bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoelectric study of the Ni- and Ni-TeO2-electrodeposited n-type CdTe interfaces
Authors: So S. M. , Hwang W. , Meyers P. V. , Liu C. H.
Published: July 2002

The barrier heights of the electrodeposited n-type CdTe thin-film metal semiconductor (MS) and metal-thin insulating layer-semiconductor (MIS) devices have been measured by internal photoemission. The data for both MS and MIS devices can be fit with the square root of the photocurrent per absorbed photon dependence consistent with the Fowler theory. The barrier height of Ni-CdTe is 0.75 eV at room temperature, and its temperature dependence is about the same as that of the CdTe band gap. This suggests that the barrier height is pinned with respect to the CdTe valence band edge. Oxidation in air at 300 °C for an hour produces a layer of about 25 Å or TeO2 on the CdTe surface. Thicker oxide can be grown for longer oxidation time. Negative oxide charges are found in some devices. At room temperature, the barrier height of Ni-TeO2-CdTe is 0.92 eV. As temperature is decreased, the barrier height increases and its rate of change with temperature is less than that of the CdTe band gap. Samples stored in room atmosphere show aging effects, one of which is the increase in surface-state density. The dips in the curve of the spectral dependence of the relative photon-induced current are caused by electrons which drift to the metal after being photoexcited from occupied surface states below the Fermi level. These dips correspond to peaks in the energy distribution of the surface state density. At zero bias and 170 °K, four peaks at 1.02, 1.06, 1.18, and 1.26 eV are observed for the MIS devices. For the MS devices zero biased at room temperature, four peaks at 0.85, 0.94, 1.02, and 1.05 eV are observed. The magnitudes of the dips at 0.85, 0.94, 1.18, and 1.26 eV vary with bulk-defect density and these levels shift towards higher energy as temperature is decreased. On the other hand, the levels at 1.02 and 1.05 eV for the MS devices and 1.02 and 1.06 eV for the MIS devices are independent of temperature and bulk defect density.
Surface waves in thin-film coatings on piezoelectric half-space and on piezoelectric plate belonging to the (622) crystal class
Authors: Vivekanandaa P. , Srinivasamoorthy V. R.
Published: July 2002

Love-type surface waves in thin-film coatings on a piezoelectric half-space of the (622) crystal class are studied. Silver and gold coatings are used on the piezoelectric half-space, and numerical results are obtained for the relationship between the velocity and the wave number. Surface waves by thin-film coatings on both sides of an infinite piezoelectric plate of the (622) crystal class are also studied. The dispersion equation has been solved for a given velocity to obtain the wave number numerically.
Characteristics of rapid thermal annealing in ion-implanted silicon
Authors: Holland O. W. , Narayan J. , Fathy D. , Wilson S. R.
Published: July 2002

Activation of implanted dopant in Si is investigated as a function of ion energy during rapid thermal annealing (RTA). It is shown that the fraction of dopant incorporated on the lattice site by RTA decreases as the implant energy increases. This is attributed to clustering or precipitation of the dopant during RTA as a result of fast diffusion of the dopant in the amorphous layer produced by implantation. The increased thickness of the amorphous layer at higher implant energies allows sufficient time for clustering before the amorphous layer recrystallizes. Similar behavior is observed for electrically inactive impurities. In this work, the diffusion of Ge was investigated to gain insight into the transient, greatly enhanced diffusion of certain dopants during RTA that has been reported. No enhancement in the diffusion of Ge was observed which is shown to be consistent with a model proposed to explain the enhanced diffusion for dopants.
Self-temperature-control plane heaters by graphite-polyethylene glycol mixed systems
Authors: Kimura T. , Yasuda S.
Published: July 2002

Mixed systems of graphite carbon and polyethylene glycol are found to show an anomalous increase in electrical resistance at certain temperatures. Making use of this property, we have made plane heaters of these graphite carbon-polyethylene glycol mixed systems. These heaters, when the power was supplied, maintained constant temperature without any temperature control device. It is also found that the constant temperature depends upon the molecular weight of polyethylene glycol used. This makes it possible to obtain a heater which maintains a desired intrinsic constant temperature without any temperature control device.
Surface segregation during reactive etching of GaAs and InP
Authors: Ameen M. S. , Mayer T. M.
Published: July 2002

We have studied the surface composition of gallium arsenide and indium phosphide under conditions of physical sputtering and reactive ion beam etching. Samples of Fe-doped (100) GaAs and InP were bombarded with 1-keV Ne+ ions under a varying amount of Cl2 dose. Low-energy ion scattering spectroscopy and sputtered neutral mass spectrometry indicate an increase of the Group V element at the surface upon addition of Cl2 to the system. This effect is believed to be due to segregation of the As and P due to an altered chemical potential at the surface/vacuum interface resulting from chlorine adsorption. The segregation and subsequent volatilization of PClx species leaves aggregates of In/InClx species at the surface, resulting in a roughened surface.
Alloy scattering limited mobility of two-dimensional electron gas in quaternary alloy semiconductors
Authors: Basu P. K. , Bhattacharya Keya
Published: July 2002

A theory of alloy scattering of two-dimensional electron gas in quaternary III-V semiconductors is developed by assuming spherically symmetric square scattering potential randomly distributed in the crystal. The theory predicts a temperature-independent mobility. Electron mobilities have been calculated for two-dimensional electrons in Ga1−x Inx P1−y Asy and Ga1−x Inx P1−y Sby, with scattering potentials expressed in terms of the differences in the band gaps, the electron affinities, and the electronegativities of the constituent materials.
A new method for displaying low-contrast optical-beam-induced contrast images in the scanning optical microscope
Authors: Wilson T. , McCabe E. M. , Hamilton D. K.
Published: July 2002

We present a new method of easily displaying optical-beam-induced contrast (OBIC) images from scanning optical microscopes. The new technique which displays the rectified, differentiated OBIC signal, is insensitive to variations in the background signal level.
Effect of a laser pump on the Weibel instability of a counter streaming plasma
Authors: Singh Raghvendra , Tripathi V. K.
Published: July 2002

Near the critical layer, laser radiation linearly mode converts into a Langmuir wave which attains a large amplitude and influences the Weibel/quasimode via a four-wave parametric process involving two Langmuir wave side bands. The growth rate for this process is obtained. Under certain conditions it is shown that a linearly unstable Weibel mode is suppressed by the pump wave.
A multilayer AgGaS2 structure for infrared (2–10 μm) electro-optic tunable filters: Fabrication and performance
Authors: Sashital S. R. , Stephens R. R. , Lotspeich J. F.
Published: July 2002

Alternating layers of high- and low-resistivity silver thiogallate (AgGaS2) were grown sequentially by liquid-phase epitaxy on AgGaS2 substrates using the vertical dipping technique. High-resistivity layers were grown by using KCl-AgGaS2 solutions while low-resistivity layers were grown from Ge-AgGaS2-KCl solutions. Layer growth of such a multilayer device and demonstration of its electro-optic response for filter application are described.
Application of digital image analysis to the study of high-order structure of polymers
Authors: Tanaka Hajime , Hayashi Takafumi , Nishi Toshio
Published: July 2002

A digital image analysis (DIA) technique has been applied directly to the study of the high-order structure of polymers probably for the first time. Using this method, various types of physical information can be obtained in real and wave-number (k) space. Included in this DIA method are operations such as two-dimensional Fourier transformation, cross sectional profiles along various curves, the size and shape distribution of droplets, etc. This technique is widely applicable to any image obtained by optical microscopy, electron microscopy, ordinary photography, etc. In this communication, we apply the DIA method to the study of the pattern formation in polymers, namely the structure of spherulite and phase separation in polymer blends.
Submicrostructural clusters and doping of amorphous silicon
Authors: Phillips J. C.
Published: July 2002

Experiments on a-Si prepared by vapor deposition or ion bombardment exhibit anomalies which are most readily explained not by a continuous random network but by arrays of morphologically oriented paracrystalline clusters with 3% unreconstructed surface atoms. The effects of hydrogenation on the cluster dimensions are small compared to the effects of deposition or annealing temperature. Substantial morphological reorientation can be induced either by substrate-driven strain or by thermal annealing. Further experiments to study cluster morphological transitions are proposed.
III-V heterostructure interfaces by metalorganic chemical vapor deposition
Authors: Coleman J. J. , Costrini G. , Jeng S. J. , Wayman C. M.
Published: July 2002

The interface characteristics of five different heterostructures grown by metalorganic chemical vapor deposition (MOCVD) have been studied using secondary ion mass spectroscopy (SIMS) and high-resolution transmission electron microscopy (TEM). Two all-binary AlAs-GaAs superlattices, ternary Al0.6Ga0.4As-GaAs and GaAs0.95P0.05-GaAs superlattices and a mismatched GaAs0.8P0.2-GaAs single interface have been examined for compositional transients and interface abruptness. When an interrupted growth process (15 s pause between layers) is used in an atmospheric pressure MOCVD reactor system, no evidence of compositional transients is observed in analysis of SIMS data interfaces of heterostructures grown in this manner and examined with high-resolution TEM and corresponding lattice imaging are found to be abrupt within a single atomic layer.
Pressure dependence of the resistivity of Mg70Zn30 metallic glass
Authors: Vassiliou John K.
Published: July 2002

The resistance of the metallic glass Mg70Zn30 has been measured as a function of hydrostatic pressure to 6 kbar at room temperature. The resistivity shows the unusual characteristic of an increase with increasing pressure. It is shown that this behavior can be understood on the basis of the Ziman theory for metallic glasses.
Active area limitation of Ge/GaAs heterojunctions by means of B ion implantation
Authors: Ishizuka F. , Sugioka K. , Itoh T.
Published: July 2002

We have investigated the limitation of the active area of p-n Ge/GaAs heterojunctions by means of B ion implantation into the interface of Ge/GaAs structure. Germanium epilayers were grown on (100) GaAs substrates by molecular beam epitaxy at a substrate temperature above 450 °C with a growth rate of about 10 nm/min. The Ge/GaAs heterojunction diode, fabricated with p-n Ge/GaAs structure which was grown at the substrate temperature of 500 °C, represented a forward current voltage shoulder of 0.44 V and a breakdown voltage of 44 V. The ideality factor and the backward step recovery time of this diode was 1.09 and about 10 ns, respectively, similar to a Schottky barrier diode with same active area. In order to use the n-GaAs substrate as an emitter of a heterobipolar transistor, it is necessary to limit the current flow into the same area of the collector through the base region. To realize this idea, B ions were implanted through the Ge epilayer, and the high-resistivity region was formed in the GaAs substrate at Ge/GaAs interface. The forward current of the B ion implanted junction was suppressed 4–5 orders of magnitude in comparison to that of a non B implanted junction.
A theoretical analysis of stimulated Raman conversion
Authors: Margalith E. , Sutton G. W.
Published: July 2002

The rate equations for stimulated electronic Raman scattering are presented for a general case, including linear absorption, atom and pump photon depletion, and variable beam geometry. Nondimensional variables are introduced, resulting in a simple procedure for optimization of Raman cell design and performance. A numerical solution of the detailed model is shown for a specific case, and the effects of the various parameters on the conversion efficiency are discussed.
Statistics of structure within solid fragments studied by 2D simulation
Authors: Jaeger Z. , Englman R. , Sprecher A.
Published: July 2002

A strongly fragmented two-dimensional medium was generated by a large number (103–104) of randomly thrown linear cracks. Various properties of fragments (e.g., number, size, shape, perimeter length, number of sides, and internal structure) were analyzed by computational geometry using a plane sweep algorithm. Asymptotically, for high crack density, the simulated fragment sizes follow the Mott distribution formula (cumulative number decreases exponentially with linear fragment size). Fragment structure, due to dangling or fully internal cracks, is identified with internal damage. The magnitude of damage as function of crack density is obtained by computation and analysis and is shown to reach a constant value asymptotically. By our results, a blasting operation leading to crack growth increases the ratio of small fragments in relation to larger ones.
Electron mobility studies of the donor neutralization by atomic hydrogen in GaAs doped with silicon
Authors: Jalil A. , Chevallier J. , Azoulay R. , Mircea A.
Published: July 2002

Hall effect and conductivity measurements have been performed on n- and n+-silicon-doped GaAs epilayers before and after hydrogen plasma exposure. We show that the reduction of the free-carrier concentration in the hydrogen diffused region is accompanied by a significant increase of the electron mobility. This increase is mainly attributed to the transformation of the ionized silicon donors into neutral complexes. This result is in quite good agreement with the model of silicon donor neutralization by formation of neutral silicon–hydrogen complexes.
Effect of an electric field on electron and hole wave functions in a multiquantum well structure
Authors: McIlroy P. W. A.
Published: July 2002

Electron and hole energy levels and eigenstates, and the overlap of electron and hole wave functions are calculated for four-well multiquantum well (MQW) structures assuming a uniform electric field with Airy function solutions. MQW are found to be much more sensitive to electric fields than single wells. Stark ladder formation is observed in the valence-band wells at low fields, and in the conduction band at high fields. It is found that the Δm=0 mode selection rule is violated by fields smaller than those thought to exist in MQW diode lasers.
Transient phase-change heat transfer in finite bodies: Universal bounds for the solidification (melting) time
Authors: Charach Chaim , Kahn Peter B.
Published: July 2002

Simple upper and lower limits for the full solidification (melting) time of isothermally heated slabs, cylinders, and spheres are derived. These bounds, valid for arbitrary wall and initial temperatures, are compared to existing approximate formulas. The bounds can be used for estimates of one-dimensional phase-change heat transfer.
Suppression of prebreakdown current by a cathode coating of CaF2
Authors: Smith Joe N.
Published: July 2002

Prebreakdown electron emission from polished stainless steel and from this surface covered with a 0.2–0.4 μm coating of CaF2 is measured at applied fields from 0.2 to 1.0 MV/cm. The CaF2 coating suppresses field emisssion by up to six orders of magnitude. In addition, the CaF2 coating increases the standoff voltage by ∼50%.
Direct experimental determination of voltage across high-low junctions
Authors: Daud T. , Lindholm F. A.
Published: July 2002

High-low (HL) junctions form part of many semiconductor devices, including back surface field solar cells. A first experimental determination and interpretation of the voltage across the HL junction under low- and high-injection conditions is presented as a function of the voltage across a nearby p/n junction. Theoretical analysis from first principles is shown to bear well on the experimental results. In addition, a test structure is proposed for measurement of the effective surface recombination velocity at the HL junctions.
Fabrication and lasing characteristics of 1.3-μm InGaAsP multiquantum-well lasers
Authors: Sasai Yoichi , Hase Nobuyasu , Ogura Mototsugu , Kajiwara Takao
Published: July 2002

This paper reports the fabrication and lasing characteristics of 1.3-μm InGaAsP multiquantum-well (MQW) buried heterostructure (BH) lasers grown by liquid-phase epitaxy (LPE) technique. The MQW active region consists of five InGaAsP well layers (λg=1.3-μm, Lz∼200 Å and InGaAsP barrier layers (λg=1.1 μm, d∼400–600 Å). These lasers have threshold currents of 15–20 mA at 25 °C, external quantum efficiencies of 50% at 25 °C, and T0 values of 130–145 °K in the temperature range of less than 300 °K. The beam divergences perpendicular and parallel to the junction plane were in the narrow range of 10–13°. Furthermore, the polarization-dependent gain-current relationship between the TE and TM mode of InGaAsP MQW lasers has been investigated in detail for the first time.
Acoustic dimensional resonance tomography: Some examples in one-dimensional systems
Authors: Testardi L. R. , Norton S. J. , Hsieh T.
Published: July 2002

A spatial map of the variation of acoustic impedance within a material structure can be made using only its resonance frequencies. We demonstrate this for a 1-D rod having a diameter D which varies along its length l by determining D(l) from fundamental and overtone resonances. We also show how the technique can locate material/processing inhomogeneities in the elastic modulus and/or density on a scale of several parts per thousand for ‘‘stock’’ rods of an aluminum alloy using nondestructive and noncontact testing. And finally, we apply dimensional resonance tomography in new measurement methods to obtain the thermal diffusivity along a rod and the heat transfer coefficient of the rod to its ambient. The latter technique provides quantitative data while allowing an arbitrary and unknown initial temperature distribution, requiring no temperature measurement or Fourier analysis, and can be done in noncontact fashion with the measurement of frequency and time, only.
Experiments on the longitudinal ion momentum balance in a magnetized plasma
Authors: Vogels J. M. M. J. , de Haas J. C. M. , Schram D. C. , Lunk A.
Published: July 2002

In the magnetized plasma of a hollow cathode arc the longitudinal and rotational drift velocities of ions have been measured, together with the electron and neutral densities and the temperatures of ions, electrons, and neutrals. The radial and longitudinal gradients of these quantities have been established. The ions drift against the electric field towards the anode with velocities between about 500 and 2500 m/s, driven by the plasma pressure gradient which is balanced by viscous deceleration and by friction against the surrounding neutral gas. The classical theory of the momentum balance with a turbulent contribution to the viscosity provides a good description of the longitudinal ion transport and explains direction and magnitude of the occurring drift velocity.
Neutron scattering studies of the spin reorientation in Er2Fe14B
Authors: Yelon W. B. , Herbst J. F.
Published: July 2002

We have probed the spin reorientation transition in Er2Fe14B by neutron powder diffraction. Our data and Rietveld analyses of them indicate that the transition is centered near 330 K, as magnetization measurements have shown, but extends over an interval of approximately 50 K. It occurs by coherent rotation of the moments from the basal plane at low temperatures to the c axis above ∼350 K. We find no evidence for any noncollinear arrangement of the Er and Fe moments.
Study on the transitional seeded crystallization variation of silicon on insulator using Gaussian laser beams
Authors: Lee El Hang
Published: July 2002

Variable distances of the transitional, defect-free, seeded crystallization of thin-film silicon on insulating substrates have been investigated using energy beams of Gaussian intensity distribution. Phenomenologically, defect-free crystals from the seed have been found to form Gaussianlike contours with respect to sub-boundary-laced crystals. The results are attributed to the thermal gradient effect upon the crystallization stability. This study bears a significant implication in the current efforts to increase the sub-boundary-free crystalline region over extended distances.
Monte Carlo simulation of AlGaAs/GaAs hot-electron transistors
Authors: Imanaga Syunji , Kawai Hiroji , Kaneko Kunio , Watanabe Naozo
Published: July 2002

Monte Carlo simulation of AlGaAs/GaAs hot-electron transistors (HET) was carried out on the following model: electrons are injected by tunneling through the emitter barrier and are scattered by polar optical phonons, acoustic phonons, ionized impurities, intervalley transitions, and plasmons in the base, and by quantum mechanical reflection at the boundary between the base and the collector barrier. Intervalley scattering and plasmon scattering are shown to play essential roles in limiting the characteristics of the HET. The simulation predicts that the transfer ratio can be as high as 0.9 with a base width of 100 A at 77 K, and that the transit time is about 1 ps with a total device length of 2200 A at a base-emitter voltage and a collector-base voltage of 1.0 V. The simulated result of the transfer ratio is in good agreement with the experimental result, if plasmon scattering is taken into account.
PtSi contact metallurgy: Comparison of different annealing sequences, annealing time and ambients, and deposition techniques of Pt
Authors: Chang Chin-An
Published: July 2002

PtSi films formed by different processes are compared, including different annealing sequences, annealing time, and annealing ambients, using either sputtered Pt or electron-beam evaporated Pt onto heated and unheated substrates. The structures and compositions, surface passivating oxide and its resistance to aqua regia, and electrical characteristics of Schottky diodes fabricated are compared. It is shown that for the Pt films deposited onto unheated Si wafers using either sputtering or evaporation, the three-temperature sequences at 200-300-500 °C using forming gas with different annealing times are superior to the various two-temperature ones, which, in turn, are better than the one-temperature one at 550 °C. Application to device fabrication and concerns of throughput using the recommended three-temperature or two-temperature processes are discussed.
The donor level of vanadium in InP
Authors: Deveaud B. , Plot B. , Lambert B. , Bremond G. , Guillot G. , Nouailhat A. , Clerjaud B. , Naud C.
Published: July 2002

We have studied p-type vanadium-diffused InP by deep-level transient spectroscopy. A level at 0.21 eV above the valence band is observed at a concentration comparable to that of vanadium. This level is interpreted as the V3+/V4+ donor state of vanadium in agreement with photoluminescence excitation experiments on n-type InP:V. Measurement of the photoneutralization cross section allows us to observe, for the first time, an excited state of a transition metal ion in resonance with the valence band. This observation confirms the charge state of the level that we have found.
Current-injection Josephson latch employing a single-flux quantum. I
Authors: Sone Jun’ichi , Yamada Toshishige
Published: July 2002

A new current-injection Josephson latch employing a single-flux quantum is proposed. It has a master-slave circuit configuration and operates under ac power supply. In the circuit, data are stored as a circulating current in a superconducting loop consisting of a single junction and inductances. A two-junction interferometer gate directly coupled to the loop reads out the stored data. Dual-rail signals are generated from the read-out data by Josephson junctions and resister-coupled Josephson logic gates. The isolation between a master circuit and a slave circuit is realized using high-impedance states in the Josephson junctions. The circuit design and computer-simulation results on the circuit operation are described in this paper.
Lasing mechanism of type-I′ PbSnTe–PbTeSe multiquantum well laser with doping structure
Authors: Ishida Akihiro , Fujiyasu Hiroshi , Ebe Hiroji , Shinohara Koji
Published: July 2002

Even though PbSnTe–PbTeSe superlattice has a type-I′ structure, its multiquantum well (MQW) laser has been realized by introducing band bending in the MQW active region. The MQW laser showed anomalous temperature dependence in the threshold current and the corresponding output photon energy. The lasing mechanism and anomalous behavior of the laser is qualitatively well explained by taking into account the variation of band bending due to large temperature dependence of the dielectric constants, assuming the barrier height ΔEc=−40 meV.
Microcrystalline domains in amorphous Pd77.5Cu6Si16.5 alloys studied by high-resolution electron microscopy
Authors: Hirotsu Yoshihiko , Uehara Masashi , Ueno Manabu
Published: July 2002

A high-contrast lattice imaging method in high-resolution electron microscopy has been applied to the observation of microstructures of amorphous Pd77.5Cu6Si16.5 alloys. Interpretable images of microcrystalline domains which prove the formation of the medium-range order have been observed in all the specimens prepared under different quenching rates. The average size of these domains was found to vary from about 3.2 to 1.7 nm depending on the quenching rate. From the lattice images and also from the microarea electron diffraction, the structure of the microcrystalline domains was identified as that of palladium with the face-centered-cubic structure.
Studies of free-to-bound acceptor photoluminescence in an applied magnetic field for undoped GaAs grown by metalorganic vapor-phase epitaxy and molecular-beam epitaxy
Authors: Zemon S. , Norris P. , Koteles E. S. , Lambert G.
Published: July 2002

Photoluminescence in an applied magnetic field is shown to be useful for the identification of trace acceptor impurities in GaAs. For an epitaxial layer grown by metalorganic vapor-phase epitaxy (MOVPE), a trace concentration of zinc acceptors was detected in a sample where the zinc transitions were obscured in zero magnetic field. In material grown by molecular-beam epitaxy (MBE), the 1.47-eV transition was identified as a conduction-band-to-deep-acceptor process. Also identified was a shallow impurity, magnesium or beryllium, not detected in zero field. Resolved Landau level transitions and the magnetic splitting of conduction-band-to-acceptor transitions were observed in both MOVPE and MBE material.
Radiation damage of germanium-doped silica glasses: Spectral simplification by photo- and thermal bleaching, spectral identification and microwave saturation characteristics
Authors: Chamulitrat Walee , Kevan Larry , Schwartz Robert N. , Blair G. Richard , Tangonan Gregory L.
Published: July 2002

Germanium-doped silica glasses are important materials used in the fabrication of preforms from which optical waveguides are drawn. The preforms consist of an outer cladding of silica and an inner core of germanium-doped silica. These separate portions have been subjected to varying types of ionizing radiation and the centers generated have been studied by electron-spin resonance spectroscopy. Core samples show the generation of a single type of germanium E′ center in the silica matrix which is surrounded by three next-nearest-neighbor germanium atoms and is specified as Ge(3) after xenon lamp irradiation at room temperature. If γ irradiation is used, several germanium E′ centers with varying numbers of next-nearest-neighbor germanium atoms ranging from 0 to 3 are generated and are designated as Ge (n) centers, where n=0, 1, 2, and 3. The Ge(1) and Ge(2) centers disappear after heat treatment at a temperature of ∼500 K leaving only the Ge(3) center as the most stable of these species. The intensity of the Ge(3) centers after γ irradiation and heat treatment increases in intensity with the γ-irradiation dose to at least ∼0.5 Mrad. Photobleaching by xenon lamp irradiation of γ-irradiated core samples also decreases the intensity of the Ge(1) and Ge(2) centers. Gamma irradiation of cladding samples generates two different types of silicon E′ centers, E′α1 and Eα2. At a lower radiation dose one sees a mixture of E′α1 and Eα2, but at a higher radiation dose, E′α2 dominates. Microwave power saturation data at different temperatures on both the core and the cladding samples are used to further differentiate and characterize these various species. It is found that a relaxation mechanism involving modulation of the g anisotropy is probable.
Direct observation of structural phase changes in proton-exchanged LiNbO3 waveguides using transmission electron microscopy
Authors: Lee W. E. , Sanford N. A. , Heuer A. H.
Published: July 2002

Transmission electron microscopy of proton-exchanged LiNbO3 waveguide channels reveals regions of diffuse intensity within the single-crystal electron diffraction patterns of LiNbO3. The diffuse intensity was not observed from areas of LiNbO3 which had been masked with Cr before exchange. Heating the waveguides in air at 550 °C for 2 h sharpened some of the diffuse intensity into diffraction spots, some of whose lattice spacings matched Nb2O5 or LiNb3O8. Other reflections also appeared which matched these phases. Small (∼20 nm diam) cavities were also observed in the exchanged channels after heating and suggest the occurrence of a dehydration reaction.
Picosecond study of near-band-gap nonlinearities in GaInAsP
Authors: Islam M. N. , Ippen E. P. , Burkhardt E. G. , Bridges T. J.
Published: July 2002

From picosecond pump-probe and forward degenerate four-wave mixing (DFWM) experiments, we obtain the near-band-gap nonlinear absorption and refraction properties of GaInAsP for λ∼1.5 μm. Using a mode-locked color center laser, the nonlinear signals are studied in room-temperature samples as a function of time and wavelength for different pump energies and for materials with different band-gap energies. Nonlinear absorption cross sections σeh as large as −5.7×10−15 cm2 are obtained from the pump-probe results, while effective nonlinear cross sections σeff as large as 7.8×10−16 cm2 (corresponding to a steady state ‖χ(3)‖∼3.8×10−3 esu for a 20-ns relaxation time) are measured in the DFWM experiments. The spectral behavior of the data shows that above the band gap, the nonlinearity is due both to band filling and screening of excitonic effects. However, the effectiveness of the screening diminishes within one or two plasma frequencies of the band edge.
Influence of sputtering pressure on the properties of hydrogenated amorphous-silicon carbon alloy films prepared by magnetron sputtering of silicon in methane-argon gas mixtures
Authors: Saito Nobuo
Published: July 2002

The structural, optical, electrical, and optoelectronic properties of magnetron sputtered hydrogenated amorphous-silicon carbon alloy films have been investigated as a function of sputtering pressure. The optical band gap, the activation energy of dark conductivity, and concentration of hydrogen increase with increasing sputtering pressure. The photoconductivity as well as the dark conductivity shows a maximum against pressure. These results are discussed from the standpoint of the structural and compositional change of the films with sputtering pressure, originating from the change of plasma reaction process composed of the decomposition of methane and the sputtering of silicon.
One-dimensional hot-electron transport in quantum-well wires of polar semiconductors
Authors: Ghosal A. , Chattopadhyay D. , Bhattacharyya A.
Published: July 2002

The velocity-field characteristics of hot electrons moving one dimensionally in the lowest subband of a polar semiconductor quantum-well wire are obtained on a drifted Maxwellian model and also by the Monte Carlo technique. No negative differential resistance is obtained in contradiction to a previous prediction. The size effects at low temperatures are found to be more significant in the drifted Maxwellian model. Our calculations show that the one-dimensional (1-D) mobility for large transverse widths may be higher than the 3-D mobility.
Dot junction solar cells
Authors: Daud T. , Crotty G. T.
Published: July 2002

A design of solar cells with reduced junction area on the cell surface is investigated for reduction of saturation current and increase in open-circuit voltage. Equidiameter dot junctions distributed across the surface of the cell offer an efficient alternative, with variations in dot diameter and in the spacing between dots giving the required variations in the ratio of junction area to total surface area. A simplified analysis for short-circuit current and other cell parameters, which enables cell design optimization, is presented. Experimental solar-cell performance results, as functions of different area ratios, are presented and compared with the model. It is shown that saturation current reduction is possible for achieving efficiencies as high as 18% in flat-plate terrestrial applications.
Effect of ion implantation on stripe- and bubble-domain coercivity
Authors: Pardavi-Horváth M. , Vértesy G.
Published: July 2002

The static coercivity of stripe and bubble domains in 5-μm (YSmCa)3(FeGe)5O12 epitaxial garnet films was measured by the oscillating-wall method. The dependence of coercivity on Ne+ implantation energy and dosage was investigated. In a wide range of energy and dosage, implantation was found to eliminate hard bubbles and decrease bubble coercivity by 25%; the decrease is a measure of the contribution of Bloch lines to coercivity. The average number of Bloch lines n in bubble walls was determined from static coercivity as 37≤n≤62, n increasing with quality factor Q. Bubble coercivity was always found to be higher than stripe coercivity measured by the same method. Implantation has no measurable effect on apparent stripe coercivity which may be a consequence of the lower Bloch line density of stripes relative to bubbles.
Model for the ∼1.28-eV double-acceptor luminescence in GaAs
Authors: Shanabrook B. V. , Moore W. J. , Bishop S. G.
Published: July 2002

The 1.283-eV luminescence band observed in GaAs grown from Ga-rich melts is attributed to a donor–double-acceptor pair transition which leaves the negatively charged final state of the double acceptor in the 2S3/2 excited state. This assignment is shown to be consistent with the estimated energy of such a transition and with the results of Hall effect, infrared absorption, and luminescence measurements. It is proposed that similar emission bands should be observed for other double acceptors and that their observation provides strong evidence for the double-acceptor nature of such impurities.
Laser-induced damage to spray pyrolysis deposited transparent conducting films
Authors: Radhakrishnan P. , Sathianandan K. , Subhash N.
Published: July 2002

Laser-induced damage study of transparent conducting coatings of tin oxide prepared by spray pyrolysis has been made using a dye Q-switched Nd:glass laser emitting 25-ns (FWHM) pulses at 1062 nm. For comparison tin oxide films prepared by chemical vapor deposition (CVD) method and indium tin oxide (ITO) prepared by the reactive rf sputtering method have also been damage tested. The study reveals that the spray pyrolysis method yields good electrical and optical quality films with a damage threshold value of 5.2±0.3 J/cm2. Though CVD technique provides the highest damage threshold coatings (14.2±0.6 J/cm2), their electrical characteristics and uniformity are inferior to rf-sputtered ITO films which have the best electrical properties and the lowest damage threshold values (1.3±0.1 J/cm2).
Thermal evolution of molybdenum disilicide grown on (100) silicon under ultrahigh vacuum conditions
Authors: Perio A. , Torres J.
Published: July 2002

Under ultrahigh vacuum conditions, molybdenum disilicide has been obtained by electron gun evaporation of molybdenum on heated monocrystalline silicon substrate. Depending on the deposition temperature, the resulting thin film is composed of tetragonal disilicide or of a mixture of hexagonal and tetragonal disilicide. Preferential orientations of MoSi2 have been observed for both phases grown on (100) silicon substrate heated at 550, 650, and 750 °C. Further annealing does not improve the crystallographic orientation of the materials.
Effect of localized grain boundaries in semicrystalline silicon solar cells
Authors: Shimokawa Ryuichi , Hayashi Yutaka
Published: July 2002

The spatial variation of minority-carrier diffusion length in the vicinity of a boundary surface in monocrystalline and semicrystalline silicon solar cells has been measured by the scanned monochromatic light beam induced current (MBIC) technique with a very small spot size (2μm in diameter) and 750–1050-nm-long wavelength light beam. The technique we developed uses a short-arc xenon lamp source with line spectra. It was found that most of the grain boundaries in cast semicrystalline silicon materials were accompanied with crystal imperfections along them, and the effect of a boundary surface extended beyond the distance of a minority-carrier diffusion length. Furthermore, the effective minority-carrier diffusion length due to crystal imperfections in the vicinity of the grain boundary was estimated and it was indicated that the grain boundary where the crystal imperfections were concentrated could be characterized using the concept of the effective influence width of grain boundary.
Heating a slab induced by a time-dependent laser irradiance—An exact solution
Authors: El-Adawi M. K. , Elshehawey E. F.
Published: July 2002

The problem of heating a homogeneous slab of material induced by time-dependent laser irradiance is studied. An exact solution for the temperature distribution of the slab is obtained using the Fourier series expansion technique. The temperatures for the front and rear surfaces are also obtained. The case of time-independent laser irradiance is considered. The exact expressions for the thermal penetration depth and the critical time required to initiate melting (i.e., damage) are recovered and compared with the published data for this special case.
Determination of the conduction-band discontinuity between In0.53Ga0.47As/In0.52Al0.48As using n+-InGaAs/InAlAs/n−-InGaAs capacitors
Authors: Peng C. K. , Ketterson A. , Morkoç H. , Solomon P. M.
Published: July 2002

The conduction-band discontinuity (ΔEc) between In0.53Ga0.47As and In0.52Al0.48As is determined by current-voltage measurements on n+-InGaAs/InAlAs/n−-InGaAs capacitors. Current is found to be dominated by thermionic emission conduction down to 180 K. Barrier heights are determined from the slope of ln(J/T2) vs 1/T where good straight-line fits are obtained in the thermionic emission range. After correcting for the Fermi level a conduction-band discontinuity of 0.51±0.04 eV is obtained representing 70% of the total band-gap discontinuity. Furthermore, capacitance-voltage measurements are fit to classical capacitance-voltage theory and show that no charge is present in the InAlAs insulating layer.
Comment on ‘‘Hydrogen depth profiles in ion-implanted magnetic bubble garnets’’
Authors: Leiberich A. , Milani E. , Paroli P. , Wolfe R.
Published: July 2002

An apparent contradiction between recent papers by Leiberich and Wolfe [Appl. Phys. Lett. 47, 241 (1985)] and by Milani and Paroli [J. Appl. Phys. 55, 2173 (1984)] on diffusion of hydrogen in magnetic garnets is reconciled. Hydrogen does diffuse in these garnets at temperatures as low as 250 °C even when they are not damaged by ion implantation, but only up to a saturation level of about 0.03 atoms per formula unit.
Electrical characterization of Ti-silicided shallow junctions formed by ion-beam mixing and rapid thermal annealing
Authors: Kwong D. L. , Alvi N. S.
Published: July 2002

We have developed a technique for the fabrication of shallow, silicided junctions with good electrical characteristics. By the implantation of suitable impurity ions into titanium silicide layers on Si formed by ion-beam mixing and low-temperature annealing, and the subsequent diffusion of the implanted ions at high temperature into the Si substrate, shallow p+/n, n+/p, and double-diffused n+-n−/p junctions with silicide ohmic contacts have been obtained. Results of contact resistance, contact morphology, junction integrity, and carrier concentration profile are reported. The effects of implantation energy, implant dose, and annealing parameters are discussed. This technique can be easily applied to the fabrication of metal-oxide-semiconductor field-effect transistors in a self-aligned fashion.
A model of radio frequency planar discharges
Authors: Pointu A. M.
Published: July 2002

A simple model, using an asymmetrical double probe theory, is presented to describe a rf planar glow discharge. It reasonably agrees with available experimental results for a capacitively coupled excitation electrode and frequencies of about 100 kHz.
Performance characteristics of the ArF excimer laser using a low-pressure argon-rich mixture
Authors: Suda Akira , Obara Minoru , Noguchi Akira
Published: July 2002

Low-pressure operation of an electron-beam excited ArF laser was experimentally compared to KrF lasers, both of which were pumped at high excitation rate by a 65 ns electron beam. We obtained the ArF laser energy of 95 J with an intrinsic efficiency of 3.4% from a 650 Torr Ar/F2 mixture pumped at an excitation rate of 2.3 MW/cm3. In the low-pressure region (near one atmosphere) the Ar/F2 mixture gave higher efficiency than that of Ne-buffered mixtures, and moreover gave higher efficiency than those of the KrF lasers operating with various mixtures under the same excitation rate. As a result, the ArF laser operating in this regime is found to be a better candidate than the KrF laser as an inertial confinement fusion driver.
Spectroscopic ellipsometry study of the In1-xGaxAsyP1-y/InP heterojunctions grown by metalorganic chemical-vapor deposition
Authors: Drevillon B. , Bertran E. , Alnot P. , Olivier J. , Razeghi M.
Published: July 2002

The dielectric functions of InP, In0.53Ga0.47As, and In0.75Ga0.25As0.5P0.5 epitaxial layers have been measured using a polarization-modulation spectroscopic ellipsometer in the 1.5 to 5.3 eV region. The oxide removal procedure has been carefully checked by comparing spectroscopic ellipsometry and x-ray photoelectron spectroscopy measurements. These reference data have been used to investigate the structural nature of metalorganic chemical-vapor deposition grown In0.53Ga0.47As/InP and In0.75Ga0.25As0.5P0.5/InP heterojunctions, currently used for photodiodes and laser diodes. The sharpness of the interfaces has been systematically compared for the two types of heterojunctions: In1-xGaxAsy/InP and InP/In1-xGaxAsyP1-y. The sharpest interface is obtained for InP growth on In0.75Ga0.25As0.5P0.5 where the interface region is estimated to be (10±10) Å thick. The importance of performing in situ SE measurements is emphasized.
Molecular-beam epitaxy and optical characterization of GaAs on CaF2 substrates
Authors: Fontaine C. , Benarfa H. , Bedel E. , Munoz-Yague A. , Landa G. , Carles R.
Published: July 2002

The growth of GaAs layers on bulk fluoride substrates is reported. The characteristics of the GaAs layers are studied by Raman and photoluminescence spectroscopies. The experimental results presented compare these GaAs layers to those grown on (Ca,Sr)F2/GaAs. It is shown that the crystalline quality of GaAs improves with the distance to the fluoride interface and that the layers are under compressive stress; in addition, it was found that the latter does not affect the photoluminescence efficiency.
Porous silicon layers and its oxide for the silicon-on-insulator structure
Authors: Takai H. , Itoh T.
Published: July 2002

Crystalline properties of Si films grown on porous Si layers were investigated. Based on the results obtained by Rutherford backscattering spectroscopy and cross-sectional transmission electron microscopy, a model of Si epitaxial growth on a porous Si layer is proposed. In our model dominant defects in the region near the epitaxial layer/porous Si interface and in the one near the surface in the epitaxial layer are dislocations and stacking faults, respectively. The oxidation rate of the porous Si layers is about 80–130× faster than that of the bulk Si, and the etching rate of the oxidized porous Si layers is almost equal to that of the bulk oxide. The effective dielectric constants of the oxidized porous Si layers have a close relation to the anodic current density, ranging from 3.8 to 4.0.
Analysis of hysteresis loops in Nd-Fe-B sintered magnets
Authors: Givord D. , Tenaud P. , Viadieu T.
Published: July 2002

At room temperature, a kink in negative fields appears in the hysteresis loops of Nd-Fe-B permanent magnets. This phenomenon can be related to the fact that the grains at the surface of the magnet exhibit a strongly reduced coercivity compared to those of the bulk. Below 130 K a kink of another nature develops. It is strictly reversible and amounts to about 30% of the spontaneous magnetization. It is caused by a combined effect of the spin reorientation occurring in the Nd2Fe14B phase and the incomplete alignment of the particles in the magnets.
Local epitaxy of TiSi2 on (111)Si: Effects due to rapid thermal annealing and to the annealing atmosphere
Authors: Wu I. C. , Chu J. J. , Chen L. J.
Published: July 2002

Localized epitaxial TiSi2 was grown on (111)Si by rapid thermal annealing (RTA) in Ar ambient. The best epitaxy was obtained in samples annealed at 1100 °C for 20 s. Almost full coverage of TiSi2 (epitaxial and nonepitaxial) on silicon surface was found. The epitaxial regions, about 20 μm in average size, were observed to cover 70% of the surface area. Some of the epitaxial regions were observed to be as large as 40 μm in size. Dominant mode and average size of TiSi2 epitaxy in RTA samples were found to be different from those in vacuum furnace annealed specimens. Ambient gas induced silicide surface and/or silicide/Si interface energy changes are suggested to promote the growth of differently oriented grains. The main advantages of RTA in inducing TiSi2 epitaxy appear to be better control of the annealing ambient, temperature, and time for short-time anneals in the small RTA apparatus than in a furnace.
Use of a carbon-alloyed graded-band-gap layer at the p/i interface to improve the photocharacteristics of amorphous silicon alloyed p-i-n solar cells prepared by photochemical vapor deposition
Authors: Kim W. Y. , Tasaki H. , Konagai M. , Takahashi K.
Published: July 2002

Amorphous silicon alloyed p-i-n solar cells have been fabricated using a separate chamber photochemical vapor deposition system. The photocharacteristics of such cells have been modestly improved by the addition of a carbon-alloyed graded-band-gap layer at the p(a-SiC:H)/i(a-Si:H) heterointerface. The best efficiency obtained for a glass/TCO (transparent conductive oxide)/p(a-SiC:H)/i(a-Si:H)/n(μc-Si:H)/metal structure of this type was 11.2% for a 3×3 mm2 cell; other parameters were Voc=0.882 V, Isc=18.05 mA/cm2, and a fill factor (FF) of 0.702.