bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermionic emission including both space-charge and image forces
Authors: Lin T. P. , Eng Genghmun
Published: July 2002

The net emission current for a uniform plane thermionic emitter is determined for a range of voltages, temperatures, and various values of the work function. Poisson’s equation is self-consistently solved, using numerical techniques, without any additional phenomenological assumptions. This work accurately specifies the net current in the transition region between space-charge-limited and temperature-limited emission, and we present the first determination of the shape of the interelectrode potential there. A comparison with earlier approximate techniques is also included.
High-pressure Raman scattering in dimethyl phenyl silanol
Authors: Cansell F. , Petitet J. P. , Fabre D.
Published: July 2002

Raman scattering of dimethyl phenyl silanol has been studied in a diamond anvil cell at room temperature and pressure up to 24 GPa. The liquid-solid transition is found near 5 GPa. Above 15 GPa, an irreversible transformation occurs to a translucent polymerlike solid which can be recovered at zero pressure with permanent internal stresses.
Physics and design of hot-electron spectrometers and transistors
Authors: Beton P. H. , Long A. P. , Kelly M. J.
Published: July 2002

We explain how Monte-Carlo simulations may be used to calculate the transfer characteristics of GaAs hot-electron transistors, from which hot-electron spectra may be derived. We present such spectra for a range of doping densities and injection energies for a base width of 500 Å. We compare our results with those derived from other theories and suggest an experiment which should indicate their relative validity. Optimum parameters for base width and doping for high-frequency hot-electron transistors are derived and compared with available experimental data.
Generalized criteria for microwave breakdown in air-filled waveguides
Authors: Anderson D. , Lisak M. , Lewin T.
Published: July 2002

Generalized threshold conditions for breakdown in air-filled high-power microwave waveguides are formulated. The analysis takes into account the temperature-dependent processes in air that affect the breakdown process. The results provide a theoretical explanation of the fact that breakdown thresholds of microwave devices are observed to be much lower than those predicted by the conventional cold-air theory.
Persistent photoconductivity in Ga0.49In0.51P/GaAs heterojunctions
Authors: Amor S. Ben , Dmowski L. , Portal J. C. , Pulsford N. J. , Nicholas R. J. , Singleton J. , Razeghi M.
Published: July 2002

We have studied the persistent photoconductivity (PPC) effect in Ga0.49 In0.51 P/GaAs heterostructures. Through time- and temperature-dependent Hall effect, we observe very small relaxation rates and the PPC remains observable at room temperature. Optical experiments show an optical energy threshold of 1.15 eV and an infrared quenching of the PPC. Thermal cycling of the samples strongly affects the PPC and the quenching temperature. The center responsible for the observed PPC, therefore, appears related to defects. Most of our observations are qualitatively understood in a large lattice relaxation DX-like center approach. However, the origin of the high quenching temperature remains to be explained.
Optical transmission of ferroelectric liquid-crystal displays
Authors: DeVos Alexis , Reynaerts Carine
Published: July 2002

The director orientation of the ferroelectric liquid crystal molecules within a surface-stabilized display is considered to be uniform. Under this simplifying assumption it is possible to calculate analytically the light transmission of the liquid-crystal display as a function of the azimuth angle φ of the director. We find that the transmission τ is a simple rational function of the polarization p=P cos φ, where P is the spontaneous polarization of the ferroelectric molecule. Experimental results confirm the usefulness of the formula.
Limitation to Shockley–Read–Hall model due to direct photoionization of the defect states
Authors: Hsieh Y. K. , Card H. C.
Published: July 2002

Restrictions on the standard Shockley–Read–Hall (SRH) model in the recombination processes due to direct photoionization of the trapping centers have been theoretically studied. We find that, for photon energies even slightly in excess of the energy gap (i.e., ℏω≥Eg+0.01 eV) photoionization via defect states may normally be neglected in comparison with interband photogeneration, even in indirect semiconductors (e.g., n-type silicon doped with gold). For photon energies below Eg, the recombination expressions for SRH are found to be simply replaced by similar expressions with suitably defined effective values n*1 and p*1, which incorporate the photoionization of the trapping centers.
Dose dependence of the silicon near-surface modifications caused by CF4 reactive ion-beam etching
Authors: Lejeune C. , Grandchamp J. P. , Gilles J. P. , Collard E. , Scheiblin P.
Published: July 2002

The ion dose dependence of the silicon near-surface modifications caused by CF4 reactive ion-beam etching was studied using on-line variation of SiF4 partial pressure, ellipsometry, and Auger electron spectroscopy. The existence of two critical doses is demonstrated. Beyond the lower critical dose, of about 5×1016 cm−2 according to the beam parameters, the steady state of the carbonaceous overlayer is reached, and the overlayer can be removed effectively by a simple dip in concentrated HF for 60 s, thus allowing the diagnostics of the damage of the underlying silicon. On the other hand, the silicon near surface is still modified up to a second critical dose, for which the steady state of both the overlayer and Si subsurface is then reached. Likewise, the conditions to minimize the contamination of the underlying crystal, as a function of the ion dose, are achieved.
Effect of recrystallization conditions on linearity of Hall output voltage of an InSb element
Authors: Iida Shosan
Published: July 2002

Recrystallizing conditions for InSb film with respect to improvement of linearity of the output voltage at Hall electrodes of the Hall element made from the recrystallized film as a function of applied magnetic flux density are studied. For recrystallization, source InSb films produced through vacuum deposition on glass substrates are covered with SiO layers, heated thoroughly into a molten phase, and then cooled to a solid phase in an Ar gas stream or vacuum. Other InSb films are covered with In2O3 layers. Uniform heating of an extensive area of the film is done in the recrystallization. Many Hall elements made from the recrystallized InSb films indicate nonlinearity output voltage as a function of the applied magnetic flux density. This phenomenon suggests that the output voltage is a result of a combination of Hall voltage and magnetoresistive voltage as Sb or In inclusions appear in the recrystallized InSb film. Superior linearity of the output voltage of the Hall element are obtained when stoichiometric InSb film is recrystallized with a relatively high cooling rate. Factors leading to excellent linearity are verified through x-ray diffractometry, fluorescent x rays, and microscopic examinations on the recrystallized InSb films and the source InSb films. In this paper, Sb and In inclusion structures in the recrystallized InSb films are discussed and the causes of linearity or nonlinearity are explained using the above experimental examinations.
Bragg resonances in a doubly periodic planar waveguide
Authors: Sandström Sven-Erik
Published: July 2002

The dispersion relation for a doubly periodic electromagnetic waveguide is determined by means of the null-field and modal approaches. The waveguide walls are assumed to be perfectly conducting and to have the form of corrugated parallel plates. Bragg resonances appear in the form of stopbands or cross-over resonances. The field inside the waveguide is obtained by means of modal theory. Numerical problems that emanate from mode degeneracy and large matrix sizes are dealt with by means of the Muller algorithm and singular value decomposition. The computed Poynting vector and the group velocity are discussed.
Novel trap state at the grain boundary: Metastable character of defects in p-HgMnTe and p-HgCdMnTe bicrystals
Authors: Suski T. , Wiśniewski P. , Dmowski L. , Grabecki G. , Dietl T.
Published: July 2002

The existence of the novel trap state in bicrystals of narrow-gap semiconductors is clearly demonstrated. It is shown that this state exhibits metastable character and its origin is related to the grain boundary. A method of tuning the concentration and mobility of electrons by means of the high-pressure freezeout of carriers on these metastable states has been applied to study two-dimensional properties of the grain boundaries in HgMnTe and HgCdMnTe semimagnetic semiconductors.
A model for including thermal conduction in molecular dynamics simulations
Authors: Wu Yue , Friauf Robert J.
Published: July 2002

A technique is introduced for including thermal conduction in molecular dynamics simulations for solids. We develop a model to allow energy flow between the computational cell and the bulk of the solid when periodic boundary conditions cannot be used. Thermal conduction is achieved by scaling the velocities of atoms in a transitional boundary layer. The scaling factor is obtained from the thermal diffusivity, and the results show good agreement with the solution for a continuous medium at long times. We have investigated the effects of different temperature and size of the system, and of variations in strength parameter, atomic mass, and thermal diffusivity. In all cases, no significant change in simulation results has been found.
Laser-damage-induced microdomain in LiNbO3:Fe
Authors: Wu Zhongkang , Wang Jinxiong , Wang Huafu , Lu Yongbin , Deng Yang , Xu Yuheng
Published: July 2002

In this communication a clear observation of ferroelectric microdomains induced by laser damage is described. The microdomains are seen clearly through crossed nicols and arise at the positive Ps side of the mark of laser damage, not at the negative Ps side. Considering the existence of oriented displacement of photostimulated carriers and local electric field in the exposed region due to the photovoltaic effect, the displacement of Li+ along the negative Ps direction is shown by an α-track technique. Therefore, the microdomain is considered originating from oriented displacements of Li+ ions along the direction of Ps. The ion moves through the triangular plane of oxygen under photovoltaic stimulation and induces the ordering of Li, Nb, and vacancy under the local electric field.
Effects of room-temperature pressure cycling on the critical currents in a YBa2Cu3O7−δ superconductor
Authors: Puźniak R. , Chen D.-X. , Gyorgy E. M. , Rao K. V.
Published: July 2002

We have studied the effects of sequential pressure cycling (0–2.8 GPa at room temperature) on the critical currents in a YBa2Cu3O7−δ superconductor. From both low- (0–100 Oe) and high- (up to 5.5 T) field dc magnetic data we identify the contributions to the total critical currents arising from inter- (transport) and intragranular aspects of the superconductor. In our studies, we find that above the pressure limit (≤1.0 GPa) of reversible changes the transport critical current is found to irreversibly decrease by as much as 40%–50% for cycling at 2.8 GPa. However, the intrinsic contribution to the critical current is unaffected. Concomitantly two lower critical fields H*c1 and Hc1 are found necessary to fully characterize the low-field hysteretic loops for these superconductors. One consequence of pressure cycling is that we find H*c1, which signifies the intergranular connectivity, is reduced to lower values. The effects of pressure cycling on the real and imaginary (lossy) components, χ′(T) and χ″(T), of the low-field ac susceptibility are found to be consistent with the dc data.
White-noise measurements and Joule heating in superconducting point contacts
Authors: Carroll Kenneth R. , Paik Ho Jung
Published: July 2002

We report measurements of the white noise in superconducting niobium point contacts. These measurements, the junction parameters, and the method of fabrication of the point contacts are compared with those of other experiments. The power spectral density was found to have an approximately parabolic dependence on the average voltage V rather than the linear dependence expected in the shot-noise limit. We also found that the magnitude of the excess noise was larger than has been previously reported. Because of these differences, the noise data presented add to the existing body of data. The V2 dependence of the power spectral density suggests that Joule heating may have been responsible for the excess noise. Joule heating was determined to be present in the junctions from the relatively small critical currents I0 ≲2 μA and the effect that a resonant cavity had on the Josephson oscillation. However, we show that Joule heating cannot account for the level of the excess noise observed in present or previous data.
Electron paramagnetic resonance study on annealing of phosphorus-implanted cadmium telluride
Authors: Hsu Y. J. , Hwang H. L
Published: July 2002

This paper presents the investigations on the p-type conduction of the phosphorus-implanted CdTe single crystals. Previous theoretical calculations predicted the existence of large amounts of phosphorus interstitials in the as-implanted and thermally annealed samples and the elimination of these defects in the pulse electron-beam-annealed samples, which is confirmed in this work by the electron paramagnetic resonance measurements. This shows the significant effect of melting crystals in the pulse electron-beam annealing process on obtaining high carrier concentrations.
The role of silicon self-interstitial supersaturation in the retardation of oxygen precipitation in Czochralski silicon
Authors: Rogers W. Boyd , Massoud Hisham Z. , Fair Richard B. , Gösele Ulrich M. , Tan Teh Y. , Rozgonyi George A.
Published: July 2002

The retardation phenomenon of oxygen precipitation in Czochralski silicon has been studied simultaneously with the growth of surface stacking faults under a silicon nitride capping layer. The surface faults were intentionally introduced to monitor the bulk self-interstitial supersaturation in the crystal during precipitate growth. It was observed that an increase in the low-temperature nucleation anneal time resulted in a reduced rate of oxygen precipitation and an enhanced rate of surface stacking fault growth at high temperatures. This indicates that as the nucleation anneal time increases, silicon self-interstitials, which must be generated for precipitation to proceed, reach a high level of supersaturation and cause the annihilation of most nuclei generated during the nucleation anneal.
Microstructural studies of epitaxial Ge films grown on [100] GaAs by laser photochemical vapor deposition
Authors: Kiely C. J. , Tavitian V. , Eden J. G.
Published: July 2002

Ge films grown on [100] GaAs by laser photochemical vapor deposition (LPVD) in parallel geometry at temperatures (Ts) ranging from ∼240 to 415 °C have been examined by transmission electron microscopy. For 285 ≤Ts≲330 °C, a thin (250–700 Å) epitaxial film is grown initially but a switch to amorphous material is subsequently observed. At higher substrate temperatures (Ts ≳400 °C), thicker (≳800 Å) epitaxial Ge films are grown before the transition to polycrystalline material takes place. In the absence of external 193-nm laser radiation (i.e., growing by conventional low-pressure chemical vapor deposition), the Ge films are completely amorphous (285 ≤Ts≤330 °C) or heavily defected polycrystalline (Ts∼400 °C). The >100 °C temperature reduction for the growth of epi Ge films made possible by LPVD is attributed to the direct production of a species (GeH3) by the laser which is collisionally converted to Ge2H6 en route to the substrate. Upon reaching the [100] GaAs surface, the digermane is pyrolyzed. Experiments with [100] substrates tilted 3° toward [110] yielded thinner (∼120 Å), but smooth, epitaxial films which is attributed to the higher density of available nucleation sites. Films grown at 280–330 °C on [111] oriented GaAs were completely amorphous which appears to arise from reduced adatom mobilities on [111] surfaces. These results clearly demonstrate the feasibility of photochemically generating a species which migrates to the surface and alters the chemistry at a substrate (which is itself not illuminated by the optical source) so as to permit the growth of epitaxial semiconductor films.
Electrical characterization of inadvertent midgap levels in GaP
Authors: Iqbal M. Zafar , Gill Asghar A. , Baber N.
Published: July 2002

Results of an electrical characterization study of two hitherto unobserved midgap deep levels in GaP using deep-level transient spectroscopy and single-shot dark capacitance transient techniques are reported. These are the dominant majority-carrier (electron) levels in the green-light-emitting diodes studied. Detailed electron emission rate and capture cross-section measurements are performed on these levels. The shallower of the two levels is found to have an activation energy to the conduction band varying from 0.88±0.02 eV to 0.93±0.02 eV from sample to sample while the activation energy of the deeper level is 0.96±0.02 eV. The results of the capture measurements give an upper limit of 1.2×10−19 cm2 for the electron capture cross sections of the two levels. A detailed comparison of the emission rate data with the published results on midgap levels in GaP is presented. It is proposed that one of these midgap levels may be the counterpart in GaP of the well-known EL2 level found in GaAs.
Lasing characteristics of 0.8-μm InGaAsP/GaAs lasers fabricated by wet chemical etching
Authors: Ishikawa Joji , Ito Toshio , Oh-iso Yoshitaka , Yamamoto Masahiro , Takahashi N. Shin-ichi , Kurita Shoichi
Published: July 2002

0.8-μm InGaAsP/GaAs stripe lasers, in which cavity mirrors were formed by two-step wet chemical etching, have been fabricated monolithically. The laser resonators were aligned along the 〈011̄〉 and the 〈010〉 directions. The first etching was done in 5% Br methanol. The secondary etching was done in H2SO4:H2O2:H2O (3:1:1 by volume) etchant for the active layers only, and gave low threshold lasers. Their threshold current densities were compared with those of the cleaved-mirror lasers made from the same wafer. Some longitudinal lasing modes were observed in the wavelength range of 805–810 nm. The characteristic temperature T0 was 116 K in the temperature range 28–87 °C. The relationship between the state of the etched facets and the near- and far-field patterns was examined. It was found that this two-step etching technique for the laser mirrors is very suitable for aligning the lasers along desirable directions on the same wafer for monolithic integrated optical circuits.
Plasma opening switch studies of an applied B
z ion diode
Authors: Struckman C. K. , Kusse B. R. , Meyerhofer D. D. , Rondeau G.
Published: July 2002

The light ion accelerator (1.5 MV, 4 Ω) at Cornell University is being used to study the characteristics of an applied Bz , or ‘‘barrel,’’ diode. We report here the results of a series of experiments utilizing a plasma opening switch. With a magnetically insulated ion diode load, the peak diode voltage increased from 1.5 to 1.8 MV and the ion power increased from 50 to 80 GW when a plasma opening switch was used. Our results are compared with existing theories of plasma opening switch operation.
Radiation-induced carbon-related defects in p-type silicon
Authors: Frederickson A. R. , Karakashian A. S. , Drevinsky P. J. , Caefer C. E.
Published: July 2002

The production and removal of carbon-related defects have been investigated in 1-MeV electron-irradiated boron-doped silicon solar cells using deep level transient spectroscopy (DLTS). In Czochralski (CZ) material, the interstitial carbon defect (hole trap at Ev+0.27 eV), CI, decays by thermal and charge injection processes. We find that irradiation by MeV electrons creates CI while simultaneously removing it through the minority-carrier injection process. Removal of CI correlates with significant growth in the density of a complex reportedly consisting of carbon and oxygen (hole trap at Ev+0.38 eV). Thermal annealing produces a different DLTS signal than does minority-carrier injection indicating that the carbon and oxygen complex (C+O) is at least two species. The effective cross section for minority-carrier-induced annealing of CI is found to be 2×10−18 cm2 in these samples.
Synchrotron radiation Bragg angle contour mapping of crack nucleation at grain boundaries
Authors: Bilello J. C. , Schmitz H. A. , Dew-Hughes D.
Published: July 2002

In technical materials a critical step leading to complete macroscopic failure is not the nucleation of cracks in isolated grains, but instead the transmission of rupture from grain to grain until the entire cross section is traversed. It is difficult, in general, to employ the usual microscopic observations which could provide the keys to a comprehensive mechanistic understanding of this problem. It is shown herein that monochromatic synchrotron radiation can be used to provide Bragg angular contour maps in a rapid and precise manner. These maps enable one to quantify the local strain field tensor associated with crack nucleation and propagation through a grain boundary. Based on this analysis it is then a straightforward process to determine the other mathematical properties usually associated with second rank tensors which lead to assessment of critical parameters for crack transmission at the boundary. The application of this analytical technique is experimentally demonstrated by studies of crack formation at grain boundaries in zinc bicrystals.
Fluorescence extended x-ray absorption fine structure study of silicon in neodymium iron boron rare-earth magnets
Authors: Brennan S. , Bienenstock A. , Keem J. E.
Published: July 2002

Rare-earth transition-metal magnetic materials consisting of Nd2Fe14B with small amounts of Si, produced by melt-spinning, have been studied using fluorescence extended x-ray absorption fine structure. A windowless Si(Li) solid-state detector was used to collect the Si fluorescence. These polycrystalline samples are unusual in that they are magnetically isotropic, yet have a very high remanent magnetization. The silicon atom is bonded to a single shell of iron atoms at a distance of 2.46±0.05 Å. The results strongly suggest that (1) Si does not segregate at the grain boundaries or cluster with other Si atoms, and that (2) Si replaces the iron atom at the ‘‘c’’ site of the standard Nd2Fe14B structural model within the grains.
V13O16 phase and the thickness dependence of the V3Si formation rate in SiO2/V reactions
Authors: Wang S. Q. , Mayer J. W.
Published: July 2002

The reactions of thin V films with either thermally grown or electron-gun evaporated SiO2 in the temperature range of 650–950 °C in vacuum have been studied by Rutherford backscattering spectrometry and glancing angle x-ray diffraction. V had identical reaction properties, such as reaction starting temperatures, reaction products, reaction rates, and reaction interface uniformities, with these two kinds of SiO2. The reactions resulted in a layer of V-rich silicide V3Si formed next to and a layer of V oxide V13O16 further away from the SiO2/V reaction interface. The formation rate for the V3Si layer increased with the thickness of the original V film.
Isolation spectra for quantum-well laser diode optical switches
Authors: Ikeda Masahiro
Published: July 2002

The spectral dependence of isolation characteristics for quantum-well laser diode optical switches, which are the level difference between the ON and OFF state attenuation, are calculated for p- and n-type quantum-well InGaAsP/InP using a semiclassical density-matrix analysis. The results show that p-type materials, which have rather large background carrier concentration, are suitable for large gain and high isolation optical switches. Broadband laser diode optical switches with a gain region of 1.3–1.55 μm can be obtained.
Hydrogen passivation of impurities in GaP as studied by photoluminescence spectroscopy
Authors: Mizuta M. , Mochizuki Y. , Takadoh N. , Asakawa K.
Published: July 2002

Hydrogen passivation of several types of impurities in GaP has been investigated by the use of low-temperature photoluminescence, secondary ion mass spectrometry, and electrical measurements. Exposure to atomic hydrogen has completely arrested optical activity of acceptor Zn, as detected by photoluminescence, whereas those of donor S and isoelectronic impurity N have not changed. Neutralization of the Zn acceptor is reversible in the sense that the original activity can be restored by a low-temperature anneal. These changes in luminescent activity are fully consistent with the results of electrical measurements and mass analysis.
Conformal mapping and the current distributions in AlxGa1−xAs/GaAs heterostructures
Authors: Li Z.-M. , McAlister S. P.
Published: July 2002

We show how the conformal mapping method can be used to map out the equipotential and current stream lines for an arbitrary Hall plate with van der Pauw geometry by reformulating the Schwarz–Christoffel equation in a form most convenient for computation. Our numerical technique is then used to determine the potential and current distributions in a AlxGa1−x As/GaAs heterostructure with parallel conduction. Our results for a single layer agree with experimental observations at low magnetic field and for regions between the plateaus of the quantum Hall effect. Equipotential and current stream lines are obtained for two previously proposed models for the heterostructures with parallel conduction: the two-band model and the isolated layer model. In the case of a large Hall angle (near the plateau of the quantum Hall effect) singularities of electric fields occur around the source-drain contacts as in a standard Hall bar. For the isolated layer model, additional singularities are formed around the side contacts due to the circulating Hall current through the side contacts which connect the two-dimensional electron gas layer and the supply layer.
A phenomenological description of strain relaxation in GexSi1−x/Si(100) heterostructures
Authors: Hull R. , Bean J. C. , Buescher C.
Published: July 2002

We describe how in situ observation of strain relaxation of Gex Si1−x /Si(100) heterostructures in a transmission electron microscope enable us to obtain the fundamental parameters which describe the nucleation, propagation, and interaction of misfit dislocations. Activation energies and prefactors are obtained for the nucleation and propagation processes for x in the range 0.20–0.35, and a simple model to account for dislocation interactions is developed. These measured parameters are then incorporated into a predictive model of strain relaxation which successfully reproduces experimental data. This model relies only upon parameters which can be directly measured.
Phase locking laser diodes using photorefractive coupling
Authors: Hillman Paul D. , Marciniak Michael
Published: July 2002

Several authors have reported strong frequency pulling while coupling laser diodes using phase conjugation. However, to our knowledge, no one has proven stable phase locking by interfering the laser outputs to show stable fringes. A stable phase lock has been obtained, and the geometry used is compared with those proposed previously.
Numerical model for degenerate and heterostructure semiconductor devices
Authors: Purbo Onno W. , Cassidy Daniel T. , Chisholm Stephen H.
Published: July 2002

A one-dimensional finite-difference numerical model appropriate for devices which require degenerate statistics to describe the carrier concentrations is reported. The Joyce–Dixon approximations [Appl. Phys. Lett. 31, 354 (1977)] to Fermi–Dirac statistics were used and found to be efficient and accurate methods to determine carrier concentrations, to calculate derivatives required in the iterative solution of the equations in the numerical model, and to compare to nondegenerate (i.e., Boltzmann statistics) models. For degenerate carrier statistics and heterostructure devices the Scharfetter–Gummell equations [IEEE Trans. Electron Devices ED-16, 64 (1969)] for the current densities must be modified to include the degenerate Einstein relations and variation of the density of states with position. These modifications, as well the possibilities of using the thermodynamic formulation of current density, are described.
Step doping in hydrogenated amorphous silicon thin-film transistors for threshold voltage shifts
Authors: Matsumoto Tomotaka , Mishima Yasuyoshi
Published: July 2002

We have developed a way to control the threshold voltage (VT ) in hydrogenated amorphous silicon thin-film transistors (a-Si:H TFTs) by boron doping. The field-effect mobility of uniformly boron-doped TFTs decreases rapidly with increased doping ratios. To keep the field-effect mobility from decreasing, we developed step-doped TFTs (SiN/undoped a-Si:H/boron-doped a-Si:H). With this structure, the decrease in the field-effect mobility by boron doping was lessened. The transfer characteristics calculated using a one-dimensional model were in good agreement with measurements below a doping ratio of 80 ppm. The difference between measurements and calculations for higher doping ratio was decreased using a new step-doped structure with the boron-doped layer under n+a-Si:H removed.
Electrical behavior of a 31-cm, thin-film YBaCuO superconducting microstrip
Authors: Hornak L. A. , Hatamian M. , Tewksbury S. K. , Burkhardt E. G. , Howard R. E. , Mankiewich P. M. , Straughn B. L. , Brandle C. D.
Published: July 2002

Electrical time domain measurements and transmission response measurements were made using a 31-cm-long, YBaCuO superconducting thin-film microstrip line and a YBaCuO ground plane, each on separate 1-cm LaGaO3 substrates, with a 125-μm sapphire substrate serving as the dielectric insulator. Degradation of the performance of the line for currents up to the critical-current density and for magnetic fields moderately above the lower critical magnetic field HC1 were evaluated in a variety of simple measurements. In addition, an evaluation of an optically switched segment of a superconducting microstrip line on a zirconia substrate is described. Direct evaluations of pulse distortion are not possible for these long serpentine lines on small substrates due to electromagnetic coupling between adjacent line segments. However, this coupling gives rise to distinctive transmission responses which may aid the evaluation of line performance.
Characterization of the TiW-GaAs interface after rapid thermal annealing
Authors: de Potter M. , De Raedt W. , Van Hove M. , Zou G. , Bender H. , Meuris M. , Van Rossum M.
Published: July 2002

We report an extensive study of the TiW/GaAs interface after rapid thermal annealing between 750 and 1050 °C. Characterization of the interface was performed by secondary ion mass-spectroscopy (SIMS), Auger, Rutherford backscattering spectroscopy (RBS), x-ray diffraction, transmission electron microscopy, and electrical measurements. Schottky barrier heights extracted from I-V and C-V data show a continuous increase with annealing temperatures up to 950 °C. The reverse I-V measurements exhibit a transition from tunneling to avalanche breakdown. SIMS, Auger, and RBS show significant motion of the Ti, resulting in surface accumulation, as well as Ti diffusion into the GaAs substrate. Interface doping by Ti produces an artificial enhancement of the Schottky barrier height.
Pressure dependence of i
n s
i
t
u boron-doped silicon films prepared by low-pressure chemical vapor deposition. II. Resistivity
Authors: Haji L. , Hamedi L. , Loisel B. , Gauneau M. , Joubert P. , Sarret M.
Published: July 2002

The effects of silane pressure and temperature on the in situ boron incorporation and resistivity of low-pressure chemical vapor deposited polycrystalline silicon films were studied in the ranges of 2.5×10−3–1 Torr and 515–700 °C. By lowering the silane pressure, the boron concentration increases (up to 1×1022 cm−3) and the resistivity decreases down to about 2×10−3 Ω cm without annealing. For high deposition pressure (≥0.1 Torr), the resistivity decreases as the temperature is lowered. In this latter case the secondary-ion mass spectrometry profiles reveal a boron accumulation at the layer-substrate interface, which is always observed independently of the substrate nature.
Microstructure of superconducting YBa2Cu3O7−δ thin films on Si and alumina substrates with buffer layers
Authors: Lee J.-W. , Migliuolo M. , Stamper A. K. , Greve D. W. , Laughlin D. E. , Schlesinger T. E.
Published: July 2002

The microstructure of YBa2Cu3O7−δ (YBCO) films grown on silicon and alumina substrates with yttria-stabilized zirconia (YSZ) buffer layers has been studied by transmission electron microscopy (TEM) and x-ray diffraction. The as-deposited films are not amorphous, but are in fact composed of small crystalline grains. The top surface of the post-annealed YBCO film consists mainly of the orthorhombic structure of YBCO with large grains. Other phases are present within the films and have been identified. The presence of a very thin interdiffused layer of BaZrO3 between the YSZ and the YBCO has been shown by cross-sectional TEM.
Microwave-induced substeps in I-V curves of a parallel array of microbridge-type Josephson junctions
Authors: Hontsu Shigeki , Ishii Junya
Published: July 2002

This paper describes the results of experiments and theoretical simulations of the microwave-induced constant voltage substeps in the current-voltage (I-V) characteristics of a parallel array of Nb microbridge-type Josephson junctions. A parallel array consists of ten junctions and the spacing between adjacent junctions is 2 or 100 μm. For the array with 2-μm spacing, in which the propagation of fluxons is possible, substeps have been observed in I-V characteristics whose width is equal to half that of the fundamental constant voltage step associated with the propagation of fluxons in the array. On the other hand, for the array with 100-μm spacing in which the propagation of fluxons is impossible, no substep appears. The mechanism of the occurrence of substeps has been clarified by a numerical calculation of the equations of the equivalent circuit of the array including the effect of microwave radiation.
High-gain, high-efficiency stimulated Raman amplification with beam clean-up
Authors: Mandl A. , Holmes R. , Flusberg A. , Fulghum S. , Angeley D.
Published: July 2002

Stokes amplification has been demonstrated in a single-stage Raman amplifier using collinear geometry with near-diffraction-limited seeds at very high efficiency and relatively high fluence, producing near-diffraction-limited Stokes beams from highly aberrated pump sources. Single-stage amplification of over 20 000 was achieved with converted fluences up to 1.5 J/cm2. We find excellent agreement between the experiment and our full Raman code for all the measured parameters. In addition, detailed calculations and measurements of the near-field-fluence distribution on the output Stokes beam agree reasonably well.
Nonlinear power coupling in the birefringent fiber form birefringence effect
Authors: Chen Yijiang
Published: July 2002

Nonlinear power coupling between two linearly polarized modes in birefringent fibers is examined. In asymmetrically shaped optical waveguides, such as rectangular and elliptical waveguides, which are typical models for polarization beam splitters making use of form birefringence, it is found that the intrinsic critical power of the antisymmetric mode, marking the nonlinear instability, approaches zero at a given aspect ratio; this aspect ratio is 1.587 for the rectangular shape and 1.376 for the elliptical shape.
Offset reduction by modulation doping in abrupt heterojunction bipolar transistors
Authors: Sibille A. , Palmier J. F. , Azoulay R. , Esnault J. C.
Published: July 2002

Conventional heterojunction bipolar transistors exhibit large δVCE offset voltages in common emitter characteristics: We experimentally show that the replacement of the large gap emitter by a thin modulation-doped GaAlAs barrier in an otherwise all GaAs structure results in a large reduction of the offset, without degradation of the gain.
Ultraviolet photon-assisted heteroepitaxy of CdTe and Hg1−xCdxTe on GaAs/Si substrates
Authors: Cody N. W. , Sudarsan U. , Solanki R.
Published: July 2002

Ultraviolet photon-assisted metalorganic vapor-phase epitaxy has been used to grow CdTe, followed by Hg1−x Cdx Te on GaAs/Si substrates at 250 °C in order to fabricate Hg1−xCdxTe/CdTe/GaAs/Si structures. For Hg1−xCdx Te growth methylallyltelluride, a new Te precursor, is used to obtain growth rates of 4 μm/h. X-ray rocking curves and transmission electron microscopy are utilized to characterize the crystalline properties of the epilayers and Hall measurements to determine the electrical properties. Hall electron mobilities of Hg1−x Cdx Te (for x∼0.2) are typically 4×104 cm2 /V s at 80 K.
Transport properties of the two-dimensional hole gas in p-type heterostructure field-effect transistors
Authors: Reemtsma J.-H. , Heime K. , Schlapp W. , Weimann G.
Published: July 2002

A fabrication process is presented for p-type AlGaAs/GaAs heterostructure field-effect transistors to be applied between 15 and 300 K. Different gate metallizations were tested. The resulting barrier heights varied between 0.4 and 0.85 eV. Two different samples were investigated. Sample I contained a thick spacer to achieve maximum mobility (μHall,15 K =27 000 cm2 /V s, ns,l5 K =4.5×1011 cm−2 ) and showed transconductances of 3, 15, and 25 mS/mm at 300, 77, and 15 K, respectively. Sample II was grown with a thinner spacer to increase the sheet carrier concentration (μHall,15 K =16 000 cm2 /V s, ns,15 K =9.2×1011 cm−2) and showed transconductances of 15, 35, and 45 mS/mm at 300, 77, and 15 K, respectively. The magnetotransconductance method was applied to investigate the transport properties of the two-dimensional hole gas within the devices. The field dependence of the mobility was measured and the drift velocity of the holes was deduced from the experimental data.
Strain-assisted p-type doping of II-VI semiconductors
Authors: Ren Shang Yuan , Dow John D. , Klemm Stefan
Published: July 2002

By incorporating a II-VI semiconductor into a strained-layer superlattice, it should be possible to overcome the effects of deep hole traps near the valence-band edge and hence to dope the semiconductor p type in many cases. This idea is illustrated for CdTe/ZnTe superlattices.
Single-stage calculation of the total energy of compositionally modulated III-V alloys
Authors: Glas Frank
Published: July 2002

We consider ternary and quaternary III-V alloys whose constituent binaries are not lattice matched. The change in energy associated with the development of a composition modulation in these alloys is calculated in a single stage, without splitting it artificially between hypothetical ‘‘chemical’’ and ‘‘elastic’’ parts, as done up to now. The calculation, which consists of a numerical minimization of the microscopic elastic energy of the valence force field model, is illustrated for InxGa1−xAs. For most modulations along low index axes, the total energy is found close to the energy calculated by the two-stage procedure. This confirms the stabilization by strain of the bulk III-V alloys, justifies the use of a strain-independent ‘‘chemical’’ energy in the description of inhomogeneous alloys, and strengthens our earlier demonstration of the reduced stability of the thin epitaxial layers of these alloys.
Observation of quantum well polarization effects in the photocurrent of multilayer diodes
Authors: Ripamonti Giancarlo , Capasso Federico , Tsang W. T.
Published: July 2002

Large electrical polarization effects in the time photoresponse of multilayer heterostructure diodes have been observed. This phenomenon manifests itself in a displacement current spike synchronous to a dark–light transition and in an opposite spike in the light–dark one. The effect is associated with the pileup and spatial separation of photogenerated electrons and holes in the wells in the space-charge region of the diode. At a particular forward bias voltage, the conduction photocurrent is eliminated, allowing accurate measurements of this phenomenon.
Stochastic character of partial discharges in insulators
Authors: Macur J. , Domanský K. , Šikula J.
Published: July 2002

Partial discharge (PD) measurements have been made under dc applied voltage at atmospheric pressure on polyethylene (PE) and polyvinyl chloride (PVC) foils without intentional defects. An automatic measuring system was used to detect and process PD parameters. Histograms of amplitudes and time intervals between impulses are presented.
Dielectric anisotropy and dielectric torque in ferroelectric liquid crystals and their importance for electro-optic device performance
Authors: Gouda F. , Anderson G. , Matuszczyk M. , Matuszczyk T. , Skarp K. , Lagerwall S. T.
Published: July 2002

Measurements of the relevant anisotropic part of the dielectric constant for ferroelectric liquid crystals allows a calculation of the dielectric torque acting upon the director during addressing conditions in a matrix-multiplexed device. The frequency dependence of the dielectric anisotropy is presented for different commercially available ferroelectric liquid-crystal materials in the range 103–106 Hz. The field dependence of the switching time has been measured for one of the materials in order to determine the field at the minimum value. The ratio between this field and the field at which switching ceases has been determined and found to be in good agreement with the theoretically calculated value. The results enable us to consider the torque balance as a function of field and frequency, and thereby identify appropriate driving conditions.
Structural properties of graphitized polyperinaphthalene fiber
Authors: Murakami Mutsuaki
Published: July 2002

Structural properties of graphitized polyperinaphthalene (GPPN) fiber were investigated with transmission electron microscopy. The GPPN fiber has a rectangular cross section consisting of two different kinds of thin and linear sheets of graphite. One graphite sheet with 5–50 layers of graphite is linearly extended normal to the direction of the fiber axis with the c axis almost parallel to the fiber axis. The sheets bend at the sides of the fiber forming a continuously joined folding structure. Another type of graphite sheet which is extended to the direction parallel to the fiber axis exists at the four edges of rectangular GPPN.
Photoluminescence studies of free-standing quantum boxes
Authors: Andrews S. R. , Arnot H. , Rees P. K. , Kerr T. M. , Beaumont S. P.
Published: July 2002

We report photoluminescence measurements made on free-standing, lattice-matched GaAs/AlGaAs and pseudomorphic InGaAs/GaAs quantum boxes fabricated by laterally patterning quantum wells using electron-beam lithography and either reactive ion etching or ion beam milling. At temperatures below 10–20 K the luminescence efficiency of most of the GaAs quantum-box arrays tends to scale with the volume of quantum-well material remaining after processing even for the smallest boxes which have lateral dimensions of only 40–50 nm. These observations indicate that the surface recombination rate in GaAs submicron structures can be small relative to the radiative recombination rate at low temperatures. In contrast, radiative recombination in the InGaAs/GaAs quantum boxes is strongly quenched for lateral dimensions less than 500 nm. We suggest that this is because photoexcited carriers are laterally localized in the GaAs boxes by potentials of the order of a few meV, possibly associated with interface disorder or strain relaxation, and that such localization effects are smaller in the InGaAs boxes.
An experimental and theoretical investigation of electrostatically charged, falling droplet pairs
Authors: Barton Scott A. , Dunn Patrick F.
Published: July 2002

Herein we report the results of an investigation of the trajectories of horizontally coplanar droplet pairs of similar charge, falling under the influence of gravity, drag, and electrostatic forces. Experiments were conducted using ethanol droplets that were generated electrostatically from the tips of two parallel needles. These droplets were subject to an external electric field and an initial electrostatic force in the vertical, downward direction, and an interdroplet electrostatic repulsive force in the horizontal direction. A model was developed to predict the measured trajectories. Within the range of applied potential differences investigated (from 1–3 kV), the theory and experiment were found to agree to within approximately 5%. The results also showed that the droplet trajectory was influenced noticeably by the axial electrostatic force on the droplet as it departed from the needle.
On a resonant-mass superconducting antenna coupled to a resonant inductance transducer
Authors: Peng Huei
Published: July 2002

We show that the gravitational-wave-induced electric field in a superconducting antenna coupled to a reconant inductance transducer is much smaller than that in a superconducting antenna without a transducer. The superconductivity property of a superconducting antenna produces an addtional shift in the resonant frequency of the displacements which might be detectable, although it is small.
Dielectric waveguide with a YBa2Cu3O6+x boundary layer at 94 GHz
Authors: Huang Cheng-Liang , Butler Donald P. , Butler Jerome K.
Published: July 2002

We report on the measurement of the millimeter wave transmission properties of a dielectric waveguide with a YBa2Cu3O6+x boundary layer. The transmitted power and phase shift of a 94 GHz signal propagating through the dielectric waveguide structure was measured over the temperature range of 77–150 K. The transmitted power was observed to depend upon temperature due to the dissipation of the millimeter wave signal in the YBa2Cu3O6+x boundary layer. Thereby the temperature dependence of the normal-state ac conductivity was measured. The experimental data were fitted to a Drude model for the normal-state ac conductivity of the YBa2Cu3O6+x. The temperature dependence of the Drude scattering time was obtained. The scattering time was found to decrease with decreasing temperature and was 7.5–11.2 ps in magnitude.
The microstructure and electrical properties of contacts formed in the Ti/Al/Si system due to rapid thermal processing
Authors: Komem Y. , Katz A.
Published: July 2002

The microstructure and electrical properties of the contacts formed in the Ti(30 nm)/Al(10 nm)/〈100〉p-type Si system due to rapid thermal processing at temperatures between 300 and 800 °C were studied extensively. An eutectic melting, initiated at the Al/Si interface, was already observed after 2 s at 580 °C. This rapid melting, which was first observed by the authors in the Ni/Al/Si system, resulted in the formation of a Al3 Ti(20 nm)/Ti7Al5Si12 (5 nm), epi-TiSi2 (45 nm)/p-type Si layered structure with smooth interfaces. The TiSi2 layer grew epitaxially on the 〈100〉Si substrate with the following relationships: (101)TiSi2 (C54)∥(001)Si and [151]TiSi2 (C54)∥[220]Si. The melting reaction influenced the sheet resistance and the Schottky barrier height of the formed contacts, which decreased from 0.67 to 0.49 eV at 580 °C. The correlation between the electrical properties and the microstructure of the contacts formed in the Ti/Al/Si system due to the rapid thermal processing is discussed in comparison with the Ni/Al/Si system.