bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic transitions in the ferromagnetic spinel LiZn0.5Mn1.5O4
Authors: Plumier R. , Sougi M.
Published: July 2002

Elastic neutron diffraction experiments performed at H=0 on a powdered specimen of LiZn0.5Mn1.5O4 have shown that this compound is a ferromagnet up to TC =22 K with a reduced moment σ(1.4 K)=2.04 μB to be compared to the expected σ0=3 μB for the Mn4+ ion. The increased linewidth of the magnetic reflections indicates that the ferromagnetic domains are about 150 Å in size. At T=21.5 K, the moment drops from m=1.3 μB to zero. Detailed isotherm and isofield magnetization curves have been obtained on the same powdered specimen up to H=10.5 T. From Arrott’s plots, a true Curie temperature T1=38.5 K is derived. The (ΔM/ΔH)Hi curves plotted as a function of T display a kink up to T1 and a maximum in the range T1<T<T2 (T2=65 K). A continuous Hc(T) first-order transition line from clusters to ferromagnetism is obtained that starts at H=0 at TC and ends at H1=25 kOe at T1. In the range T1<T<T2  all the magnetic measurements may be described by a slightly modified Langevin function for ferromagnetically coupled clusters made of an average of 4.51 Mn4+ ions. The unusual ferromagnetism of this oxygen spinel is discussed.
Magneto-optical properties of the Ca:(yttrium iron garnet) epitaxial-layer–substrate interface on gadolinium gallium garnet
Authors: Gualtieri D. M.
Published: July 2002

Calcium oxide is a growth rate inhibitor of the liquid-phase epitaxy (LPE) of garnet layers. Calcium oxide additions to a melt for the growth of yttrium iron garnet (YIG) will reduce the epitaxial growth rate from its typical value of 1.0 to 0.1 μm/min [W. H. De Roode and J. M. Robertson, J. Cryst. Growth 63, 105 (1983)], allowing precise thickness control for the fabrication of optical waveguides and magnetic heterostructures. LPE growth of YIG from calcium-free melts produces a 0.1-0.5 μm interface layer between the YIG layer and the gadolinium gallium garnet (GGG) substrate. This interface is caused by a transient crystal growth that occurs before equilibrium epitaxy, and it consists of a nonstoichiometric layer composition that includes flux and impurity components. Calcium oxide addition would be especially useful if it reduced the thickness of the interface layer in proportion to its inhibition of growth rate. This, however, is not the case. A series of Ca:YIG layers was grown by LPE on GGG substrates in the thickness range 0.05–10 μm. Faraday rotation spectroscopy in the wavelength range 475–575 nm distinguished the layer, interface, and substrate contributions to the optical rotation and revealed the presence of a 0.25-μm-thick interface layer with properties characteristic of Pb-substituted YIG. Double-crystal x-ray diffraction confirmed the existence of the interface by the angular broadening of the layer diffraction and a shifting to lattice constants intermediate between YIG and GGG as the layer thickness decreased. The importance of this interface as a graded refractive index layer in optical waveguides should not be overlooked.
Magnetoreflectivity study of excitons in ZnCoSe
Authors: Liu X. , Petrou A. , Jonker B. T. , Krebs J. J. , Prinz G. A. , Warnock J.
Published: July 2002

Magnetization and magnetoreflectivity studies of two Zn1−xCoxSe epilayers (x=0.0076 and 0.0104) were carried out. These experiments yield a value for the exchange parameter difference N0(α−β)=2420±40 meV, which is significantly higher than the values observed in other diluted magnetic semiconductors. The study verified that ZnCoSe is a Brillouin paramagnet.
Determination of three-dimensional force distribution on soft magnetic powder composite electrical machine cores (abstract)
Authors: Gair S. , Yang S. J.
Published: July 2002

The paper presents three new aspects to the design and analysis of electrical machines in general, and the manufacture of small electrical machines which utilize new powder-metallurgical, soft-magnetic-core material in particular. First, a comparison of the Maxwell-stress and Poynting-vector methods of determining power-flow conditions in electrical machines is made. Calculations are based on three-dimensional (3D) field data, which include the full harmonic spectra due to excitation and load conditions, conductor slotting, and winding factors. The method employed to obtain the 3D field data is based on a new computed tomography technique in which the spatial distribution of the fields are accurately obtained in the air gap of the machine. The machines studied in the investigation are characterized by the use of soft magnetic powder-metallurgical core materials used in their construction. A detailed appraisal of the properties of these new powder-metallurgical materials and examples of their use in small electrical drives will be given in the paper. The method of force calculation adopted, together with the use of new soft magnetic materials, has resulted in a significant advance for the manufacture of small electrical machines.
Observation of domain-wall pinning in melt-spun SmCo5−xNix alloys
Authors: Strzeszewski J. , Hadjipanayis G. C.
Published: July 2002

SmCo5−xNix ribbons show a giant magnetic hysteresis with the maximum coercivity obtained in the x=1 sample. For the same composition, x-ray diffraction studies show the existence of some texture with the c axis perpendicular to the ribbon. For x=2, 3, where the coercivity is much lower, the c axis is predominantly within the ribbon plane. Electron microscopy reveals a microstructure with polygonal grains for x=0, 1, elongated grains for x=2, and some coherent Sm2(Co,Ni)17 precipitates for x=3. Domain walls show a strong interaction with the grain boundaries for SmCo5 and an even stronger interaction with some unidentified localized pins in the case of SmCo4Ni.
Spin glass freezing and superconductivity in YBa2(Cu0.94Fe0.06)3O7
Authors: Mirebeau I. , Hennion M. , Dianoux J. , Caignaert V. , Moorjani K.
Published: July 2002

We have studied the dynamics of the iron spins in a superconducting YBa2(Cu0.94Fe0.06)3O7 sample by neutron time-of-flight measurements. The range of scattering vector q was 0.1<q<2.1 Å−1, and the energy resolution 80 μeV. The temperature was varied in the range 1.8 K<T<300 K. In the whole temperature range, the q dependence of the magnetic intensity mainly reflects the magnetic form factor of iron which shows that the iron spins are almost uncorrelated. The elastic and quasielastic intensities strongly vary with temperature. A spin-glass-like freezing is revealed at low temperature by a sharp decrease of the quasielastic intensity, an increase of the elastic, or resolution limited intensity and a minimum in the quasielastic width. The freezing temperature (Tf≂18 K) corresponds to that already determined by a magnetic splitting in Mössbauer experiments. Above Tf, the relaxation of the iron spins in the paramagnetic state is modified by the occurrence of superconductivity. We observe a slight increase of the quasielastic intensity and of the quasielastic width at the superconducting transition (Tc≂74 K), possibly related to the electron-spin coupling.
Rotational magnetic processes in YBa2Cu3O7
Authors: Liu Liwen , Kouvel J. S. , Brun T. O.
Published: July 2002

A polycrystalline superconducting thin-disk sample was rotated in a fixed field (H) at 4.2 K, and the vector magnitude and orientation of the total magnetization (M) were measured as the sample-rotation angle (θ) was slowly cycled between 0° and 360°. The measured M was decomposed into a penetrating (vortex) flux component Mp that rotates rigidly with the sample at very small θ and a diamagnetic (shielding) component Md that stays antiparallel to H. As θ is raised, Mp deviates from rigid rotation, and the deviations are very different for the zero-field-cooled (ZFC) and field-cooled (FC) states at the same H, indicating different distributions in the strengths of the initial pinning forces. However, Md is exactly the same for both states and closely equals χ0H, where χ0 is the low-H (ZFC) diamagnetic susceptibility. At still higher θ, Mp rotates up to some critical angle relative to H, where it remains as the sample continues to turn. This frictional motion of Mp relative to the sample presumably derives from a sequential hopping of vortices between pinning centers.
Magnetism in nonsuperconducting La2−xSrxCuO4+y: Observation of bulk spin-glass-like behavior (abstract)
Authors: Filipkowski Mark E. , Budnick Joseph I.
Published: July 2002

Recent results of perturbed-angular-correlation experiments on La2−xSrxCuO4+y, for x zero1 or small,2 indicate that as-prepared materials contain an excess of oxygen which may be removed by annealing in vacuum. Inspired by these results, we have explored the magnetic behavior of Sr-doped materials that have received treatment by vacuum annealing, our primary interest being the observation of a bulk transition to the apparent spin-glass phase which occurs at low temperatures (Tf<20 K) for 0.02≤x≤0.07.3 While as-prepared materials do not exhibit a bulk transition at Tf, we observe a clear anomaly at Tf in vacuum-annealed samples, below which the latter also display the magnetic irreversibility characteristic of spin glasses. The values of Tf obtained from bulk magnetization correspond closely to those derived from microscopic probes.3 We will discuss the results of measurements of the bulk magnetization in vacuum-annealed samples with varying Sr content, together with information from recent experiments, utilizing ESR and NMR, designed to improve our understanding of the microscopic nature of the moments which participate in the ordering at Tf and of the nature of the ordering itself.
Ferromagnetism and crystal lattice stability of bcc and fcc iron
Authors: Krasko Genrich L. , Olson G. B.
Published: July 2002

The Stoner theory of itinerant ferromagnetism was used in calculating the magnetic properties of iron within the self-consistent linear muffin-tin orbital approach. The Stoner exchange parameter, I, was found from the linear-response theory as a function of volume and then adjusted by a constant enhancement factor determined by fitting the equilibrium atomic volume of the ferromagnetic (FM) bcc phase. No other adjustments of any quantities were performed. The calculations revealed a somewhat unusual behavior of phases. The nonmagnetic (NM) bcc phase is unstable with respect to spontaneous magnetization. Moreover, the enthalpy of the NM phase exhibits a monotonic decrease with c/a along the so-called Bain deformation path, the bcc modification being unstable with respect to the shear deformation. Ferromagnetism stabilizes the bcc phase. However, the FM fcc phase is unstable with respect to the shear deformation. The enthalpy curve along the deformation path has a cusp corresponding to a first-order phase transition between FM and NM states. The FM contributions to the energy versus atomic volume for different c/a valves are tabulated.
Structural and superconducting properties of Bi-Sr-Ca-Cu superconductors studied by Fe doping
Authors: Tang H. , Qiu Z. Q. , Du Y. W. , Walker J. C.
Published: July 2002

1.5% of Fe has been substituted for Cu in several ‘‘2212’’ and ‘‘2223’’ Bi-Sr-Ca-Cu superconductors. All of the samples show a reduction of Tc by about 13 K due to the Fe impurities. Mössbauer measurements at room temperature reveal structural characteristics such as stacking faults and intergrowth of different phases in these Bi-based compounds on the microscopic scale. The suppression of Tc due to Fe doping in the Bi ‘‘2212’’ or ‘‘ 2223’’ system is comparable to that of the ‘‘123’’ system, but much smaller than that of the ‘‘214’’ system. The interplanar correlation existing in the ‘‘123’’ and the Bi ‘‘2212’’ and ‘‘2223’’systems seems to play an important role in sustaining the high-temperature superconductivity and weakening the detrimental effect of impurity elements on superconductivity in these two systems.
Temperature dependence of the magnetization of Co/Pt multilayers (abstract)
Authors: Bloemen P. J. H. , Swüste C. H. W. , Poodt G. J. M. , Hoving W. , den Broeder F. J. A.
Published: July 2002

Co/Pt multilayers with perpendicular anisotropy have recently been shown to be candidate materials for magneto-optic recording.1 In this application the Curie temperature has to be sufficiently low in order to switch the magnetization with the available laser powers. Apart from this technological importance, it is also of fundamental interest to investigate the effect of coupling between two-dimensional systems on their critical behavior. We therefore studied the influence of the Pt thickness on the temperature dependence of the magnetization for Co/Pt multilayers. The multilayers were prepared by vapor deposition in ultrahigh vacuum. X-ray-diffraction measurements confirmed the layered structure. The spontaneous magnetization was obtained by extrapolating the high-field part of the magnetization curves back to zero field. The experiments showed that the changes in the magnetization are reversible up to 450 K. Above 500 K we detected slight irreversible changes probably due to interdiffusion. The Curie temperature decreased with increasing Pt thickness up to about 27 Å, above which no dependence was found. This phenomenon is ascribed to a long-range interaction between the thin (4 or 6 Å) Co layers. The development of a model describing the Curie-temperature dependence on the Pt thickness is in progress. Some preliminary calculations will be given.
Effect of compositional and structural heterogeneities on the magnetic properties of amorphous CoZrNb thin films (abstract)
Authors: Jeong I. S. , Louis E. , Walser R. M.
Published: July 2002

Nanometer-scale thin-film heterogeneities are important for determining the magnetic properties of amorphous, soft magnetic films.1 The remanent-magnetization distributions in ultrasoft films appear to result from the balance of magnetostatic and exchange energies associated with the nanometer-scale heterogeneity.2 In sputtered films this balance is determined by the deposition and annealing parameters. Previous work focused on CoB binary-alloy films which were compositionally inhomogeneous with a two-phase amorphous structure.3 To determine whether compositional inhomogeneities are a requirement for ultrasoft-film behavior, we studied amorphous, Co-rich alloy (Co87Zr5Nb8) films not expected to be compositionally inhomogeneous in the as-deposited state. Electron-diffraction-scanning analysis in a scanning-transmission-electron microscope showed that the morphologies of the as-deposited films were featureless. On the other hand, the morphology of films annealed in a rotating field coarsened and detailed electron probe analysis (EPMA) confirmed that the annealed films were compositionally inhomogeneous with two amorphous phases. Magnetic-hysteresis and rf-susceptibility measurements clearly revealed that the onset of ultrasoft-film response was correlated with the latter. We discuss the possible magnetostriction in these inhomogeneous films and its effect on the experimentally observed high-frequency susceptibilities.
Ordering and oxygen content effects in YBa2(Cu1−xFex)3O7 samples observed by high-temperature Mössbauer spectroscopy
Authors: Saitovitch E. Baggio , Scorzelli R. B. , Azevedo I. Souza , dos Santos C. A.
Published: July 2002

We report here in situ high-temperature 57Fe Mössbauer measurements on YBa2(Cu1−xFex)3O7 samples in controlled oxygen atmosphere, in air, or in vacuum. In these conditions, fundamental information can be obtained related to the thermal stability of the different Fe species, as well as the mechanism of oxygen loss.
Coupling of Ni and NiFe films through an intervening nonmagnetic film
Authors: Layadi A. , Artman J. O. , Hoffman R. A. , Jensen C. L. , Saunders D. A. , Hall B. O.
Published: July 2002

The magnetic coupling of 20-nm-thick Ni and Ni78Fe22 films through intervening Ag film has been investigated by ferromagnetic resonance (FMR) at 33 GHz. Films were deposited by e-beam evaporation on glass in the order glass/Ag/Ni/Ag/NiFe/Ag. The Ag over- and underlays were 20 nm thick; the central Ag-film thickness was varied between 0 and 20 nm. The coupling of the two ferromagnetic films, A and B, through the interface is modeled by adding −KMA⋅MB to the free energy per unit area. The FMR-mode positions are found from the solutions of a quadratic in K. Subsequently, FMR-mode intensities and linewidths are computed. Input data for these calculations were obtained from observations made on uncoupled Ni and NiFe films. From in-plane dc-field date a variation of K was deduced with a coupling film thickness t of the form exp(−t/τ) with τ equal to 2.68 nm. Limited FMR data taken with the dc field normal to the specimen are consistent with a weak coupling, K∼t−0.83. Little coupling was found in a glass/SiO2/Ni/SiO2/NiFe/SiO2 sequence with the SiO2 films spanning the same thickness range as the Ag in the first sequence. It is believed that the coupling in Ni/Ag/NiFe is dominated by conduction-electron-spin polarization. Some of the coupling may be magnetostatic in origin.
Ce-substituted garnet media for magneto-optic recording
Authors: Alex M. , Shono K. , Kuroda S. , Koshino N. , Ogawa S.
Published: July 2002

The magnetic and magneto-optical properties of crystallized as-deposited Ce-substituted sputtered garnet films were measured as a function of temperature. The films were found to exhibit large Faraday rotation and high coercivity at room temperature. The small grain size and high squareness ratios of these films suggests that this media holds promise as a potential magneto-optical recording media candidate for use at laser diode wavelengths. Furthermore, it was found that depending upon the value of the sputtering system background pressure prior to film deposition the compensation temperature of these films varied from below room temperature to the Curie point. The temperature dependence of magnetization of these two types of films was found to be very different and ESCA analysis was performed in order to ascertain the origin of these differences.
Rare-earth promoters of semiconductor oxidation: The case of GaAs(110)/Yb
Authors: Chang S. , Philip P. , Wall A. , Yu X. , Franciosi A.
Published: July 2002

Synchrotron radiation photoemission studies show that thin Yb overlayers (0.3–4.1) monolayers) enhance the oxidation of GaAs(110) surfaces. The magnitude of the promotion effect varies as a function of Yb coverage. The oxidation reaction products involve several nonequivalent oxidation states of As and Ga. The specific catalytic activity of the pure divalent Yb overlayers in promoting GaAs oxidation appears lower than that of Sm overlayers containing both Sm2+ and Sm3+ species. The spectroscopic signature of the oxidation reaction products, instead, is compellingly similar for the two rare-earth promoters. We propose that the oxidation promotion mechanism is related, in both cases, to the decomposition of metal/semiconductor interface reaction products upon exposure to oxygen, and that the rare-earth atomic valence has only a limited influence on the promotion mechanism.
Microwave-detected optical response of YBa2Cu3O7−x thin films
Authors: Kaplan R. , Carlos W. E. , Cukauskas E. J. , Ryu J.
Published: July 2002

Microwave-detected optical response (MDOR) of YBa2Cu3O7−x and other oxide superconductor thin films is shown to yield information complementary to that provided by trasnport photoconductivity measurements. The MDOR technique yields a superposition of response from all illuminated portions of a sample, irrespective of the existence of a resistive macroscopic percolative current path. The response is found to be bolometric at temperatures for which resistance appears in transport measurements. At low temperatures MDOR results imply a nonbolometric response which in some respects is consistent with nonequilibrium quasiparticle concentration due to radiative pair breaking.
Highly uniform ion implants into GaAs by wafer rotation
Authors: Uchitomi Naotaka , Mikami Hitoshi , Toyoda Nobuyuki
Published: July 2002

The influence of wafer rotation on implanted dose uniformity was investigated using thermal-wave measurement to realize highly uniform ion implants into a (001) wafer. It was found that conically rotating ion implantation is an effective way to scramble the scanning ion beam during implantation by using an electrostatic-scan implantation system with a specially designed wafer station. Furthermore, two-fold ion implantation was employed to correct the dose inhomogeneity caused by the variation of the tilt angle across a wafer. Based on these considerations, a high dose uniformity of less than 1% across a wafer was achieved.
CHmDn and C2HmDn formation due to interaction of implanted hydrogen and deuterium with graphite
Authors: Yamada Reiji
Published: July 2002

The formation and release of hydro- and deuterocarbons from pyrolytic graphite bombarded with 6-keV H+3 ions and subsequently with 6-keV D+3 ions as well as vice versa have been investigated using a quadrupole mass spectrometer (QMS) at a target temperature of 500 °C. For both cases the signal intensities of masses 17 (CHD2,CH3D) and 19 (CHD3) first increased and then decreased with increasing the fluence of subsequent bombardment. A similar tendency was also observed in those of masses 29 (C2H3D, C2HD2) and 31 (C2HD3). These results indicate that the mixing of hydro- and deuterocarbons, forming CHmDn and C2HmDn, occurs during the subsequent bombardment. A simple calculation of QMS signal intensities has been performed, assuming that the fully saturated hydro- and deuterocarbons (CH4, C2H2, and C2H4 types) are formed and then released, and that their radicals are only produced through cracking in the ion source of QMS. The calculated results qualitatively agreed with the measured ones. They suggest that the mixing of hydro- and deuterocarbons becomes maximum when the product of the local H and D concentrations has the maximum value, and that the mixing mainly takes place around the depth at which the H and D profiles mostly overlap.
Steady-state mobility lifetimes and photoconductivity in a-SiGe:H thin films
Authors: Hegedus Steven S. , Cebulka James M.
Published: July 2002

The steady-state mobility-lifetime products (ημτ) and photoconductivity spectra of a-Si:H and a-SiGe:H films with band gaps from 1.74 to 1.10 eV have been determined. The importance of obtaining the bulk ημτ at an appropriate wavelength for films of differing compositions and absorption spectra is demonstrated. We show that ημτ measured at a wavelength such that the absorption-thickness product is unity (αt=1) is proportional to the standard photoconductivity measured at one sun illumination for films having a wide range of band gaps and deposition conditions.
Device geometry and temperature dependence of deep level transient spectroscopy spectra of GaAs metal-semiconductor field-effect transistors
Authors: Zhao J. H.
Published: July 2002

A resistance deep level transient spectroscopy (DLTS) model is presented which shows how the surface electron traps in GaAs metal-semiconductor field-effect transistors may result in the extensively reported signals attributed to hole trapping at the channel and substrate interface. By considering the detailed electron capture and emission processes of the surface states, the following have been successfully explained for the strong dependence of the surface state DLTS peak height on the device geometry and temperature: (i) the device geometry dependence of DLTS peak height is found to result from the fact that the amount of surface states involved in electron capture and emission in a DLTS study is proportional to the dimension of the ungated region; (ii) the drastic decrease of surface state DLTS peak height with decreased temperature is shown to be a direct result of the strong temperature dependence of the surface leakage current; and (iii) it is shown that the ‘‘holelike’’ DLTS signals can be used directly to determine the surface electron trap energy level ET.
Doping density dependence of intersubband transitions in GaAs/AlxGa1−xAs quantum-well structures
Authors: Ramsteiner M. , Ralston J. D . , Koidl P. , Dischler B. , Biebl H. , Wagner J. , Ennen H.
Published: July 2002

Intersubband transitions in GaAs/AlxGa1−xAs quantum wells have been studied as a function of the doping level by Raman scattering and infrared absorption. The n-type dopant concentration placed in the well was varied between 1×1018 and 8×1018 cm−3. With increasing doping level Raman scattering reveals a frequency down-shift of the single-particle intersubband transition and a shift to higher frequencies of the collective intersubband plasmon-phonon mode. The resonance in infrared absorption follows closely the collective mode observed in Raman scattering, demonstrating clearly that the doping-dependent depolarization shift of the absorption peak is an important parameter that must be taken into account in device design. Possible models for the frequency down-shift of the single-particle transition are also discussed.
A study of proton exchange in congruent single-crystal LiNbO3 by atomic absorption spectroscopy
Authors: Loni A. , De La Rue R. M. , McCaig J. , Winfield J. M.
Published: July 2002

Atomic absorption spectroscopy has been used to determine Li+ concentrations in benzoic acid after proton exchange with x- and z-cut LiNbO3 as a function of exchange time and temperature. The atomic absorption results, in agreement with our previous infrared spectroscopic and optical waveguide measurements, indicate that there is no evidence for saturation of the melt by Li+ at typical melt volumes.
Formation of superconducting pellets and oriented films from Y2BaCuO5 (green phase)
Authors: Fournier P. , Gagnon R. , Aubin M.
Published: July 2002

One of the derivatives of the 1-2-3 high-Tc superconductors is known as the green phase (Y2BaCuO5). In a novel approach, the latter is proposed as the starting material to make oriented films deposited on MgO (001) by a simple painting method. Best results are obtained with a heat treatment up to 1040 °C and a slow cooling rate from 980 to 920 °C, giving films with Tc,50%=83 K and ΔTc=6 K. Scanning electron microscopy assisted by localized x-ray fluorescence permitted us to correlate the Tc’s and Jc’s with the general morphology of these films. Test pellets made with the 2:1:1 phase are also shown to be superconducting with a transition mid-point at Tc,50%=93 K and width of around 2 K.
Numerical simulation of temperature distributions during electron beam annealing of multilayer semiconductor structures
Authors: Meglicki Z. , Sumich R. J. , Faraone L. , Nassibian A. G.
Published: July 2002

A finite element method has been used to study temperature profiles in multilayer semiconductor structures. Of particular interest is the modeling of a continuous wave energy beam similar to those typically used for electron, laser, or ion beam annealing of semiconductor layers. The intensity of the heat source has been modeled in the form of a Gaussian disk on the surface of the structure. Using experimental data and appropriate curve fitting, mathematical expressions are derived that model both thermal conductivity and specific heat as a function of both temperature and sample composition. The resulting expressions give interpolation errors of less than 1% when compared with tabulated experimental values. The simulated temperature distributions are obtained by numerically solving the Helmholtz equation in cylindrical coordinates. Results are presented of simulations involving multilayer structures consisting of metal, insulating, and semiconducting films typically used in both silicon and gallium arsenide technology. The calculated temperature distributions point to possible large variations in substrate temperature as a consequence of lack of thorough control over the beam parameters. More specifically, the diameter of the energy beam is found to strongly affect the resultant peak temperature. The presence of either metal and/or dielectric layers on the surface of the semiconducting substrates is found to have a profound effect on the simulated temperature distributions.
Outdiffusion of Be during rapid thermal annealing of high-dose Be-implanted GaAs
Authors: Baratte H. , Sadana D. K. , de Souza J. P. , Hallali P. E. , Schad R. G. , Norcott M. , Cardone F.
Published: July 2002

The outdiffusion of Be implanted into GaAs has been found to be identical after capless or capped (Si3N4 or SiO2 ) rapid thermal annealing (RTA) at 900–1000 °C and to depend on the Be dose and its proximity to the surface. The outdiffusion is more pronounced when the Be implant is shallow (<0.1 μm) and/or the Be+ dose is high (>1×1015 cm−2 ). It is demonstrated that the Be outdiffusion is driven by the presence of a highly damaged surface layer. Auger results suggest the formation of a BeOx compound at the surface of a high-dose (1×1016 cm−2 ) Be-implanted sample that underwent capless RTA at 1000 °C/1 s. It appears that BeOx formation occurs when the outdiffused Be interacts with the native Ga/As oxides during annealing. All the Be remaining in the GaAs after a >900 °C/2 s RTA is electrically active.
Schottky barrier height enhancement of n-In0.53Ga0.47As by a novel chemical passivation technique
Authors: Hwang K. C. , Li Sheng S. , Park C. , Anderson T. J.
Published: July 2002

A novel method of enhancing Schottky barrier height, while reducing the surface-state density on n-type In0.53Ga0.47 As surfaces using P2S5/(NH4)2S and (NH4)2Sx passivation is described in this communication. The current-voltage and capacitance-voltage characteristics show that passivated diodes have lower reverse leakage current and higher effective barrier height than that of the unpassivated diodes. The electrical characteristics of passivated diodes have not changed after one month of exposure to the air.
A theory of weak transient electrical discharges on dielectric surfaces
Authors: Kadish A. , Maier II William B. , Robiscoe R. T.
Published: July 2002

The nonlinear evolution of transient electrical discharges initiated from a small charge spot on dielectric surfaces is analyzed with a transmission line model. The relation between the resistance per unit length, R̂, and the current, I, is assumed to be given by a local Arc Welder’s Ansatz: R̂‖I‖=E*, where E* is a positive constant. Comparison is made with a similar study of discharges initiated from a large charge spot. While both studies predict conditions under which charge is, or is not, transported to a dielectric edge, significant differences in the two cases are revealed. For example, if charge is not transported to an edge, current reversal is possible if the charge spot is small, but can only be unidirectional if the spot is large.
Limitations of the integrated sub-band-gap absorption for determining the density of defects in amorphous silicon
Authors: Nobile G. , McMahon T. J.
Published: July 2002

We discuss the procedure of calculating the density of states in the gap for amorphous silicon by integrating the excess sub-band-gap absorption. We show that in general the proportionality coefficient between the density of states and the integrated sub-band-gap absorption is not unique. The sum rule has been used improperly since integration of the excess subgap absorption is terminated either at a fixed energy or at an energy which does not include all optical transitions to the conduction band. We estimate the errors that can arise from this procedure.
Mössbauer study of Fe2+/Fe3+ order–disorder and electron delocalization in K3Fe5F15 at the 490-K phase transition
Authors: Calage Yvon , Abrahams S. C. , Ravez Jean , de Pape Robert
Published: July 2002

The prediction made in J. Appl. Phys. 65, 3987 (1989) that the ferroelectric–ferroelastic phase transition at Tc =490 K in K3Fe5F15 will be accompanied by a change from order to disorder among the Fe2+/Fe3+ ions has been confirmed by Mössbauer spectroscopy. The thermal dependence of both the Fe3+ quadrupolar splitting and the Fe3+ isomer shift exhibits a smooth decrease with increasing temperature to Tc, each with a sharp and reproducible change in slope above Tc. The average Fe2+ quadrupolar splitting (QS) similarly undergoes a major decrease with increasing temperature, with a clear change in slope above Tc. Furthermore, the thermal dependence of the Fe2+ QS distribution shows that the Fe2+/Fe3+ order required crystallographically below Tc is not conserved at higher temperatures. The proportion of Fe2+ present below Tc is close to the stoichiometric 60% value; the proportion decreases above Tc rapidly with temperature and becomes less than 50% by 543 K, consistent with increasing delocalization of an Fe2+ electron.
Tantalum etching in fluorocarbon/oxygen rf glow discharges
Authors: Martz J. C. , Hess D. W. , Anderson W. E.
Published: July 2002

Etch rates of tantalum in tetrafluoromethane-oxygen and hexafluoroethane-oxygen rf glow discharges were measured in situ as functions of pressure, reactor residence time, temperature, and applied plasma power. A dramatic increase in the etch rate was observed as the pressure increased. In addition, two distinct temperature regimes occurred in Arrhenius plots. Such data suggest strong effects due to heat of reaction in the Ta/CF4-O2 etch system. The observed etch-rate pressure dependence can be explained by assuming first-order kinetics for the reaction of fluorine atoms with tantalum. Evidence for etch-rate quenching at high pressures due to an increase in the deposition of an inhibiting fluorocarbon surface layer is presented.
Optical absorption in In0.72Ga0.28As0.60P0.40:Ge
Authors: Rajalakshmi R. , Arora B. M.
Published: July 2002

A prominent Urbach tail is introduced in the absorption spectra of In0.72Ga0.28As0.60P0.40, by Ge doping, due to transitions from disorder-induced localized states at the valence-band edge to conduction band. Different components of the disorder have been considered. A model calculation, considering multiphonon emission, has been made.
Lattice-mismatched In0.53Ga0.47As/In0.52Al0.48As modulation-doped field-effect transistors on GaAs: Molecular-beam epitaxial growth and device performance
Authors: Chang Kevin , Bhattacharya Pallab , Lai Richard
Published: July 2002

We describe here the properties of In0.53Ga0.47As/In0.52Al0.48As modulation-doped heterostructures and field-effect transistors grown directly by molecular-beam epitaxy on GaAs substrates. The generation and nature of dislocations in the films have been studied by transmission-electron microscopy. The final heterostructure contains a series of compositional steps of InxGa1−xAs (0≤x≤0.53) to generate and control the dislocation movement. The modulation-doped heterostructures are characterized by μ300 K=8 150 cm2/V s (ns=2.7×1012 cm−2) and μ20 K=26 100 cm2/V s (ns=2.1×1012 cm−2) which compare very favorably with values measured in similar lattice-matched heterostructures on InP. 1.4-μm gate-modulation-doped field-effect transistors exhibit gm(ext)=240 mS/mm and fT=21 GHz. The drain current variation with gate bias is linear and the transconductance is uniform over a sizeable voltage range. These material and device characteristics indicate that InxGa1−xAs/InxAl1−xAs transistors (with x varying over a certain range to vary ΔEc) can be designed on GaAs or even other mismatched substrates.
The morphology changes in diamond synthesized by hot-filament chemical vapor deposition
Authors: Kim Jong Sung , Kim Myong Hyon , Park Soon Sup , Lee Jai Young
Published: July 2002

Hot-filament-assisted chemical vapor deposition has been used to study the growth morphology of synthetic diamond deposited on silicon substrate in a dilute (1 vol %) CH3COCH3/H2 at high substrate temperature (about 777 °C). Scanning electron microscope pictures of the diamond particles show that the surfaces of synthetic diamond consist of rough-octahedral (111) faces and smooth-cubic (100) faces, which is cubo-octahedron. And also the (110) facets on the octahedral face are observed. The relative growth rate of (111) faces to that of (100) faces in the cubo-octahedron is double that derived from the calculated specific surface energy. So the apparent growth rate of the octahedral face must be explained by the growths of two constituent crystallographic planes of (100) and (110). The observed roughness of (111) faces arises from the competing growths of (100) and (110) planes. The (110) faces separate the (111) faces into three (110) planes. For the study of diamond crystal growth during deposition, it is suggested that the growth mechanism of cubo-octahedral diamond is the competing growths of (100) and (110) crystallographic planes.
Near-infrared reflectance modulation with electrochromic crystalline WO3 films deposited on ambient temperature glass substrates by an oxygen ion-assisted technique
Authors: Arntz F. O. , Goldner R. B. , Morel B. , Hass T. E. , Wong K. K.
Published: July 2002

Electrochromic, crystalline WO3 films have been deposited on glass substrates at ambient temperature by an oxygen-ion-assisted technique using oxygen ion energies ≥300 eV and oxygen ion to vapor molecule (WO3) ratios, γ≥2.5. After lithiation, the resulting LixWO3 films exhibited >50% reflectivity in the near infrared, and the reflectivity dispersion was fit by a Drude free-electron model, yielding the Drude parameters: plasma energy, Ep=3.3 eV; and the loss (damping) parameter, EΓ=1.0 eV. (The bound electron permittivity, εb, was fixed at 4.0.) These values are comparable to those obtained with WO3 films rf sputter deposited onto substrates at temperatures >420 °C. During the ion-assisted deposition the substrate temperature reached approximately 90 °C, caused primarily by radiation from the WO3 evaporant source. This indicates that economical low-temperature substrates, such as plastics, could be used. These results suggest that practical electrochromic smart windows for energy-efficient buildings might be produced using ion-assisted deposition techniques.
Hot-electron scattering by neutral hydrogenic donors
Authors: LaViolette Randall A. , Callaway Joseph
Published: July 2002

Accurate rates computed for electron-hydrogen scattering are applied to intravalley scattering of electrons by neutral hydrogenic donors in moderately doped semiconductors (at low compensation) held at cryogenic temperatures. The differential rates for both elastic and impact-excitation scattering are included explicitly. In contrast to the traditional assumption of exclusively isotropic elastic scattering, we show that the elastic scattering strongly favors the foward directions for energies well below impurity ionization. Near the impurity ionization energy, the inelastic impact excitation ignored in traditional treatments accounts for about 10% of the total impurity scattering rate and dominates impurity scattering for higher energies. Inelastic scattering strongly favors the forward directions for all energies. The consequences of both anisotropic and inelastic scattering for hot-electron transport are demonstrated in a sample calculation for a Si:As layer subject to an electric field. In particular, the threshold for non-Ohmic transport is found at much lower field strengths in calculations employing our proposed neutral-impurity scattering rates than in calculations employing an extrapolation of the traditional isotropic elastic rate.
Impact ionization avalanche breakdown in short crystal regions of p-Ge
Authors: Clauss W. , Rau U. , Parisi J. , Peinke J. , Huebener R. P. , Leier H. , Forchel A.
Published: July 2002

The low-temperature impact ionization avalanche breakdown in p-Ge is investigated on a series of samples with various lengths of the electrically active region located between the ohmic contacts. We have studied the breakdown behavior as a function of the contact distance together with the response to an applied magnetic field. A simple model considering the specific hot-carrier situation in the prebreakdown regime can explain the experimental results.
Deep levels and impurities at growth-interrupted interfaces: Temperature- and gas-switched metalorganic chemical vapor deposition of GaAs with tertiarybutylarsenic
Authors: Vook D. W. , Gibbons J. F.
Published: July 2002

In this work the interrupted growth interfaces between successive layers of GaAs grown by metalorganic chemical vapor deposition are examined. The chemical impurities and deep levels at the interfaces are investigated by secondary ion mass spectroscopy and deep level transient spectroscopy. Under high-growth-rate conditions of 6 μm/h, four deep traps are observed at the interfaces for which layer growth is switched by using the substrate temperature. No traps are observed for this temperature-switched growth when the growth rate is reduced to 1 μm/h. When the growth is interrupted for 1.5 min by halting the supply of the column-III precursor, no traps are observed. The traps observed are confined to the interrupted growth interfaces. The concentration of these deep levels decreases upon subsequent annealing at or above the growth temperature. The common midgap trap in GaAs, EL2, is not observed in the vicinity of interrupted growth interfaces but may appear after annealing. The data presented suggest that there is a direct relationship between the thickness of material deposited during the temperature transient and the sheet dose of traps at the interface. The results also suggest that the electronic configuration, but not concentration, of EL2 is governed by the local arsenic concentration.
Mechanism of the growth of amorphous and microcrystalline silicon from silicon tetrafluoride and hydrogen
Authors: Okada Y. , Chen J. , Campbell I. H. , Fauchet P. M. , Wagner S.
Published: July 2002

We study the growth of amorphous (a-Si:H,F) and of microcrystalline (μc-Si) silicon over trench patterns in crystalline silicon substrates. We vary the conditions of the SiF4-H2 glow discharge from deposition to etching. All deposited films form lips at the trench mouth and are uniformly thick on the trench walls. Therefore, surface diffusion is not important. The results of a Monte Carlo simulation suggest that film growth is governed by a single growth species with a low (∼0.2) sticking coefficient, in combination with a highly reactive etching species.
Pulsed laser melting of Si-As supersaturated solid solutions
Authors: Baeri P. , Reitano R. , Malvezzi A. M. , Borghesi A.
Published: July 2002

The T0 curve of the Si-As system has been determined by pulsed laser melting of supersaturated solid solutions in the As concentration range between 0 and 12.5 at. %. Samples were irradiated with both 20-ns 347-nm-wavelength and 20-ps 532-nm-wavelength laser pulses, and surface melting has been revealed by time-resolved reflectivity measurements. Melting temperatures of the solutions have been derived from the measurement of the energy absorbed at melting threshold. Some implications of our results on the thermodynamics of the Si-As system are discussed.
Crystallization and diffusion in progressively annealed a-Ge/SiOx superlattices
Authors: Williams G. V. M. , Bittar A. , Trodahl H. J.
Published: July 2002

Raman spectroscopy is used to investigate the structural changes in isochronally annealed a-Ge/SiOx superlattices. The Ge crystallization temperature is found to be higher in superlattices with thinner Ge layers, which can be interpreted in terms of the retardation of nucleation and growth of Ge microcrystallites near the Ge/SiOx interface. Before and after the Ge layers crystallize there is Si diffusion into the Ge layers. The Si appears to be uniformly distributed throughout the Ge layers.
A comparison of electrical and chemical profiling of doping superlattices in silicon
Authors: Casel A. , Jorke H. , Pawlik M. , Groves R. , Frenzel E.
Published: July 2002

Molecular-beam epitaxy was used to grow vertical silicon structures with extremely sharp doping transitions. Hereby a series of modulation-doped multilayer structures was prepared which had successively reduced period lengths from 100 down to 4 nm. These test samples are appropriate to study the depth resolution of standard electrical and chemical profiling techniques. Secondary ion mass spectrometry is able to resolve doping modulations down to 4 nm. Electrical measurement techniques are fundamentally limited by the out-diffusion of carriers from the highly to the lowly doped layers. Such effects become of increased importance in small period superlattices. Spreading resistance is only able to resolve the doping modulations of the test sample with the largest period length (100 nm).
Breakdown voltage enhancement by wall charges in repetitively pulsed discharge tubes
Authors: Curzon F. L. , Suzuki M. , Mikoshiba S.
Published: July 2002

It is shown that, over a narrow range of amplitudes, applied voltage pulses can deposit wall charges inside a discharge tube without causing breakdown of the interelectrode gas: these charges enhance the breakdown voltage of the interelectrode gas for subsequent pulses, and the enhancement decays exponentially with the pulse interval. The enhancement decays more rapidly when the temperature of the discharge tube is increased so as to reduce its surface resistance, which furnishes the main leakage path of the wall charges. It is suggested that breakdown voltages of closely packed, repetitively pulsed discharge tubes are frequently enhanced by wall charges.
Atomic profiles and electrical characteristics of very high energy (8–20 MeV) Si implants in GaAs
Authors: Thompson Phillip E. , Dietrich Harry B. , Eridon James M.
Published: July 2002

High-energy Si implantation into GaAs is of interest for the fabrication of fully implanted, monolithic microwave integrated circuits. Atomic concentration profiles of 8, 12, 16, and 20 MeV Si have been measured using secondary ion mass spectroscopy (SIMS). The range and shape parameters have been determined for each energy. The theoretical atomic concentration profile for 12 MeV Si calculated using TRIM-88 corresponded to the SIMS experimental profile. No redistribution of the Si was observed for either furnace anneal, 825 °C, 15 min, or rapid thermal anneal, 1000 °C, 10 s. The activation of the Si improved when coimplanted with S. The coimplanted carrier concentration profiles did not show dopant diffusion. Peak carrier concentration of 2×1018/cm3 was obtained with a Si and S dose of 1.5×1014/cm2 each.
Deep level transient spectroscopy analysis of fast ion tracks in silicon
Authors: Hallén A. , Sundqvist B. U. R. , Paska Z. , Svensson B. G. , Rosling M. , Tirén J.
Published: July 2002

Deep level transient spectroscopy measurements of electron traps in MeV proton- and alpha-irradiated n-type silicon have been performed. Six deep levels are found in proton-irradiated samples, while only three appear after alpha irradiation. The influence of the irradiation dose on the defect production is investigated together with the depth concentration profiles. The profiles scale with the nuclear energy deposition, but in the case of the doubly negative charged state of the divacancy at EC −0.24 eV, the peak concentration at the end of the track is less pronounced relative to the tail region towards the surface. It is proposed that the singly negative charged state at EC −0.42 is more probable in a highly distorted lattice and it is shown that the formation of the singly negative charged state of the divacancy dominates the defect production for higher doses.
Triplet extinction coefficients of some laser dyes. II
Authors: Pavlopoulos Theodore G. , Golich Daniel J.
Published: July 2002

We measured the triplet extinction coefficients εT over the laser action spectral region of DODC, DMC, Sulforhodamine B, Rhodamine 575, Coumarin 523, Coumarin 521, Coumarin 504, Coumarin 498, Coumarin 490, LD466, bis-MSB, and BBO. We employed the different lines from an argon- and a krypton-ion cw laser for excitation. McClure’s method [J. Chem. Phys. 19, 670 (1951)] was again employed to measure the triplet extinction coefficients. We provide a simplified derivation of McClure’s equation. The triplet extinction coefficient of Rhodamine 575 was also measured by using the depletion method and improving it by reconstructing for true triplet-triplet (T-T) absorption. The εT value obtained is in good agreement with the one obtained by McClure’s method.