bluuebunny/crossref_metadata_2025 huggingface dataset:
Thin upper-confining layer AlxGa1−xAs-GaAs quantum well heterostructure laser diodes
Authors: Caracci S. J. , Kish F. A. , Krames M. R. , Ries M. J. , Holonyak N. , Smith S. C. , Burnham R. D.
Published: July 2002

AlxGa1−xAs-GaAs quantum well heterostructure (QWH) laser diodes with much thinner upper confining layers (0.6, 0.45, 0.3, and 0.2 μm) than usual (1–2 μm) are demonstrated. The diodes exhibit well behaved transverse far-field patterns, low broad-area pulsed threshold current densities, and high differential quantum efficiencies. The diodes with thinnest upper confining layers, ∼0.2 μm, have broad-area pulsed threshold current densities as low as Jth∼169 A/cm2 and a total external differential quantum efficiency ηT∼53% (∼500 μm long cavities). Stripe-geometry (40 μm wide) laser diodes made from the crystals with 0.2 μm upper confining layers exhibit room-temperature continuous (cw) threshold currents of 60 mA, output powers of ∼200 mW/facet (uncoated), and transverse far-field patterns with a full angle half power (FAHP) of 48°. Nonoptimized narrow-stripe (∼4 μm) native-oxide index-guided laser diodes fabricated on the same 0.2 μm confining layer QWH crystal operate at pulsed thresholds as low as 9 mA and continuous thresholds of 16 mA, with total external differential quantum efficiencies of 39% pulsed and 30% cw.
High temperature superconducting resonator for use in nuclear magnetic resonance microscopy
Authors: Black R. D. , Roemer P. B. , Mogro-Campero A. , Turner L. G. , Rohling K. W.
Published: July 2002

We describe surface coil resonators made with thin-film Y1Ba2Cu3O7 (YBCO) for use in high-resolution nuclear magnetic resonance imaging. At the operating temperature of the coil, 10 K, we have measured Q values (quality factor) in excess of 50 000 at 300 MHz in magnetic fields as high as 9 T. Noise temperature measurements of this superconducting probe indicate that the dominant noise source is Johnson noise. We describe a coupling circuit comprised of the YBCO coil that is inductively coupled to a room-temperature copper resonator. This circuit preserves the high signal-to-noise ratio that accrues to the YBCO resonator.
High brightness blue and green light sources pumped with a 980 nm emitting laser diode
Authors: Mita Yoh , Wang Y. , Shionoya S.
Published: July 2002

Efficient frequency upconversion from 980 nm infrared light to 480 nm wavelength blue emission has been observed in Tm3+-activated, Yb3+-sensitized fluoride glass. Similar upconversion to green emission has been obtained with higher efficiency in Er3+-containing luminescent materials. The conversion efficiencies have been markedly improved when the luminescent material small in size is contained in a reflective cavity. The improvement effect is pronounced when transparent luminescent material is adopted. Processes leading to the generation of visible emission have been examined and criteria for optimizing the upconversion efficiency are presented.
Reflection high energy electron diffraction intensity oscillations during the growth by molecular beam epitaxy of GaAs(110) films
Authors: Neave J. H. , Zhang J. , Zhang X. M. , Fawcett P. N. , Joyce B. A.
Published: July 2002

Reflection high energy electron diffraction (RHEED) intensity oscillations are reported for GaAs growth by molecular beam epitaxy (MBE) on singular GaAs (110) substrates. The behavior is quite different from that observed for any other system involving a singular surface and elemental sources, in that the oscillation period is a function of temperature, flux ratio, and growth time. The results are discussed in terms of possible growth modes and relative adatom populations.
Surface sublimation of zinc blende CdTe
Authors: Wu Y. S. , Becker C. R. , Waag A. , von Schierstedt K. , Bicknell-Tassius R. N. , Landwehr G.
Published: July 2002

The surface sublimation of Cd and Te atoms from the zinc blende (111)A CdTe surface has been investigated in detail by reflection high energy electron diffraction and x-ray photoelectron spectroscopy. These experiments verify that Te is much easier to evaporate than Cd. The experimental value for the Te activation energy from a Te stabilized (111)A CdTe surface is 1.41±0.10 eV, which is apparently inconsistent with recent theoretical results.
Transient electron paramagnetic resonance hydrogen hyperfine doublet in low-OH content synthetic silica optical fibers during isothermal annealing
Authors: Li J. , Kannan S. , Lehman R. L. , Sigel G. H.
Published: July 2002

A transient 75 G electron paramagnetic resonance (EPR) hydrogen hyperfine doublet was observed for the first time in low-OH content silica optical fibers during isothermal annealing in the temperature range between 250 and 400 °C in air. The results are consistent with the diffusion of hydrogen molecules into the glass with subsequent interaction with E′ centers to form an intermediate E′/H and, in turn, an EPR-inactive end product. The response of the doublet to trace amounts of hydrogen was used to monitor hydrogen diffusion and the reaction between E′ and hydrogen in the glass.
Picosecond response of steady-state photovoltaic effect in an asymmetrical graded semiconductor superlattice structure
Authors: Liu J. M. , Chen L. P. , Liu C. T. , Burrus C. A. , Cho A. Y.
Published: July 2002

A steady-state photovoltaic effect of picosecond response speed has been observed in an asymmetrical graded InAlGaAs superlattice structure with a responsivity of ∼0.3 V/W and a saturation photovoltage of ∼0.3 V. For 10 devices of varying sizes ranging from 51 to 502 μm in diameter, the measured full width at half-maximum of the impulse response to a 1.6-ps laser pulse varies only twofold from 29 to 58 ps. The intrinsic rise time of each device is less than 10 ps. Steady-state photovoltage signals were observed in all the devices when excited with 100-ps–2-μs laser pulses. No dc bias voltage is needed.
Saturation of multiplication factor in InGaAsP/InAlAs superlattice avalanche photodiodes
Authors: Kagawa Toshiaki , Kawamura Yuichi , Iwamura Hidetoshi
Published: July 2002

The saturation of the multiplied photocurrent at an intense illumination was studied for InGaAsP/InAlAs superlattice avalanche photodiodes. The dependence of the multiplication factor on the illumination intensity is small in comparison with conventional bulk APDs because the ionization rate ratio is larger. The multiplication factor decreases at an intense illumination mainly because of the space charge effect.
Single transistor static memory cell: Circuit application of a new quantum transistor
Authors: Chen J. , Yang C. H. , Wilson R. A. , Wood C. E. C.
Published: July 2002

An experimental realization and application of a new quantum transistor is reported herein. The conduction mechanism is a resonant-tunneling process between regions of two-dimensional density of states. As a result, the transistor displays new current-voltage characteristics. A static memory cell using a single transistor is demonstrated.
Highly accurate etching of ridge-waveguide directional couplers using in situ reflectance monitoring and periodic multilayers
Authors: Vawter G. A. , Klem J. F. , Hadley G. R. , Kravitz S. H
Published: July 2002

A novel periodic multilayer structure has been used in conjunction with in situ reflectance monitoring to give ±10 nm endpoint detection during reactive-ion-beam etching. The method has been used to fabricate ridge-waveguide directional couplers in GaAs/AlGaAs having coupling lengths within 100 μm of the desired 650 μm value. The added loss due to coupling length error was only 0.3 dB per guide. The method is directly applicable to photonic integrated circuits employing complex optical routing of waveguides, directional couplers and y-junctions where total height of the waveguide plays a key role in performance of the circuit.
Ion implanted, outdiffusion produced diamond thin films
Authors: Hoff H. A. , Vestyck D. J. , Butler J. E. , Prins J. F.
Published: July 2002

A thin film, produced by carbon ion implantation and outdiffusion at the temperature of irradiation, has been confirmed to be diamond using micro-Raman spectroscopy and electron diffraction. The Raman spectra contained a definitive diamond peak shifted slightly from that of natural diamond. This shift may be due to residual strain and is consistent with the broad linewidth. Fragments of the film over a micron in size were examined with transmission electron microscopy and found to be untwinned, single crystals. The film had been produced on a polycrystalline copper substrate. The carbon ions were at an ion energy of 120 keV and the irradiation was carried out to a high dose.
Suppression of abnormal Zn diffusion in InP/InGaAs heterojunction bipolar transistor structures
Authors: Kobayashi Takashi , Kurishima Kenji , Gösele Ulrich
Published: July 2002

It is known that highly n+-doped subcollector layers in InP/InGaAs heterojunction bipolar transistor structures lead to drastically enhanced zinc diffusion in the subsequently grown base layer. We show that this abnormal zinc diffusion can be suppressed by interrupting growth before the zinc-doped layer is grown. It is speculated that this growth interruption allows excess nonequilibrium group III self-interstitials coming from the n+-doped subcollector layer to disappear before they have a chance to enhance zinc diffusion in the base layer.
Enhancement of laser-induced defect-initiated Ga0 emission from GaAs(110) surfaces by Br adsorption
Authors: Kanasaki Jun’ichi , Matsuura Anne Y. , Nakai Yasuo , Itoh Noriaki , Haglund R. F.
Published: July 2002

High sensitivity measurements of Ga emission, produced by laser irradiation of fluences below the ablation threshold, from a Br-adsorbed GaAs(110) surface were carried out. It was found that bromine adsorption enhances Ga0 emission: the amount of enhancement is linearly proportional to the amount of adsorbates but much smaller in the absolute value. The result is interpreted as a Br-induced weakening of the Ga—As bond on defect sites by Br adsorption.
Effect of oxidizing activity on the low-temperature growth of HoBa2Cu3Ox thin films
Authors: Tsukamoto Akira , Hiratani Masahiko , Akamatsu Shoichi
Published: July 2002

The effect of oxygen plasma on the growth of HoBa2Cu3Ox thin films is investigated. Lowering the growth temperature introduces excess oxygen vacancies, which are formed in a nonequilibrium state regardless of whether the plasma is applied. At growth temperatures as low as 500 °C, the crystallinity of thin films grown in molecular oxygen is superior to that of films grown in oxygen plasma, since the growth conditions close to the decomposition line of the 123 compound enhance the surface migration. At temperatures above 540 °C, no significant difference can be seen between films grown in molecular oxygen and those grown in oxygen plasma. This is thought to be because, at higher temperatures, thin-film growth is dominated by the thermal energy supplied from the heated substrate.
Rutherford backscattering analysis of phosphorus gettering of gold and copper
Authors: Hartiti B. , Hage-Ali M. , Muller J. C. , Siffert P.
Published: July 2002

The extrinsic gettering of Au and Cu by phosphorus diffusion in a classical or rapid thermal furnace has been analyzed by Rutherford backscattering (RBS) measurements. Accumulation of Au and Cu in the phosphorus-doped region has been clearly evidenced after classical or rapid thermal diffusion of phosphorus from a spin-on deposited silicon glass source in the temperature range 950–1050 °C for typical durations of 15 min and 25 s, respectively, confirming the existence of classical as well as a rapid thermal gettering effect.
Carrier lifetimes in strained InGaAs/(Al)GaAs multiple quantum wells
Authors: Moloney M. H. , Hegarty J. , Buydens L. , Demeester P. , Grey R. , Woodhead J.
Published: July 2002

The effect of strain, strain relief, and barrier design on the carrier lifetime in InGaAs/(Al)GaAs multiple-quantum-well samples is investigated. Carriers lifetimes are measured in samples with varying amount of strain, due to increasing indium concentration in the wells, as well as in samples subject to strain relief, with thick barriers and GaAs barriers. Lifetimes of the order of 0.5 ns are measured. The lifetime is sensitive to the presence of indium in the wells but remarkably insensitive to the indium concentration, the strain in the samples, and the barrier composition.
Comparison of Al electromigration in conventional Al alloy and W-plug contacts to silicon
Authors: Oates A. S. , Martin E. P. , Alugbin D. , Nkansah F.
Published: July 2002

We examine the impact of the presence of a W plug on electromigration-induced voiding of the Al alloy layer of contacts to silicon. By comparing conventional Al alloy and W-plug contacts we show that the presence of the plug does not significantly improve the intrinsic susceptibility of contacts to Al voiding despite the elimination of the Al step coverage problem. Both the conventional Al alloy and W-plug contacts degrade by drift of the Al layer with a velocity that is not influenced by the contact structure. The sheet resistance of the underlayer material of multilayer conductors plays an important role in influencing failure times since it determines the rate of resistance increase due to electromigration.
Minimization of the offset voltage in heterojunction dipolar transistors by using a thick spacer
Authors: Wang Q. , Yang E. S. , Chen Y. K. , Sivco D. , Cho A. Y.
Published: July 2002

We have successfully fabricated and characterized two-dimensional electron gas emitter heterojunction bipolar transistors (2DEG emitter HBTs) of AlInAs/InGaAs and AlGaAs/GaAs compound materials. With a 50 nm thick undoped InGaAs spacer employed in the emitter junction, the offset voltage of the AlInAs/InGaAs HBT is reduced from 500 to 70 mV. Experimental data of the offset voltage obtained at different spacer thickness show that a spacer of 30 nm would be optimum for both AlGaAs/GaAs and AlInAs/InGaAs HBTs. This is basically in agreement with the numerical calculation of the electron sheet density of the 2DEG. The reduction of the offset voltage by using a 2DEG emitter is particularly important for the AlInGa/InGaAs or InP/InGaAs HBTs, since the breakdown voltage of these devices is usually low and the composition grading in the emitter is either very complicated or not applicable.
All in situ deposition and characterization of YBa2Cu3O7−x thin films by low-energy electron diffraction and low-energy ion scattering spectroscopy
Authors: Tanaka S. , Nakamura T. , Tokuda H. , Iiyama M.
Published: July 2002

In an ultrahigh vacuum apparatus, c-axis oriented YBa2Cu3O7−x (YBCO) thin films were deposited by an ozone-assisted reactive coevaporation method and characterized by low-energy electron diffraction (LEED) and low-energy ion scattering spectroscopy (LEISS). A clean surface with crystal perfection within the top two monolayers was confirmed by LEED for the first time. LEISS analysis showed that this clean surface is terminated by Cu(1)-O chains. These experiments also indicate that the oxygen pressure and the vacuum condition are one of the essential factors in keeping an outermost surface clean.
Light-controlled vapor deposition by light-induced drift
Authors: Kleinfeld J. A. , Streater A. D.
Published: July 2002

Light-controlled deposition of potassium atoms onto a glass surface by light-induced drift (LID) is demonstrated. The collection of atoms by wave-front curvature is found to be important for maximizing the deposition rate. The light control of diffusive deposition is demonstrated by using LID to push atoms away from surface regions where a layer is not wanted. The measured spatial resolution of this process in the experiment was about 100 μm. Pressure and intensity effects on both deposition processes are discussed.
Numerical evaluation of amorphous silicon p-i-n solar cell degradation
Authors: Kopetzky W. J. , Schwarz R.
Published: July 2002

Through numerical simulation of several hypotheses concerning the degradation of hydrogenated amorphous silicon p-i-n solar cells under illumination, we have established a set of ‘‘degradation rules.’’ Comparing the measured white-light characteristic as a function of intensity, the internal collection efficiency as a function of wavelength, and the i-layer thickness dependence of the conversion efficiency with these rules allows one to distinguish between the degradation of the i layer, the buffer layer, and the buffer/i-interface layer.
Double step-edge weak links integrated with spiral antenna structure in epitaxial Tl2CaBa2Cu2O8 films for millimeter wave mixing
Authors: Hong J. P. , Fetterman H. R. , Forse R. J. , Cardona A. H.
Published: July 2002

High-temperature superconducting mixers have been fabricated from epitaxial films of Tl2CaBa2Cu2O8 utilizing surface double step-edge junctions on LaAlO3 substrates. These mixers were integrated with spiral antenna structure designed for broadband millimeter wave coupling of the radiation into weak links. Under the optimum bias current condition heterodyne mixing of signals at W band (94 GHz) frequencies has been measured, and noise performance operating at V band (60 GHz) has been characterized both at liquid nitrogen and liquid helium temperatures. By using an etching technique, two orders of magnitude improvement in noise performance over the earlier results have been obtained. Strong mixing signals were achieved right up to Tc (102 K).
Monte Carlo investigation of carrier-carrier effects in femtosecond pump and probe experiments
Authors: Rota L. , Ferry D. K.
Published: July 2002

We present a Monte Carlo simulation of ultrafast absorption saturation studies of hot carriers in GaAs. We show that carrier-carrier scattering is the dominant scattering mechanism in the femtosecond time regime and that pump and probe experiments are the ideal tool for the study of the strength of this interaction. Three different approaches are used to study carrier-carrier scattering and the best agreement with experimental results is obtained by molecular dynamics.
High-frequency modulation and suppression of chirp in semiconductor lasers
Authors: Gorfinkel Vera B. , Luryi Serge
Published: July 2002

We propose a new method for modulating laser radiation by controlling simultaneously the pumping current and the optical gain in the active region. The latter can be independently varied by modulating the effective carrier temperature. The method allows to eliminate the relaxation oscillations and enhance the modulation frequency to 50 GHz. It also allows to suppress the wavelength chirping in optical communication systems operating at pulse repetition rates of 10 Gb/s.
Photoplastic effect in a II-VII semiconductor with van der Waals interlayer bonding (HgI2)
Authors: Marschall Jochen , Milstein Frederick
Published: July 2002

Experimental evidence of a small, positive photoplastic effect during the shear deformation of single-crystal red mercuric iodide is presented. This is apparently the first observation of a photoplastic effect in a II-VII semiconductor, as well as in a material in which the bonding between slip planes is of van der Waals type.
Implantation temperature dependent distribution of NiSi2 formed by ion beam synthesis in silicon
Authors: Vanhellemont J. , Bender H. , Wu M. F. , De Wachter J. , Hendrickx P. , Pattyn H. , Van Bavel A. M. , Langouche G. , Maenhoudt M. , Bruynseraede Y.
Published: July 2002

The formation and distribution of NiSi2 in (111) silicon by Ni-ion implantation with a fluence of 1.1×1017 cm−2 and an energy of 90 keV is studied as a function of the temperature during implantation. For temperatures below 200 °C, a buried layer of NiSi2 precipitates is formed. Increasing the temperature gradually from 200 to 350 °C leads first to the formation of a double buried NiSi2 layer which with increasing temperature evolves into an epitaxial NiSi2 surface layer. A tentative model to explain for the observed anomalous behavior is presented.
Pitfalls in the measurement of metal/p-Si contacts: The effect of hydrogen passivation
Authors: Sullivan J. P. , Graham W. R. , Tung R. T. , Schrey F.
Published: July 2002

Chemical etching of Si, used in the preparation of clean, hydrogen-terminated Si surfaces, was found to inject hydrogen—leading to the passivation of acceptors at depths over 0.5 μm. This effect explains the ‘‘high’’ barrier heights, the nonlinear capacitance-voltage plots, and the nonuniform dopant profiles observed for metals deposited on unannealed, etched p-type substrates. Room-temperature metal deposition on atomically clean, well-annealed p-type substrates showed no changes in the active dopant profile, in disagreement with metal-acceptor complex mechanisms recently proposed.
Admittance spectroscopy characterization of InP/InGaAsP single quantum wells grown by low-pressure metalorganic chemical vapor deposition
Authors: Zhao J. H. , Lu Z. , Buchwald W. , Coblentz D. , McAfee S.
Published: July 2002

A set of sulfur-doped low pressure metalorganic vapor phase epitaxy InP/InGaAsP single quantum wells have been studied by admittance spectroscopy and a variety of other techniques. Admittance spectroscopy allows the studies of carrier emission from both the sulfur shallow impurity state and a quantum well which is seen to behave like a giant trap. The electron emission rates will be reported and the sulfur shallow impurity level is found to be 10 meV, in agreement with a simple theoretical calculation.
Propagation of ultrashort electrical pulses on microstriplines with submicron dielectrics
Authors: White J. D. , Woodgate I. K. , Cleaver J. R. A.
Published: July 2002

We present and analyze a new waveguide structure for the transmission of ultrashort electrical pulses over relatively long distances. By using the method proposed in the present work, microstrip waveguides with submicron dielectric thickness can be formed with III-V semiconductors on highly conducting (metallic) substrates for the first time. In order to minimize signal attenuation, three conventional superconducting materials have been considered to form the metallization. At 4.2 K it is found that pulse propagation is best when the lines are formed with Nb3Sn although NbN performs only slightly less well, with Nb giving the poorest performance. Such waveguides are shown to be extremely good media for the transmission of signals with components in the range 1011–1012 Hz.
Heteroepitaxial growth of InP/In0.52Ga0.48As structures on GaAs (100) by gas-source molecular beam epitaxy
Authors: Chin T. P. , Tu C. W.
Published: July 2002

High quality In0.52Ga0.48As, InP, and In0.52Ga0.48As/InP single quantum wells were grown on GaAs (100) by gas-source molecular beam epitaxy (GSMBE) with a 2-μm thick InxGa1−xAs buffer layer where x was linearly graded from 0 to 0.52. Reflection high-energy electron diffraction patterns and specular beam intensity oscillations showed that the growth mode of In0.52Ga0.48As and InP were layer by layer despite the lattice mismatch (Δa/a=3.8%) between InP and GaAs. Photoluminescence line widths at 10 K of a 1-μm thick InP and a 5-nm wide In0.52Ga0.48As/InP single quantum well are 4.9 and 10 meV, respectively, which are comparable to the values measured from similar structures grown lattice matched on an InP substrate (3.5 and 7 meV, respectively) by the same GSMBE system. The quantum-well luminescence intensity is also comparable to lattice-matched samples.
Observation of staggered band lineup in In0.5Ga0.5P/Al0.43Ga0.57As heterojunction grown by liquid phase epitaxy
Authors: Lee Jong Boong , Kim Kwan-Shik , Choe Byung-Doo
Published: July 2002

The conduction band discontinuity for n-N isotype In0.5Ga0.5P/Al0.43Ga0.57As heterostructure grown on (100) GaAs substrate by liquid phase epitaxy was measured by the capacitance-voltage profiling method. The composition of each ternary was determined by photoluminescence and double-crystal x-ray diffraction measurement. The measurement of conduction band discontinuity shows staggered band lineup with both bands of In0.5Ga0.5P above those of Al0.43Ga0.57As, and the calculated conduction-band discontinuity ΔEc and the fixed interface charge density σi are 157 meV and −3×1010 cm−2, respectively. The nonoptimized fabrication of the light emitting devices with AlGaAs/InGaP/AlGaAs double heterostructure can be explained by the staggered band lineup of In0.5Ga0.5P/AlxGa1−xAs heterointerface for x(AlAs)≳0.43.
Observation of period doubling, period tripling, and period quadrupling in a directly modulated 1.55 μm InGaAsP distributed feedback laser diode
Authors: Ngai Wan Fung , Liu Hai-Feng
Published: July 2002

Dynamic characteristics of a directly modulated 1.55 μm InGaAsP distributed feedback semiconductor laser are investigated up to a modulation index of 12. Period doubling, period tripling, and period quadrupling are observed for the first time. The irregular behavior is examined at various bias current levels and modulation frequencies. The route to chaos is found to be via period doubling followed by period quadrupling and period tripling. The observed irregular behavior is attributed to the relatively small fraction of the spontaneous emission coupled into the lasing mode (β factor) of distributed feedback lasers, which is confirmed by a separate experiment.
W(Zn) selectively deposited and locally diffused ohmic contacts to p-InGaAs/InP formed by rapid thermal low pressure metalorganic chemical vapor deposition
Authors: Katz A. , El-Roy A. , Feingold A. , Geva M. , Moriya N. , Pearton S. J. , Lane E. , Keel T. , Abernathy C. R.
Published: July 2002

Self-aligned, locally diffused W(Zn) contacts to InGaAs/InP structures were fabricated by means of rapid thermal low pressure metalorganic chemical vapor deposition (RT-LPMOCVD), using a reactive gas mixture that contained diethylzinc (DEZn), WF6, H2, and Ar. W(Zn) layers of about 30 nm thick were deposited at 500 °C for 20 s and at a total pressure of about 2 Torr, onto InGaAs and InP. Spontaneous formation of highly doped underlying InGaAs and InP layers about 150 nm thick with Zn concentration levels higher than 1×1018 cm−3 took place through the deposition of the W(Zn) layers. Post-deposition, in situ annealing at temperatures of 500 °C or lower enhanced the indiffusion of Zn into the underlying semiconductor and reduced the specific resistance of the W(Zn)/InGaAs contact to a minimum value of 5×10−6 Ω cm−2.
Direct measurement of near-band-gap electrorefraction in Al0.3Ga0.7As/GaAs/Al0.3Ga0.7As thin-film structures
Authors: Calhoun K. H. , Jokerst N. M.
Published: July 2002

We report the first direct measurement of near-band-gap Franz–Keldysh electrorefraction in Al0.3Ga0.7As/GaAs/Al0.3Ga0.7As p-i-n single-crystal thin-film Fabry–Perot structures with semitransparent metallic mirror contacts. These measurements are performed for various reverse biases and at photon energies ranging from 9 to less than 1 meV from the GaAs band edge. The measured refractive index variation is several times larger than that predicted by the effective mass approximation theory.
Effect of wire width variation on the conductance of a silicon quantum wire
Authors: Tang Y. S. , Jin G. , Wilkinson C. D. W.
Published: July 2002

The effect of wire width variation on the conductance of a 1 μm×30 nm silicon quantum wire has been studied. Both resonant tunneling features and conductance fluctuations superimposed on the quantized steps have been observed and explained by the existence of a step-wise constriction in the wire due to the nonideality in the fabrication process.
Graded-index polymer-based waveguide lens working at visible wavelengths on GaAs substrate for optoelectronic interconnects
Authors: Chen Ray T.
Published: July 2002

A polymer-based graded index (GRIN with n=1.4–1.6) waveguide lens was demonstrated on a semi-insulating GaAs substrate. The transparent bandwidth of the polymer film (photolime gel) is from ∼280 to ∼2800 nm. Therefore, UV (ultraviolet), visible and near-IR (infrared) light can be employed as the signal carrier wavelength. In this letter, an off-axis chirped grating lens working at 632.8 nm with 35 mm focal length, 680/mm chirp rate, and angular field of view of 6° was demonstrated. Measured focal spot size of the main lobe is 5.6 μm which is very close to the theoretical prediction (4.2 μm). The crosslink-induced index modulation is as high as 0.2. Therefore, an array of chirped phase grating lenses can be multiplexed onto the same holographic emulsion for one- and two-dimensional massive fanout optical interconnects and signal processing.
Water trapping of point defects in interlayer SiO2 films and its contribution to the reduction of hot-carrier degradation
Authors: Takahashi Jun-ichi , Machida Katsuyuki , Shimoyama Nobuhiro , Minegishi Kazusige
Published: July 2002

The water-blocking effect of plasma chemical vapor deposition (CVD) SiO2 film is investigated. Using electron spin resonance measurements, point defects in the electron cyclotron resonance (ECR) plasma CVD SiO2 used in this work can be identified as dangling bonds belonging to Si atoms. The defect density is reduced by capping water-containing film on it, suggesting that the defect is capable of trapping water. The hot-carrier degradation in a metal-oxide-semiconductor (MOS) device is successfully prevented when ECR plasma CVD SiO2 is used as a water-blocking layer that keeps water in the overlayer from diffusing to the gate oxide. This result indicates that ECR plasma CVD SiO2 effectively blocks water due to the water trapping ability of the Si dangling bonds.
Hole transport in microcrystalline chlorophyll a
Authors: Kassi H. , Hotchandani S. , Leblanc R. M.
Published: July 2002

In order to study the hole transport in chlorophyll a (Chl a), time-of-flight measurements have been performed on Al/Chl a/Au sandwich cells. The hole transients are almost featureless and the transit times have been determined from log-current-log time plots. In view of the lack of universality in post-transit region and the tendency of mobility to decrease with increasing field, as observed from log μ vs √E plots, the hole transport in Chl a has been described in terms of charge transport based on the disorder formalism of Bässler and co-workers. The decrease of hole mobility with field suggests a strong involvement of off-diagonal disorder.
Gibbs free-energy difference between the glass and crystalline phases of a Ni-Zr alloy
Authors: Ohsaka K. , Trinh E. H. , Holzer J. C. , Johnson W. L.
Published: July 2002

The heats of eutectic melting and devitrification, and the specific heats of the crystalline, glass, and liquid phases have been measured for a Ni24Zr76 alloy. The data are used to calculate the Gibbs free-energy difference, ΔGAC, between the real glass and the crystal on an assumption that the liquid-glass transition is second order. The result shows that ΔGAC continuously increases as the temperature decreases in contrast to the ideal glass case where ΔGAC is assumed to be independent of temperature.
Transient response of lateral photodetectors
Authors: Böttcher E. H. , Hieronymi F. , Kuhl D. , Dröge E. , Bimberg D.
Published: July 2002

A two-dimensional physical device model for characterizing the transient operation of lateral photodetectors is presented. It is based upon a corpuscular approach where the impulse response is constituted by the superposition of a large number of photocurrent pulses originating from spatially distributed discrete electron-hole pairs generated by an optical impulse. The motion of photogenerated carriers and the resulting photocurrent pulses in the external circuit are related by Ramo’s theorem which is shown to be fundamental for gaining a correct understanding of the time response of lateral detectors. The accuracy of the predictions obtained from the modeling is underpinned by their excellent agreement with experimental data on the impulse response of InP:Fe/InGaAs:Fe metal-semiconductor-metal detectors.
Phase characteristics of reflection electroabsorption modulators
Authors: Liu Daxin , Pezeshki B. , Lord S. M. , Harris J. S.
Published: July 2002

The influence of refractive index changes on the phase characteristics of a reflection Fabry–Perot quantum well modulator is discussed and compared with experiment. Although a Fabry–Perot cavity can reduce the effective chirp near resonance, the phase change is highly nonlinear and critically dependent on the wavelength.
High-temperature continuous operation above 200 °C of GaAs lasers using an InGaAlP cladding layer
Authors: Itaya K. , Hatakoshi G. , Nishikawa Y. , Ishikawa M. , Okajima M.
Published: July 2002

A new GaAs laser diode employing InGaAlP for the cladding layer has been successfully fabricated. A large band-gap difference between the GaAs active and InGaAlP cladding layers reduced the electron overflow, which drastically improved the temperature characteristics. The highest temperature continuous wave operation of 212 °C was obtained. A large characteristic temperature, T0 of 190 K was maintained up to 140 °C. Any significant problem due to a heterointerface of GaAs/InGaAlP including high Al composition was not observed through the laser characteristics.
Lattice location and electrical activity of ion-implanted Sn in InP
Authors: Kringho/j Per , Weyer Gerd
Published: July 2002

The lattice location and electrical activity of ion implanted Sn in InP after rapid thermal annealing has been determined by, respectively, Mössbauer spectroscopy using the 119mSn isomer and differential Hall resistivity measurements. Sn is preferentially located on the In sublattice for concentrations below 2×1019 cm−3 resulting in a high electrical activation and mobility. For Sn concentrations above 2×1019 cm−3, in addition different electrically inactive Sn complexes are observed. No indication of a Sn location on P-sublattice sites has been found.
Visible light emission from heavily doped porous silicon homojunction pn diodes
Authors: Chen Zhiliang , Bosman Gijs , Ochoa Romulo
Published: July 2002

We observed visible light emission with a peak wavelength of 640 nm from forward biased, heavily doped porous silicon homojunction pn diodes. The light emission is attributed to electron-hole recombination across the direct band gap of the monocrystalline quantum wires which make up the porous silicon junction layers.
Electron paramagnetic resonance observation of trigonally symmetric Si dangling bonds in porous silicon layers: Evidence for crystalline Si phase
Authors: Mao J. C. , Jia Y. Q. , Fu J. S. , Wu E. , Zhang B. R. , Zhang L. Z. , Qin G. G.
Published: July 2002

In photoluminescent porous Si layers is observed a dominant intrinsic EPR signal of trigonal symmetry with g∥=2.0023±0.0003 and g⊥=2.0086±0.0003 as principal g values. This EPR signal can be identified with Si dangling bonds by its symmetry and characteristic g values. The rotation pattern of the EPR signal indicates that the axial directions of the dangling bonds are distributed in all the four 〈111〉 crystal axes of the original silicon lattice. These results can be exclusively explained by the existence of the crystalline Si phase with retention of the original crystal orientation in porous Si. The dangling bond formation is found to be closely related to the surface oxidation.
Enhanced superconducting properties in ultrathin YBa2Cu3O7−δ layers
Authors: Norton David P. , Lowndes Douglas H.
Published: July 2002

The superconducting properties of ultrathin c-axis-oriented YBa2Cu3O7−δ(YBCO) layers can be significantly enhanced by use of more conductive buffer and cap layers. In particular, Pr0.5Ca0.5Ba2Cu3O7−δ/YBCO/Pr0.5Ca0.5Ba5 Cu3O7−δ trilayer structures, with YBCO layer thickness as small as 1 unit cell, have superior transport properties to PrBa2Cu3O7−δ/YBCO/PrBa2Cu3O7−δ structures, including an increase in Tc and a narrower superconducting transition. The enhanced superconducting properties that result from using Ca-(hole) doped buffer and cap layers may be a result of a diminished perturbation of the order parameter at growth-related steps in the electrical continuity of the YBCO layer.
Reflection noise in vertical cavity surface emitting lasers
Authors: Bae J. W. , Temkin H. , Swirhun S. E. , Quinn W. E. , Brusenbach P. , Parsons C. , Kim M. , Uchida T.
Published: July 2002

We describe the effect of back reflections on the relaxation-oscillation peaks of low threshold (<6 mA), high intrinsic bandwidth (31 GHz) vertical cavity surface emitting lasers. With the largest feedback possible with our experimental arrangement, x=−5.8 dB, the relaxation-oscillation peak breaks up into a series of sharp resonances with the spacing corresponding to the round tip frequency of the external cavity. In contrast to edge emitting lasers, no effect of reflections is observed for feedback levels x<−12.9 dB. This relative immunity of vertical cavity lasers to reflection noise is expected to be of interest for their applications to fiber communications.
Mirrorless all-optical bistability in bacteriorhodopsin
Authors: Rao D. V. G. L. N. , Aranda F. J. , Wiley B. J. , Akkara J. A. , Kaplan D. L. , Roach J. F.
Published: July 2002

We report direct observations of all-optical mirrorless bistability associated with saturable absorption in three kinds of bacteriorhodopsin (BR) samples: wild-type BR in water solution and dispersed in thin films of a polymer matrix as well as water solution of the genetically engineered mutant BRD96N. The experiments are carried out with picosecond pulses at 532 nm. The values measured for the saturation intensity are explained in terms of the relaxation of the excited M state population to the B state of the BR photocycle for the three kinds of samples studied.
Determining band offsets with triple quantum-well structures
Authors: Bryant Garnett W. , Bradshaw J. L. , Leavitt R. P. , Tobin M. S. , Pham J. T.
Published: July 2002

Coupled triple quantum-well GaAs/AlGaAs heterostructures have been designed to exhibit simultaneous electron and hole tunneling from the central well to opposite side wells at a fixed applied bias. Band offset is the critical parameter for the design of structures with simultaneous resonances. Photocurrent measurements reveal which triple quantum-well structures exhibit simultaneous resonances. A band offset ratio near 62:38 is required to correctly engineer structures with simultaneous resonances.
Numerical analysis on temperature dependence of XeCl-lasing characteristics
Authors: Imada Go , Masugata Katsumi , Yatsui Kiyoshi , Masuda Wataru
Published: July 2002

The recombination rate constants for Xe++Cl−+Ne→XeCl*+Ne and NeXe+ +Cl−+Ne→XeCl*+2Ne have been calculated in a temperature range of 100–400 K. At 7.34×1019 cm−3 of gas density, both rate constants of the recombinations are found to increase to ∼7.5×10−6 cm3/s at 120 K, a factor of ∼4 higher than that at room temperature. The temperature dependence of XeCl-lasing characteristics has also been simulated by a steady-state kinetic-simulation code. The simulation has indicated not only the enhancement of the laser output, but also the reduction of the halogen concentration in the lower temperature range.
Electrically switchable window using a suspension of TiOxNy particles
Authors: Saito Yasuhiro , Hirata Masahiro , Tada Hiroaki , Hyodo Masato
Published: July 2002

A dipole particle suspension device was fabricated by sandwiching rodlike TiOxNy particles dispersed in a poly(dimethylsiloxane) derivative between two indium-tin-oxide coated glass substrates. On applying and removing an electric field of 2 kV mm−1 with a frequency of 200 Hz, a reversible solar transmittance change as much as 54.1% was obtained. The transmittance change was attributed to the large absorption coefficient (∼105 cm−1) of the particle and a drastic decrease in the number of particles taking part in the light absorption due to particle chain formation along the electric field.
Charge-carrier mobilities in Cd0.8Zn0.2Te single crystals used as nuclear radiation detectors
Authors: Burshtein Z. , Jayatirtha H. N. , Burger A. , Butler J. F. , Apotovsky B. , Doty F. P.
Published: July 2002

Charge-carrier mobilities have been measured for the first time in Cd0.8Zn0.2Te single crystals using time-of-flight measurements of charge carriers produced by short (10 ns) light pulses from a frequency-doubled Nd:YAG laser (λ=532 nm). The electron mobility displayed a T−1.1 dependence on the absolute temperature T in the range 200–320 K, with a room-temperature mobility of 1350 cm2/V s. The hole mobility displayed a T−2.0 dependence in the same temperature range, with a room-temperature mobility of 120 cm2/V s. Cd0.8Zn0.2Te appears to be a very favorable material for a room-temperature electronic nuclear radiation detector.
High-speed photoresponse in a reverse biased InGaAs/InP laser structure at 1.54 μm: Experiment and modeling
Authors: Charbonneau S. , Aers G. C. , McGreer K. A. , Davies M. , Landheer D. , Li Z.-M. , Delâge A. , Dion M. , Takasaki B. , Conn D. , Moss D.
Published: July 2002

We report extremely efficient (∼100% internal quantum efficiency) and high-speed (∼120 ps lifetime) photodetection in a reversed biased InGaAs/InP ridge-waveguide multiple quantum well p-i-n laser structure operating at 1.54 μm. The impulse response of this monolithically integratable detector is analyzed in terms of the escape of photogenerated carriers from the InGaAsP quantum well barrier to the InP cladding contact layer.
Observations on interfacial segregation and precipitation of arsenic-doped polycrystalline silicon on silicon (100) substrate
Authors: Tung Chih-Hang , Lee Kay-Yuan , Deng Ray-Chern , Lee Lurng-Sheng
Published: July 2002

The interface structural evolution of arsenic-doped polycrystalline silicon thin films on a silicon (100) single crystal substrate was studied by cross-sectional high resolution transmission electron microscopy and secondary ion mass spectrometry. Native silicon dioxide thin film was observed to agglomerate into discrete oxide particles along with stable arsenic-oxygen compound precipitates. Arsenic influence upon the interfacial evolution is discussed.
In situ optical investigation of the etching process in the silicon HCl system
Authors: Ohshita Y. , Hosoi N.
Published: July 2002

Surface reactions in Si(100) etching with HCl gas are studied using the surface photoabsorption (SPA) method and a quadrupole mass spectrometer. The adsorption of Cl atoms on the Si surface causes the intensity of the SPA signal to increase, when HCl gas is supplied. After HCl gas injection is stopped, the signal intensity decreases due to the etching reactions. By studying the time constants and the activation energies, two types of etching reactions are found. Below 1000 K, the etching products are SiCl4, and the activation energy for this etching process is estimated at about 22 kcal/mol. On the other hand, above 1000 K, mainly SiCl2 molecules are desorbed from the Si surface, and the activation energy is evaluated to be 59 kcal/mol.
Dephasing of three- and two-dimensional magnetoexcitons in InxGa1−xAs
Authors: Rappen T. , Mohs G. , Wegener M.
Published: July 2002

We investigate the dephasing of three- and two-dimensional magnetoexcitons in InxGa1−xAs at low temperatures by femtosecond four-wave mixing. In both cases the dephasing time T2 increases substantially with magnetic field. For a cyclotron energy one order of magnitude larger than the three-dimensional exciton binding energy, T2 rises by a factor of about 4. This is interpreted in terms of a considerably reduced scattering cross section of the 1s magnetoexciton due to the magnetic confinement.
Aluminium layers as nonalloyed contacts to p-type GaAs
Authors: Ragay F. W. , Leys M. R. , Wolter J. H.
Published: July 2002

We have investigated the electrical characteristics of a metallic aluminum layer, deposited on top of heavily doped p-type GaAs, as a means of fabricating nonalloyed ohmic contacts to epitaxial semiconductor structures. The aluminum layer was deposited immediately after growth by molecular beam epitaxy (MBE) of a beryllium-doped GaAs layer, i.e., without exposing the sample to air, or by deposition of an aluminum layer on the same sample in conventional vacuum evaporation equipment. Both types of structures were characterized via the transmission line model (TLM) to obtain the contact resistivity of such nonalloyed ohmic contacts. It appears that planar tunneling contacts grown entirely in an MBE process show contact resistance values which are comparable to alloyed contacts.
Influence of hot phonons on electronic noise in GaAs
Authors: Bordone Paolo , Varani Luca , Reggiani Lino , Rota Lucio , Kuhn Tilmann
Published: July 2002

We present a Monte Carlo investigation of the influence of the nonequilibrium phonon population on second-order transport properties in GaAs. We calculate the velocity and energy autocorrelation functions and the velocity–energy cross-correlation functions, both for the case with and without phonon perturbation. By comparing the results, we find significant modifications in the correlation functions and consequently in the equivalent noise temperature due to the presence of the nonequilibrium phonons.
Defects in photorefractive CdTe:V: An electron paramagnetic resonance study
Authors: von Bardeleben H. J. , Launay J. C. , Mazoyer V.
Published: July 2002

Vanadium-doped CdTe has recently been shown to have a high sensitivity for optical processing at 1.5 μm but the role of the vanadium dopant has been questioned. We present the results of an electron paramagnetic resonance study of this material, which demonstrates that vanadium is the dominant paramagnetic defect, which pins the Fermi level and gives rise to photoconductivity at 1.5 μm. The vanadium is substitutionally incorporated on a Cd site at concentrations of ≊5×1016 cm−3 and acts as a deep donor with a 2+/3+ level at Ev+0.8 eV. The defect is only observed in the 3+ charge state. The spin Hamiltonian parameters of the V3+ defect are determined as follows: electron spin S=1, Landé g-factor g=1.962±0.001, central hyperfine interaction constant A=60×10−4 cm−1, Cd Ligand hyperfine interaction constant T=4×10−4 cm−1.
Real-time in situ detection of SF6 in a plasma reactor
Authors: Sun H. C. , Whittaker E. A.
Published: July 2002

We report on the real-time in situ detection of SF6 in a plasma etching reactor with μTorr sensitivity using a tunable diode laser absorption spectrometer. The spectrometer employs combined wavelength and frequency modulation of the laser diode, an approach which allows for sensitive, interference fringe-free detection of the SF6. The dual modulation scheme also provides a feedback signal which enables the laser to be frequency locked to the absorption line.
Ion channeling effect on lattice relaxation in strained In1−xGaxAs/InP multiple-quantum-well structure
Authors: Takahashi Yukimi , Kuriyama K. , Matsui Y. , Kamijoh T.
Published: July 2002

The ion channeling phenomena for the strained and strain partially relaxed In1−xGaxAs/InP multiple-quantum-well (MQW) structures, which are grown by metalorganic vapor phase epitaxy, are presented. In addition to a well-known channeling phenomenon of strained-layer MQW structures, which cause an enhanced dechanneling along 〈110〉, it was found that dechanneling in the substrate covered with strained MQW structure is enhanced in comparison with the strain partially relaxed MQW structure. This phenomenon is observed clearly for the 〈100〉 oriented substrate rather than that along the inclined 〈110〉 axis. It is suggested that a distortion perpendicular to the 〈100〉 growth direction is induced near the interface between the buffer layer and the MQW structure by the strain stored in MQW structure. This effect is less observed in the strain partially relaxed MQW structure than in the strained MQW structure.