bluuebunny/crossref_metadata_2025 huggingface dataset:
Band alignments for pseudomorphic InP/InxGa1−xAs heterostructures for growth on (001)InP
Authors: People R.
Published: July 2002

Estimates of the anticipated band alignments for pseudomorphic InP/InxGa1−xAs heterostructures for growth on (001) InP are presented; wherein 0≤x≤1.0. Linearity and transitivity of the valence-band offset, ΔEv, are assumed for a given in-plane lattice parameter, a∥≡a0(InP). Valence-band offsets for ternary heterojunctions are obtained via linear interpolation of the self-consistent interface calculations of Van deWalle and Martin (unpublished), whereas ΔEv for the lattice matched (In, Ga) As/InP heterojunction is taken as an input parameter. It is found that ΔEc shows a rather gradual increase for 0≤x<0.53, with an abrupt change in slope for x>0.53. The present estimates imply an increase in ΔEc by more than 0.2 eV as x→1.0 relative to the lattice matched value, and that the partitioning of ΔEg between conduction and valence band in strained heterostructures maintains its lattice matched value. Potential applications are reviewed in brief.
Photoinduced transient spectroscopy and photoluminescence studies of copper contaminated liquid-encapsulated Czochralski-grown semi-insulating GaAs
Authors: Tin C. C. , Teh C. K. , Weichman F. L.
Published: July 2002

Photoinduced transient spectroscopy (PITS) studies of samples of copper contaminated annealed semi-insulating GaAs in the temperature range of 274–384 K show two dominant levels at about Ev +0.5 eV and about Ec −0.59 eV in addition to the EL2 levels at about Ec −0.80 eV. Depth profiling using chemical etching followed by PITS measurements shows a competing process between the defects responsible for the level at Ev +0.5 eV and that at Ec −0.59 eV. The former is predominantly found near the surface and the latter is dominant in the interior. From the depth profiling results, we have determined that the diffusion constants for these two types of defects are about 4.7×10−10 cm2 s−1 and 5.2×10−10 cm2 s−1, respectively. We propose that the level at Ev +0.50 eV is due to a copper related complex and the level at Ec −0.59 eV is due to native defects. The copper related level at about Ev +0.50 eV is different from the often seen copper related defect level at around Ev +0.40 eV. The presence of these two levels would explain the variety of results reported by different workers on the deep levels attributed to copper. Photoluminescence measurements on a copper contaminated sample at 4.2 K show a peak at 1.36 eV which is due to CuGa acceptor level. This peak appears even after repeated etching of the sample, showing the presence of copper throughout the sample. Comparison data were also obtained for both ‘‘copper-free’’ annealed and unannealed samples.
Influence of an a-SiNx:H gate insulator on an amorphous silicon thin-film transistor
Authors: Hiranaka Kouichi , Yoshimura Tetsuzo , Yamaguchi Tadahisa
Published: July 2002

The effect of an a-SiNx:H gate insulator on the threshold voltage and field-effect mobility in amorphous silicon thin-film transistors has been investigated by using different compositions of a-SiNx:H, and the threshold-voltage shift is found to be reduced at an a-SiNx:H composition of x=1.0. Photoluminescence measurements reveal that the threshold-voltage shift for x<1.0 is due to electron trapping in the localized states of the a-SiNx:H layer, while that for x>1.0 is due to electron trapping in the deep states near the a-Si:H/a-SiNx:H interface, arising from lattice strain. Field-effect mobility decreases as x increases and is due to the increased number of deep states in the a-Si:H near the a-Si:H/a-SiNx:H interface.
Focused ion-beam milling of a submicrometer aperture for a hydrodynamic Josephson-effect experiment
Authors: Sudraud P. , Ballongue P. , Varoquaux E. , Avenel O.
Published: July 2002

We describe the technique used to manufacture a submicron aperture in a nickel microfoil used to look for the Josephson effect in superfluids. The size requirements for a superfluid weak link are briefly discussed. The micromachining is performed by means of a focused Ga ion beam. The ion probe is produced by a liquid-metal-ion source that is known to act as a near pointlike source. The source, optical lens, and deflection assembly are lumped as an attachment to a commercial scanning electron microscope. The obtained machining capabilities and scanning ion images are compatible with a probe size of 150–200 nm, a size that corresponds to our theoretical estimates.
A multiple scattering interaction analysis of intersecting waveguides
Authors: Agrawal Niraj , McCaughan L. , Seshadri S. R.
Published: July 2002

A multiple scattering technique is developed for describing the physics of intersecting waveguides. In this picture the two waveguides interact by scattering the fields of each other in a self-consistent manner. The development of such an analysis is motivated by the fact that the previous theory, which is based on the idea of symmetric and antisymmetric modes of the composite waveguide structure, has a limited validity. The analysis reveals new features of this geometry with important device applications in integrated optics.
The effects of substrate temperature on the donor ionization energy and on the material properties of selectively doped short-period GaAs:Si/AlAs superlattices
Authors: Yao Takafumi , Okada Yasumasa , Matsui Susumu , Nagase Hiroki , Ishida Kohtaro
Published: July 2002

The effects of substrate temperature on the donor ionization energy and on the electrical and photoluminescent properties of selectively doped short-period GaAs:Si/AlAs superlattices are studied. The superlattice structure is characterized by means of double-crystal x-ray diffraction. It is found that the interface between the GaAs and AlAs layers slightly degrades even at a low substrate temperature of 550 °C, and that the degradation is enhanced with an increase in the substrate temperature. The Si donor level is still shallow for substrate temperatures lower than 600 °C, since only a slight degradation occurs in this temperature range. However, the Si donor forms an excess deep DX center near the interface region for higher substrate temperatures. Accordingly, the donor binding energy increases with increasing substrate temperature, since the contribution from the mixed interface region becomes larger. With an increase in the substrate temperature, the photoluminescence peak intensity increases, although the electron concentration at room temperature decreases. This phenomenon is discussed in relation to the formation of donorlike deep levels in AlAs/GaAs short-period superlattices.
The work function of sputter-formed Re-1% Pd
Authors: Gordon R. L.
Published: July 2002

Appearance potential spectroscopy has been applied to the investigation of the relation between work function and surface composition for a sputter-formed alloy of Re-1% Pd. This approach permits point-by-point estimates of the work function to be compared to corresponding measurements of surface composition. Developed techniques permit the use of nonlinear regression to analyze appearance potential and scanning Auger microprobe data from a single line scan on the Topping model of dipole layer formation. Resistively heated samples suffer segregation of Pd to the alloy surface and consequent increase in work function, with the amount of increase dependent upon the Pd-to-Re ratio at the surface. Preliminary results yielded different Topping parameters for low- and high-coverage regions. Values for dipole moment at zero electric field P0 and polarizability α are [P0,α]=[(6.1±1.5)×10−30 C m, (14.6±6.6) Å3] or [(1.7±0.6)×10−30 C m, (1.4±0.4)Å3], with Pd/Re less than or greater than 0.7, respectively. When the surface concentration of Pd is at least 0.2, a local increase in O concentration causes a local reduction of the work function on an otherwise clean alloy surface. On pure Re, or on a surface with substantial concentrations of other metallic impurities, oxygen adsorption causes an increase in work function. It is suggested that the appearance potential technique may be of value to the study of catalysis.
Phase separation in reactions of Ni-Ta thin films with GaAs
Authors: Lahav A. , Eizenberg M. , Komem Y.
Published: July 2002

Interfacial reactions of a Ni60Ta40 alloy film deposited on (001) GaAs substrate were studied and compared to the reactions between GaAs and single or double layer metals: Ni, Ta, Ni/Ta, and Ta/Ni. The reaction of Ni films started at a temperature as low as 100 °C by formation of Ni2GaAs and, following annealing in vacuum at 600 °C, resulted in an epitaxial β′-NiGa. On the contrary, the Ta/GaAs reaction started only at 650 °C, yielding TaAs compound. The above difference in reaction temperatures was explained by differing reaction mechanism, namely dominant diffusion of Ni atoms in Ni/GaAs reaction versus dominant diffusion of Ga and As atoms in Ta/GaAs reaction. The as-deposited alloy film was found to be amorphous and its interaction with the substrate started only at 450 °C. The reaction resulted in a phase separation where Ni diffused toward the GaAs substrate forming Ni2GaAs at the early stages of reaction, and epitaxial β′-NiGa at a later stage. The depleted Ta reacted with the out-diffusing As, forming TaAs. The reacted bilayer metal structures exhibited similar phase separation, where Ni was accumulated adjacent to the substrate and Ta in the outer layer. The presence of Ni phases at the interface with GaAs was correlated with the variation of the Schottky barrier height.
Temperature compensation of the threshold voltage of a 270° twist (SBE) cell
Authors: van Sprang H. A. , Koopman H. G.
Published: July 2002

We have measured the temperature dependence of the helical pitch of a chiral nematic mixture and we show that a second-order polynomial in T*=Tc−T is a good approximation of the behavior. We determined the dependence of the threshold voltage on temperature for a sample with a helical pitch that is independent of temperature and we can show that the contribution of the liquid crystal obtained in this way is linear in temperature. Combination of this linear dependence with the expression for the temperature dependence of the helical pitch on the mixing ratio in mixtures of chiral compounds leads to an expression for the conditions of minimum temperature dependence of the threshold voltage. These data are compared with experimental results and the discrepancies are discussed.
Reply to ‘‘Comment on ‘Numerical calculations of the temperature distribution and evolution of the field-ion emitter under pulsed and continuous-wave laser irradiation’ ’’ [J. Appl. Phys. 5
9, 1334 (1986)]
Authors: Liu H. F. , Tsong T. T.
Published: July 2002

We estimate the contribution of the ∂κ/∂T term to be less than 15% in the worst case, and will not affect the general validity of the conclusions derived from our calculations.
The effects of magnetic fields on carnauba wax electret formation
Authors: Clator Irvin G.
Published: July 2002

The results of thermally stimulated depolarization current and effective surface charge-density measurements indicate that magnetic fields do not produce carnauba wax electrets and that previously reported data can be attributed to nonmagnetic effects.
A novel method of selective epitaxial growth of InP by metalorganic chemical vapor deposition
Authors: Wakahara Akihiro , Pak Kangsa , Yamada Hiroyuki , Yoshida Akira , Nakamura Testuro
Published: July 2002

A novel method of the selective epitaxy of InP was developed by employing a two-step growth in atmospheric pressure metalorganic chemical vapor deposition. By this method, selective epitaxy, without ridge and/or lateral growth, and with uniform deposition of the polycrystalline layer on the SiO2 mask, could be achieved. First, a thin uniform InP polycrystalline layer was deposited on a SiO2/InP substrate and a stripe pattern was formed by photolithography, and then selective epitaxial growth was performed. Selective epitaxial layers thus obtained were found to have a photoluminescence half width of ∼40 meV at room temperature, which was comparable to the one reported by other workers in homoepitaxial metalorganic chemical vapor deposition growth of InP. The resistivity of the polycrystalline layer was ∼700 Ω cm at room temperature, which was four orders of magnitude larger than that of the selective epitaxial layer. Therefore, electrical isolation may be sufficient for fabrication of InP planar devices.
Depletion of interstitial oxygen in silicon and the thermal donor model
Authors: Borenstein Jeffrey T. , Singh Vijay A. , Corbett James W.
Published: July 2002

Recent experimental studies which monitor the loss of oxygen interstitials during 450 °C annealing of Czochralski silicon have been argued to be in conflict with the predictions of existing thermal donor (TD) kinetic models. In this paper we show that a recently proposed model predicts an oxygen depletion rate which is in excellent agreement with the experimental findings.
Low-temperature crystallization of hydrogenated amorphous silicon films in contact with evaporated aluminum electrodes
Authors: Ishihara Shin-ichiro , Kitagawa Masatoshi , Hirao Takashi
Published: July 2002

Measurements are reported on x-ray diffraction and Auger electron spectroscopy studies of Al films on phosphorous-doped hydrogenated amorphous silicon (a-Si:H) prepared by rf glow discharge deposition. Infrared absorption and current-voltage characteristics of and Al electrode a-Si:H p-i-n diodes are also presented. Si and Al Auger depth profile data show that Si was detected at the free surface of the 5000-Å Al film on the 1500-Å a-Si:H film after a 185 °C anneal, while a constant Si signal was detected in the Al film from its free surface to the interface with the a-Si:H after a 200 °C anneal. The 200 °C anneal reduced the p-i-n diodes to resistors. The a-Si-H in contact with the Al film crystallized at 300 °C. A 360 °C anneal prior to the Al deposition raised the recrystallization temperature above 300 °C. The evolution of hydrogen is proposed as a mechanism for lowering the recrystallization temperature in a–Si:H.
Nontrap capacitance dispersion in Se-Schottky diodes
Authors: Champness C. H.
Published: July 2002

In Schottky diodes fabricated by evaporating thallium on a layer of crystallized selenium, incremental capacitance and resistance, measured at zero bias, were found to decrease considerably with frequency over the range 100 Hz to 3 MHz. This variation is interpreted in terms of series resistance of the contacts and a layer in the selenium, some 0.4 μm in thickness, near the junction which is depopulated of acceptors.
Soliton phase shifts in a dissipative lattice
Authors: Islam Nayeem , Singh J. P. , Steiglitz Kenneth
Published: July 2002

We measured the amplitude, width, velocity, and phase-shift characteristics of solitons in the LC lattice of Hirota and Suzuki [Proc. IEEE 61, 1483 (1974)], an inexact electrical analog of the Toda lattice. We found that dissipative effects are important in this lattice, and that amplitudes decrease, widths increase, and velocities remain constant as solitons propagate along the lattice. We found that there are distinct families of solitons, distinguished by the shape of the amplitude-width curve, and determined by the reverse bias of the input pulses that generate them. Within a family, the properties of a soliton are determined by the input amplitude and width of its generating pulse. Marked phase shifts occur when solitons of different families collide head-on, and these phase shifts are found to be independent (within experimental error) of the location of the collision on the lattice. Thus, the positional phase of solitons can be used to encode information in a simple way, and the lattice used to perform computation, of which parity checking is a simple example.
Colored noise in the ring-laser gyroscope: Theory and simulation
Authors: Vogel K. , Risken H. , Schleich W. , James Mark , Moss Frank , Mannella R. , McClintock P. V. E.
Published: July 2002

We present a theoretical analysis of the effect of noise color on the mean beat frequency of a ring-laser gyroscope based on the matrix continued-fraction technique. The results are compared to measurements made on an electronic circuit model, and to digital simulations.
Oxidation resistance of Pb-Te-Se optical recording film
Authors: Terao Motoyasu , Horigome Shinkichi , Shigematsu Kazuo , Miyauchi Yasushi , Nakazawa Masatoshi
Published: July 2002

The dependence of oxidation resistance of metal-Te-Se optical recording films on film composition is investigated, as well as the effects of oxidation on laser beam recorded hole shape. The films are deposited by vacuum evaporation on substrates with a glass/UV light curing resin/cellulose nitrate structure. The role of Se in the film is to inhibit the oxidation. With at least 14% Se addition, film oxidation is completely inhibited even at 60 °C, relative humidity 95%. Depth profiles of elements in the recording films are analyzed by Auger electron and x-ray photoelectron spectroscopy to clarify the mechanisms of oxidation inhibition by Se addition. A selenium condensed layer is found at the inner part of an oxidized surface layer. The surface Te oxide layer and the Se-rich layer should inhibit the film inside from oxidizing. The role of the metallic elements In, Pb, Sn, Bi, and Sb in the film is to inhibit cracking and to decrease noise in reproduced signals by decreasing the size of crystal grains. Lead is found to be the best among these metallic elements, because the recorded hole shape is clean even when recorded after 15 days accelerated oxidation at 60 °C, relative humidity 95%. A very long storage life is expected for the Pb-Te-Se optical recording film.
Simulation of carrier diffusion with random walks
Authors: Holloway H.
Published: July 2002

A random walk algorithm is applied to the problem of the diffusion of a particle in a lossy medium. The formulation used is computationally more efficient than previous algorithms for the particular problem of carrier diffusion in semiconductors; first, because losses are handled with ‘‘fractional’’ carriers that average over many possible walks and, second, because use of a constant length step allows integer arithmetic. The procedure is verified by application to a three-dimensional diffusion problem that may also be solved by the method of images. The improvement appears to be applicable to a range of problems that are handled by random walks.
Improved forward-voltage p/n junction space-charge region capacitance based on time-domain reasoning
Authors: Liou J. J. , Lindholm F. A.
Published: July 2002

The time-domain reasoning employed in deriving a previous p/n junction space-charge region capacitance model is elaborated for semiconductor p/n junctions under forward voltage. The previous model is improved by defining the applicable voltage range and by discussing high-injection effects. Results obtained from this model agree well with experimental and numerical results obtained previously. This treatment also provides the dependence of the space-charge region thickness at large forward voltage.
A nuclear magnetic resonance study of phosphorus-doped polycrystalline silicon
Authors: McCarthy Michael J. , Meyerson Bernard S. , Reimer Jeffrey A.
Published: July 2002

We report the results of a phosphorus-31 and silicon-29 nuclear magnetic resonance spectroscopy study. Amorphous silicon thin films were deposited by plasma-enhanced chemical vapor deposition with one percent phosphine in silane. The films were subsequently annealed at 700 and 800 °C to produce a fine-grained polycrystalline material with the majority of phosphorus atoms segregated at grain boundaries. The chemical shift of the phosphorus spectra indicates that the phosphorus nuclei are fourfold coordinated at the grain boundaries. Results of spin-echo experiments show that phosphorus atoms segregated to grain boundaries reside in at least three regions of differing phosphorus density. Silicon-29 data show a large dispersion of chemical shifts characteristic of disordered materials.
Enhancement of soft x-ray emission using prepulses with 2ω and 4ω laser plasmas
Authors: Tanaka K. A. , Yamauchi A. , Kodama R. , Mochizuki T. , Yamanaka T. , Nakai S. , Yamanaka C.
Published: July 2002

Dependence of x-ray emission efficiencies on a plasma volume were obtained for a 527 nm laser with Cu targets and for 263 nm with Cu and Au targets using the same prepulse technique as the one used by Kodama et al. [Appl. Phys. Lett. 50, 720 (1987)]. 4ω results indicate that a maximum of three times increase was observed in soft x-rays(hν=100–200 eV), while no appreciable increase was observed in hard x rays(hν=1–3 keV). From 2ω results, a factor of 2 for the soft x rays and a factor of 3 for the hard x rays were observed.
Photovoltaic mechanism of Pb2CrO5 ceramic disk with a pair of planar electrodes
Authors: Toda Kohji , Yoshida Shinzo
Published: July 2002

The photovoltaic mechanism of a Pb2CrO5 ceramic disk with a pair of planar metal electrodes is described. A theoretical relation between open-circuit photovoltage and short-circuit photocurrent for the device is considered in the device constructed of two metal-Pb2CrO5 contacts with a high resistivity Pb2CrO5 ceramic layer between them. The contact is regarded as one of metal-semiconductor contacts. From the measurement of the spectral photoresponse, we find that a light absorption in the metal electrode dominates in the photovoltaic effect of the device with Au or Ag electrode. The Schottky barrier heights are estimated to be 2.04 and 2.14 eV for the Au-Pb2CrO5 and Ag-Pb2CrO5 contacts, respectively.
Multiple scattering from a randomly rough surface
Authors: Jin Ya-Qiu
Published: July 2002

Multiple scattering from a randomly rough surface is studied with the Kirchhoff approach. High-order scatterings from the surface are contributed from the statistically distributed pairs of specular points. The shadowing effects in sequential scatterings are taken into account. An explicit formula is developed to compute the bistatic double-scattering coefficient of polarized scattered waves.
Refractive index gradients and dye solution flow characteristics in pulsed copper vapor laser pumped dye laser cells
Authors: Amit M. , Bialolenker G. , Levron D. , Burshtein Z.
Published: July 2002

A study of dye solution flow characteristics in a planar dye laser cell, and their influence on the thermal properties affecting the optical quality of the lasing medium, particularly thermal lensing, is presented. Steady temperature gradients generated in the dye laser cell (∼10−3 M rhodamine-6G in methanol) by a high-frequency repetitive copper vapor laser, extended from 1 to 2 mm upstream relative to the pump laser impact position to the entire cell length downstream. The steady nature of the gradients is related to vorticity of the dye solution flow, resulting in a 3–4 orders of magnitude apparent enhancement of the thermal diffusivity.
Transient dynamics of multiplexed short-pulse amplification in KrF
Authors: Kannari F. , Kimura W. D.
Published: July 2002

Time-dependent calculations of multiplexed short-pulse amplification are presented which show that cascaded short pulses in KrF lasers, with an appropriate time interval between the pulses, can extract energy with only a small cost in extraction efficiency as compared to a single long pulse. This dynamic characteristic of KrF* permits the design of a novel, simpler angular multiplexing system. Calculations include nonsaturable and saturable absorption, amplified spontaneous emission effects, and an end mirror for double-pass amplification. The dependence of the extraction efficiency and the energy gain on the time interval and pulse shape are calculated.
A Monte Carlo study of an electron beam pumped cw argon ion laser
Authors: Sogard M. R. , Feng I.-J.
Published: July 2002

We have modeled the properties of a transverse electron beam pumped argon ion laser using Monte Carlo techniques. We studied the lasing transitions at 4765 and 4880 Å for electron energies up to 300 eV, for conditions of pressure and degree of ionization similar to those employed in conventional lasers. We find lasing efficiencies to be comparable to those in the conventional axial discharge argon ion laser. However, it may be possible to attain higher efficiencies if much higher degrees of ionization can be reached.
Distribution of electron energy in an electrostatically confined silane plasma
Authors: Andreu J. , Sardin G. , Lloret A. , Esteve J. , Morenza J. L.
Published: July 2002

A hot-cathode silane dc discharge with electrostatic confinement devoted to the deposition of hydrogenated amorphous silicon is analyzed by using a Langmuir probe. The electron energy distribution of the plasma shows the existence of two pseudo-Maxwellian populations with densities depending on the electrostatic confinement. The electron density of electrostatically confined plasma is higher than in the case of an unconfined one. In the electrostatically confined plasma, the hydrogenated amorphous silicon deposition rate is high (0.33 nm/s at 6 μbar).
Density of ZnS thin films grown by atomic layer epitaxy
Authors: Oikkonen M. , Tuomi T. , Luomajärvi M.
Published: July 2002

The density of ZnS thin films is determined as a function of the film thickness. The films were prepared using atomic layer epitaxy. Two experimental techniques are used, namely, (1) spectroscopic ellipsometry combined with He-ion backscattering spectrometry and (2) spectroscopic ellipsometry alone using an effective medium approximation. Both methods give approximately the same results. In the ZnS thin films having a cubic crystal structure, the mean density increases from about 2.5 to about 4.0 g/cm3 with increasing film thickness in the thickness range of 25–400 nm. In the films thicker than 500 nm the density starts to decrease from the value 4.0 g/cm3. In the thickness range of 1000–2000 nm the density is 3.7–3.8 g/cm3. When the distance from the substrate is between 50 and 300–400 nm the local density of the cubic thin films has a maximum value which is close to the bulk density 4.1 g/cm3. The stoichiometric atomic ratio of sulfur to zinc is found to be between 0.9 and 1.0. The ratio has a tendency to increase with increasing film thickness.
Structural aspects of superlattices of Fe-W, Fe-Mo, and Fe-Nb metals
Authors: Window B.
Published: July 2002

X-ray diffraction and Mössbauer absorption results are reported for the layered structures Mo/Fe, Nb/Fe, and W/Fe, with layer periodicities in the range 0.5–50 nm. The films are amorphous for periodicities of 0.5–2 nm, but with composition modulation, and are crystalline with coherency in the growth direction for periodicities of 2–50 nm. The superlattice diffraction patterns are in agreement with a one-dimensional model, provided the effects of depositing part-plane layers are taken into account. In the intermediate region near periodicities of 2 nm, mixed crystalline and amorphous phases are observed, with sharp diffraction patterns from the crystalline regions. It is suggested that the lattice mismatch is taken up by deposition defects for periodicities above 3 nm, and by these defects and columnar boundaries with the amorphous phase for periodicities near 2 nm.
Light-activated silicon diode switches
Authors: Giorgi D. , Yu P. K. L. , Long J. R. , Lew V. D. , Navapanich T. , Zucker O. S. F.
Published: July 2002

An experimental study of the fundamental limits to current density, power, and speed of light-activated semiconductor switches (LASS) is described. The LASS investigated are high-voltage silicon junction devices illuminated with 1.06-μm laser light. A novel optical delay line is designed in sampling the laser pulses. Experimental results to date demonstrated a switch power of 6.7 MW, a peak electrical pulse power of 4.8 kW, a current density of 150 kA/cm2, a power density of 5.3 GW/cm3, and an electrical pulse rise time of 100 ps. The results of theoretical analysis indicate that the circuit configuration is the main limitation to the pulse rise time.
Effects of polyimide passivation on the photoluminescence of high-purity epitaxial GaAs
Authors: Hsu Jung-Kuei , Lau Kei May
Published: July 2002

Polyimide has been used as interlayer dielectric and passivation material. We studied the optical passivation property of polyimide by examining the spectral changes in the photoluminescence (PL) spectra of high-purity epitaxial GaAs coated with polyimide. Before full cure, the polyimide is nearly transparent to visible and near-infrared radiation. After full cure, the typical PL of GaAs was unobservable at liquid nitrogen or higher temperatures, but clear and distinct at liquid-helium temperature. The resolution of the GaAs exciton spectrum was improved in the coated sample. The polyimide-GaAs system also resulted in very weak luminescence extending over a wide spectral range from the red to near infrared.
Low thermal expansion polymide buried ridge waveguide AlGaAs/GaAs single-quantum-well laser diode
Authors: Sato F. , Imamoto H. , Asai M. , Inoue T. , Imanaka K. , Shimura M.
Published: July 2002

A novel ridge waveguide laser diode has been developed in which the ridge is buried in a newly developed polyimide with a low thermal expansion coefficient close to that of AlGaAs which reduces the thermal stress to the junction and simplifies the wafer processing. A planar configuration, which is suitable for optoelectronic integration and an episide down mount for high-power operation, has been achieved by an etch-back process. Under cw operation, a low threshold current of 15 mA at 25 °C, a characteristic temperature T0 of 145 K, and maximum power output higher than 30 mW/facet have been obtained in a molecular-beam-epitaxial-grown graded-index separate confinement heterostructure single-quantum-well laser emitting at 780 nm.
On the decoupling of a system of diffusion equations
Authors: Mikhailov M. D. , Özişik M. N.
Published: July 2002

Matrix formalism is used to decouple system of linear diffusion equations of monotype boundary conditions.
Amorphous phase formation in Ni3B by low-temperature deuterium implantation
Authors: Thomé L. , Pons F. , Ligeon E. , Fontenille J. , Danielou R.
Published: July 2002

The amorphous phase formation in Ni3B single crystals implanted at 15 K with deuterium ions is studied via in situ Rutherford backscattering and channeling experiments, and the lattice site of implanted deuterium was determined by using the D(3He,p)4He nuclear reaction. The amorphization kinetics is found to present a sigmoidal shape, indicating that amorphization results from a defect-accumulation mechanism. At D fluences below the amorphization threshold, implanted D atoms are located in interstitial sites of the Ni3B orthorhombic structure, while they are trapped in the strained region between amorphous clusters as soon as amorphization occurs.
Photoluminescence linewidth systematics for semiconductor quantum well structures with graded interface composition profile
Authors: Ogale S. B. , Madhukar A. , Cho N. M.
Published: July 2002

Photoluminescence linewidth systematics for the case of semiconductor quantum well structures with a graded interface composition profile are studied within a model which attributes the linewidth to alloy disorder and alloy composition fluctuation effects. Results are presented for two specific types of gradations derived from consideration of typical experimental situations, and comparison is made with the available experimental data.
Transport processes in glasses on electron irradiation
Authors: Landron Claude
Published: July 2002

The effect of electron irradiation in alkali glasses is studied. A quantitative model is described in which the scattering and the energy loss of the primary electrons are investigated. The theory of multiple collisions is derived in a mathematically simple way, permitting the calculation of the potential inside the irradiated volume. Our analysis enables us to explain the alkali migration reported by several authors.
Propagation characteristics of laser-generated acoustic waves in glass
Authors: Kanemitsu Yoshihiko , Harada Yoshinao , Tanaka Yuichi , Kuroda Hiroto
Published: July 2002

Propagation characteristics of laser-generated acoustic waves in glass were studied by using picosecond laser pulses and an optical detection technique. Longitudinal waves propagate at the direction of the normal to the surface plane, but shear waves propagate at about ±45° to the normal. At the early stage of propagation, the propagation velocity of the wavefront exceeds the sound velocity in glass. Moreover, it is pointed out that the generation and propagation behavior of shear waves is very sensitive to the surface conditions.
Relationship between layer thickness uniformity and statistical device property distribution over a wafer grown by molecular-beam epitaxy
Authors: Svensson Stefan P.
Published: July 2002

In this article we analyze the combined effects of the deterministic nonuniform flux distribution in a molecular-beam epitaxy system, and the random variations in device parameters induced by processing. As a case study, the distribution of the saturation current (Idss) before gate metallization of a high-electron mobility transistor is investigated. The magnitude of the observed statistical variations has been compared to calculated values given by a theoretical expression for the saturation current. Using a semiempirical method to describe the radial dependence of a device parameter and its variation, simple expressions describing the shape of the wafer distribution, mean value, standard deviation, yield, and radial probability of finding devices within set limits, have been derived. The expressions can be used to relate the layer properties in the wafer center to the mean value of the same properties as obtained from a map of the whole wafer. The expressions for radial probability of finding a working device can be easily added to the software of an automatic wafer tester in order to speed up the screening procedure of wafers.
Off-axis spatial localization with frequency modulated nuclear magnetic resonance rotating ( ρ) pulses
Authors: Hardy Christopher J. , Bottomley Paul A. , Roemer Peter B.
Published: July 2002

Nuclear magnetic resonance (NMR) rotating ( ρ) pulses produce two-dimensional spatially selective inversion of nuclear magnetization with a single NMR excitation. A technique employing frequency modulation of the excitation waveform is described here for offsetting the sensitive volume defined by these pulses to any preselected location within the sample. The technique is demonstrated in a whole-body 1 H NMR imaging system, and can be used to provide simple, automated relocation or interleaving of selectively excited volumes in NMR imaging and spectroscopy.
Sodium diffusion in plasma-deposited amorphous oxygen-doped silicon nitride (a-SiON:H) films
Authors: Osenbach J. W. , Voris S. S.
Published: July 2002

The dependence of 22Na diffusivity in a-SiN:H and a-SiON:H films on hydrogen content, N/Si ratio, oxygen content, and temperature was determined. Measurements were made at 350, 375, and 400 °C. The diffusion profiles for sodium in a-SiN:H films have two regions; a short Gaussian region and shallow linear region. We have interpreted these results using a structural model which describes the film as a two-phase mixture of a highly ordered Si3N4-like phase and a highly disordered phase. Using this model we argue that the Gaussian region of the diffusion profile is due to ‘‘bulk’’ diffusion through the Si3N4-like phase and the shallow linear region is due to ‘‘fast’’ diffusion through the interfacial region. At 400 °C the ‘‘fast’’ diffusivity is on the order of 103 times larger than the ‘‘bulk’’ diffusivity. However, at 80 °C the ‘‘fast’’ diffusion is approximately 105 times smaller than the bulk diffusivity. This large change in the ratio of the diffusion coefficients is due to the large difference in activation energy for the two mechanism. For ‘‘bulk’’ diffusion it is approximately 1.8 eV, whereas it is approximately 2.6 eV for ‘‘fast’’ diffusion. The high activation energy for ‘‘fast’’ diffusion is due to an interaction (association) of the diffusing Na+ ion with a (N-Si-N)− group to form a Na-N-Si-N complex. The association energy for this complex is approximately 1.2 eV. We have observed only one region in the diffusion profiles in the oxygen-doped films. This region is due to ‘‘bulk’’ diffusion. The magnitude and activation energy for diffusion is strongly dependent upon the oxygen content. It decreases from approximately 1.8 to 1.3 eV when the oxygen content of the film increases from 0% to 25%. These results are then used to discuss possible device reliability problems which may occur in oxygen-doped films.
High-quality GaAs/Ga0.49In0.51P superlattices grown on GaAs and silicon substrates by low-pressure metalorganic chemical vapor deposition
Authors: Razeghi M. , Maurel Ph. , Omnes F. , Defour M. , Boothroyd C. , Stobbs W. M. , Kelly M.
Published: July 2002

We report the successful growth of Ga0.49 In0.51 P-GaAs superlattices on GaAs and Si substrates by low-pressure metalorganic chemical vapor deposition. The high quality of the structure grown on GaAs and silicon substrates has been evidenced by transmission electron microscopy photographs, that show very sharp interfaces between GaAs wells and Ga0.49 In0.51 P barriers, with perfect control of thicknesses and compositions. Classical Hall measurements performed on the sample further demonstrated the presence of a two-dimensional electron gas with a mobility at T=4 K , μ(4 K)=50 000 cm2 /V/s, and a carrier concentration n−(4 K)=2.9×1011 cm−2. GaAs/Ga0.49In0.51P superlattices have been used, as well as buffer layer in order to grow GaAs on silicon substrates. Mirrorlike single-crystal GaAs has thus been obtained. A GaInP/GaAs heterostructure with electron Hall mobility as high as 6000 cm2 /V/s at 300 K and 80 000 cm2/V/s at 4 K has been grown, which is the highest mobility that has yet been reported for these materials.
Thermal behavior and range distribution of 209Bi implanted into the Al/V bilayer structure
Authors: Olivieri C. A. , Behar M. , Grande P. L. , Fichtner P. F. P. , Zawislak F. C. , Biersack J. P. , Fink D.
Published: July 2002

350-keV 209Bi+ was implanted into an Al (1000 Å)/V bilayer system. The Bi depth distribution measured by Rutherford backscattering agrees well with predictions obtained via the Monte-Carlo simulation method (trim code). Diffusion coefficients for Bi in both the V substrate of the Al/V system and the pure V foil are extracted after thermal annealings in a temperature range between 200 and 700 °C. The results show that the Bi ions follow a hindered diffusion at the Al film of the Al/V bilayer and for temperatures higher than 580 °C diffuse regularly in the V bulk.
Torque relaxation in a CuMn spin glass
Authors: Giovannella C. , Campbell I. A.
Published: July 2002

Torque relaxation data on a Cu 5-at. % Mn sample at different temperatures are presented. The relaxations after field cooling and after zero-field cooling are different at each temperature, implying that the in-field states of the sample after these two procedures are different. Torque data for the effective anisotropy K are compared with values from experiments having shorter time windows so as to obtain information on relaxation over a very wide time spectrum. The estimated effective Tg values tend to a frequency-independent limit at low frequencies.
Short-range ordering in structural relaxation of an amorphous Fe32Ni36Cr14P12B6 alloy
Authors: Arai J. , Asahi N.
Published: July 2002

Short-range ordering and its kinetics in the structural relaxation of an amorphous Fe32Ni36Cr14P12B6 alloy are studied by measurement of electrical resistance. When the specimens are annealed below 250 °C, the resistance rises and its temperature coefficient (TCR) decreases, while the resistance is reduced and the TCR increases when annealed above 250 °C. This fact is analyzed through the change of structure factor using Nagel’s approach for amorphous metals based on the extended Ziman theory. This analysis indicates that the structural relaxation can be classified into two types of short-range rearrangement of atoms; a chemical short-range ordering (CSRO) and a topological short-range ordering (TSRO). Consequently, it can be concluded that the structure factor S(K) at K=2kF increases when CSRO is formed, whereas it decreases in the progress of TSRO and the cause is attributable to the difference in the second moment of the atomic-level internal stress distribution 〈p2〉 in both states. Furthermore, the kinetics in the formation of the CSRO are analyzed on the assumption that the relaxation time obeys logarithmic normal distribution and from there the distribution width and the mean activation energy are determined to be 3.4 and 1.83 eV, respectively.
Effects of hydrogen and nitrogen ion bombardments on soft magnetism of iron films during double-ion-beam sputtering
Authors: Nagakubo M. , Yamamoto T. , Naoe M.
Published: July 2002

The dependence of the crystal structure and magnetic properties of iron films on preparation conditions has been investigated in detail by using a double-ion-beam sputtering system. During sputtering of an iron target by argon ions, the growing surfaces of iron films were bombarded by nitrogen or hydrogen ions with different kinetic energies below 500 eV. It has been found that these ions changed significantly the film structure and magnetic properties through the process of collision and reaction with iron atoms at the surface layer of growing film. As a result, the small amount of hydrogen or nitrogen added into iron films by ion bombardment improved effectively the soft magnetic properties of iron films. The iron films with saturation magnetization 4πMs as large as 22 kG and coercive force Hc as low as about 5 Oe were prepared by adjusting the accelerating voltage in the range of 100–300 V and the partial pressure of hydrogen or nitrogen in the range of 10−4 –10−5 Torr.
EPR, magnetization, and resistivity studies in doped (4-f or 3-d ions) and undoped RBa2Cu3Oy high T
C superconductors (R=Y,Pr,Nd,Eu,Gd,Ho,Er, or Yb) (abstract)
Authors: Vier D. C. , Smyth J. F. , Salling C. T. , Schultz S. , Dalichaouch Y. , Lee B. W. , Yang K. N. , Torikachvili M. , Maple M. B. , Oseroff S. B. , Fisk Z. , Thompson J. D. , Smith J. L. , Zirngiebl E.
Published: July 2002

We have measured electron paramagnetic resonance (EPR), resistivity, and dc susceptibility from 2 to 300 K for the oxide high Tc superconductors (R)Ba2Cu3Oy (R=Y,Pr,Nd,Eu,Gd,Ho,Er,Tm, or Yb). Selected systems were doped with 3-d ions (Cr,Mn,Fe,Ni,Co, or Zn) or 4-f ions (Gd or Er) which presumably substitute for the Cu or R site, respectively. In the systems studied we have observed an EPR line at low temperatures (T<40 K), which exhibits an increase in intensity and decrease in field for resonance as the temperature is lowered. The ESR linewidth is also temperature dependent and exhibits a minimum at about 15 K. An additional EPR line that can be associated with a Gd3+, Mn2+ or Er3+ ion was observed for those samples where these ions were present as dilute impurities. In some of the samples another EPR signal is observed with properties that depend on sample preparation conditions. The behavior and origin of all lines will be discussed. The variation of Tc with concentration of the added impurities over the range (1%–15%) will also be presented, and compared with previous studies in other superconducting systems.
Magnetization of high-temperature superconductors (abstract)
Authors: Nam Sang Boo
Published: July 2002

Superconducting Ba (X=Y, Nd, Sm, Gd, Dy, Er, Yb) CuO were made independently by the solid reaction method via mixing barium carbonate, (X) oxides, and copper oxide with atomic ion ratio Ba:X:Cu=R:1:R+1 with R=1−4, and sintering at 900–1000 °C for 24–72 h. (1) The best superconductor was found to be formed via R=2 and sintering near 950 °C. All samples studied were found to have layered perovskite x-ray diffraction patterns. Samples via R=1,3, and 4 were also found to have structures similar to those via R=2, and found to have two phases by the x-ray diffraction. The temperature-dependent magnetizations M(T) were measured by using the BTi SQUID susceptometer. The transition temperature Tc was determined by extrapolating M(T) and was found to be sensitive to the cooling rate of the sample during its synthesis. The Meissner effect was observed up to 78–92 K, and the fluxoids were found to be trapped while the samples cooled in a finite field at all temperatures below Tc. M(T) was found to be of three types: type 1 being similar to that of Pb, type 2 having a knee perhaps due to the two crystal structures, and type 3 having zero slope near Tc, perhaps due to the sample crystal sizes being less than the effective penetration depth. Samples with large crystal sizes were found to be of type 1 or 2. The measured M(T) can be understood in the framework of the BCS theory, and 2Δ(0)/k Tc were deduced to be in the range of 3–4.4. However, the magnetic hysteresis was found to be present at even low field 30 G at 10 K, and M(T) near Tc was found to be sensitive to thermal fluctuations. Various mechanisms for superconductivity in these systems will also be discussed.
Superconductivity above 110 K in the orthorhombic phase of the Y-Ba-Cu-O ceramic compounds (abstract)
Authors: Baszyński J.
Published: July 2002

We present the results of the study the crystalline structure of the high-temperature superconducting (above 110 K) phase in the ceramic compounds Y-Ba-Cu-O. These ceramics were prepared with nominal compositions represented by the formula Y1.2Ba0.8CuO4−δ.1 From Fig. 1 it is evident that the diamagnetic shift starts at 126 K and at 112 K the air value of the solenoid inductance is achieved. The detailed HTS phase structure was evaluated from x-ray diffractograms (Fig. 2) which are obtained from the samples of the same chemical nominal compositions but have essentially diverse physical properties—see Fig. 2. We have concluded that the crystal symmetry of HTS phase is orthorhombic: a=3.756 Å, b=3.45 Å, and c=13.186 Å with peculiar superstructure in plane (112), which could be also attributed to the plane (311) diamond type too.
Studies at IBM on anisotropy in single crystals of the high-temperature oxide superconductor Y1Ba2Cu3O7−x (invited)
Authors: Gallagher W. J.
Published: July 2002

A series of studies carried out at IBM on the magnetic, transport, and optical properties of single crystal Y1Ba2Cu3O7−x demonstrate the overriding importance of anisotropy in its superconducting and normal-state properties.
New glassy features in high-T
c superconductors
Authors: Yeshurun Y. , Wolfus Y. , Felner I.
Published: July 2002

Magnetic measurements on a high-Tc superconductor YBa2Cu3O7 reveal new spin-glass-like features. At low temperatures and low fields the irreversible part of the field-cooled magnetization Mirr rotates with the sample as a rigid entity. The rigidity is broken and part of Mirr disappears above an angle φ* which decreases with increasing temperature or field. This behavior resembles that of spin glasses and differs qualitatively from the behavior found for Nb.
Discharge current of a semi-insulating GaAs crystal previously submitted to a high electric field
Authors: Pistoulet B. , Abdalla S.
Published: July 2002

The existence of long-range potential fluctuations (PF) in compensated semiconductors results from the nonuniform distribution of ionized impurities, and it was observed that PF can be erased when the material is submitted to a critical field, the value of which depends on the sample. Data on the temperature and time dependence of the discharge current of a semi-insulating GaAs crystal, which has been submitted to a critical field, are reported. The discharge current decreases with a time constant equal to the reverse of the electron emission coefficient of deep centers brought out of equilibrium by the external field. Not only the activation energy of the emission coefficient, but also the density of the deep center species responsible for the discharge current, can be determined from the data. In the case of the GaAs sample studied in this paper, the observed discharge current results from the return to equilibrium of the Cr acceptor center HL1.