bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural properties of graphitized poly-peri-naphthalene whiskers
Authors: Murakami Mutsuaki , Yoshimura Susumu , Iijima Sumio
Published: July 2002

The poly-peri-naphthalene (PPN) whisker is a typical graphitizing carbonaceous material. Graphitized PPN consists of linear graphite chains oriented perpendicular to the direction of the whisker axis and folded at the whisker edges. The formation of such a unique whisker structure can be explained from the original structure of the PPN whisker.
Double-crystal x-ray topographic studies of bulk and epitaxially grown ZnxCd1−xTe (0.0≤x≤0.06)
Authors: Qadri Syed B. , Fatemi M. , Dinan J. H.
Published: July 2002

The first double-crystal topographic studies of epitaxial layers of ZnxCd1−xTe (0≤x≤0.06) grown by molecular beam epitaxy are reported in this letter. A comparison of bulk and epitaxially grown ZnCdTe clearly indicates that the epitaxial layers are of better structural quality and are more suitable for use as substrates for growth of HgCdTe.
Low-temperature nuclear magnetic resonance with a dc SQUID amplifier
Authors: Freeman M. R. , Germain R. S. , Richardson R. C. , Roukes M. L. , Gallagher W. J. , Ketchen M. B.
Published: July 2002

We report the detection of nuclear magnetic resonance at 4 K and 1.9 MHz with a receiver based on a thin-film dc superconducting quantum interference device. The noise temperature of the spectrometer is 300 mK, limited by the second stage amplifier.
Thin, highly doped layers of epitaxial silicon deposited by limited reaction processing
Authors: Gronet C. M. , Sturm J. C. , Williams K. E. , Gibbons J. F. , Wilson S. D.
Published: July 2002

Limited reaction processing was used to deposit ultrathin, highly doped layers of epitaxial silicon. Multilayer structures consisting of alternating undoped and heavily boron-doped regions were fabricated in situ. The interlayer doping profiles of these structures, as determined by secondary ion mass spectroscopy, are abrupt. Van der Pauw measurements indicate that the electrical characteristics of the p+ epitaxial films are comparable to bulk material.
Photoluminescence efficiency recovery due to enhanced annealing of radiation defect in p-type InP by photogenerated carrier recombination
Authors: Kamada H. , Ando K. , Yamaguchi M.
Published: July 2002

Photoluminescence efficiency recovery in 1-MeV electron irradiated InP due to photon excitation is demonstrated. Photoluminescence intensity recovers with incident excitation power in an exponential-like manner and its recovery rate increases when temperature rises. These phenomena are explained via the recovery of the minority carrier diffusion length which is degraded through recombination center introduction by electron irradiation. Temperature dependence of recovery rate is quite similar to that of annealing rate of a dominant hole trap named H4 and recombination enhanced annealing of this defect is responsible for photoluminescence recovery.
Forward bias induced annealing of the E center in silicon
Authors: Barnes C. E. , Samara G. A.
Published: July 2002

It has been well established that the annealing of the E center (phosphorus vacancy) in Si is charge state dependent with the recovery proceeding more rapidly in the neutral charge state than in the negative state. Herein, we report for the first time a third annealing condition with a strongly enhanced annealing rate for the E center: forward bias induced recovery with a significantly lower activation energy of 0.48 eV.
Quantum well AlxGa1−xAs-GaAs lasers with internal (Si2)x(GaAs)1−x barriers
Authors: Burnham R. D. , Holonyak N. , Hsieh K. C. , Kaliski R. W. , Nam D. W. , Thornton R. L. , Paoli T. L.
Published: July 2002

Data are presented showing that the alloy (Si2)x(GaAs)1−x can be formed in a GaAs quantum well (QW) and shifts the operation of an AlxGa1−xAs-GaAs QW laser to higher energy. The (Si2)x(GaAs)1−x barrier, which is formed by sheet deposition (metalorganic chemical vapor deposition) of Si on the initial portion of a GaAs QW layer and then by ‘‘capping’’ this with the remaining part of the QW, can be observed directly by transmission electron microscopy.
Transmission electron microscopy studies on lateral reaction of GaAs with Ni
Authors: Chen S. H. , Carter C. B. , Palmstro/m C. J. , Ohashi T.
Published: July 2002

A method is described for preparing lateral Ni-GaAs diffusion couples for transmission electron microscopy (TEM) investigations. The diffusion couples are annealed in situ in a TEM using a hot stage. The growth of a ternary phase has been observed, and shows parabolic time dependence of the growth. At 200–300 °C, Ni is the predominant diffusion species while Ga and As are essentially immobile. The experimental results are compared with previous investigations of the reactions of Ni thin films with bulk GaAs.
Recrystallization of amorphous silicon film by tungsten halogen lamp annealing
Authors: Arai Hitoshi , Nakazawa Kenji , Kohda Shigeto
Published: July 2002

The transformation of amorphous silicon films to polycrystalline materials induced by tungsten halogen lamp annealing has been studied by x-ray diffraction and transmission electron microscopy. Tungsten halogen lamp annealing shortens annealing time, requiring only 1/10– 1/100 the time needed to grow the same size grains as by furnace annealing. Isochronal annealing by a tungsten halogen lamp reveals that the activation energy for grain growth is 0.64 eV, while that by furnace annealing is 0.23 eV. The cause of this difference is not clear; however the nucleation and following recrystallization process at low temperatures are found to depend on the heating rate and annealing time.
Stacking and layer disordering of AlxGa1−xAs-GaAs quantum well heterostructures
Authors: Meehan K. , Hsieh K. C. , Costrini G. , Kaliski R. W. , Holonyak N. , Coleman J. J.
Published: July 2002

Data are presented showing that an AlxGa1−x As-GaAs quantum well heterostructure (QWH) or superlattice (SL) can be selectively disordered into higher gap bulk crystal by impurity (Si) diffusion and then have grown epitaxially on it (‘‘stacked’’ on it) another SL (or QWH), which can be subjected to further impurity-induced layer disordering in a patterned form. The resulting three-dimensional array can be operated as a photopumped laser.
Photochemical organometallic vapor phase epitaxy of mercury cadmium telluride
Authors: Morris B. J.
Published: July 2002

Mercury cadmium telluride has been successfully grown by the photolysis of dimethylmercury, dimethylcadmium, and dimethyltelluride, using an ArF excimer laser operating at 193 nm as the radiation source. Growths were accomplished on CdTe substrates at a temperature of 150 °C, with a growth rate of 4 μm per hour. Films are shiny, and x-ray diffraction indicates epitaxial growth. Secondary ion mass spectroscopy and infrared transmission measurements indicate that the composition of the initial films is Hg0.2Cd0.8Te. Details of the growth apparatus and additional data is presented.
New ‘‘diamondlike carbon’’ film deposition process using plasma assisted chemical vapor transport
Authors: Zarowin Charles B. , Venkataramanan Natarajan , Poole Richard R.
Published: July 2002

We have deposited ‘‘diamondlike carbon’’ films on various substrates using a new plasma assisted chemical vapor transport process in a high rf power density presssure ratio gas discharge. The films reported here exhibit the following properties: (1) high transparency for wavelengths greater than 300 nm; (2) an index of refraction of ∼2 at 850 nm; (3) a hardness between that of quartz and sapphire, increasing with ion energy bombarding the deposition surface; (4) strong adhesion to KBr, sapphire, and Si substrates; (5) high dielectric strength; (6) inertness to highly reactive chemicals.
Double probe model of radio frequency capacitively coupled planar discharges
Authors: Pointu A. M.
Published: July 2002

A simple model, using a quasi-stationary, asymmetric, double probe theory, is presented to describe radio frequency planar glow discharge with a capacitively coupled excitation electrode. It reasonably agrees with available experimental results at frequencies lower than the ionic plasma frequency.
Photosensitive capacitance-voltage characteristics of molecular beam epitaxially grown GaAs/AlGaAs/GaAs heterostructures
Authors: Qian Q-D. , Melloch M. R. , Cooper J. A.
Published: July 2002

We report photosensitive capacitance-voltage characteristics of n+-GaAs/Al0.3Ga0.7As/p-GaAs heterostructures grown by molecular beam epitaxy. Inversion layers are observed due to minority charge retention in the triangular potential well at the AlGaAs/p-GaAs interface. Details of the device structure and experimental evaluation utilizing capacitance-voltage and current-voltage techniques are presented.
Diffusion of Ag and Hg at the Ag/(Hg, Cd)Te interface
Authors: Friedman D. J. , Carey G. P. , Shih C. K. , Lindau I. , Spicer W. E. , Wilson J. A.
Published: July 2002

The room-temperature Ag/(Hg, Cd)Te interface has been studied in ultrahigh vacuum with x-ray and ultraviolet photoelectron spectroscopy. The Ag evaporated onto (Hg, Cd)Te diffuses 102–103 Å into the bulk of the semiconductor, displacing Hg as it does so. The bands bend 0.05–0.1 eV upward at low coverage. No significant chemical reaction is observed.
100-μm-wide silicon-on-insulator structures by Si molecular beam epitaxy growth on porous silicon
Authors: Lin T. L. , Chen S. C. , Kao Y. C. , Wang K. L. , Iyer S.
Published: July 2002

100-μm silicon-on-insulator structures have been achieved by first utilizing silicon molecular beam epitaxial (Si MBE) growth on porous silicon and subsequently oxidizing the porous silicon through the patterned Si MBE film windows. A Si beam method is used for the low-temperature surface cleaning of porous silicon prior to Si MBE growth. By using a two-step growth technique, the Si MBE film shows good crystallinity checked by Rutherford backscattering channeling spectroscopy and cross-sectional transmission electron microscopy. An electron mobility of 1300 cm2 V−1 s−1 with a doping concentration of 6×1015 cm−3 has been achieved.
Temperature dependence for the onset of plastic yield in undoped and indium-doped GaAs
Authors: Hobgood H. M. , McGuigan S. , Spitznagel J. A. , Thomas R. N.
Published: July 2002

The onset of plastic yield in undoped and highly indium-doped GaAs, prepared by liquid encapsulated Czochralski (LEC) growth, has been determined by uniaxial compression tests over the temperature range 250–600 °C. No distinguishable difference in yield stress is observed between undoped and indium-doped GaAs; however, LEC GaAs exhibits a modest increase in yield strength over undoped Bridgman-grown material. The absence of a significant increase in the yield strength of indium-doped over undoped LEC GaAs implies that the mechanism by which indium reduces the dislocation density in GaAs is significantly effective only at temperatures near the melting point.
Influence of the donor depth on the determination of the band discontinuity of isotype heterojunctions by the capacitance-voltage technique
Authors: ’t Hooft G. W. , Colak S.
Published: July 2002

Capacitance-voltage measurements have been simulated to find the conduction-band discontinuity in an n-type GaAs-Al0.3Ga0.7As heterojunction. In the calculations the partial ionization of the donor level in the (Al,Ga)As is taken into account. It is found that exact knowledge of the donor depth is a prerequisite in order to infer the conduction-band discontinuity from capacitance-voltage measurements. For a dopant concentration of 3×1016 cm−3 on either side of the heterojunction the same apparent carrier profile is obtained with a conduction-band discontinuity equaling 65% of the total band-gap difference and zero donor depth as with 75% discontinuity and 100 meV donor depth. It is also shown that compensation influences the apparent carrier profile. Taking literature values for the donor depth in Al0.3Ga0.7As the discontinuity of the conduction band is estimated to be 70% of the total band-gap difference.
Oxygen isotope effect on the 889 cm−1 band in silicon
Authors: Stein H. J.
Published: July 2002

Implantation studies with 16O and 18O isotopes have been used to evaluate a recent proposal that an 889 cm−1 absorption band in O-containing Si is produced by two oxygen atoms in a vacancy. The present isotope studies indicate that the 889 cm−1 mode is determined by a single oxygen atom bonded to Si. Thus, O-O interactions in the 889 cm−1 mode must be weak or nonexistent. Possible relationships of the 889 cm−1 band to oxygen-vacancy defects and thermal donors are considered.
Nickel-zinc microwave ferrite with stress-insensitive square hysteresis loop
Authors: Dionne Gerald F. , West Russell G.
Published: July 2002

By substitution of Mn3+ ions for 0.2 Fe3+ ions per formula unit of dense polycrystalline 5000-G Ni0.65Zn0.35Fe2O4, the hysteresis loop becomes square (remanent magnetization increases by a factor of 2) without deterioration of X-band microwave dielectric properties or significant increase in coercive field. In addition, the loop is rendered virtually insensitive to externally applied stress. The results are explained by the strong positive magnetostriction contributions from octahedral-site Mn3+ ions that cancel the negative magnetostriction of the NiZn ferrite. An energy balance model, based primarily on the extrinsic hysteresis loop parameters, is used to illustrate the dependence of remanent magnetization on magnetostriction, coercive field, and saturation magnetization. With this simple composition change, high magnetization NiZn ferrites can be stress-insensitive square-loop materials with superior ceramic and microwave dielectric properties.
Magnetic and optical measurements on Ti:Al2O3 crystals for laser applications: Concentration and absorption cross section of Ti3+ ions
Authors: Aggarwal R. L. , Sanchez A. , Fahey R. E. , Strauss A. J.
Published: July 2002

The optical absorption coefficient of Ti:Al2O3 samples at 490 nm for the π polarization (E∥ĉ) is found to be proportional to the concentration of Ti3+ ions, as determined by measurement of the paramagnetic moment as a function of temperature and magnetic field. The experimental data yield the value σ=(9.3±1.0)×10−20 cm2 for the absorption cross section of Ti3+, the active ion in the tunable Ti:Al2O3 laser, at the peak of the laser pump band.
Effects of indium lattice hardening upon the growth and structural properties of large-diameter, semi-insulating GaAs crystals
Authors: McGuigan S. , Thomas R. N. , Barrett D. L. , Hobgood H. M. , Swanson B. W.
Published: July 2002

The high-pressure liquid encapsulated Czochralski growth of indium lattice-hardened GaAs, from 3 kg melts, has resulted in low-dislocation, large-diameter crystals which exhibit thermally stable, semi-insulating properties. Post-growth boule annealing is found to be an effective stress-relief treatment, which assures high wafer yields and extremely uniform electrical properties. Observed reductions in dislocation density for mid 1019 cm−3 In-doped GaAs substrates indicate an apparent 28-fold increase in the critically resolved shear stress of this material over undoped GaAs near the melting point. Polished substrates obtained from these crystals exhibit very little subsurface damage, approaching high-quality silicon wafers in this respect.
High-throughput high-yield fabrication of selectively doped AlxGa1−xAs/GaAs heterostructures by molecular beam epitaxy
Authors: Ploog Klaus , Fischer Albrecht
Published: July 2002

A new etching procedure for GaAs substrates and a modified configuration of selectively doped n-AlxGa1−xAs/GaAs heterostructures have been developed for molecular beam epitaxy to reduce the density of oval defects and the epitaxial growth time. The new simplified substrate preparation method reduces the oval defect density to less than 100 cm−2 and allows storage of prepared substrates in air under dust-free conditions for several weeks without any degradation. Modification of the layer structure reduces the throughput time to less than 30 min per wafer including epitaxial growth, wafer exchange, heat and cool times. High mobilities of the two-dimensional electron gas and excellent reproducibility are achieved. The new process uses the favorable growth rate of <1 μm/h for GaAs and thus allows growth of nearly 500 high-quality heterostructure wafers for device fabrication without exposure of the growth chamber to atmosphere for effusion cell recharging.
Microcrystalline to amorphous transition in silicon from microwave plasmas
Authors: Schellenberg J. J. , McLeod R. D. , Mejia S. R. , Card H. C. , Kao K. C.
Published: July 2002

An experimental study has been made of Si:H thin films prepared by microwave plasma deposition, in which conditions of electron cyclotron resonance can be obtained in the plasma due to an externally applied axial dc magnetic field B. It is observed that as B is increased through resonance, the structure of the deposited films changes from microcyrstalline to amorphous.
Simulations of fine structures on the zero field steps of Josephson tunnel junctions
Authors: Scheuermann M. , Chi C. C. , Pedersen N. F. , Chang Jhy-Jiun , Chen J. T.
Published: July 2002

Fine structures on the zero field steps of long Josephson tunnel junctions are simulated for junctions with the bias current injected into the junction at the edges. These structures are due to the coupling between self-generated plasma oscillations and the traveling fluxon. The plasma oscillations are generated by the interaction of the bias current with the fluxon at the junction edges. On the first zero field step, the voltages of successive fine structures are given by Vn=ℏ/2e(2ωp/n), where n is an even integer.
Room-temperature continuous-wave operation of an AlGaInP mesa stripe laser
Authors: Ikeda Masao , Nakano Kazushi , Mori Yoshifumi , Kaneko Kunio , Watanabe Naozo
Published: July 2002

Continuous-wave (cw) operation at temperature up to 33 °C of an AlGaInP/GaInP mesa stripe laser has been achieved for the first time. The threshold current was 106 mA at 30 °C for a device with a mesa stripe 6 μm wide and 250 μm long. The emission wavelength was 678 nm under cw operation at 20 °C. The wafer, which was grown by atmospheric pressure metalorganic chemical vapor deposition, had a dually stacked cladding structure in addition to a conventional double heterostructure. The mesa structure was formed by selective chemical etching of GaAs/AlGaAs over layers. The effect of the mesa structure on threshold current density, thermal resistance, and other characteristics was examined.
High pressure dry oxidation kinetics of silicon—evidence of a highly stressed SiO2 structure
Authors: Camelin C. , Demazeau G. , Straboni A. , Buevoz J. L.
Published: July 2002

The kinetics of monocrystalline silicon oxidation using dry oxygen have been investigated over a wide range of pressure (14<P<1000 bars) within a low-temperature domain (600<T <780 °C). In this unexplored domain, the linear and parabolic rate constants are dependent on the pressure as B/A∼P0.7 and B∼P. The activation energy of B/A (1.70 eV) is lower than the experimental values observed in conventional thermal oxidation. Very high residual stress values have been found for these oxides together with high values of refractive index suggesting that the oxidation proceeded under compressive in-grown stresses.
Highly efficient waveguide phase modulator for integrated optoelectronics
Authors: Alping A. , Wu X. S. , Hausken T. R. , Coldren L. A.
Published: July 2002

The characteristics of novel reverse-biased waveguide phase modulators are reported. These devices, which use the translation of a depletion edge, have provided the highest efficiency figure of merit (56 °/Vmm) ever reported for a reverse-biased device. Furthermore, the speed of the device is only limited by the RC time constant. The investigated devices were GaAs/AlGaAs ridge waveguide modulators, a geometry which is well suited for integrated optoelectronics.
Growth of strained-layer semiconductor-metal-semiconductor heterostructures
Authors: Tung R. T. , Gibson J. M. , Levi A. F. J.
Published: July 2002

Single crystal epitaxial strained-layer semiconductor-metal-semiconductor heterostructures have been grown for the first time. Silicon layers were grown by molecular beam epitaxy over thin (<100 Å) NiSi2 layers on Si(111). The presence of ∼20 Å Si template layers formed at low temperature (<500 °C) on the silicide was shown to have a dramatic effect on subsequent Si growth. The overgrown Si layers were rotated 180° with respect to the NiSi2 and had a channeling minimum yield of ∼3%. Epitaxial strained-layer semiconductor-metal-semiconductor heterostructures represent a new class of material system with potential for high-speed device applications.
Ion beam etching and surface characterization of indium phosphide
Authors: Bouadma N. , Devoldere P. , Jusserand B. , Ossart P.
Published: July 2002

A new method of Ar ion beam etching of InP using a LN2 cooled sample holder is described. Smooth and low-damage etched surfaces have been obtained using this technique. Auger electron spectroscopy measurements and laser Raman spectroscopy analysis indicated that the morphology degradation was significantly reduced.
Formation of a new deep emission in Si+, S+, Se+, and Te+ ion-implanted GaAs
Authors: Makita Yunosuke , Takeuchi Yoshinori , Nomura Toshio , Tanaka Hideki , Kanayama Toshihiko , Tanoue Hisao , Irie Katsuhiro , Ohnishi Nobukazu
Published: July 2002

Photoluminescence studies of Si+, S+, Se+, and Te+ ion-implanted GaAs made by molecular beam epitaxy were carried out at 2 K. A new emission denoted by [D] was commonly obtained at 1.408 eV. It was also found that the controversial near band-edge emissions, ‘g’ and [g-g], which were originally produced by the ion implantation of acceptor impurities, were not formed by donor ion implantation.
Light-induced metastable defects in amorphous silicon: The role of hydrogen
Authors: Stutzmann M. , Jackson W. B. , Smith A. J. , Thompson R.
Published: July 2002

The role of hydrogen in the creation and annealing kinetics of the light-induced metastable defects in hydrogenated amorphous silicon is investigated using electron spin resonance. Deuterated and hydrogenated films exhibited the same defect creation rate and nearly identical distributions of annealing energies. Implications of these results for various microscopic models for the creation of metastable defects are discussed.
Optical processing of acoustical holograms in a liquid crystal convertor
Authors: Beaulieu R. , Dion J. L. , Lessard R. A.
Published: July 2002

Acoustical image holograms have been recorded at 3.6 MHz using a specially designed nematic liquid crystal convertor. These holograms are reconstructed with He-Ne laser light. The figures presented illustrate the practicability of the system, particularly in the field of nondestructive testing.
Effect of substrate temperature on the nucleation of glow discharge hydrogenated amorphous silicon
Authors: Collins R. W. , Cavese J. M.
Published: July 2002

The effect of substrate temperature (Ts) on the initial nucleation of hydrogenated amorphous silicon (a-Si:H) prepared by glow discharge has been studied using an in situ ellipsometry probe. Evidence in the ellipsometry data for clustering of Si–Si bonds at nucleation centers, for films prepared with Ts ∼250 °C, gradually disappears as Ts is reduced below ∼200 °C. This indicates that the clustering process accompanies defect reduction during growth commonly observed in glow discharge a-Si:H as Ts is increased. For Ts >200 °C, a sufficiently high surface mobility may enable the depositing species to bind at lower energy sites, thus explaining the observed results.
Transmission electron microscope study of the initial stage of formation of Pd2Si and Pt2Si
Authors: Aboelfotoh M. O. , Alessandrini A. , d’Heurle F. M.
Published: July 2002

Transmission electron microscopy of the compounds formed from the reaction between amorphous Si and thin (0.5–20 nm) layers of Pd and Pt reveals the early formation of crystalline silicides. The presence of phase in an amorphous state prior to crystallization is not observed. These results appear to be in agreement with earlier results of surface electron spectroscopy studies on these systems.
Interface width of anodic native oxide—InSb structures
Authors: Shapira Yoram , Bregman J. , Calahorra Z.
Published: July 2002

Using our improved quantitative analysis of Auger electron spectroscopy (AES) depth profiles, we have found a linear relationship between the interface width of plasma- and wet-anodized InSb (111) and the oxide thickness in the range of 15–180 nm. Using a simple etching technique we have been able to ascertain that the effect was inherent to the oxidation process and not a result of the sputtering process. We have developed a theoretical model that explains the linear relationship in terms of field-enhanced diffusion and oxidation reaction. The model is based on our earlier experiments that demonstrated the oxygen diffusion through the oxide to the interface. Application of the model to the results of over 30 different AES depth profiles yields excellent agreement with the experimental observations that show that the interface width is about 0.25 of the total oxide thickness. The results support the thermodynamic model of anodization, indicating that interface formation is the last step of the oxide growth process.
Anomalous distance dependence in scanning tunneling microscopy
Authors: Bryant A. , Smith D. P. E. , Binnig G. , Harrison W. A. , Quate C. F.
Published: July 2002

In this work it is found experimentally that the appearance of surfaces in scanning tunneling microscope (STM) images can change drastically as the distance between the STM tip and sample is varied. Defects are found on gold-sputtered graphite samples which appear as protrusions in charge density when the spacing exceeds a critical value. At smaller distances the protrusions are not evident in the images. It is possible to model these defects as gold atoms which lie just below the surface layer. We discuss possible mechanisms that give rise to the distance dependence.
High-speed response of a quasi-graded band-gap superlattice p-i-n photodiode
Authors: Parker D. G. , Couch N. R. , Kelly M. J. , Kerr T. M.
Published: July 2002

The photoresponse to a short optical pulse of a GaAs p-n junction containing an undoped asymmetric GaAs/AlAs superlattice is reported. The response to a light pulse of <400 fs duration has been measured and a rise time of 80 ps is observed. The trailing edge of the response exhibits a long time tail, which is thought to be dominated by the time taken to tunnel through the thickest barrier, being the Γ-Γ separation of the GaAs and AlAs of a 3-nm barrier.
Enhancement of film deposition rate due to the production of Si2H6 as an intermediate in the photodecomposition of SiH4 using an ArF excimer laser
Authors: Taguchi Toshihiro , Morikawa Masato , Hiratsuka Yasuyuki , Toyoda Koichi
Published: July 2002

Deposition of amorphous hydrogenated silicon films (a-Si:H) on a glass substrate by photodissociation of SiH4 using a focused ArF excimer laser beam directed parallel to the substrate has been demonstrated. The rate of film deposition increased with irradiation time at constant laser power, with a fixed initial quantity of reactant gas. This result indicates the formation of Si2H6, which is excited by a single incident photon. The small amount of Si2H6 formed promoted photodecomposition of SiH4.
High peak power and gateable picosecond optical pulses from a diode array traveling-wave amplifier and a mode-locked diode laser
Authors: Andrews John R. , Burnham Robert D.
Published: July 2002

A traveling-wave amplifier made from an AlGaAs laser diode array has been used to selectively amplify individual pulses from a 250-MHz pulse train of a mode-locked laser diode. A coherent average output power of 35.3 mW was obtained for 14.2 mW incident on the final objective. Peak powers as high as 4.75 W have been obtained with application of both continuous and pulsed current to the amplifier. This represents a 5.7-fold enhancement of the peak power over the power of the incident signal. When the mode-locked laser source had a single spatial mode, the amplifier output was dominated by a single lobe, ∼0.82° wide.
Boron oxide interaction with silicon in silicon molecular beam epitaxy
Authors: de Frésart E. , Rhee S. S. , Wang K. L.
Published: July 2002

B2O3 decomposition by reaction with Si has been studied in situ by Auger electron spectroscopy in a Si molecular beam epitaxy environment as a function of the silicon flux (0<JSi<14.5 Å/min) and the growth temperature (25 °C<Ts<800 °C). Quantitative analysis of Auger signals indicates that oxygen is associated with both SiO2 and B2O3. Below a critical substrate temperature (Ts<500 °C), no reaction occurs between B2O3 and Si. When the substrate temperature is higher than 500 °C, the atomic fraction of Si and B increases while that for SiO2 and B2O3 decreases. The chemical reaction which causes the signal changes is thermally activated, as shown by the dependence of the oxygen on boron concentration ratio, I[O/B], which drops rapidly according to an Arrhenius relation with an activation energy Ea=4.5±1.0 eV. From the experimental results, we propose a model which involves B2O3 reduction by Si to form the (Si-B) and SiO2 phases. SiO2 is then decomposed by Si bombardment on the surface to produce SiO which subsequently desorbs.
Compositional profile of the amorphous silicon/nitride interface studied with Rutherford backscattering
Authors: Abelson J. R. , Tsai C. C. , Sigmon T. W.
Published: July 2002

The compositional profile of the interface between plasma-deposited amorphous silicon (a-Si:H) and silicon nitride (a-SiNx:H) thin films has been examined using high depth resolution Rutherford backscattering spectrometry. We have optimized the grazing exit angle geometry of the measurement using a model calculation which predicts a ∼20 Å interface depth resolution. The fundamental noise sources considered in the calculation are the energy straggling and angular divergence of ions traversing the target, detector noise, and geometrical effects. Experimentally, the major compositional change for both Si and N is found to take place within the interface depth resolution which is 18 Å. However, we find a tail of ∼3 at. % nitrogen extending through a 50-Å a-Si:H layer deposited on top of a-SiNx:H. Such a tail is not expected for the reverse order of layer deposition. The compositional asymmetry depending on the order of deposition is presumably associated with the reported asymmetry in the charge density at interfaces. The nitrogen contamination further implies that most a-Si:H/a-SiNx:H quantum well structures are in fact based on nitrogen alloyed a-Si:H layers.
Large room-temperature effects from resonant tunneling through AlAs barriers
Authors: Goodhue W. D. , Sollner T. C. L. G. , Le H. Q. , Brown E. R. , Vojak B. A.
Published: July 2002

At room temperature, we have observed negative differential resistance in AlAs double-barrier structures and a large hysteresis in the current-voltage characteristic of a stack of five AlAs double-barrier structures. The peak-to-valley ratio of the current was as high as 3.5:1 in a double-barrier structure. To the best of our knowledge, this is the largest room-temperature peak-to-valley ratio observed to date in a double-barrier structure and the first report of a room-temperature hysteresis in a stacked structure. These structures were grown by molecular beam epitaxy using thin AlAs barriers in GaAs. Both the first and second resonances were observed, and are well explained by simple tunneling theory assuming a value of 1.0±0.1 eV for the GaAs-AlAs conduction-band discontinuity seen by the tunneling electrons. This value is very close to the difference in conduction-band energy at the Γ points found by using the accepted values of GaAs and AlAs band gaps with 65% of the band-gap difference appearing in the conduction band. This suggests that negligibly few electrons relax to the lower AlAs X valley as they tunnel through the 1.5–2.5-nm-thick AlAs barriers. These results indicate that AlAs should be a high quality barrier material for a variety of heterojunction devices.
High resolution transmission electron microscopy of silicon-on-insulator formed by high dose oxygen implantation
Authors: Chang Peng-Heng , Mao Bor-Yen
Published: July 2002

The structure of silicon-on-insulator formed by oxygen implantation at 150 keV with a dose of 1.6×1018 cm−2 is studied by high resolution transmission electron microscopy. Polyhedral oxygen precipitates are observed both in the top Si layer and in the substrate after 1150 °C annealing. The oxygen precipitates in the top Si layer coarsen at 1250 °C, but no precipitate can be found in the substrate at this temperature. A layer of polycrystalline silicon (polysilicon) exists near the top Si/buried oxide interface. Silicon crystals in the polysilicon layer also coarsen when the annealing temperature is changed from 1150 to 1250 °C. At 1150 °C, the buried oxide/substrate interface has many Si lamellas roughly parallel to the {100} wafer surface. The lamellar structure is broken up after 1250 °C annealing and is replaced by islandlike crystals which are strongly faceted on {100} planes. Defects are present in Si microcrystallites in both the polysilicon layer and the islandlike particles.
Electroabsorption in GaAs/AlGaAs coupled quantum well waveguides
Authors: Islam M. N. , Hillman R. L. , Miller D. A. B. , Chemla D. S. , Gossard A. C. , English J. H.
Published: July 2002

A novel GaAs/AlGaAs coupled quantum well structure, consisting of two 46 Å wells separated by a 11.5 Å barrier, was embedded in a leaky waveguide. Polarization anisotropy and quantum-confined Stark effect absorption changes are observed, and a 14:1 modulator is demonstrated operating at the peak of the first light-hole transition. Although the lowest energy transitions behave as predicted by tunneling resonance calculations, higher energy states exhibit unusual behavior due to valence-band mixing.
Efficient holmium:yttrium lithium fluoride laser longitudinally pumped by a semiconductor laser array
Authors: Hemmati H.
Published: July 2002

Optical pumping of a holmium:yttrium lithium fluoride (Ho:YLF) crystal with a 790-nm continuous-wave diode-laser array has generated 56 mW of 2.1 μm laser radiation with an optical-to-optical conversion slope efficiency of 33% while the crystal temperature is held at 77 K. The lasing threshold occurs at 7 mW of input power, and laser operation continues up to a crystal temperature of 124 K.
Stripe-geometry AlxGa1−xAs-GaAs quantum well lasers via hydrogenation
Authors: Jackson G. S. , Pan N. , Feng M. S. , Stillman G. E. , Holonyak N. , Burnham R. D.
Published: July 2002

Data are presented on stripe-geometry gain-guided AlxGa1−xAs-GaAs quantum well heterostructure lasers fabricated via masked (SiO2) hydrogen compensation (‘‘hydrogenation’’) of the Mg and Se dopants in the multiple layer heterostructure. Continuous room-temperature laser operation is achieved with a threshold current of 24 mA and 24 mW total output at 50 mA. Near-field emission patterns show strong current confinement in the stripe-active region, and significant hydrogenation ‘‘undercutting’’ of the oxide mask.
Integration of a resonant-tunneling structure with a metal-semiconductor field-effect transistor
Authors: Woodward T. K. , McGill T. C. , Chung H. F. , Burnham R. D.
Published: July 2002

We report experimental realization of a three-terminal negative differential resistance (NDR) device. The device consists of a GaAs-AlxGa1−xAs double-barrier tunneling heterostructure in series with a recessed-gate metal-semiconductor field-effect transistor on a semi-insulating substrate. Basic dc characteristics for three samples grown by metalorganic chemical vapor deposition are shown. All samples exhibit NDR at 77 K, with peak-to-valley current ratios between 2 and 7. Current densities at the peak of the NDR range from 0.5 to 380 A/cm2. The peak-to-valley current ratio and the voltage location of the NDR can be modulated with gate bias.
Chemical beam epitaxial growth of high-purity GaAs using triethylgallium and arsine
Authors: Chiu T. H. , Tsang W. T. , Schubert E. F. , Agyekum E.
Published: July 2002

The growth of high-purity GaAs by chemical beam epitaxy using triethylgallium and arsine is reported. Purity of the epilayer is affected by the cracking efficiency of arsine, V/III ratio, and the substrate temperature. Samples generally show p-type conductivity with carbon as the residual impurity. The growth conditions to achieve net carrier concentration below 1014 cm−3 are identified. The low-temperature photoluminescence spectrum shows well-resolved excitonic structures, an indication of excellent optical quality.
55 kW, 240 fs pulse generation from a cavity dumped, synchronously pumped dye laser and its application to pulse compression
Authors: Nakazawa Masataka , Nakashima Takashi , Kubota Hirokazu , Seikai Shigeyuki
Published: July 2002

A cavity dumped, synchronously pumped femtosecond dye laser is newly described. The laser has a linear cavity configuration with a controller of group velocity dispersion, resulting in pulses as short as 160–240 fs with a peak power of 55 kW. Utilizing a polarization-preserving fiber and a pair of Brewster-angled TeO2 prisms, optical pulses as short as 56 fs with a peak power of 188 kW have been realized at a repetition rate of 3.8 MHz.
Dose dependence of crystallization in implanted polycrystalline silicon films on SiO2
Authors: Iverson R. B. , Reif R.
Published: July 2002

Crystallization of 1500 Å polycrystalline silicon films self-implanted at doses of 2×1015–6×1015 ions/cm2 is investigated. For doses of 2×1015–5×1015 ions/cm2, crystallization is due to the growth of crystallites which nucleate at a rate which decreases with increasing dose. Above 5×1015 ions/cm2, the nucleation rate is comparable to that of amorphous silicon, though a transient time is observed during which little or no nucleation occurs. The growth velocity does not appear to be dose dependent.
Evidence for photon recycling in InP
Authors: Lester S. D. , Kim T. S. , Streetman B. G.
Published: July 2002

An examination of low-temperature photoluminescence from chemically thinned InP illustrates the effect of multiple absorption and reemission of photons in bulk liquid-encapsulated Czochralski grown material. Luminescence spectra show that such photon recycling dramatically increases the nonequilibrium carrier density in the material and causes excess carrier distribution to penetrate tens of micrometers beneath the sample surface, an order of magnitude more than a diffusion length. Nonequilibrium carriers also penetrate deeper with increasing excitation levels as a consequence of more efficient radiative recombination. Although these effects have not been widely recognized, they have important consequences in the interpretation of luminescence spectra and the design of electronic and optical devices based on InP that are sensitive to minority-carrier diffusion lengths.
Controversy of critical layer thickness for InGaAs/GaAs strained-layer epitaxy
Authors: Gourley P. L. , Fritz I. J. , Dawson L. R.
Published: July 2002

The critical layer thickness for InxGa1−xAs layers in InxGa1−xAs/GaAs single strained quantum wells (SSQW’s) and strained-layer superlattices (SLS’s) are investigated. Photoluminescence microscopy (PLM) images and x-ray rocking curves for two series of SSQW and SLS structures corresponding to many different layer thicknesses were obtained. We find that the PLM technique, which directly images dislocations and is sensitive to low dislocation densities, is much more suitable for determining the onset of dislocation creation. The x-ray technique can detect lattice relaxation by dislocations but only at relatively high densities of dislocations. Using the former technique, we determine critical thicknesses of 190 Å for SSQW’s and 250 Å for SLS’s with x≊0.2. These results are near the theoretical predictions of J. W. Matthews, S. Mader, and T. B. Light [J. Appl. Phys. 41, 3800 (1970)] (150 and 300 Å, respectively) and are much lower than results obtained by x-ray or other techniques which sense lattice relaxation.
Extremely wide modulation bandwidth in a low threshold current strained quantum well laser
Authors: Suemune I. , Coldren L. A. , Yamanishi M. , Kan Y.
Published: July 2002

Lasing characteristics of strained quantum well (QW) structures such as InGaAs/AlGaAs on GaAs and InGaAs/InAlAs on InP were analyzed by taking into account the band mixing effect in the valence band. A relaxation oscillation frequency fr, which gives a measure of the upper modulation frequency limit, was found increased three times in a 50 Å In0.9Ga0.1As/In0.52Al0.48As QW structure compared with that in a 50 Å GaAs/Al0.4Ga0.6As QW structure for the undoped case. One of the main factors for this improved frequency bandwidth is attributed to the reduced subband nonparabolicity as well as the reduced valence-band density of state in the strained QW structure. The corresponding lasing threshold current is one order of magnitude smaller than that of the GaAs/AlGaAs QW structure. With a p doping in the QW the fr value increases, and the 3 dB cutoff frequency of about 90 GHz will be expected with an acceptor concentration of 5×1018 cm−3 in the In0.9Ga0.1As/In0.52Al0.48As QW.
The elasticity and failure of fluid-filled cellular solids: Theory and experiment
Authors: Warner M. , Thiel B. L. , Donald A. M.
Published: July 2002

We extend and apply theories of filled foam elasticity and failure to recently available data on foods. The predictions of elastic modulus and failure mode dependence on internal pressure and on wall integrity are borne out by photographic evidence of distortion and failure under compressive loading and under the localized stress applied by a knife blade, and by mechanical data on vegetables differing only in their turgor pressure. We calculate the dry modulus of plate-like cellular solids and the cross over between dry-like and fully fluid-filled elastic response. The bulk elastic properties of limp and aging cellular solids are calculated for model systems and compared with our mechanical data, which also show two regimes of response. The mechanics of an aged, limp beam is calculated, thus offering a practical procedure for comparing experiment and theory. This investigation also thereby offers explanations of the connection between turgor pressure and crispness and limpness of cellular materials.
Translocation of a functional protein by a voltage-dependent ion channel
Authors: Slatin Stephen L. , Nardi Angèle , Jakes Karen S. , Baty Daniel , Duché Denis
Published: July 2002

The voltage-dependent gating of the colicin channel involves a substantial structural rearrangement that results in the transfer of about 35% of the 200 residues in its pore-forming domain across the membrane. This transfer appears to represent an unusual type of protein translocation that does not depend on a large, multimeric, protein pore. To investigate the ability of this system to transport arbitrary proteins, we made use of a pair of strongly interacting proteins, either of which could serve as a translocated cargo or as a probe to detect the other. Here we show that both an 86-residue and a 134-residue hydrophilic protein inserted into the translocated segment of colicin A are themselves translocated and are functional on the trans side of the bilayer. The disparate features of these proteins suggest that the colicin channel has a general protein translocation mechanism.
A double-hexamer archaeal minichromosome maintenance protein is an ATP-dependent DNA helicase
Authors: Chong James P. J. , Hayashi Mariko K. , Simon Martha N. , Xu Rui-Ming , Stillman Bruce
Published: July 2002

The minichromosome maintenance (MCM) proteins are essential for DNA replication in eukaryotes. Thus far, all eukaryotes have been shown to contain six highly related MCMs that apparently function together in DNA replication. Sequencing of the entire genome of the thermophilic archaeon
Methanobacterium thermoautotrophicum
has allowed us to identify only a single MCM-like gene (ORF Mt1770). This gene is most similar to MCM4 in eukaryotic cells. Here we have expressed and purified the
M. thermoautotrophicum
MCM protein. The purified protein forms a complex that has a molecular mass of ≈850 kDa, consistent with formation of a double hexamer. The protein has an ATP-independent DNA-binding activity, a DNA-stimulated ATPase activity that discriminates between single- and double-stranded DNA, and a strand-displacement (helicase) activity that can unwind up to 500 base pairs. The 3′ to 5′ helicase activity requires both ATP hydrolysis and a functional nucleotide-binding site. Moreover, the double hexamer form is the active helicase. It is therefore likely that an MCM complex acts as the replicative DNA helicase in eukaryotes and archaea. The simplified replication machinery in archaea may provide a simplified model for assembly of the machinery required for initiation of eukaryotic DNA replication.
The
defective kernel 1
(
dek1
) gene required for aleurone cell development in the endosperm of maize grains encodes a membrane protein of the calpain gene superfamily
Authors: Lid Stein Erik , Gruis Darren , Jung Rudolf , Lorentzen Jennifer A. , Ananiev Evgueni , Chamberlin Mark , Niu Xiaomu , Meeley Robert , Nichols Scott , Olsen Odd-Arne
Published: July 2002

Endosperm of cereal grains is one of the most important renewable resources for food, feed, and industrial raw material. It consists of four triploid cell types, i.e., aleurone, starchy endosperm, transfer cells, and cells of the embryo surrounding region. In maize, the aleurone layer is one cell layer thick and covers most of the perimeter of the endosperm. Specification of maize aleurone cell fate is proposed to occur through activation of the tumor necrosis factor receptor-like receptor kinase CRINKLY4. A second maize gene essential for aleurone cell development is
defective kernel 1
(
dek1
). Here we show that DEK1 shares high homology with animal calpains. The predicted 2,159-aa DEK1 protein has 21 transmembrane regions, an extracellular loop, and a cysteine proteinase domain that shares high homology with domain II of
m
-calpain from animals. We propose that DEK1 functions to maintain and restrict the aleurone cell fate imposed by CR4 through activation of its cysteine proteinase by contact with the outer endosperm surface. DEK1 seems to be the only member of the calpain superfamily in plants,
Arabidopsis
DEK1 sharing 70% overall identity with maize DEK1. The expression of
dek1
in most plant tissues in maize and
Arabidopsis
, as well as its presence in a variety of higher plants, including angiosperms and gymnosperms, suggests that DEK1 plays a conserved role in plant signal transduction.
Defensive use of a fecal thatch by a beetle larva (
Hemisphaerota cyanea
)
Authors: Eisner Thomas , Eisner Maria
Published: July 2002

The larva of the tortoise beetle,
Hemisphaerota
cyanea
(Chrysomelidae, Cassidinae), constructs a thatch from
long filamentous fecal strands, beneath which it is totally concealed.
The thatch is not discarded at molting but is enlarged by addition of
strands as the larva grows. Thatch construction begins when the larva
hatches from the egg. Pupation occurs beneath the thatch. Two
predators, a coccinellid beetle larva (
Cycloneda
sanguinea
) and a pentatomid bug (
Stiretrus
anchorago
), were shown to be thwarted by the thatch. However,
one predator, a carabid beetle (
Calleida viridipennis
),
feeds on the larva by either forcing itself beneath the thatch or
chewing its way into it. The attack behavior is stereotyped, suggesting
that the beetle feeds on
Hemisphaerota
larvae as a
matter of routine.