bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties of Au-Zn Ohmic contacts to p-GaSb
Authors: Oliveira J. B. B. , Olivieri C. A. , Galzerani J. C. , Pasa A. A. , de Prince F. C.
Published: July 2002

Ohmic contacts to p-GaSb were prepared by the deposition of (100 Å Au+100 Å Zn+800 Å Au) and their characteristics were analyzed. Measurements of specific contact resistance as a function of annealing temperature show a minimum value of ∼1×10−5 Ω cm2 for alloying at 300 °C for 15 min. Auger electron spectroscopy depth profiles and Rutherford backscattering spectroscopy analysis for samples annealed at different temperatures show the diffusion of Au into GaSb and also give evidence of Ga outdiffusion and Zn in-diffusion. The presence of oxygen in the film surface and at the interface is discussed.
Long-pulse transversely excited 12CO2 and 13CO2 lasers
Authors: Chakrabarti A. , Reid J.
Published: July 2002

A conventional, transversely excited CO2 discharge module is fitted with a pulse-forming network to produce current and laser pulses with a duration of ≥20 μs. Detailed measurements of laser pulse energies and small-signal gain coefficients are made for both 12CO2 and 13CO2 gas mixtures, and the results compared with a computer model. In the long-wavelength band, the two isotopes are found to give very similar performance; the ratio of gain coefficients is measured as 1.00±0.05, while the 12CO2 pulse energy exceeds that of 13CO2 by approximately 20%.
State distribution and ambipolar diffusion length in n-type hydrogenated amorphous silicon
Authors: Balberg I. , Weisz S. Z.
Published: July 2002

Measurements of the deep state distribution and the ambipolar diffusion length were carried out on the same n-type a-Si:H materials. It was found that the concentration of active recombination centers [D−] is proportional to N1/2P, where NP is the total concentration of deep states. This result indicates that states other than D− states are present around the midgap of P-doped materials, and that the other states are probably associated with donor-D− pairs.
Intense 1.315-μm atomic iodine emission from TlI/Xe discharges
Authors: Schlie L. A. , Rathge R. D.
Published: July 2002

Results are presented showing that cw, rf discharge excitation of low-pressure gas mixtures of TlI and Xe produce very strong atomic iodine emission at 1.315 μm. An examination of previous electron beam excitation observations coupled with these results suggest that there exist two pumping processes for the excited atomic iodine. These are resonant energy transfer of Tl metastables to the excited iodine level and photolytic excitation/collisional TlI dissociative excitation from excited Xe metastable atoms. The overall results suggest a potential for this system as a cw, completely cyclic, self-contained atomic iodine laser at 1.315 μm.
Modulated optical reflectance measurements on bulk metals and thin metallic layers
Authors: Alpern P. , Wurm S.
Published: July 2002

We present modulated optical reflectance experiments with several bulk metals as well as thin AlSi and Ti layers sputtered on SiO2 and Si substrates. The measurement technique is able to detect variations of thermal conductivity, layer thickness, and local thermal contact between metallization and substrate. Furthermore, it provides the possibility of characterizing effects of temperature processes on thin metallic films as used in microelectronic technology in a more sensitive way than sheet resistance does.
Cleavage energies in semiconductors
Authors: Berding M. A. , Krishnamurthy Srinivasan , Sher A. , Chen A.-B.
Published: July 2002

We present a method for the calculation of the surface and cleavage energies, Eγ, for semiconductors, based on a tight-binding Green’s function approach and a difference-equation solution for the layered structure. Energies are calculated for a representative group of semiconductors, and cleavage energies are found to agree well with the available experimental data. We find ESiγ(111)=1360 ergs/cm2, and Eγ(110)=1000, 180, and 120 ergs/cm2 for GaAs, CdTe, and HgTe, respectively.
On the model of metastable phase formation by a diffusion process
Authors: Grushko B. , Shechtman D.
Published: July 2002

It is proposed that the structure of a new layer AB, which forms between the components A and B, is defined by parameters of two-stage interfacial reactions. The two stages, namely transition of A atoms through the AB/B boundary and rearrangement of atoms in B into AB, have independent rates. In the initial stage of the interaction between the two components the flow through the thin new layer does not control the reaction rate. The high rate of atomic flow through the interface combined with the relatively low rate of diffusion at the interface will result in the formation of metastable (amorphous, quasicrystalline, or crystalline) phases. The additional growth of the layer results in a decrease in the growth rate down to a critical value. The thickness of the metastable layer is thus limited and a stable crystalline phase starts to form at the interface. The critical thickness of the metastable phase depends on the diffusion parameters of the initial and intermediate phases.
Evolution of terrace size distributions during thin-film growth by step-mediated epitaxy
Authors: Gossmann H.-J. , Sinden F. W. , Feldman L. C.
Published: July 2002

Under certain conditions the process of thin-film epitaxy can be envisioned as atom deposition onto a crystalline substrate with subsequent surface diffusion along the surface terraces and eventual atomic bonding at a surface step. This process of step-mediated growth is currently being explored as a mechanism to form two-dimensional periodic structures. Such schemes require a periodic step distribution, i.e., uniform terrace lengths, to succeed. In this paper we use a model based on step-mediated growth to present an analytical derivation of the approach to uniform terrace lengths on a stepped surface, given a terrace length distribution of finite width at the outset. The results show that growth interruption is of no advantage and that in general the approach to uniform terrace lengths is quite slow. The width of the terrace length distribution varies approximately as the inverse 4th root of the deposited coverage. This will only occur if the atoms attach themselves predominately at the up-step of each terrace. Otherwise, the width of the distribution will grow without bounds. The model further predicts characteristic oscillations of terrace lengths in the vicinity of multiple height steps.
Electron transport in fluorenylidene malononitrile doped polyester
Authors: Borsenberger P. M. , Kung T.-M. , Vreeland W. B.
Published: July 2002

Electron mobilities have been measured in binary solid solutions of (4-n-butoxycarbonyl-9-fluorenylidene)malononitrile and a polyester. The temperature and electric field dependences of the mobility can be described as exp(T0/T)2 and exp(βE1/2), respectively. The results are discussed within the framework of a model involving hopping within a distribution of states broadened by disorder. A comparison of these results with those observed for hole transport in doped polymers is briefly discussed.
Shockley–Read recombination and trapping in p-type HgCdTe
Authors: Fastow R. , Goren D. , Nemirovsky Y.
Published: July 2002

The concepts and definitions of the steady-state minority-carrier lifetime, the steady-state majority-carrier lifetime, and the transient excess-carrier lifetime in semiconductors are reviewed. The effects that Shockley–Read centers have on these lifetimes are discussed, with emphasis given to the case of p-type Hg0.775Cd0.225Te containing traps. Measurements of the excess-carrier lifetime in Hg0.775Cd0.225Te (Na∼1×1016/cm3) using various experimental techniques are then summarized in view of the above definitions.
Semi-insulating epitaxial GaAs
Authors: Castenedo R. , Mimila-Arroyo J. , Bourgoin J. C.
Published: July 2002

Semi-insulating GaAs material results from the compensation of residual acceptor impurities and intrinsic defects by the so-called EL2 donor defects which possess a level at midgap. A semi-insulating layer can therefore be produced if it is possible to introduce a large enough concentration of EL2 defects. We describe a vapor-phase epitaxy technique which allows to introduce an EL2 concentration in the range 1015–1016 cm−3. This technique is made to reach very large growth rates, based on the fact that the EL2 concentration increases with the growth rate. The variation of the EL2 concentration versus the various growth parameters (substrate temperature, partial pressure, growth rate) have been monitored. The mechanism by which the incorporation of EL2 defects occurs has been determined, thus allowing one to get a given EL2 concentration reproducibly. This technique of growth, being inexpensive and fast, requiring no toxic gases, appears to be a reasonable alternative to the production of semi-insulating substrates.
Interactions of Cu with CoSi2, CrSi2 and TiSi2 with and without TiNx barrier layers
Authors: Olowolafe J. O. , Li Jian , Mayer J. W.
Published: July 2002

Interactions of Cu with CoSi2, CrSi2, and TiSi2 with and without interposed TiNx layers have been studied using Rutherford backscattering spectrometry, Auger electron spectrometry, x-ray diffraction, and in situ sheet resistivity measurements. Cu diffuses through a preformed CoSi2 layer to form the structure CoSi2/Cu3Si/Si(100). No dissociation of CoSi2 has been observed. For the Cu/CrSi2/Si system, the outdiffusion of Si leads to the formation of Cu3Si/CrSi2/Si at temperatures above 300 °C. At about the same temperature, Cu diffuses into a TiSi2 layer and to the TiSi2/Si interface to react with both Ti and Si forming Cu3Ti, Cu3Si, and Cu4Si phases. A 50-nm TiNx layer prepared by reactive sputtering was observed to be an effective diffusion barrier between Cu and CoSi2 or CrSi2. A 30-nm layer of TiNx simultaneously grown with TiSi2 by rapid thermal annealing proved effective between Cu and TiSi2 up to 500 °C.
Is T
c(P) for lead suitable as a low-temperature manometer?
Authors: Thomasson J. , Ayache C. , Spain I. L. , Villedieu M.
Published: July 2002

The superconducting transition temperature of lead has been reexamined as a function of pressure to 17 GPa (170 kbars). Tc(P) determined with helium as the pressure medium differed from that when 4:1 methanol:ethanol was used. The disagreement is particularly net in the fcc phase and can be ascribed to a sensitivity of Tc to the state of shear stress. This implies that Tc(P) for Pb is unsuitable as a manometer. The possibility that the hcp phase, occurring above about 14 GPa, may be useful as a manometer is discussed, but a definite conclusion cannot be reached at the present time.
Y-Ba-Cu-O thin films grown on rigid and flexible polycrystalline yttria-stabilized zirconia by pulsed laser ablation
Authors: Norton David P. , Lowndes Douglas H. , Budai J. D. , Christen D. K. , Jones E. C. , McCamy J. W. , Ketcham Thomas D. , Julien Dell St. , Lay K. W. , Tkaczyk J. E.
Published: July 2002

I n situ growth of highly oriented YBa2Cu3O7−x thin films (200–500 nm in thickness) has been obtained by pulsed KrF (248 nm) laser ablation on both rigid and flexible randomly oriented polycrystalline yttria-stabilized zirconia substrates. It is shown that c-axis-perpendicular YBa2Cu3O7−x films with a mosaic spread of only 1.0° can be grown on these randomly oriented polycrystalline substrates. Superconducting thin films were obtained with Tc(R=0)∼89 K on well-polished substrates. For the films deposited on the flexible substrates, the superconducting Tc is not degraded by repeated bending of the flexible substrate/film composite over a 2.25-cm-radius arc although the normal-state resistivity increases slightly, suggesting the creation of microcracks. The YBa2Cu3O7−x films grown on rigid polycrystalline yttria-stabilized zirconia substrates have a critical current density Jc(H=0)∼1400 A/cm2 at 77 K.
Partial oxygen pressure effects on the morphology of Y-Ba-Cu-O thin films in laser deposition process
Authors: Hase Takashi , Izumi Hirohiko , Ohata Katsumi , Suzuki Katsumi , Morishita Tadataka , Tanaka Shoji
Published: July 2002

The characterization of Y-Ba-Cu-O thin films prepared by 193-nm-ArF laser deposition at partial oxygen pressures ranging wide from 0.01 mTorr to 5 Torr has been investigated. These films have been grown on (100) SrTiO3 substrates held at 700 °C. Surface morphology, superconducting transition temperature and crystalline orientation strongly depend on a partial oxygen pressure during deposition. The smooth and highly crystal-oriented films with the superconducting transition temperature above 80 K and transport critical current densities of 1.0×105 A/cm2 (without magnetic field at 77 K) have been obtained at 10 to 50 mTorr of oxygen.
A photomodulated spectroscopy study of InxGa1−xAs/GaAs superlattices and quantum wells
Authors: Vazquez-Lopez C. , Ribeiro E. , Cerdeira F. , Motisuke P. , Sacilotti M. A. , Roth A. P.
Published: July 2002

We present here a detailed study of photomodulated transmission and reflectivity at room and liquid-nitrogen temperatures of a series of InxGa1−xAs/GaAs superlattices and a single quantum well. Our samples span a variety of alloy compositions and quantum-well widths. We compare the results of our measurements with the predictions of an envelope-function calculation, which includes wave-vector dependence of the minibands. This comparison allows identification of several spectral features unmistakably arising from miniband dispersion. Also, accurate determination is made of the band-offset parameter, whose value is discussed in the context of those obtained by other authors.
Universal efficiency and gain computations for high-gain free-electron-laser amplifiers
Authors: Booske J. H. , Bidwell S. W. , Levush B. , Antonsen T. M. , Granatstein V. L.
Published: July 2002

The free-electron-laser (FEL) equations are reduced to a set of one-dimensional, normalized equations that allow a universal (dimensional) analysis. In universal parameters, numerical integration of the FEL equations indicates a relatively constant saturated ponderomotive wave amplitude independent of both the normalized wiggler potential amplitude and the injected signal level. The constant ponderomotive wave amplitude and an empirical fit for the universal saturation length as a function of normalized wiggler potential amplitude and gain permits unnormalized design calculations for saturated power and saturated length over a wide parameter range. Tapering is considered by deriving analytical expressions for the intrinsic efficiency and taper length. Design values for a high-gain, high-efficiency, tapered amplifier at 280 and 560 GHz are presented.
I
n s
i
t
u thermal annealing of InP amorphous layer induced by Si+ implantation
Authors: Zheng P. , Ruault M.-O. , Denanot M. F. , Descouts B. , Krauz P.
Published: July 2002

I n situ transmission electron microscopy was used to investigate recrystallization during InP annealing up to 700 K after room-temperature Si+ implantation (50 keV) with fluences from 2×1013 to 5×1014 Si/cm2. The formation of perfect interstitial dislocation loops was observed during InP crystal regrowth (<1×1014 Si/cm2 ). At high total fluences (≳5×1013 Si/cm2 ) epitaxial precipitation of orthorhombic PSi and P2Si phases are unambiguously identified for the first time and several epitaxial relationships were found. This precipitation process confirms the high mobility of P atoms and leads us to assume that at lower fluence small PSi (<1.5 nm) clusters are present after annealing and could be accounted to the presence of faulted loops observed at the lowest total fluence of ∼2×1013 Si/cm2.
Critical parameters in the single-target sputtering of YBa2Cu3O7
Authors: Gavaler J. R. , Talvacchio J. , Braggins T. T. , Forrester M. G. , Greggi J.
Published: July 2002

The critical parameters in the single-target magnetron sputtering of YBa2Cu3O7 have been identified and sufficiently optimized to allow the reproducible deposition of films with Tc’s of ≳90 K and Jc’s of ≫ 106 A/cm2 at 77 K. It was found that during film growth the bombardment of the YBa2Cu3O7 by energetic particles must be minimized and also a stronger oxidizing agent than molecular oxygen must be present to obtain films with these properties. Otherwise, films are deposited that, by x-ray diffraction and energy dispersive x-ray spectroscopy analyses, are indistinguishable from the highest-Tc 1:2:3 stoichiometric material but which have critical temperatures of ≪90 K. Films need not have 1:2:3 overall stoichiometry to have optimum superconducting properties. In such cases the excess elements are present as second-phase particles.
Electrophotographic and structural studies on novel photoconductive polyimide films
Authors: Takimoto Akio , Wakemoto Hirofumi , Ogawa Hisahito
Published: July 2002

Novel photoconductive polyimides have been developed, whose monomer units are composed of a series of thiophenylene moieties, -C6H4S-, and imide groups. The most photosensitive polyimide shows an excellent photosensitivity of less than 1.0 μJ/cm2 in the visible light region, 400–570 nm. These photosensitive polyimide films are prepared by polymerizing the cast prepolymer films and annealing at the melting points of the polyimides. In this process their photosensitivities remarkably increase with the increase of crystallinity. From the structural studies by ultraviolet visible absorption, x-ray diffraction, infrared absorption, and x-ray photoelectron spectroscopy measurements, it is proposed that the coplanary conformation takes place in the crystallizing. The overlapped π orbitals, perpendicular to the polymer chains, lead to the more expanded conjugate system.
Temperature dependence of photoluminescence from Mg-doped In0.5Ga0.5P grown by liquid-phase epitaxy
Authors: Lu S. C. , Wu M. C. , Lee C. Y. , Yang Y. C.
Published: July 2002

The temperature dependence of photoluminescence from the Mg-doped In0.5Ga0.5P layers on (100) GaAs substrates grown by liquid-phase epitaxy has been studied. At low temperature, the spectra show only two major emission peaks involving intrinsic recombination and conduction–band-to-acceptor transition. The intrinsic recombination dominates in the doping concentration range studied (1.0×1017–7.0×1018 cm−3) above 60 K. Below 50 K, these two peaks merged with each other when the doping concentration is higher than 1×1018 cm−3. The temperature dependence of band gap in In0.5Ga0.5P layers determined from the photoluminescence peak energy varies as 1.976 − [7.5 ×10−4 T2/(T + 500)] eV. For the moderately doped concentration (p < 1.4 × 1018 cm−3), the Mg acceptor ionization energy obtained from 50-K photoluminescent spectra is in the range from 37 to 40 meV.
Magnetic hysteresis properties of BaFe12−xInxO19 ceramic ferrites with c-axis oriented grains
Authors: Dionne Gerald F. , Fitzgerald James F.
Published: July 2002

To study the effects of reduced magnetic anisotropy on hysteresis loops of hard magnets for possible use in self-biased microwave devices, a new family of magnetically oriented (c-axis) In-substituted Ba ferrite was prepared by conventional ceramic techniques. Earlier studies of BaFe12−x(In,Sc)xO19 series in single-crystal form have shown that magnetization 4πM and anisotropy field Hk decrease sharply with increasing x. Since hysteresis loops with optimum energy products require uniformly small grains (1 to 3 μm), sintering temperatures were carefully controlled over a range from 1180 to 1075 °C for 2 h, depending on In content. For nominal values of x ranging from 0 to 1.5, square hysteresis loops with Hc values decreasing from 3500 to 150 Oe were recorded with a high-field hysteresisgraph. The effective Hk values were measured and compared with single-crystal data to estimate the degree of grain alignment for each composition.
High-coercivity Co/Pd multilayer films by heavy inert gas sputtering
Authors: Brucker Charles F.
Published: July 2002

Co/Pd multilayer thin films with enhanced coercivity have been prepared by sputter deposition in Kr or Xe instead of Ar. The roughly twofold increase in coercivity is thought to be due to suppression of energetic sputtering species by the heavier inert gases, resulting in reduced damage to the metastable Co/Pd interface. High coercivity is achieved at practical sputtering pressures, broadening the range of magneto-optical recording applications that can be addressed using the new class of Co/Pd and Co/Pt multilayer materials.
Passivation of InP using In(PO3)3-condensed phosphates: From oxide growth properties to metal-insulator-semiconductor field-effect-transistor devices
Authors: Robach Y. , Besland M. P. , Joseph J. , Hollinger G. , Viktorovitch P. , Ferret P. , Pitaval M. , Falcou A. , Post G.
Published: July 2002

Fabrication of high-quality InP metal-insulator-semiconductor field-effect-transistor (MISFET) devices implies that adequate passivation of the surface can be achieved. In this paper, a passivation process of the InP surface, is presented using In(PO3)3-like condensed phosphates. An extensive study of the physicochemical and structural properties of these oxides and of the microscopic properties of its interface with InP is carried on, using a combination of various techniques (reflection high-energy electron diffraction, x-ray photoelectron spectroscopy, ellipsometry, and high-resolution transmission electron microscopy). High-quality MISFET devices have been fabricated; the high performances obtained in terms of transconductance and stability are well correlated with the good intrinsic properties of the oxides.
Three-dimensional effects in the acceleration of test electrons in a relativistic electron plasma wave
Authors: Mora P.
Published: July 2002

The acceleration of test electrons in a relativistic electron plasma wave is computed. The plasma wave is either due to the beating of two laser beams or constitutes the wake of an ultrashort laser pulse. The plasma wave geometry reflects the geometry of the laser. The electron beam has a finite emittance. The parameters of the calculation correspond to experiments now in progress. This 3D model is able to predict the corresponding electron spectrum.
Copper vapor laser machining of polyimide and polymethylmethacrylate in atmospheric pressure air
Authors: Ventzek P. L. G. , Gilgenbach R. M. , Ching C. H. , Lindley R. A. , McColl W. B.
Published: July 2002

A repetitively pulsed copper vapor laser (510 and 578 nm) is used to machine an opaque polymer (polyimide-Vespel) and a transparent polymer (polymethylmethacrylate-Lucite). Lucite is machinable by coating the surface with an ink which is semi-opaque to the green and yellow laser light. The repetition rate of the laser was 10 kHz with approximately 0.35 mJ/pulse and 3.5 W average power at the copper vapor laser wavelengths for a pulse width of 40 ns. The copper vapor laser thermally loads the target, generating thermal waves and sound waves in the gas which are investigated using HeNe laser beam deflection. The gas adjacent to the target is heated to steady state on the order of 100–400 s. Above the etching threshold, at approximately 10 mJ/cm2/pulse, the target is rapidly machined: 2-mm-diam, 2-mm-deep holes are drilled in 300 s in Vespel. At higher fluences of 100–150 mJ/cm2/pulse in 760 Torr of air it takes 180 s to bore through a 2-mm-thick disk of Vespel. The machined surfaces of the two polymers are very different. Machined Vespel samples are charred and cratered, whereas the Lucite samples show evidence of melting with little charring. The machining of polymers by visible-light copper vapor lasers is being compared to UV photoablation by KrF excimer laser light in order to study thermal versus nonthermal etching mechanisms.
Atomically flat gold films grown on hot glass
Authors: Hwang Jeeseong , Dubson M. A.
Published: July 2002

The results of a scanning tunneling microscope (STM) study of the morphology of Au films thermally evaporated onto heated glass substrates are presented. Au films of thickness 20–80 nm were evaporated onto Corning glass cover slips at temperatures of 20–465 °C. Before the evaporation, the glass substrates were prebaked at 300–400 °C for 12 h to remove surface contamination. Grain size and surface roughness of the films have been measured, and the best results were obtained with Au films 80 nm thick evaporated onto 300 °C substrates. These films have 250-nm-diam grains with large, atomically flat tops exhibiting step-free terraces as large as 200×200 nm2. These results are comparable to the best reported results for Au grown on heated mica and show that epitaxial growth is not required for the production of films with large atomically flat regions. This study of Au on glass was motivated by failed attempts to produce flat films of gold on mica using recipes in the literature. Possible reasons for the poor results with mica are discussed.
Effects of annealing ambient on the electrical properties in heavily C-doped p+-AlGaAs
Authors: Watanabe Kazuo , Yamazaki Hajime
Published: July 2002

The thermal behavior of the carrier concentration and the lattice constant in heavily carbon-doped p+-AlGaAs epilayers grown by metalorganic chemical vapor deposition are dramatically dependent on the annealing ambient at temperatures between 500 and 700 °C. Annealing in a hydrogen and arsine mixed gas ambient decreases the carrier concentration and increases the lattice constant. On the other hand, annealing in a hydrogen gas ambient increases the carrier concentration and decreases the lattice constant between 500 and 600 °C, which is consistent with our previous data for annealing in a nitrogen gas ambient. However, the carrier concentration after annealing at 700 °C is a little lower in hydrogen than in nitrogen. The above behavior of the carrier concentration and the lattice constant is well explained by incorporating and removing the hydrogen atoms in the epilayers during annealing.
A stress gettering mechanism in semi-insulating, copper-contaminated gallium arsenide
Authors: Kang Nam Soo , Zirkle Thomas E. , Schroder Dieter K.
Published: July 2002

We have demonstrated a stress gettering mechanism in semi-insulating, copper-contaminated gallium arsenide (GaAs) using cathodoluminescence (CL), thermally stimulated current spectroscopy (TSC), and low temperature Fourier transform infrared spectroscopy (FTIR). Cathodoluminescence shows a local gettering effect around dislocation cores in bulk semi-insulating GaAs qualitatively. This gettering result was confirmed by low temperature FTIR data, which show absorption features resulting from the transition of electrons from the valence band to copper levels. The energy level of each absorption shoulder corresponds to the various copper levels in GaAs. After gettering, the absorption depth at each shoulder decreases. Thermally stimulated current measurements show changes after copper doping. The characteristic returns to that of uncontaminated GaAs after gettering. On the basis of these qualitative and quantitative data, we conclude that copper was gettered, and we propose a stress gettering mechanism in semi-insulating, copper-contaminated GaAs on the basis of dislocation cores acting as localized gettering sites.
Study of surface states in (110) n-GaAs by exoelectron emission measurements
Authors: Railkar T. A. , Bhide R. S. , Bhoraskar S. V. , Manorama V. , Rao V. J.
Published: July 2002

Native surface defects on gallium arsenide are detected by thermally stimulated exoelectron emission measurements. Two emission peaks were identified that were correlated to the AsGa antisite defect. Plasma polymerized polythiophene grown on cleaned gallium arsenide is shown to improve the photoluminescence intensity of gallium arsenide and consequently the exoelectron emission measurements indicated the disappearance of one of the peaks. The results thus confirm the passivation of one of the AsGa antisite defects. The effects are also discussed in view of the low angle x-ray diffraction spectrum for cleaned and polythiophene treated gallium arsenide. Growth of species involving gallium sulfur and arsenic sulfur were also detected.
Influence of surface atomic steps on in-plane magnetic anisotropy of ultrathin Fe films on W(001)
Authors: Huang Di-Jing , Lee Jaeyong , Mulhollan G. A. , Erskine J. L.
Published: July 2002

Previous magneto-optic Kerr effect studies of ultrathin epitaxial Fe films grown on stepped W(001) surfaces yielded evidence of in-plane uniaxial magnetic anisotropy with magnetization perpendicular to the steps. We report spin-polarized secondary electron emission spectroscopy studies of the same system that confirms this novel micromagnetic phenomena, and provides a more detailed characterization of the zero-field in-plane spin configuration as a function of initial applied field direction.
Magnetic anisotropy in the Nd(Fe,Co)10Mo2 system
Authors: Xu Xie , Shaheen S. A.
Published: July 2002

The NdFe10−xCoxMO2 alloy system (x=0,1,3,5,7,10) has been synthesized and studied by x-ray and magnetometry techniques. All of the compounds in this series crystallize in the tetragonal ThMn12-type structure. X-ray-diffraction analyses on aligned powders indicate that the anisotropy in this system is strongly modified by Co substitution. A distinctive feature we observe is that, with increasing Co content, the easy direction of magnetization at 300 K appears to deviate from the c axis for x≤3, and becomes axial for x≥5. The spin reorientations are observed for x=0,1,3. For x≥5, the room-temperature anisotropy field increases with the increase of Co content, i.e., from 18 kOe at x=5 to 34 kOe at x=10, and no spin reorientations are observed. The first-order magnetization process is observed for x≥5. The Curie temperature is considerably enhanced by Co substitution in this system.
Resolution in collection-mode scanning optical microscopy
Authors: Buckland E. L. , Moyer P. J. , Paesler M. A.
Published: July 2002

The use of small apertures or sharpened tips as sensing elements in scanned-probe optical sensing devices has led to the development of a number of instruments that provide lateral spatial resolution much finer than that available in conventional optical imaging instruments. Such a device might generally be classified as a scanning optical microscope, or SOM. One particular mode of SOM operation involves the use of a sharpened optical fiber to collect light emanating from a surface. The lateral spatial resolution of such a collection-mode SOM is discussed in terms of the electromagnetic mode solutions of the probe tip. Numerical results indicate that, though bound modes solutions exist for increasingly fine unclad tips, classical diffraction effects limit resolution to a finite fraction (approximately 1/3) of the source wavelength λ. A second mechanism for signal transduction is shown to involve molecular scattering at the probe tip. An analysis of signal collection efficiency demonstrates that at tip radii below λ/5 for metallic-clad probes, and λ/10 for probes in a dielectric ambient, scattering dominates and imaging resolution scales with tip size, thus defeating limits imposed by diffraction.
High coercivity Sm2Fe17Nx and related phases in sputtered film samples
Authors: Rani R. , Hegde H. , Navarathna A. , Cadieu F. J.
Published: July 2002

High coercivity film samples of the ordered Sm2Fe17Nx phase with intrinsic coercivities, iHc, up to 23 kOe at 293 K, and 35 kOe at 10 K, were synthesized by rf sputtering. Random orientation Sm2Fe17 films were formed by the subsequent crystallization of originally amorphous deposits. The iHc of the original Sm2Fe17 films was 0.75 kOe at 293 K. X-ray diffractometer traces from 2Θ=28° to 73°, CuKα, exhibited 14 lines. Before nitriding all 14 lines were fit to the 2–17 rhombohedral structure with a=8.555 Å, c=12.445 Å, with a weighted root-mean-square deviation in 2Θ of 0.01°. After nitriding the cell volume increase was ≊7%. Nitriding of the ordered 2–17 films had to be performed in a very narrow temperature range to optimize the magnetic properties. The best magnetic properties were obtained by crystallizing the amorphous deposits in situ at a temperature of ≊900 K for 1 h and then subsequently nitriding in N2 gas at 0.75 atm., at 675–725 K, for 2 h. The room temperature coercivity as a function of the Sm concentration reached a maximum value of ≊23 kOe at a slightly richer than stoichiometric Sm composition.
Properties of ion assisted deposited titania films
Authors: Ghanashyam Krishna M. , Narasimha Rao K. , Mohan S.
Published: July 2002

Thin films of titanium dioxide have been deposited using ion assisted deposition with oxygen ions in the energy range 100–500 eV and current densities up to 100 μA/cm2. It has been observed that the refractive index of the films increases up to 300 eV and the extinction coefficient increased only nominally up to 300 eV. Optical band gap calculations have shown a strong dependence of the gap on the energy of incident ions. Beyond a critical energy and current density of the ions the refractive index and extinction coefficient of the films start deteriorating. It has also been found that beyond the critical values the optical band gap value decreases. The maximum refractive index obtained was 2.49 at an energy of 300 eV and 50 μA/cm2 current density. Post-deposition annealing of the films at 500 °C resulted in a slight increase in refractive index without affecting the extinction coefficient. X-ray diffraction studies revealed a monophasic anatase structure in these films.
Depth profiling of the Ge concentration in SiGe alloys using in situ ellipsometry during reactive-ion etching
Authors: Kroesen G. M. W. , Oehrlein G. S. , Frésart E. de , Haverlag M.
Published: July 2002

The complex refractive index of SiGe alloys at 632.8 nm has been measured as a function of the Ge concentration using in situ ellipsometry while the material is slowly removed from a silicon substrate using reactive-ion etching (RIE). Homogeneous, strained epitaxial SiGe films on silicon substrates were used. The Ge concentration was obtained by Rutherford backscattering. If an unknown SiGe structure is etched with RIE, in situ ellipsometry yields combinations of the ellipsometric angles Ψ and Δ with time. Starting at the Si substrate, these points are, on a point-to-point basis, converted into combinations of complex refractive index and depth in a numerical procedure. For this inversion of the ellipsometry equations, the known relation between the real and the imaginary part of the refractive index of SiGe is used. Finally the refractive indices are converted into Ge concentrations. Thus the depth profile of the Ge concentration in an unknown epitaxial SiGe structure can be inferred from an in situ ellipsometric measurement during RIE of the unknown structure. The obtained resolutions in depth and Ge concentration are 0.3 nm and 0.3%, respectively.
Effect of thermal noise on the characteristics of a high T
c superconducting quantum interference device
Authors: Enpuku K. , Shimomura Y. , Kisu T.
Published: July 2002

Effects of thermal noise on the characteristics of the dc superconducting quantum interference device (SQUID) have been studied. Numerical simulation on the SQUID characteristics operating at T=77 K has been performed by taking into account the thermal noise. It is shown that the voltage versus flux relation of the dc SQUID is degraded considerably with the thermal noise. The degradation becomes significant when the inductance of the SQUID increases. Due to this degradation, there exists significant limitation for the range of the inductance available at T=77 K, unlike the case at T=4.2 K. The maximum inductance should be around 200 pH in order to avoid significant degradation of the transfer function. This limited value of the inductance must be taken into account when we realize the SQUID coupled to an input coil. The analytical expression for the degradation of the transfer function due to the thermal noise is also obtained. The theoretical result explains experimental results reported recently.
Dependence of electromigration damage on current density
Authors: Hinode Kenji , Furusawa Takeshi , Homma Yoshio
Published: July 2002

Detailed analysis of electromigration damage, voids and hillocks, formed in layered conductors of aluminum over tungsten, revealed the following: (i) The number densities (numbers of voids and hillocks formed per unit conductor length) by electromigration are proportional to the current density; (ii) even when the void number density changes, the average growth rate of each void is still proportional to the current density; (iii) the positions of all the voids are uniformly distributed on a line; however, there is a regularity in intervals between one void to the next void and one void to the next hillock. From these results, especially from (i) and (ii), it is suggested that the dependence of void number density on the current density contributes to the higher than expected dependence of electromigration lifetime on the current density.
Direct and post-injection oxide and interface trap generation resulting from low-temperature hot-electron injection
Authors: Van den bosch Geert , Groeseneken Guido , Maes Herman E.
Published: July 2002

We have studied direct and post-injection trap generation, induced by low-temperature (∼77 K) hot-electron injection. At these temperatures the main degradation mechanism, attributed to the release, migration, and subsequent reaction of a hydrogenic species is inoperative, not only due to the suppressed release but also to the freeze-out of the species motion. As a result, trap creation is strongly reduced as compared to room-temperature injection. Additional interface traps are created during warmup following low-temperature injection. Two post-injection generation processes have been observed: a low-temperature (120 K), bias-independent process believed to be related to the migration of neutral atomic hydrogen released during stress, and a high-temperature (250 K), negative-bias enhanced process that apparently cannot be attributed to the migration of a species, but rather resembles the negative-bias-temperature instability phenomenon.
The Ag photodoping mechanism in As2S3
Authors: Lavine J. M. , Dumford S. A.
Published: July 2002

We have measured the number of photons/cm2 over the energy range 1.95 to 3.35 eV, required to form a negative-relief image in 2000 Å films of As2S3 using 100 Å films of evaporated Ag, Ag2Te, Ag2Se, and AgBr. We have observed sensitivity below the band gap of As2S3 in all cases. We have observed an increase in sensitivity by several orders of magnitude with increase of photon energy between 1.95 and 3.35 eV. The sensitivity decreases from Ag to the semimetals Ag2Te and Ag2Se to the wide band gap AgBr by the ratio 1:50:2500 at 2.4 eV. Assuming an internal photoemission model as proposed by Goldschmidt and Rudman, we extract barrier heights of 1.71, 2.10, 2.22 and 2.42 eV for Ag, Ag2Te, Ag2Se, and AgBr.
Breakdown mechanism in buried silicon oxide films
Authors: Mayo Santos , Suehle John S. , Roitman Peter
Published: July 2002

Charge injection leading to catastrophic breakdown has been used to study the dielectric properties of the buried oxide layer in silicon implanted with high-energy oxygen ions. Current versus gate bias, current versus time, and capacitance versus gate bias were used to characterize, at various temperatures, MOS metal-oxide-semiconductor capacitors with areas in the 1×10−4–1×10−2 cm2 range fabricated with commercially available single- or triple-implant separation by implanted oxygen silicon wafers. The data show that injected charge accumulates in the buried oxide at donorlike oxide traps ultimately leading to catastrophic breakdown. Both Poole–Frenkel and Fowler–Nordheim conduction, as well as impact-ionization mechanisms, have been identified in the oxide. The charge and field to breakdown in the best buried oxides are, respectively, near 1 C cm−2 and 10 MV cm−1, similar to the thermally grown oxide parameters. Cumulative distributions of these parameters measured over a large number of capacitors show that the frequency of breakdown events caused by extrinsic defects is scaled with the capacitor area. Intrinsic and extrinsic defect distributions are broader than with thermally grown oxides.
Photoluminescence spectra of trivalent praseodymium implanted in semi-insulating GaAs
Authors: Erickson Lynden E. , Akano Usman , Mitchell Ian , Rowell Nelson , Wang Aiguo
Published: July 2002

The photoluminescence spectrum of trivalent praseodymium, obtained by implantation and annealing of semi-insulating GaAs, is reported. The photoluminescence spectrum, observed at 2, 10, 20, and 40 K, extends from 9716 to 4000 cm−1. Sharp lines are observed in groups centered at 9500, 7400, 6200, 5200, and 4500 cm−1. Nineteen 3HJ energy levels are identified from these data. Only one Pr3+ site is observed. These energy levels were fitted by a D4 crystal-field model with a rms deviation of 64 cm−1. The zero phonon line at 4687.7 cm−1 is strongly coupled to the 62 and 79 cm−1 lattice phonons. All other groups show either a very weak coupling (6200 cm−1) or none to the lattice phonons.
A numerical analysis of the double periodic reflection metal grating for multiquantum well infrared photodetectors
Authors: Wang Yeong-cheng , Li Sheng S.
Published: July 2002

Two normalized parameters (i.e., s=λ/g and h=a/g, where g is the grating period and a is the width of metal dot) are introduced to characterize the two-dimensional (2D) double periodic reflection metal grating coupler for a multiquantum well infrared photodetector (QWIP). The ‘‘method of moments’’ is used to analyze this square metal grating structure for coupling the normal incident infrared (IR) radiation into the quantum wells. The main advantage for such a grating structure is that the coupling of the normal incident IR radiation is independent of its polarization direction. Two universal graphs relating the higher-order diffracted power and diffracted angle to the normalized wavelength have been constructed for the design of 2D metal grating coupled QWIPs. By using a simple scaling rule, the coupling quantum efficiency versus wavelength over a broad IR spectrum can be obtained for the grating coupled QWIPs.
Performance of the multiquantum well infrared photodetector
Authors: Peng Jian-Ping , Mu Yao-Ming , Shen Xue-Chu
Published: July 2002

A theoretical study of the performance of the multiquantum well infrared photodetector is carried out in this article. We first calculate the current response and dark current as a function of bias voltage and temperature within the sequential tunneling approach. Then we discuss in detail the noise characteristics of such a detector. The influence of the background radiation is also considered. The calculated detectivity D*λ is consistent with that found in experiments. It is shown that the detector is generally background limited at temperature lower than about 80 K with a D*λ of order 1010 cm Hz1/2/W.
Investigation of DX centers in AlxGa1−xAs by space charge spectroscopy
Authors: Wöckinger J. , Jantsch W. , Wilamowski Z. , Köhler K.
Published: July 2002

We present a critical analysis of both deep level transient spectroscopy and transient microwave absorption spectroscopy (MAS) for the case of DX centers in AlGaAs. We show that, even for a single level, a strongly nonexponential time dependence of the transients occurs. Our MAS experiments on Si-DX centers in Al0.3Ga0.7As extend the available data for the emission rates by more than three orders of magnitude. They are successfully interpreted by a single emission time constant using our model whereas at least three decay time constants are needed to explain the data by a pure exponential. Observed recapture processes in the neutral region of the sample underline the complexity of space charge spectroscopy in the case of the DX center.
Microscale evaluation of the viscoelastic properties of polymer gel for artificial muscles using transmission acoustic microscopy
Authors: Kolosov Oleg , Suzuki Makoto , Yamanaka Kazushi
Published: July 2002

Local viscoelastic properties and a micromechanical structure of polymer hydrogel were studied using transmission acoustic microscopy (AM) with a spatial resolution up to 5 μm. Utilizing various amplitude, phase, and pulse techniques provided by the transmission AM, a velocity and an attenuation of the acoustic wave in the local point of the polymer sample as well as a frequency dependence (dispersion) of these values were evaluated in the frequency range from 30 to 320 MHz. Using these facilities a poly(vinylalcohol) polymer hydrogel for the artificial muscle was studied at the succeeding steps of its manufacturing process of cyclic freezing–thawing. It was found that synchronously, with the increase of the compressional elasticity and acoustic attenuation, a micromechanical nonuniformity of the gel also profoundly enhances it. Fiber-like structures of 10–50 μm width possessing higher elastic modulus appear in the gel which can play a significant role in the macroscopic mechanical properties of the gel.
Cathodoluminescence and microRaman analysis of oxygen loss in electron irradiated YBa2Cu3O7−x
Authors: Gómez P. , Jiménez J. , Martin P. , Piqueras J. , Domínguez-Adame F.
Published: July 2002

The effect of oxygen loss on the luminescence of YBa2Cu3O7−x has been investigated by cathodoluminescence (CL) in the scanning electron microscope (SEM) and by Raman microprobe measurements. The results herein indicate that a CL band at 530 nm is related to oxygen loss rather than to impurity phases such as Y2O3 formed in the material by electron irradiation in the SEM.
Transport and optical properties of AlGaAs/GaAs and pseudomorphic AlGaAs/InGaAs/GaAs heterostructures subjected to CH4/H2 reactive ion etching
Authors: van Es C. M. , Eijkemans T. J. , Wolter J. H. , Pereira R. , Van Hove M. , Van Rossum M.
Published: July 2002

We investigate the effect of methane/hydrogen (CH4/H2) reactive ion etching (RIE) and a subsequent annealing process on AlGaAs/GaAs and pseudomorphic AlGaAs/InGaAs/GaAs heterostructures. We use low temperature Hall, Shubnikov–de Haas, and photoluminescence measurements. We observe that the electron density and mobility of the two-dimensional electron gas in the heterostructure is strongly reduced by the RIE process. After annealing the electron density fully recovers for both types of structures, whereas the electron mobility responds differently. While for the pseudomorphic AlGaAs/InGaAs/GaAs heterostructures thermal annealing restores the electron mobility completely, for the AlGaAs/GaAs heterostructures the electron mobility recovers only to 60% of the original value. This indicates that in the AlGaAs/GaAs heterostructures the structural damage induced by reactive ion etching is not fully removed by thermal annealing. This is confirmed by photoluminescence measurements at low temperatures.