bluuebunny/crossref_metadata_2025 huggingface dataset:
Implementation of differential phase contrast Lorentz microscopy on a conventional transmission electron microscope
Authors: McFadyen I. R.
Published: July 2002

Differential phase contrast (DPC) Lorentz microscopy is a powerful technique for investigating magnetization distributions within magnetic thin films. Previously this imaging technique has only been used on microscopes with nonstandard electron optical configurations because of two conflicting requirements: (1) The electron beam must be focused to a very fine probe on the specimen to obtain a high spatial resolution. (2) The specimen cannot be in the magnetic field of the objective lens, as this would destroy the magnetic domain structures of interest. This paper will describe the implementation of the technique on a conventional microscope, a JEOL JEM 2000 FX fitted with an ASID 20 scanning attachment, which satisfies these two requirements. We have modified the controls for the lenses and deflection coils in the microscope to allow an electron probe of less than 40 nm to be formed using the three condenser lenses, with the objective lens off. A position sensitive quadrant detector, required for DPC imaging, is mounted on a sliding O-ring below the projector lens and can be moved in for DPC work or out for standard microscope operation. Attached to the microscope is a digital image acquisition system based on an IBM PC AT. This system is used to acquire signals from the four quadrants of the detector simultaneously. The signals are then mixed digitally to produce the DPC images and an incoherent bright-field image. These images can be further processed to produce vector maps of the in-plane magnetization distributions within the sample. The spatial resolution of 40 nm is less than that of the VG HB501 STEM vacuum generators (VG) HB501 scanning transmission electron microscope (STEM) previously used for DPC imaging. This is due to the larger emitting area of the LaB6 filament compared to the field emission gun of the VG. The LaB6 has a much lower brightness than the FEG and this necessitates long image acquisition times. DPC images and the corresponding vector map from a NiFe film will be shown to demonstrate the technique.
FMR studies of spin-spray Ni-Zn ferrite films
Authors: Talisa S. H. , Yoo K. C. , Abe M. , Itoh T.
Published: July 2002

Spin-spray is a low-temperature plating technique for which application to the growth of ferrite polycrystalline thin films on various substrates was introduced by Abe et al. a few years ago. This technique is particularly attractive because of the possibility it offers for integrating ferrite devices with GaAs microwave monolithic integrated circuits, since growth occurs at temperatures on the order of 90 °C. In particular, the growth of Ni-Zn ferrite films has been demonstrated and these films could be used to build microwave nonreciprocal devices such as isolators and circulators. In order to understand and utilize the microwave magnetic properties of these films, a study of their ferromagnetic resonance (FMR) characteristics, as a function of composition and growth conditions, has been conducted. Important parameters such as saturation magnetization, FMR linewidth, and gyromagnetic ratio were calculated from the data obtained. Compositional and structural nonuniformities were also revealed in the analysis in the form of multiple resonances present in some of the samples analyzed.
Analysis of single-domain particle flow orientation data
Authors: Karis Thomas E. , Jhon Myung S.
Published: July 2002

Rodlike single-domain particles tend to orient parallel to the streamlines in an extensional flow, resulting in anisotropy of the bulk magnetic permeability. The suspension is made to flow from a large chamber into a narrow tube which has an oscillator coil wound near its entrance. Particle orientation parallel to the magnetic field of the coil decreases the inductance. (Small changes in orientation can then be accurately measured with a countertimer.) Since both hydrodynamic orientation and Brownian motion depend on the shape characteristics of the particle, the orientation data provide information about the ‘‘effective-particle’’ shape. The gradients of the inductance with respect to flowrate, in the limits of high and low flowrate, are used to calculate relative changes in the effective-particle rotary diffusion coefficient. This method is demonstrated with a γ-Fe2O3 suspension over a wide range of surfactant concentration. Changes in the particle magnetic properties calculated from the flow orientation data are consistent with an increase in the magnetic anisotropy coefficient by the adsorbed surfactant.
Magnetic properties and structure of Fe/Al multilayered films prepared by ion-beam sputtering
Authors: Nagakubo M. , Yamamoto T. , Naoe M.
Published: July 2002

Fe/Al multilayered films with the thicknesses of the Fe and Al layers (δFe and δAl) below 300 Å have been prepared by means of an ion-beam sputtering method, and the dependence of their crystal structure and magnetic properties on δFe and δAl has been investigated. The saturation magnetization 4πMs and the coercivity Hc of the multilayered films decreased monotonically and the d(110) spacing of α-Fe crystallites in the Fe layers increased as δFe decreased in the range below 100 Å for δAl of 20 Å. Such an increase in d spacing was removed substantially by annealing at 300 °C in vacuum. The x-ray diffractometry of the multilayered films with δFe of 100 Å and δAl below 15 Å indicated only the (200) orientation of α-Fe crystallites. In the range of δAl from 20 to 15 Å the preferentially oriented plane of Fe crystallites changed from (110) to (200) and Hc took a minimum value lower than 4 Oe. These results might be attributed to the alternate epitaxial growth at the interfaces between the Fe and Al layers.
Composition-structure relationships for multisource evaporated CuGaSe2 thin films
Authors: Albin D. , Noufi R. , Tuttle J. , Goral J. , Risbud S. H.
Published: July 2002

X-ray diffraction (XRD) analysis of doublet formation and peak shifts were used to observe the compositional dependence of the order–disorder transition in polycrystalline CuGaSe2 thin films deposited by multisource evaporation. Cu-poor material had a strong tendency to disorder as evidenced by the simultaneous presence of both the chalcopyrite and sphalerite phases. Stoichiometric and Cu-rich material contained only the tetragonal phase as observed by XRD. Comparison of Cu-poor XRD patterns with theoretical calculations reflecting probable defect chemistries (VCu, GaCu, VSe) suggests an interesting microstructure. The absence of higher index group (iii) reflections, notably the (103) and (211) peaks, in chalcopyrite material suggest that the tetragonal phase maintains a near-stoichiometric composition. Overall Cu-poor film compositions may therefore be obtained by adjustment within the cubic phase which implies compositional segregation between the phases.
Chain-of-spheres calculation on the coercivities of elongated fine particles with both magnetocrystalline and shape anisotropy
Authors: Kuo P. C.
Published: July 2002

Using the chain-of-spheres model, coercivities of elongated CrO2, Fe3O4, and γ-Fe2O3 particles due to the combined effect of shape and crystal anisotropies are calculated. Coercivities of these particles are treated in detail with respect to the particle axis orientation. The hysteresis loop is plotted so that each point of demagnetization curve is obtained by minimizing the total energy in which shape anisotropy energy, magnetocrystalline anisotropy energy, and the interaction energy of magnetic moments with applied field are all considered. The magnetocrystalline anisotropy energy of a chain during magnetization reversal is formulated. This model is applicable to single particle or very diluted particle assembly for which the effect of particle interactions can be neglected. Calculated coercivities are compared with the published experimental data.
Soft x-ray spectra from a gas-puff z pinch
Authors: Nave G. , Challis C. D. , Dangor A. E. , Lunney J. G.
Published: July 2002

XUV and x-ray emission spectra of the elements carbon, oxygen, neon, and argon, in the spectral range 3–300 Å, generated in a gas-puff z pinch, are presented. The spectra are analyzed to give time-integrated measurements of the density, electron temperature, and dimensions of the imploded plasma and the ‘‘hot spots’’ that often occur in the gas-puff pinch. In particular, dielectronic satellite lines are used to measure the electron density and temperature, and Stark broadening to measure electron density. The effect of optical depth is included.
Tantalum nitride as a diffusion barrier between Pd2Si or CoSi2 and aluminum
Authors: Farooq M. A. , Murarka S. P. , Chang C. C. , Baiocchi F. A.
Published: July 2002

Reactively sputtered tantalum nitride (Ta2N) has been investigated as a diffusion barrier between Pd2Si and aluminum and CoSi2 and Al. Ta2N is found to be an excellent matallurgical diffusion barrier for the two systems up to 555 °C, with no intermixing observed in Rutherford backscattering and Auger electron spectroscopic studies. Schottky barrier devices n-Si/Pd2Si/Ta2N/Al were excellent and showed no deterioration after annealing at 500 °C. However, similar devices with CoSi2 contacts and Ta2N barrier showed a creation of high contact resistance between the silicide and the as-deposited nitride.
The thickness dependency of the dielectric constant in certain thin-film dielectrics
Authors: Feldman Charles
Published: July 2002

An anomalous peak in the dielectric constant in ZnS thin films observed in 1962 is discussed in light of a recent observation of a similar phenomenon in BaTiO3 films. Other attempts to observe the phenomenon are also reviewed.
Determination of band offsets and effective masses in quantum wells using optical data
Authors: Cohen R. M. , Fang Z. M.
Published: July 2002

A type-I semiconductor quantum well inherently consists of two quantum wells, one each in the conduction and valence bands. A new method to decouple and independently analyze these two wells is presented. The interband 3e-3h and 1e-1h transitions are decoupled by using the commonly observed 1e-3h transition. The resulting intraband 3h-1h and 3e-1e transitions are used to independently estimate the band offset and carrier mass in each well. Decoupling of the wells in each band adds a degree of freedom to the problem and allows an independent calculation of the average well width to be made. In addition, an accurate linear approximation is developed for use in place of the usual trigonometric solution to the quantum-well problem. For Al0.30Ga0.70As/GaAs quantum wells, results are found to be highly consistent with Qc =0.605, and m*hh =0.321 and m*e =0.0671 in the well.
The X-valley transport in GaAs/AlAs triple barrier structures
Authors: Cheng Peng , Park Byung Gook , Kim Sam-dong , Harris James S.
Published: July 2002

Electron transport through the X valley of GaAs/AlAs triple-barrier structures (TBS) grown by molecular-beam epitaxy has been studied. Negative differential resistance is observed at 77 K in one type of TBS and is identified as the result of electron transport through both the Γ and X valleys of TBS. In another type of TBS, resonant tunneling through the X valley of GaAs/AlAs TBS is observed. The Γ and X energy-band profiles under bias have been calculated in order to identify the observed features.
Influence of illumination intensity on negative photoconductivity of Si ion-implanted GaAs:Cr
Authors: Papaioannou G. J. , Nowak M. , Euthymiou P. C.
Published: July 2002

Negative photoconductivity (PC) was observed in Si ion-implanted GaAs:Cr below the fundamental band gap. The dependence of this effect on wavelength and intensity of illumination is reported. For photon energies slightly smaller than the optical energy gap the negative PC reverts into positive PC with increasing illumination intensity. Complementary investigations of PC in Si ion-implanted, undoped GaAs also are presented. The physical reasons for the negative PC are discussed.
Effect of hydrogen on the magnetic properties of Ho0.85Tb0.15Fe2 and Dy0.73Tb0.27Fe2
Authors: Annapoorni S. , Markandeyulu G. , Rama Rao K. V. S.
Published: July 2002

X-ray powder photographs on Ho0.85Tb0.15Fe2Hx (x=0–3.1) and Dy0.73Tb0.27Fe2Hx (x=0–3.3) revealed that there is an expansion of the lattice upon hydrogenation. Magnetization measurements were performed using a PAR vibrating sample magnetometer in the temperature range 100–700 K. The total magnetic moment is found to decrease with increase of hydrogen content. The Curie temperature of the hydrides is considerably lowered, though the exact TC in hydrides could not be determined due to desorption. Both Ho0.85Tb0.15Fe2 and Dy0.73Tb0.27Fe2 do not exhibit any compensation, whereas Tcomp is observed and found to decreasse with x in the case of the Ho0.85Tb0.15Fe2Hx system, x=0.18–3.1. No compensation was observed even in the hydrides of the Dy0.73Tb0.27Fe2 system. The temperature variation of magnetization of Ho0.85Tb0.15Fe2Hx and Dy0.73Tb0.27Fe2Hx suggests the occurrence of a spin-reorientation transition.
Microstructure of YBa2Cu3O7−x thin films grown on single-crystal SrTiO3
Authors: Chan Siu-Wai , Hwang D. M. , Nazar L.
Published: July 2002

YBa2Cu3O7−x thin films on (001) and (014) SrTiO3 were prepared by coevaporation of Y, BaF2, and Cu, and annealing in oxygen at 850 °C. Cross-sectional samples prepared by cutting films and substrates along the SrTiO3 (100) plane were studied with transmission electron microscopy. The growth of YBa2Cu3O7−x in as-deposited films is extremely anisotropic with the [001] being the slow direction and the (001) plane being the fast growth plane. When the (001) planes of YBa2Cu3O7−x grains are parallel to the film plane, as on (001) SrTiO3, there is a dominance of this orientation over the whole film. Three types of YBa2Cu3O7−x grains, 90° misoriented from each other, are observed to grow on both (001) and (014) surfaces of single-crystal SrTiO3 substrates with their c directions aligned with one of the three 〈100〉 directions of cubic SrTiO3. This ambiguity creates a threefold degenerate epitaxy of YBa2Cu3O7−x on SrTiO3, which results in 90° grain boundaries in the final YBa2Cu3O7−x thin films. These boundaries are free of any second phase and decorations. While some extraneous phases were observed in these films, they were located away from the crystallographically special, 90° boundaries. Therefore, the presence of extraneous phases elsewhere in the films was not damaging to the superconducting transport.
Photoluminescence and double-crystal x-ray study of InGaAs/InP: Effect of mismatch strain on band gap
Authors: Bassignana I. C. , Miner C. J. , Puetz N.
Published: July 2002

Epitaxial layers of InGaAs on InP are the building blocks in optoelectronic device fabrication, where the dependence of the band gap on composition is utilized in device design. The band gap can be determined from the photoluminescence peak energy and composition from lattice size. This work reports a detailed correlation between both the room-temperature (300 K), and low-temperature (7 K) photoluminescence peak energy of epitaxial InGaAs, and the lattice mismatch relative to InP as measured by x-ray double-crystal diffraction. Nominally undoped 1- and 2-μm-thick layers of high quality InGaAs were grown on InP (001) by metalorganic chemical vapor deposition. The relaxed mismatch for these coherent layers was between −0.18% and 0.12%. The observed dependence of the 7-K photoluminescence energy on lattice mismatch confirms the theory of People [Appl. Phys. Lett. 50, 1604 (1987); Phys. Rev. B 32, 1405 (1985)] and Kuo et al. [J. Appl. Phys. 57, 5428 (1985)] which includes the effect of strain on the J= (3)/(2) valence band. The 7 K photoluminescence energy of zero mismatch InGaAs grown on semi-insulating InP substrates ([Fe]=1016 cm−3) was 0.804±0.002 eV and of zero mismatch InGaAs grown on n-type ([S]=2×1019 cm−3) substrates was 0.801±0.002 eV. This difference is attributed to the difference in absolute lattice constant for the two types of substrates. The correlation was extended to room-temperature photo- luminescence where the peak recombination energy depends on the excitation conditions. Simple spectral line-shape analysis showed that the λ 1/2  max (taken from the low-energy side of the peak) was a reliable figure of merit and could be used to estimate the degree of lattice mismatch independent of excitation conditions. This algorithm is applied to the nondestructive mapping of whole wafers.
Hydrodynamic aspects of the amorphous alloy ribbon fabrication
Authors: Imaizumi M. , Tenan M. A.
Published: July 2002

Conditions for as-quenched amorphous ribbon fabrication by a single roll-casting method are analyzed from a hydrodynamic standpoint. The analysis is based on the investigation of the processing conditions for Fe40Ni40P14B6 amorphous ribbons. It is shown that the dependence of ribbon thickness on the ejection pressure for different roll angular velocities and different dimensions of crucible and orifice can be obtained from general considerations on the melt flow regime.
Low-power deposition of fluorinated microcrystalline silicon hydrogen alloy films
Authors: Ray Swati , De S. C. , Ganguly Gautam , Barua A. K. , Mascarenhas A. J. , Al-Jassim M. M. , Deb S. K.
Published: July 2002

Fluorinated microcrystalline silicon hydrogen alloy films have been prepared by the radio frequency glow-discharge decomposition of silicon tetrafluoride/hydrogen mixtures. Thereby, μc-Si:F:H films with high dark conductivity (∼10−3 Ω−1 cm−1), high photoconductivity (∼10−4 Ω−1 cm−1), showing crystalline structure in selected-area transmission electron microscope diffraction patterns as well as sharp infrared absorption and Raman shift spectra have been obtained under conditions of low-power density (∼0.15 W cm−2) and hydrogen dilution (∼20%).
Infrared characterization of natural and cultured quartz: The effect of electrodiffusion and irradiation
Authors: Bahadur Harish
Published: July 2002

A study of OH−-related stretching vibrations showing infrared absorption bands in natural and cultured quartz has been made to include the effect of exchange of monovalent ions and irradiation at 77 and 300 K using 1.75-MeV electrons from a Van de Graaff accelerator. A variety of natural quartz crystals of different origins from Brazil and Arkansas used in the present investigation is found to contain a large number of absorption bands of uncorrelated strength in the 3200–3600 cm−1 region in the near infrared. Most of these bands are found to be associated with the presence of Li+ ions. Studies on samples of matching thickness from different cultured quartz specimens show that the bands present in the natural quartz do not get transferred to cultured quartz during their growth. While cultured quartz has always a set of bands at 3350, 3400, 3437, and 3581 cm−1, called s1, s2, s3, and s4, the set of major bands found to be present in all natural quartz are 3476 cm−1 (designated in the present work as the N1-Li+ band), 3367 cm−1 (e2), and 3306 cm−1 (e1) bands.

Other bands in natural quartz may or may not be present in conjunction with these bands. Electrodiffusion (sweeping) of unswept natural quartz with Na+ and H+ shifts the N1-Li+ band to N1-Na+ at 3451 cm−1 and N1-H+ at 3468 cm−1; e1 and e2 bands are unaffected by alkali sweeping. Other bands are also affected by sweeping. Alkali sweeping in cultured quartz does not affect the position of any of the s bands. On the other hand, H sweeping carried out introduces e1 and e2 bands in cultured quartz and saturates them while their strength is augmented in natural quartz to saturate all the substitutional aluminum. Irradiation at 77 K suppresses all the bands except e1. N1-H+ centers deplete much faster in relation to N1-M+ centers, where M+ is either Li+ or Na+. Subsequent irradiation at 300 K further suppresses the N1-M+ centers in about the same proportion as on 77-K irradiation. The N1-H+ centers do not show any depletion at 300-K irradiation. Isochronal annealing on N1-M+ and N1-H+ centers shows that they all recover during annealing. The recovery is essentially complete at about 760 K.
Negative differential capacitance of amorphous silicon films
Authors: Chen I. , Jansen F.
Published: July 2002

The surface voltage V of undoped amorphous silicon films has been measured as a function of the applied surface charge Q as in electrophotographic photoreceptor applications. It is found that the Q-V characteristic is nearly linear at low charge, but that the voltage saturates and eventually decreases with continued charging. This phenomenon of negative differential capacitance is explained by considering a field-dependent carrier generation and subsequent carrier transport in an amorphous solid. It is shown that the observed results arise from the buildup of space charge when the electron and the hole μτ products are sufficiently different.
A vector moving model of both reversible and irreversible magnetizing processes
Authors: Oti John , Della Torre Edward
Published: July 2002

We propose a moving-vector model of magnetic hysteresis that computes the media magnetization as the convolution of an applied-field-dependent vector D(H) with a Preisach distribution function P(M,H). The effect of the interaction field is to offset the asteroid which is normally symmetric. In order to relate the parameters to physical distributions, the Preisach field variables used are the isolated particle switching field and the interaction field. The vector D(H) is a function of the same Preisach variables and is process dependent and includes both reversible and irreversible magnetization changes. The asteroids can be rotated to simulate imperfectly aligned particles.
Soft magnetic properties of sputtered Co-Fe films
Authors: Iwasaki Hitoshi
Published: July 2002

This paper reports on the relationships between the crystal structure and the magnetic properties of Co-rich Co-Fe films prepared by rf diode sputtering in a mixed Ar and N2 gas atmosphere. The crystal structure changed from a bcc phase (110) preferred orientation to an fcc phase (100) preferred orientation while maintaining the nitrogen content in the film at less than 1 at. % as the N2 partial pressure increased to 3.8×10−4 Torr. Corresponding to this change, the Bs, λs, and Hk values decreased from 21 kG, 2×10−5, and 20 Oe to 19 kG, 1×10−6, and 14 Oe, respectively, though the hard-axis Hc of about 3 Oe did not change. The nitrogen content in the film, the compressive internal stress, the resistivity, and the lattice constant for the fcc phase increased as the N2 partial pressure increased from 3.8×10−4 Torr. Corresponding to these increases, Bs and Hc decreased while λs and Hk increased. It was found that Co-Fe films with an fcc phase (100) preferred orientation show good soft magnetic properties.
Optimum design of yokeless permanent magnets
Authors: Abele M. G. , Rusinek H.
Published: July 2002

This paper discusses the selection of the design parameters and the optimum geometry of yokeless permanent magnets that generate a uniform field H0 within an arbitrary closed cavity. The optimum design minimizes the volume of magnetic material and it is determined by the geometry of the cavity, the magnitude of intensity H0, and a characteristic point F that controls the configuration of the magnetostatic potential as well as the flux of the magnetic induction. The optimization procedure is applied to a two-dimensional magnet with a quadrilateral cross section.
The magnetic properties of Nd-Fe-B magnets produced by liquid dynamic compaction
Authors: Harada Tetsuji , Ando Teiichi , O’Handley Robert C. , Grant Nicholas J.
Published: July 2002

Several Nd-Fe-B magnets were prepared by the liquid dynamic compaction (LDC) process, one of the newer rapid solidification techniques. The LDC processed magnets, when produced at low-atomization gas pressures (coarse spray and low cooling rates), showed a dendritic structure and showed a mostly amorphous structure when produced at high gas pressures (fine spray and high cooling rates). Low coercivity values, less than 1 kOe, were found for the mostly amorphous magnets. Subsequent heat treatment of the latter magnets dramatically improved the magnetic properties, particularly the coercivity, up to 15.6 kOe. Energy products as high as 10 MGOe were obtained after selected heat treatments. The magnets produced by LDC were magnetically isotropic as is the case for melt-spun ribbons and hot-pressed magnets.
Thin quantum-well superlattices of GaAs and (GaAs)1−x (ZnSe)x with ZnSe: Possibility of band gaps in the blue-green
Authors: Shen Jun , Dow John D. , Ren Shang Yuan
Published: July 2002

It is predicted that thin quantum-well superlattices or spike superlattices of GaAs in ZnSe will produce band gaps in the yellow-green, and that (GaAs)1−x(ZnSe)x spikes will lead to green and blue-green gaps. These thin quantum-well structures should have better doping properties than ZnSe for x<0.6.
Dislocation injection in strained multilayer structures
Authors: Kamat S. V. , Hirth J. P.
Published: July 2002

Nucleation of dislocations within a strained multilayer and at a singular or vicinal multilayer surface is considered for typical compound semiconductor and metal cases. The results indicate that strained multilayer structures are stable against dislocation injection, even when the layer thickness exceeds the thermodynamic critical thickness for misfit dislocation stability, in the absence of defects or large external stresses. An exact energy calculation for spreading of a threading dislocation in GaAs layer is also presented. The results show that in the absence of any jog formation, there is no barrier to spreading at or above the thermodynamic, Matthews–Blakeslee critical layer thickness. Moreover, reversible spreading to an equilibrium standoff distance occurs for thicknesses smaller than the critical thermodynamic value, an effect that can lead to dissipative reversed dislocation motion under alternating driving forces.
X-ray interferometry and its application to determination of layer thickness and strain in quantum-well structures
Authors: Holloway H.
Published: July 2002

An analysis is made of x-ray interference that occurs at the Bragg condition when two epitaxially related regions of the same material are separated by a thin layer of a different material. With optimal conditions, the effects of the separator layer are shown to be detectable at thicknesses down to one or two unit cells (6–12 Å), and its thickness may be measured with a precision of about 0.02 Å. Application of these results to the determination of misfit-induced strain is discussed with particular reference to thin layers of Ga0.8In0.2As enclosed by GaAs.
A deep-level transient spectroscopy technique for the characterization of charge-carrier emission centers in nonabrupt p-n junctions
Authors: Andersson Gert I. , Engström Olof
Published: July 2002

A measurement method has been developed which makes it possible to determine the thermal emission rates, the concentrations, and position of the thermal emission region for charge-carrier emission centers in nonabrupt p-n junctions. A computerized deep-level transient spectroscopy (DLTS) technique for current transients is used in combination with capacitance measurements. Numerical, iterative calculations of the shallow doping profile of the p-n junction and capacitance change connected with thermal emission of charge carriers from the emission centers are compared with measured data. Generalized expressions for the determination of carrier emission data from thermal current and capacitance transients are derived for nonabrupt p-n junctions. The method is applicable when the properties of the p-n junction cannot be chosen arbitrarily, for example, for the study of deep impurity centers in standard types of semiconductor devices where conventional DLTS methods fail.
Range distributions of ion-implanted fluorine in Hg1−xCdxTe, CdTe, and Pb1−xSnxTe
Authors: Xia Yueyuan , Tan Chunyu , Hu Xierong , Yang Hong , Sun Xiufang , Zheng Zongshuang , Zhu Peiran , Liu Jiarui
Published: July 2002

Depth profiles of ion-implanted fluorine in Hg1−xCdxTe, CdTe, and Pb1−xSnxTe have been measured by use of the 19F(p,αγ)16O resonance nuclear reaction at 872.1 keV with width Γ=4.2 keV. In order to obtain the true range distribution of implanted fluorine from the experimental excitation yield curve, a convolution calculation method is presented, from which the range distribution parameters such as the average projected range RP, the projected range straggling ΔRP and the skewness of the projected range distribution SK were obtained. These experimental range parameters were compared with those obtained by a theoretical calculation and by use of the trim89 program, and shows that for all the materials studied here the experimental RP values agree with the theoretical and the trim values very well but the experimental range straggling ΔRP are larger than those obtained by the theoretical calculation and the trim89. This phenomenon may be attributed to the enhanced diffusion during the ion implantation.
A study of polar CdTe (111) surfaces using angle-resolved x-ray photoelectron and Auger electron spectroscopy and low-energy electron diffraction
Authors: Lu Y.-C. , Feigelson R. S. , Route R. K.
Published: July 2002

X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and low-energy electron diffraction (LEED) have been used to study the polar (111)Cd and (111)Te surfaces of intrinsic CdTe crystals. Complementary information on surface composition, chemical state of the surface elements, and surface structure was obtained. The Auger parameters were used to identify the chemical states of elements on surfaces of semi-insulating undoped CdTe crystals which suffered from static charging effects. With this approach, we were able to determine that after chem-mechanical polishing, the Te-rich surface layer was mostly in the pure Te state. Only a trace amount of TeO2 was detectable. Sputtered and vacuum annealed (111) surfaces were found to be stoichiometric: both Cd and Te were in the chemical state of CdTe. Both (111) Cd and (111) Te surfaces showed sixfold symmetric LEED patterns. No evidence of surface reconstruction was found. Angle-resolved XPS showed no significant difference between 0° and 70° tilt on either the (111) Cd or (111) Te surfaces. Angle-resolved AES, however, showed significant differences between (111) Cd and (111) Te at 0° and 70° tilt, and the crystallographic polarity identified this way was consistent with results based on chemical etching and standard AES techniques, and with reported results of x-ray diffraction and transmission electron microscopy.
Interfacial traps in Ga0.47In0.53As/InP heterostructures
Authors: Dansas P. , Pascal D. , Bru C. , Laval S. , Giraudet L. , Allovon M.
Published: July 2002

This paper reports on a study of n-type GaInAs layers grown by molecular-beam epitaxy on semi-insulating Fe-doped InP substrates. Hall measurements are performed on bevelled layers to obtain carrier concentration and mobility profiles. An infrared transient spectroscopy technique (backgating effect induced by infrared illumination in the 0.8–2 μm wavelength range) is used to detect the deep level responsible for the reduction of both carrier concentration and mobility near the heterointerface. An electronlike trap with an activation energy of ≊0.32 eV is found. Optical ionization and neutralization energies are also obtained. The results are compared with those obtained by others from electron paramagnetic resonance, photoconductivity, and deep level transient spectroscopy measurements. It is concluded that the electronlike trap, tentatively ascribed to an Fe acceptor level, is located at the heterointerface.
Diffusion of Zn and Mg in AlGaAs/GaAs structures grown by metalorganic vapor-phase epitaxy
Authors: Nordell N. , Ojala P. , van Berlo W. H. , Landgren G. , Linnarsson M. K.
Published: July 2002

The diffusion of thin, highly p-doped layers in AlGaAs/GaAs single- and double-heterostructures, grown by metalorganic vapor-phase epitaxy, was studied with C-V etch profiling and secondary ion mass spectroscopy. The effect of different post-growth heat treatments was investigated and diffusion coefficients for both magnesium and zinc were measured. It was found that Mg diffuses about twice as fast Zn and that the order of magnitude of the diffusion coefficient is 10−14 cm2 s−1 at 900 °C, the exact value being process and concentration dependent. A model based on the interstitial–substitutional diffusion mechanism with suitable kinetic limitations was successfully used to simulate the observed dopant concentration profiles.We also found an anomalous strong diffusion of zinc from GaAs into highly n-doped AlGaAs. Detailed results on this and other structures are presented and implications for optimal design of heterostructure devices such as bipolar transistors are discussed.
Functional dependence of the real part of the initial permeability of the YIG family of ferrites
Authors: Bush Gary G.
Published: July 2002

In previous papers, the dependence of the complex initial permeability of various ferrites on applied magnetic fields and on crystalline structure was explored. During these research efforts, a significant change in the real and imaginary part of the permeability was observed. It is known that the magnetic properties of prototype YIG can be modified in a deterministic way by substitution of various ions for yttrium and iron. To complement the previous investigation of crystalline structure, the current study of the effect of magnetization was undertaken. The measured real initial permeability is shown to be a strong function of frequency and applied magnetic field in the 100-MHz–1-GHz frequency range. In addition, the substitution of various ions for yttrium and iron in the prototype YIG crystal structure was shown to modify the initial permeability spectrum in a predictable way as a function of the magnetic properties of the substituted atoms for substitutions that lower the magnetization.
Specific-heat measurements of a one-dimensional Ising ferromagnet, FeTAC
Authors: Landee C. P. , Kuentzler R. , Williams J. J. M.
Published: July 2002

Previous magnetic measurements on FeTAC, [(CH3)3NH]FeCl3⋅2H2O, have shown it to behave as a one-dimensional Ising ferromagnet with an exchange constant J/k=17.4 K. A transition to an ordered state was observed near 3.1 K. Whether the transition was to a state of two- (2D) or three-dimensional long-range order could not be determined from the magnetic study. The specific-heat measurements reported here confirm the value of the intrachain exchange constant and show the critical temperature to be 3.135 K. Lattice dimensionality crossover is observed. The data are well described by Onsager’s rectangular 2D Ising lattice, with a ratio of exchange constants ‖J′/J‖=1.3×10−3. The high degree of one-dimensional isolation found for FeTAC makes it an attractive candidate for studies of linear-chain magnetism.
Experimental evaluation of a yokeless permanent magnet
Authors: Bertora F. , Trequattrini A. , Abele M. G. , Pan P.
Published: July 2002

A recently developed theory of yokeless permanent magnets allows the design of magnetic structures capable of generating intense and uniform fields confined to arbitrarily assigned regions of space. A structure of particular interest for clinical application of nuclear magnetic resonance imaging is a magnet designed around a prismatic cavity of square cross section. A laboratory scale model of such a magnet has been constructed using ferrite as the magnetic material. This paper presents the results of a series of measurements of the magnet performance. In particular, the experimental results obtained with a thin magnet section are correlated with the theoretical model and the effects of the material and construction tolerances are analyzed.
Deposition and i
n s
i
t
u annealing of YBa2Cu3O7 films on polycrystalline BeO substrates
Authors: Bernstein P. , Lamarti S.
Published: July 2002

Superconducting YBa2Cu3O7 films with Tc=84 K were deposited on polished polycrystalline BeO substrate by reactive evaporation and in situ annealing in a low-pressure oxygen atmosphere. By this process the surface quality of the films is the very same as the substrate. At low annealing temperature (TR=650 °C) the film is not textured but shows good superconducting properties. The c-axis orientation perpendicular to the plane of the substrate is observed for TR=780 °C.
The charge transport in a silicon resistor at liquid-helium temperatures
Authors: Simoen E. , Dierickx B. , Deferm L. , Claeys C. , Declerck G.
Published: July 2002

A simple, one-dimensional model describing the steady-state charge transport in a silicon n+nn+ (p+pp+) resistor at liquid-helium temperatures is derived. This model includes both space-charge and (contact) barrier limitations to the current flow, typically occurring at these temperatures (T<30 K) in Si. Furthermore, account is made for the interactions between the injected free carriers and the shallow doping atoms, i.e., mainly trapping and shallow level impact ionization, yielding breakdown of the material at rather low electrical fields F. Good qualitative agreement with measured current-voltage characteristics is found. In addition, the model is able to describe the flow of avalanche-generated current through the substrate/well of a metal-oxide-semiconductor transistor, which is essential for developing a truly analytical description of the low-temperature drain current kink.
Depth distribution of Hg ions at energies from 50 to 400 keV implanted in potassium titanyl phosphate
Authors: Wang Ke-Ming , Shi Bo-Rong , Wang Zhong-Lie , Zhao Qing-Tai , Liu Xiang-Dong , Liu Yao-Gang
Published: July 2002

Mercury ions were implanted in amorphized potassium titanyl phosphate (KTiOPO4) in the range of 50–400 keV. The implanted depth distribution was measured by Rutherford backscattering of 2.1 MeV He ions. The mean projected ranges and range stragglings obtained are compared with our calculation based on Biersack’s angular diffusion model and Monte Carlo simulation. The results show that the experimental mean projected range is in good agreement with the calculated value within the experimental errors but the range straggling is systematically higher than the calculated value. However, significant deviations from the transport of ions in matter (TRIM’89) prediction for mean projected range and range straggling are found.
A thermally activated solid state reaction process for fabricating ohmic contacts to semiconducting diamond
Authors: Moazed K. L. , Zeidler J. R. , Taylor M. J.
Published: July 2002

Techniques have been developed to produce ohmic contacts to naturally occurring boron doped semiconducting diamond. Thin films of Mo, Mo/Au, and Mo/Ni/Au deposited on diamond produced adherent ohmic contacts after annealing at 950 °C. A thermally activated solid state reaction which produces a refractory carbide precipitate at the original diamond/metal interface is the principal factor in affecting the properties of the contacts. The interface reaction has been characterized using Auger electron spectroscopy, scanning electron microscopy, x-ray diffraction, metallography, and I-V measurements.
Thermal degradation of InP in open tube processing: deep-level photoluminescence
Authors: Banerjee S. , Srivastava A. K. , Arora B. M.
Published: July 2002

Thermal processing of InP at temperatures above 500 °C is indispensable in the growth and device fabrication of InGaAsP alloy semiconductors for optoelectronic and microwave applications. Incongruous loss of P at these temperatures creates native defects and their complexes. The presence of such defects modifies the electrical and optical properties of the material resulting in poor device performance. In addition, native defects play a significant role in dopant diffusion which is a topic of current interest. We have measured deep-level photoluminescence (PL) on undoped InP after heat treatments at 500 and 550 °C in an open-tube processing system in different protective environments of powder InP, and Sn-InP melt together with an InP cover. In this paper we shall present the PL results which have bearing on the question of defects. We find that (1) the Sn-InP melt provides better protection in preserving the overall luminescence in InP; (2) the deep-level PL related to defects has at least two components in the virgin samples, viz., MnIn, and band C, which is a native defect complex related to VP; (3) a new defect appears in samples heated in a P-deficient environment; and (4) the enhancement in the deep-level luminescence intensity after heat treatment can be attributed to the excess defect concentrations existing under nonequilibrium conditions of an open-tube processing environment.
Electrical and structural study of partially relaxed Ga0.92In0.08As(p+)/ GaAs(n) diodes
Authors: Choi Y. W. , Wie C. R. , Evans K. R. , Stutz C. E.
Published: July 2002

The effects of in-plane lattice mismatch have been studied for Ga0.92In0.08As(p+)/GaAs(n)/GaAs(n+) diodes. Different in-plane mismatch at the p–n junction was introduced by a variation of the GaInAs layer thickness (h=0.1, 0.25, 0.5, and 1 μm). Capacitance-voltage (C-V) measurements with different frequencies show a higher-frequency dispersion for a greater lattice-mismatched sample. From the frequency dependence of the C-V curve, single-level charged interface-state density (Ns) was estimated using the effective parallel capacitance and conductance components. The average charged interface density Nss was also estimated using Voltage-intercept (Vint) method. Nss shows a linear dependence on the in-plane mismatch. The charged interface state density is approximately 2.7 Δa∥/a30 for partially lattice-relaxed heterojunctions. For the 1 μm sample, the forward I-V characteristic shows quasi-Fermi level pinning effect. Admittance spectroscopy measurement gives an equilibrium Fermi energy at about Ev+0.36 eV with hole capture cross section cp=2.7×10−15 cm2 for the 1 μm sample and at Ev+0.21 eV and cp=2.4×10−16 cm2 for the 0.5 μm sample.
An efficient self-consistent model for resonant tunneling structures
Authors: Alam Muhammad A. , Khondker A. N.
Published: July 2002

We present an efficient self-consistent current-voltage model for the double-barrier resonant tunneling (RT) structure. In the existing self-consistent models, normalized wave functions are used to describe the distribution of space charge in the RT structure. The present model, instead, uses the concept of group velocities for electrons. The use of group velocities for electrons simplifies the model by eliminating the need for the calculation of normalized wave functions.
Thin-film Al/diamond Schottky diode over 400-V breakdown voltage
Authors: Jeng David G. , Tuan H. S. , Salat Robert F. , Fricano Glenn J.
Published: July 2002

Diamond Schottky diodes were developed by growing diamond film (DF) on n-type silicon followed by evaporating aluminum (Al) contacts on the top of the DF. A high breakdown voltage (over 400 V) and a high forward-to-reverse current ratio (IF/IR over 105) have been observed. In spite of the high internal resistance, an ideality factor of 1.85 was determined.
Pulsed laser deposition of diamondlike hydrogenated amorphous carbon films
Authors: Malshe A. P. , Kanetkar S. M. , Ogale S. B. , Kshirsagar S. T.
Published: July 2002

Diamondlike hydrogenated amorphous carbon films have been deposited for the first time by pulsed ruby laser deposition (PLD) from pyrolytic graphite in hydrogen partial pressure. A hint in the IR absorption spectrum at 2920 cm−1 provides an evidence for the incorporation of hydrogen in the film. Raman scattering (RS) measurements display a large downward shift in the position of the intense G line to 1500 cm−1, whereas the relatively weak D line is observed near 1350 cm−1 along with a strong enhancement in RS near 1210 and 800 cm−1. These features are attributed to an increased proportion of tetrahedral (sp3) character in the amorphous carbon network due to formation of hydrogen-related complexes. Additional support for this proposal is sought from the enhanced band gap of the PLD a-C:H films compared to those of unhydrogenated PLD a-C films.
Impurity effect on the creation of Ga vacancies in a Si-doped layer grown on Be-doped GaAs by molecular-beam epitaxy
Authors: Lee Jong-Lam , Wei Long , Tanigawa Shoichiro , Kawabe Mitsuo
Published: July 2002

The impurity effects on the creation of Ga vacancies in Si-doped GaAs grown on a Be-doped epilayer by molecular-beam epitaxy were investigated through slow positron beam measurements. Doping of Si impurities enhances the creation of Ga vacancies in GaAs. The experimental results support the theoretical prediction of the creation of Ga vacancies in terms of the change in the Fermi-level position by the Si doping into GaAs, and also suggest that a Si atom diffuses in GaAs as a neutral complex of SiGa-VGa rather than that of SiGa-SiAs. The change in the S parameter distribution at the interface between Si and Be-doped regions is explained by the Be carryforward phenomenon which occurs during the growth of Si-doped GaAs on a Be-doped epilayer.
Current-generated spatially periodic space charge in semiconductors
Authors: Zitter R. N.
Published: July 2002

A steady-state current can generate significant regions of space charge in semiconductors. A first integral is given here for the nonlinear differential equations describing the process, which should be helpful in reducing computing time for calculations. A rigorous proof is presented to show that spatially oscillating charge distributions are produced when ωpτ ≳1/2 where ωp is the plasma frequency and τ is the average scattering time. For collisionless transport, a complete analytic solution is obtained showing perfect periodicity with properties determined by the injecting contact.
Control of sidegating effects in AlGaAs/GaAs heterostructure field-effect transistors by modification of GaAs wafer surfaces
Authors: Gray M. L. , Reynolds C. L. , Parsey J. M.
Published: July 2002

Sidegating characteristics of AlGaAs/GaAs heterostructure field-effect transistors, fabricated on molecular-beam epitaxially grown layers, were investigated with emphasis on the material properties. A systematic analyses of the epitaxial layers concluded with the identification of the substrate–superlattice-buffer-layer interface as the predominant cause of the sidegating effect. Remnant carbon contamination on the GaAs surface was found to produce a p-type, conducting interfacial region. Controlled oxidation of the carbon on the wafers was accomplished using ultraviolet radiation. This oxide was desorbed in situ before epitaxial growth. Secondary-ion-mass spectroscopy was employed to estimate the carbon concentration at the substrate–epitaxial-layer interface for standard cleaned and ultraviolet-ozone-treated wafers. The carbon concentration of the interfacial region decreased by two orders of magnitude for the wafers exposed to the ultraviolet radiation. Hall-effect measurements of standard cleaned and ultraviolet-ozone-treated heterostructure wafers, prepared with various buffer layer thicknesses, demonstrated the dominant influence of the interfacial p-type region on the electronic properties of the material. A comparison of sidegating characteristics for devices fabricated on the two types of wafers is presented and discussed. A dramatic improvement in sidegating was observed for the wafers subjected to the ultraviolet-ozone cleaning procedure.
Optical characterization of thermal mixing in quantum wells and heterostructures using a Green’s function model
Authors: Homewood K. P. , Dunstan D. J.
Published: July 2002

We describe a simple Green’s function model of interface mixing in quantum wells that provides exact quantitative solutions for real structures. Examples are given of several important low-dimensional heterostructures. The model enables the energy of the band-edge optical transition to be predicted as mixing proceeds, so that optical characterization techniques such as photoluminescence or absorption provide a powerful tool for studying mixing and obtaining interdiffusion constants.