors: Yoon Dong-Soo , Baik Hong Koo , Kang Byoung-Sun , Lee Sung-Man
Published: July 2002

The thermal stability of Cu/Ta/Cr/Si structure is analyzed and compared with that of Cu/Ta/Si and Cu/Ta/Cr/Ta/Si structures. The Cu/Ta/Si and Cu/Ta/Cr/Ta/Si systems retained their structures up to 600 °C without increase in resistivity but the Cu/Ta/Cr/Si structure was degraded after annealing at 400 °C. In the latter case, the degradation was dominated by the outdiffusion of free Si, probably released from the substrate in the formation of CrSi2. It is suggested that the released Si is reactive and its outdiffusion through Ta layer is facilitated by the high affinity of Si toward Ta, as expected from the large negative value of mixing enthalpy between Ta and Si.
Photodissolution and photoluminescence quenching of porous silicon in HF
Authors: Létant S. , Vial J. C.
Published: July 2002

A photodissolution process occurs when porous silicon samples, immersed in HF solutions, are continuously illuminated. In situ reflectivity measurements allow us to deduce the time evolution of: the optical index; the thickness of the porous layer; and the number of atoms dissolved per unit time, which is found to be proportional to the specific surface of the sample exposed to HF. We have also compared photoluminescence properties of porous samples dried and immersed in HF under continuous and pulsed UV excitations. Photoluminescence can be totally or partially quenched and lifetimes are at least two orders lowered in HF solutions. The relevant parameter of the quenching is again the specific surface of porous silicon in contact with the liquid, suggesting that photoluminescence quenching and photodissolution have the same origin.
Electron emission from ferroelectric/antiferroelectric cathodes excited by short high-voltage pulses
Authors: Benedek G. , Boscolo I. , Handerek J. , Riege H.
Published: July 2002

Un-prepoled lead zirconate titanate lanthanum doped-PLZT ferroelectric cathodes have emitted intense current pulses under the action of a high voltage pulse of typically 8 kV/cm for PLZT of 8/65/35 composition and 25 kV/cm for PLZT of 4/95/5 composition. In the experiments described in this paper, the exciting electric field applied to the sample is directed from the rear surface towards the emitting surface. The resulting emission is due to an initial field emission from the metal of the grid deposited over the emitting surface with the consequent plasma formation and the switching of ferroelectric domains. These electrons may be emitted directly form the crystal or from the plasma. This emission requires the material in ferroelectric phase. In fact, PLZT cathodes of the 8/65/35 type, that is with high titanium content, showing ferroelectric-paraelectric phase sequence, emit at room temperature, while PLZT cathodes of the 4/95/5 type, with low titanium content, having antiferro-ferro-paraelectric phase sequence, emit strongly at a temperature higher than 130°C.
The effect of boron implant energy on transient enhanced diffusion in silicon
Authors: Liu J. , Krishnamoorthy V. , Gossman H.-J. , Rubin L. , Law M. E. , Jones K. S.
Published: July 2002

Transient enhanced diffusion (TED) of boron in silica after low energy boron implantation and annealing was investigated using boron-doping superlattices (DSLs) grown by low temperature molecular beam epitaxy. Boron ions were implanted at 5, 10, 20, and 40 keV at a constant dose of 2×1014/cm2. Subsequent annealing was performed at 750 °C for times of 3 min, 15 min, and 2 h in a nitrogen ambient. The broadening of the boron spikes was measured by secondary ion mass spectroscopy and simulated. Boron diffusivity enhancement was quantified as a function of implant energy. Transmission electron microscopy results show that 〈311〉 defects are only seen for implant energies ⩾10 keV at this dose and that the density increases with energy. DSL studies indicate the point defect concentration in the background decays much slower when 〈311〉 defects are present. These results imply there are at least two sources of TED for boron implants (B-I): short time component that decays rapidly consistent with nonvisible B-I pairs and a longer time component consistent with interstitial release from the 〈311〉 defects.
Spatial distributions of electron temperature and density in electron cyclotron resonance discharges
Authors: Cronrath W. , Bowden M. D. , Uchino K. , Muraoka K. , Muta H. , Yoshida M.
Published: July 2002

Spatial profiles of electron density and temperature of electron cyclotron resonance discharge plasmas have been successfully measured using laser Thomson scattering. The results, thus obtained, were valuable for quantitative comparison with results of a computer simulation. Measurements were performed for two cases with different locations of the electron cyclotron resonance zones. Simulation results obtained from a hybrid code, which treats ions and neutral particles as discrete particles and electrons as a fluid, were fitted to the experimental profiles of the electron density and temperature by adjusting the microwave power deposition profiles. From these comparisons and an analysis of other simulation data, it was found that the large difference of radial electron density profiles for two discharge conditions was caused by the difference of radial space-charge electric-field distributions. The radial electron temperature distribution determined the radial electric field that drove the ions radially and also resulted in a peaked electron density profile for one case and a more uniform profile for the other case. It is also shown that Coulomb collisions of electrons with ions as well as electron–neutral collisions are important for the analysis of electron behavior along the magnetic field lines.
Control of the II–VI/GaAs interface reaction using hydrogen radical and Zn/As fluxes
Authors: Taike A. , Kawata M. , Kikawa T. , Momose M. , Gotoh J. , Nakatsuka S.
Published: July 2002

The lifetime of II–VI-based blue-green laser diodes on GaAs substrates is limited by rapid degradation in the active layers. This degradation has been observed as dark defects in the active layer during the laser operation, where defects occurred due to stacking faults that originated from the Ga2Se3 compounds at the ZnSe/GaAs interface. The reported value of the density of stacking faults of the II–VI lasers was in the order of 105 cm−2. To extend the lifetime, surface treatment of the GaAs substrate and control of the interface reaction are necessary. We investigated a new treatment technique using hydrogen-radical and Zn/As fluxes. We fabricated ZnSe-based double-hetero (DH) structures on a treated GaAs substrate and measured the density of dark defects in the light emitter area by electroluminescence microscopy. Chemical bonds at the interface were evaluated by x-ray photoelectron spectroscopy. A dark defect density of less than 105 cm−2 was obtained when the As-terminated GaAs surface was Zn treated. The Zn treatment prevented the formation of the Ga2Se3 layers. When we alternated the exposure between Zn and As fluxes, excess ZnAsx interfacial layers were formed and the quality of the DH structure was unacceptable. However, hydrogen-radical exposure before and during the Zn/As treatment effectively removed the excess ZnAsx compounds, and the density of dark defects fell to 2×104 cm−2.
Envelope soliton formation length in magnetic films (abstract)
Authors: Fetisov Yu. K. , Slavin A. N. , Lesperance T.
Published: July 2002

Envelope solitons of magnetostatic waves (MSW) propagating in magnetic films have recently become an object of intensive experimental and theoretical study.12 It has been shown experimentally1 that the amplitude of a fully formed envelope soliton in a weakly dissipative magnetic film decreases with propagation distance (or delay time) twice as fast as the amplitude of a sinusoidal wave in the same film. In the present paper, we report a detailed study of the process of envelope soliton formation for MSW in a high-quality, yttrium iron garnet (YIG) film. As a result of this study, we propose to define the soliton formation length L as a distance at which the doubled “solitonic” dissipation of the propagating pulse starts to manifest itself. Figure 1 shows the evolution of an input rectangular pulse (duration T=12 ns, power 1.1 W, carrier frequency 5.6 GHz of backward volume MSW propagating in a YIG film [thickness 14.6 μm, ferromagnetic resonance (FMR) linewidth 2ΔH=0.8 Oe] as a function of the propagation time Tp=Lp/Vg, where Lp is the propagation distance, and Vg=6.67×106 cm/s is the group velocity. It is clear that linear (in logarithmic scale) decrease of the output pulse amplitude starts at propagation time Tp=45 ns corresponding to Lp=Lf=0.3 cm. Our measurements have shown that the soliton formation distance Lf is practically independent of the power of the input rectangular pulse (in the interval 0.5 W<Pin<1.3 W, corresponding to the formation of a single soliton), and is determined mainly by the input pulse duration T. It is interesting to compare the experimentally determined value of Lf to the value of dispersion length Lp, which is widely used in literature.3 For a rectangular input pulse (of duration T) we get LD=T2Vg3/π2|D|, where D=5×103 cm2/s is the wave dispersion. Calculation using Eq. (Equation 1) shows that for the conditions of our experiment LD=0.86 cm or roughly three times larger than Lf.