bluuebunny/crossref_metadata_2025 huggingface dataset:
In situ infrared evidence for the electrochemical incorporation of hydrogen into Si and Ge
Authors: Mandal K. C. , Ozanam F. , Chazalviel J.-N.
Published: July 2002

The electrochemical incorporation of hydrogen into n-Si and n-Ge has been studied by Fourier-transform electrochemically modulated infrared spectroscopy. Fresh (111) silicon (resp., germanium) surfaces exhibit a vibrational band at 2080 (resp., 1960) cm−1 corresponding to a surface Si—H (resp., Ge—H) bond perpendicular to the surface. Prolonged cathodic treatment results in a new band at 2000 (resp., 1900) cm−1. The position and polarization dependence of this band indicate that it is associated with hydrogen inside the semiconductor lattice. These observations directly show for the first time that cathodically hydrogenated samples contain a thin, disordered, and highly hydrogenated layer, which is probably responsible for the improvement of the hydrogen evolution kinetics observed on these electrodes.
Analysis of SF6 and F2 plasma etched silicon surfaces: An x-ray photoelectron spectroscopy investigation
Authors: Brault P. , Ranson P. , Estrade-Szwarckopf H. , Rousseau B.
Published: July 2002

X-ray photoelectron spectroscopy measurements have been performed on silicon surfaces etched with SF6 and F2 plasmas. It is shown that even if the same number of fluorine atoms is involved in both etching processes, the surfaces are quite different. The SF6 etched surface shows an overlayer thinner than the F2 etched one, but both overlayers have similar compositions.
Measurement of the gain saturation spectrum in InGaAsP diode lasers
Authors: Frankenberger Rudolf , Schimpe Robert
Published: July 2002

The origin of nonlinear gain suppression in InGaAsP lasers is analyzed by experiments sensitive to small gain changes. The spectral distribution of gain change is determined by measuring the intensity modulation spectra of current modulated Fabry–Perot lasers with nearly single longitudinal mode emission. The gain change spectra show a cross saturation behavior as expected for spectral hole burning with a polarization relaxation time of about 0.07 ps. They do not reveal a dominant contribution of the gain and index grating induced by the cavity standing waves.
Frequency stabilization of an external-cavity diode laser
Authors: Lee W. David , Campbell Joe C. , Brecha R. J. , Kimble H. J.
Published: July 2002

Using a hybrid optical/electronic technique, an external-cavity diode laser was frequency stabilized with respect to the sub-Doppler spectrum of cesium vapor. Laser linewidths of 65 kHz and frequency stabilities of ±10 kHz were obtained.
Intraplane guided wave massive fanout optical interconnections
Authors: Chen Ray T. , Wang Michael R. , Jannson Tomasz
Published: July 2002

One-to-30 guided wave optical interconnections are demonstrated at 632.8 nm using a highly multiplexed waveguide volume hologram. This technology is capable of providing intrachip and intrawafer optical interconnections. The theoretical limit of the fanout number is addressed and experimentally confirmed. The measured data show that the diffracted beams have an average diffraction efficiency of 2.3% with ±0.2% variation. The demonstrated results can save surface space of electronic chips and also provide a large fanout capability due to the high index modulation of the volume hologram. Further applications based on this technology are very promising. Head-up display, high-speed optical data bus, surface enhanced Raman spectrometer, and optical sensors are some of the attractive ones.
Vapor phase hydrocarbon removal for Si processing
Authors: Kasi Srinandan R. , Liehr M.
Published: July 2002

Ultraviolet/Oxygen (UV/O2) based vapor phase cleaning of Si(100) surfaces dosed with specific organic molecules has been studied by surface and gas phase analytical techniques. The treatment results in chain scission and carbon volatilization as CO and CO2. At room temperature partial trapping of carbon-containing species in the oxide is observed, while at elevated temperatures complete hydrocarbon removal occurs. UV/O2-cleaned samples closely resemble those produced by the standard RCA clean in terms of hydrocarbon removal and oxide formation and this process appears suitable as vapor phase final Si wafer clean.
External-beam switching in monolithic bistable GaAs quantum well étalons
Authors: Sfez B. G. , Oudar J. L. , Michel J. C. , Kuszelewicz R. , Azoulay R.
Published: July 2002

Monolithic bistable étalons with a GaAs/Al0.3Ga0.7As multiple quantum well active layer and AlAs/Al0.1Ga0.9As Bragg reflectors have been fabricated by metalorganic vapor phase epitaxy. They exhibit a very good memory effect. Experiments with an additional external beam at the same and at a different wavelength have been performed. They demonstrated thresholding, pulse shaping, amplification, and wavelength conversion. Moreover, the use of a diode laser external beam showed the possibility of controlling an intense beam with a weaker beam. We describe an experimental configuration in the reflection mode and at normal incidence, which allows mixing the two input beams and extracting the output beam with an ideal 100% efficiency.
High-current lattice-strained In0.59Ga0.41As/In0.52Al0.48As modulation-doped field-effect transistors grown by molecular beam epitaxy
Authors: Kuang J. B. , Chen Y. K. , Sivco D. , Cho A. Y. , Eastman L. F.
Published: July 2002

High-current driving capability is realized in submicron-gate lattice-strained In0.59Ga0.41As/In0.52Al0.48As (Δa/a=4×10−3) modulation-doped field-effect transistors. Full-channel drain current in excess of 1.10 and 1.90 A/mm are obtained at 80 K for the singly doped and doubly doped structure, respectively. By using the double modulation technique and a buried p-buffer layer, excellent high-frequency performance and flat transconductance characteristics were realized over a very broad range of gate and drain bias voltages. These devices are very suitable for large-signal or power device operations. The high quality In0.52Al0.48As buffer layer eliminates the hysteresis and current instability (or the kink effect) in submicron-gate devices at both 300 and 80 K.
Random well width superlattices as one-dimensional artificial amorphous materials and their possible exploitation in a new Ovshinsky switch
Authors: Brennan Kevin F.
Published: July 2002

Random variations in the well widths of a superlattice structure are shown theoretically to result in band structure features which mimic amorphous materials. In direct analogy to uniform superlattices in which the periodic potential results in minibands, a randomly varying potential within a superlattice, arising from random variations in well width, gives rise to the formation of states within the miniband gap resembling band tailing effects. Calculations are made of the electron transmissivity through the superlattice based on the effective mass solution of the Schrödinger equation. Superlattice structures consisting of 30 wells of both randomly varying and uniform width are studied. Random variations governed both by a Poisson and a uniform distribution are analyzed. A possible new switching device based on the Ovshinsky effect [Phys. Rev. Lett. 21, 1450 (1968)] is proposed.
Crystallographically oriented superconducting Bi2Sr2CaCu2O8 by shock compaction of prealigned powder
Authors: Seaman C. L. , Weir S. T. , Early E. A. , Maple M. B. , Nellis W. J. , McCandless P. C. , Brocious W. F.
Published: July 2002

Highly textured specimens of Bi2Sr2CaCu2O8 were obtained by shock compaction of powder at 30–140 kbar and by sintering. The compacts were characterized by x-ray diffraction, magnetic susceptibility, electrical resistance, optical microscopy, and scanning electron microscopy data. Preferential orientation with the a-b plane in the plane of the disk-shaped compacts was achieved by tapping platelet-shaped powder with a controlled size distribution, followed by shock compaction or by sintering. The shocked compacts were annealed to induce metallic resistance while maintaining preferential crystallographic orientation. The electrical and magnetic data demonstrate that shock compaction heterogeneously heats and bonds grain boundaries.
Growth characteristics of silicon dioxide produced by rapid thermal oxidation processes
Authors: Chiou Y. L. , Sow C. H. , Li G. , Ports K. A.
Published: July 2002

Silicon dioxide growth curves produced by a rapid thermal processor were analyzed. No break point was observed in the growth curves. Of the kinematical models being compared, the linear-parabolic equation gave the best fit. However, the coefficients of the equation are thickness dependent as in the case of diffusion furnace oxide growth data. The correlation in the growth curves indicated similar oxide growth kinematics for the two types of oxidation equipment. Under certain oxidation conditions, the coefficient of the linear term may have a negative value and appears to be determined by the oxidation temperature and oxygen flow rate.
Critical current density enhancement in YBa2Cu3O6.8 films on buffered metallic substrates
Authors: Narumi E. , Song L. W. , Yang F. , Patel S. , Kao Y. H. , Shaw D. T.
Published: July 2002

A transition buffer, consisting of subbuffers grown at different temperatures, was used to enhance the crystallinity and the transport properties of YBa2Cu3O6.8 (YBCO) films on metallic substrates. Films were fabricated using in situ laser deposition and were strongly c-axis oriented. Critical temperature of 87 K and critical current density of 3×104 A/cm2 at 77 K were obtained for a 0.5-μm-thick YBCO film with a 0.2 μm transition yttrium- stabilized ZrO2 buffer layer. Also, the magnetic field dependence of Jc could be enhanced by using Pt-coated metallic substrates.
Up-conversion of red light to green by a new type of light transducer using organic electroluminescent diode combined with photoresponsive amorphous silicon carbide
Authors: Hiramoto Masahiro , Yoshimura Kanji , Miyao Tomoya , Yokoyama Masaaki
Published: July 2002

Light up-conversion from red to green was performed in a new type of light transducer composed of an organic electroluminescent diode and a photoresponsive amorphous silicon carbide (a-SiC:H) film as an electron photoinjecting electrode. Quantum efficiency of photon conversion reached 1% with the assistance of newly observed photocurrent multiplication in a-SiC:H film.
All-high T
c Josephson tunnel junction: Ba1−xKxBiO3/Ba1−xKxBiO3 junctions
Authors: Pargellis A. N. , Sharifi F. , Dynes R. C. , Miller B. , Hellman E. S. , Rosamilia J. M. , Hartford E. H.
Published: July 2002

We have fabricated all-high Tc superconducting tunnel junctions in the material Ba1−xKxBiO3. The junctions are of very high quality and have a Josephson supercurrent. For the low-resistance junctions, the IcR product approaches the theoretical limit.
Dopant-enhanced low-temperature epitaxial growth of in situ doped silicon by rapid thermal processing chemical vapor deposition
Authors: Hsieh T. Y. , Jung K. H. , Kim Y. M. , Kwong D. L.
Published: July 2002

We have demonstrated, for the first time, that the epitaxial growth temperature can be lowered by dopant incorporation using rapid thermal processing chemical vapor deposition. Heavily arsenic-doped epitaxial layers with very abrupt dopant transition profiles and relatively uniform carrier distributions have been achieved at 800 °C. In addition, it is found that defect formation is closely related to dopant concentration.
Partial ordering and enhanced mobility in Ga0.47In0.53As grown on vicinal (110)InP
Authors: Chin Albert , Chang T. Y. , Ourmazd A. , Monberg E. M.
Published: July 2002

Very high quality GaInAs/AlInAs modulation-doped heterostructures have been obtained by molecular beam epitaxy on InP oriented 6° off (110) towards the (111̄) pole. The results indicate partial ordering in the epitaxial layers and also suggest reduced background acceptor concentration. In spite of the high density of interface steps, the electron mobility obtained on the vicinal (110) substrate exceeds the state-of-the-art value obtained on (100) oriented substrates.
Growth and structural characterization of embedded InAsSb on GaAs-coated patterned silicon by molecular beam epitaxy
Authors: De Boeck J. , Dobbelaere W. , Vanhellemont J. , Mertens R. , Borghs G.
Published: July 2002

The molecular beam epitaxial growth of InAsSb on GaAs-coated patterned Si substrates is reported. The epilayers are grown embedded in wells so a coplanar Si-InAsSb surface can be obtained. The InAsSb epilayer morphology is compared for different substrate conditions (Si−well, Si−mesa, GaAs) using Nomarski contrast microscopy. High-voltage electron microscopy shows that the threading defect density of the InAsSb layers is high but decreases with thickness. In the reduced area electron diffraction pattern of the GaAs-InAsSb interface, additional diffraction spots are visible due to microtwins in the InAsSb. High-resolution electron microscopy reveals a regular array of misfit dislocations relieving the 14.2% lattice mismatch in the early stage of growth. Stripping Hall measurements for InAs0.05Sb0.95 show a constant mobility as a function of depth for the top 2 μm of the film and the 300 and 77 K mobility values are comparable.
p-n junction diode made of semiconducting diamond films
Authors: Okano Ken , Kiyota Hideo , Iwasaki Tatsuya , Kurosu Tateki , Iida Masamori , Nakamura Terutaro
Published: July 2002

A diamond p-n junction diode fabricated by the chemical vapor deposition technique, shows distinct rectification characteristics. From the electron beam induced current measurement, the existence of a depletion region or a space-charge region around the interface between the n- and p-type semiconducting diamond layers was identified.
Study on microstructure of ordered InGaAs crystals grown on (110)InP substrates by transmission electron microscopy
Authors: Ueda Osamu , Nakata Yoshiaki , Fujii Toshio
Published: July 2002

CuAu-I type ordered structures in InGaAs grown on (110)InP substrates by molecular beam epitaxy, have been studied by transmission electron microscopy. In the electron diffraction pattern from the InGaAs, superstructure spots associated with CuAu-I type ordered structure are found. The intensity of the superstructure spots becomes stronger as the tilting angle of the substrate increases up to 5°. In high-resolution images of the crystal, doubling in periodicity of 220 and 200 lattice fringes is found, which is associated with CuAu-I type ordered structure. Moreover, anti-phase boundaries are very often observed in the ordered regions, which has been suggested by Kuan et al. [Appl. Phys. Lett. 51, 51 (1987)]. It is also found that ordering is not perfect, and that ordered regions are plate-like microdomains lying on planes slightly tilted from the (110) plane. From these results, it is suggested that atomic steps on the growth surface play an important role in the generation of ordered structures.
Morphological stability of facet growth on nonplanar substrates
Authors: Ratsch C. , Zangwill A.
Published: July 2002

We study the morphological stability of layer growth by chemical vapor deposition onto a nonplanar substrate patterned with a facetted groove. Our analytic treatment indicates that, except under conditions of very modest supersaturation, diffusion effects in the gas phase generally preclude the stable growth of crystallographic facets that form the sidewalls of the groove. Instead, heterogeneous nucleation and the kinetics of step flow combine to promote the evolution of an initially perfect facet into a stably propagating vicinal surface. Under more diffusion-limited conditions, even these ‘‘facets’’ do not survive and a characteristic rough morphology results.
Reflection electron energy loss spectroscopy during initial stages of Ge growth on Si by molecular beam epitaxy
Authors: Atwater Harry A. , Ahn Channing C.
Published: July 2002

Using a conventional reflection high-energy electron diffraction gun together with an electron energy loss spectrometer, we have combined in situ measurements of inelastic scattering intensities from Si L2,3 and Ge L2,3 core losses with reflection electron diffraction data in order to analyze the initial stages of Ge heteroepitaxy on Si(001). Diffraction data indicate an initial layer-by-layer growth mode followed by island formation for Ge thicknesses greater than 0.8–1.1 nm. The electron energy core loss data are consistent with a simple model of grazing incidence electron scattering from the growing Ge film. Reflection electron energy loss spectroscopy is found to be highly surface sensitive, and the energy resolution and data rate are also sufficiently high to suggest that reflection electron energy loss spectroscopy may be a useful real-time, in situ surface chemical probe during growth by molecular beam epitaxy.
Picosecond optical parametric amplification in lithium triborate
Authors: Zhang J. Y. , Huang J. Y. , Shen Y. R. , Chen Chuangtian , Wu Bochang
Published: July 2002

We report the performance of a type-I lithium triborate (LBO) optical parametric amplifier pumped by 15 ps, 355 nm laser pulses. It is seen that with proper design, LBO can be as efficient as barium borate for such an application.
Gain spectra and gain compression of strained-layer multiple quantum well optical amplifiers
Authors: Wiesenfeld J. M. , Raybon G. , Koren U. , Eisenstein G. , Burrus C. A.
Published: July 2002

Optical amplifiers with strained-layer multiple quantum well active regions are shown to exhibit a bandwidth of 100 nm with a saturation output power larger than 25 mW. For a 780-μm-long device, the small-signal gain exceeds 25 dB. The combination of high gain with large saturation output power is obtained by properly tailoring the mode confinement factor and differential gain coefficient of the strained-layer gain medium.
Criteria for the observation of one-dimensional transport in split-gate field-effect quantum wires
Authors: Eugster Cristopher C. , del Alamo Jesús A. , Belk Paul A. , Rooks Michael J.
Published: July 2002

We have fabricated AlGaAs/GaAs split-gate field-effect quantum wires with different lengths and widths in order to study the effect of the dimensions of the confining gates on one-dimensional (1D) transport. Two threshold voltages arise as the two-dimensional (2D) electron gas is turned off first underneath the gates and then as the 1D electron gas is turned off in between the split-gates through their fringing fields. In particular, our room-temperature experiments reveal the existence of a critical width of 0.2–0.25 μm between the confining gates below which the 1D regime is not observed in 1.0-μm-long split-gate quantum wires. This can be explained if the potential at the surface near the metal confining gates is influenced by the gate voltage through exchange of electrons between the metal gates and the surface states.
Direct observation of optical anisotropy in a GaAs/AlAs quantum well wire array
Authors: Kanbe H. , Chavez-Pirson A. , Ando H. , Saito H. , Fukui T.
Published: July 2002

Using reflectance difference spectroscopy and transmittance difference spectroscopy, optical anisotropy in a quantum well wire array is directly observed at room temperature. The quantum wire array is a fractional-layer superlattice grown by metalorganic chemical vapor deposition on a vicinal (001)GaAs substrate. The size for quantum confinement of the wires is nominally 4×4 nm. Polarization dependence of optical absorption and refractive index is clearly observed between the directions parallel and perpendicular to the wires.
Mechanically alloyed nanocrystalline Ni-Mo powders: A new technique for producing active electrodes for catalysis
Authors: Trudeau M. L. , Huot J. Y. , Schulz R.
Published: July 2002

We report on the effect of strong mechanical deformations on various mixtures of Ni and Mo metallic powders. The high-energy mechanical alloying process produces metastable fcc nanocrystals of Ni with a large amount of Mo in solid solution. The solubility limit of Mo in fcc Ni at room temperature is directly related to the total interface area between the crystallites. These new solids show an extremely high electrocatalytic activity for the hydrogen evolution reaction (HER) in alkaline solutions which can be directly related to their nanostructure.
Time-resolved luminescence spectroscopy of plasma emission from laser ablation of Bi-Sr-Ca-Cu oxide superconductor and related materials
Authors: Fukumura Hiroshi , Nakaminami Hiroshi , Eura Shigeru , Masuhara Hiroshi , Kawai Tomoji
Published: July 2002

Time-resolved spectroscopy of the plasma state produced by laser ablation of Bi2Sr2Ca1Cu2 oxide, an amorphous solid of the same composition, and unreacted mixture of the components is reported. The difference in the spectra among the samples indicates that the ablation products depend on the chemical structures of the irradiated samples. Effects of the ambient gas revealed that ionic species in the electronic ground states are mainly generated at the initial stage of the ablation, while atomic species are produced by collisions between the surrounding-gas molecules and plasma plume.
Residual stress at fluid interfaces with application to silicon oxidation
Authors: Murray Paul E.
Published: July 2002

A fluid may undergo a constrained volume change as a result of the presence of a soluble chemical species. Corresponding to every constrained volume change is a residual stress. We present a method to include in the equations of fluid motion a body force to allow for the presence of residual stress. This method is used to calculate the residual stress associated with the chemical transformation of silicon to silicon dioxide in the presence of water vapor.
Critical-layer thickness of a pseudomorphic In0.8Ga0.2As heterostructure grown on InP
Authors: Tacano Munecazu , Sugiyama Yoshinobu , Takeuchi Yukihiro
Published: July 2002

A very high electron mobility pseudomorphic In0.8Ga0.2As heterostructure is successfully grown on InP both by the elimination of the overshoot of flux densities and by the precise control of the flux ratio through a new calibration technique of reflection high-energy electron diffraction oscillations in a molecular beam epitaxy system. The critical-layer thickness for the pseudomorphic growth of InGaAs on InP is found to follow the energy balance model, and a very high 2DEG mobility of over 1.5 m2/V s and over 15 m2/V s at 293 and 10 K, respectively, is obtained.
Effect of waveguide uniformity on phase matching for frequency conversion in channel waveguides
Authors: Cao Xiaofan , Natour Jamal , Ramaswamy Ramu V. , Srivastava Ramakant
Published: July 2002

We have studied the effect of nonuniformity in graded index, channel waveguide dimensions on the phase-matching condition for guided-wave nonlinear frequency conversion. Both theoretical and experimental results using normalized waveguide parameters and quasi-phase matching for second- harmonic generation in annealed proton-exchanged LiNbO3 waveguides show the existence of an optimum waveguide design which is insensitive to inhomogeneities in the waveguide dimensions. Application of such a waveguide design using normalized approach can significantly relax the fabrication tolerance, leading to nonlinear guided-wave devices with long interaction lengths and useful conversion efficiencies.
Current gain enhancement in bipolar transistors by low-energy ion beam modification of the polycrystalline silicon emitter
Authors: Jalali B. , King C. A. , Higashi G. S. , Bean J. C. , Hull R. , Hsieh Y.-F. , Macaulay J. , Poate J. M.
Published: July 2002

The current gain of polycrystalline silicon emitter transistors has been improved by modification of the polycrystalline silicon/silicon interface using a low-energy ion beam. The base current is reduced by a factor of 3 while maintaining ideal current-voltage characteristics. No change in the collector current and the emitter series resistance is observed.
KTiOPxAs1−xO4 optical waveguides grown by liquid phase epitaxy
Authors: Cheng L. K. , Bierlein J. D. , Ballman A. A.
Published: July 2002

We report on a new type of optical waveguide based on the nonlinear optical material KTiOPO4 (KTP). Thin films of KTiOPxAs1−xO4 (5–50 μm) were grown on KTP substrates by liquid phase epitaxy using a tungstate flux. Energy-dispersive x-ray spectrometry reveals an abrupt increase in the arsenic concentration in the film, suggesting an abrupt, step-like refractive index profile in these guides. Optical waveguiding at 0.633 μm was demonstrated in a 20-μm-thick KTiOP0.76As0.24O4 film grown on a {011} KTP substrate. The refractive index difference between the film and the substrate (Δn) was measured to be ∼0.012, which compares favorably with the value estimated from bulk crystal measurements of the end members. Variations in the design of these waveguides and several potential applications are discussed.
Permanent photoinduced birefringence in a Ge-doped fiber
Authors: Ouellette François , Gagnon Daniel , Poirier Michel
Published: July 2002

We report the observation of permanent photoinduced birefringence in a Ge-doped fiber exposed to cw mode locked at 532 nm. This effect is enhanced by increasing the Ge concentration in the core of the fiber, or by submitting it to a thermal hydrogen treatment. The photoinduced birefringence is however very weak, or nonexistent, with irradiation by 514 or 488 nm cw argon laser light.
Electrical properties of selectively grown homoepitaxial diamond films
Authors: Grot S. A. , Hatfield C. W. , Gildenblat G. Sh. , Badzian A. R. , Badzian T.
Published: July 2002

Boron-doped homoepitaxial diamond films were selectively grown using sputtered SiO2 as a masking material. Uniform thickness, down to 50 nm, over a large area can be achieved with this technique. Hall mobility of selectively grown films is comparable to that of high-pressure high-temperature synthetic bulk diamond with a corresponding carrier concentration.
Optically stabilized AlxGa1−xAs/GaAs laser using magnetically induced birefringence in Rb vapor
Authors: Lee W. David , Campbell Joe C.
Published: July 2002

Narrow-band optical feedback is an effective method of reducing the linewidth and stabilizing the frequency of diode lasers. We have constructed an optically stabilized AlxGa1−xAs/GaAs laser using a rubidium vapor cell immersed in a dc magnetic field as an optical feedback element. The diode laser’s frequency locks to sub-Doppler features of the rubidium spectrum and exhibits a reduction in linewidth from 30 MHz to 35 kHz.
Behavior of zone-center, subband energies in narrow, strongly coupled quantum wells
Authors: Biermann Mark L. , Stroud C. R.
Published: July 2002

Narrow, symmetric coupled quantum wells (CQWs) are studied using a k⋅p, pseudopotential method. GaAs wells that range in width from 11.4 to 99.0 Å and Al0.3Ga0.7As barriers that range in width from 11.4 to 17.0 Å are treated. Features of the systems such as energy positions as a function of well and barrier width, subband crossing, and subband splitting about the single well subband position are described. A simple function with subband-dependent constants is fit to both the subband-pair splitting as a function of barrier width and the subband energy position as a function of well width. This function provides an accurate and simple aid in CQW design for devices and experiments.
Observation of vacancy type defects in Ga-doped ZnSe using a monoenergetic positron beam
Authors: Miyajima T. , Okuyama H. , Akimoto K. , Mori Y. , Wei L. , Tanigawa S.
Published: July 2002

We studied vacancy type defects in Ga-doped ZnSe films grown by molecular beam epitaxy using an energy-variable monoenergetic positron beam. We found that the concentration of negative charged vacancies, such as Zn vacancies, increases as the Ga atom concentration increases. This result indicates that the doping by Ga atoms induces the formation of Zn vacancies in a ZnSe film. We believe that these defects will cause the saturation of active carriers in n-type ZnSe films.
Surface modification of Bi-Sr-Ca-Cu-O films deposited in situ by radio frequency plasma flash evaporation with a scanning tunneling microscope
Authors: Terashima Kazuo , Kondoh Minoru , Takamura Yuzuru , Komaki Hisashi , Yoshida Toyonobu
Published: July 2002

The surface modifications of as-grown superconducting Bi-Sr-Ca-Cu-O (BSCCO) films prepared by radio frequency plasma flash evaporation were carried out with a scanning tunneling microscope (STM). The as-grown films were identified as highly c-axis-oriented, low Tc (80 K) phase Bi2Sr2Ca1Cu2Ox with some residue such as (Sr,Ca)3Cu5Ox from x-ray diffraction patterns. The as-grown film deposited at about 750 °C exhibited a superconducting critical temperature Tc of 76 K and a critical current density Jc of 8.8×104 A/cm2 under zero magnetic field at 27 K. The nanometer-size surface modifications between 2 and 50 nm, especially layered etching, of the prepared BSCCO films were successfully performed by using a STM in air.
Synthesis of a bulk YBa2Cu4O8 superconductor by addition of Ag2O at an ordinary pressure of oxygen
Authors: Ohara Satoshi , Matsuda Motohide , Watanabe Yuichi , Takata Masasuke
Published: July 2002

The superconducting bulk YBa2Cu4O8 compound has been successfully synthesized by the addition of Ag2O as a reaction-rate enhancer at an ordinary pressure of oxygen. An almost single YBa2Cu4O8 phase together with the compositionally reasonable metallic silver phase could be formed when the added amount of Ag2O was larger than 30 wt. %. The obtained bulk YBa2Cu4O8 compound showed a Tc(zero) of 70 K in resistivity curve and a Tc(onset) of 80 K in alternating-current magnetic susceptibility curve. The results well evidenced that the YBa2Cu4O8 can be directly prepared by the conventional solid-state reaction.
Monolithic two-dimensional surface-emitting strained-layer InGaAs/AlGaAs and AlInGaAs/AlGaAs diode laser arrays with over 50% differential quantum efficiencies
Authors: Goodhue W. D. , Donnelly J. P. , Wang C. A. , Lincoln G. A. , Rauschenbach K. , Bailey R. J. , Johnson G. D.
Published: July 2002

Monolithic two-dimensional surface-emitting arrays of strained-layer InGaAs/AlGaAs and AlInGaAs/AlGaAs diode lasers have been fabricated and operated pulsed with low-threshold current densities and differential quantum efficiencies greater than 50%. The InGaAs/AlGaAs arrays emit at 1.03 μm, while the AlInGaAs/AlGaAs arrays emit at 0.815 μm. Thus, it should be possible to fabricate monolithic arrays with comparable performance over a wide wavelength range. The individual lasers of the arrays are horizontal folded-cavity devices with two 45° internal reflectors and two top-surface facets. The design is simple to implement using optical pattern-generator masks, optical projection printing, and chlorine ion-beam-assisted etching in key fabrication steps.
Cooperative quantum confinement of excitons bound to isoelectronic impurity complexes in Si1−xGex/Si superlattices
Authors: Modavis R. A. , Hall D. G. , Bevk J. , Freer B. S.
Published: July 2002

Excitons bound to isoelectronic impurity complexes in strained Si1−xGex/Si superlattices (SLs) grown on Si(100) substrates exhibit a novel type of cooperative quantum confinement. The small conduction-band and much larger valence-band offsets in this material system confine an electron much less effectively than a hole. The short-range potential associated with isoelectronic electron traps located within the alloy layers of the SL provides an additional mechanism for localizing electrons within the wells of the SL. We use Be isoelectronic complexes to demonstrate and explore this cooperative confinement of excitons in Si1−xGex/Si superlattices.
Separation of intrinsic and extrinsic optical absorption in a fluoride glass
Authors: Jewell John M. , Williams Glen M. , Jaganathan James , Aggarwal I. D. , Greason Paul
Published: July 2002

The contribution of impurity ions to the total optical absorption of a heavy metal fluoride glass has been determined at 532 and 1064 nm. Four ZrF4-BaF2-LaF3-AlF3-NaF glasses were prepared from various purity raw materials. The absorption coefficients of these glasses range from 0.92 to 45.4×10−4 cm−1 at 1064 nm and from 7.43 to 11.1×10−4 cm−1 at 532 nm as determined by laser calorimetry. The concentrations of Fe, Ni, Cu, and Co ions in each glass were determined by graphite furnace atomic absorption spectroscopy. These two measurements enable the absorption, due to transition metal ions to be differentiated from the intrinsic absorption of the glass. At 1064 nm, the absorption coefficient of these glasses is controlled entirely by the transition metal ion content. However, at 532 nm, the absorption by the transition metal ions accounts for 4–42% of the total absorption depending on impurity concentration. The intrinsic absorption of this fluoride glass calculated from these data at 532 nm is (7.69±0.99)×10−4 cm−1.
Corrosion protection of aluminum surfaces using pyrolytic tin oxide
Authors: Roos Arne , Hedenqvist Per
Published: July 2002

Thin films of tin oxide have been pyrolytically deposited on both bulk and evaporated aluminum surfaces. Using optical reflectance spectroscopy it is shown that the chemical stability of tin-oxide-coated aluminum is greatly improved compared to uncoated or anodized aluminum. Exposure to sulphuric acid and sodium hydroxide solutions left the tin-oxide-coated surfaces unaffected, while uncoated or anodized surfaces were completely dissolved in the solutions.
Low-energy ion scattering spectroscopy observations of c-axis-oriented YBa2Cu3O7−x thin films: Effects of in-vacuum annealing
Authors: Tanaka S. , Nakamura T. , Iiyama M. , Yoshida N. , Takano S. , Shoji F. , Oura K.
Published: July 2002

The atomic structure of (001) surfaces of c-axis-oriented YBa2Cu3O7−x (YBCO) thin films was studied by low-energy ion scattering spectroscopy (ISS) after annealing in ultrahigh vacuum. This is the first report on the surface analysis of superconducting oxide evaluated by ISS. A clean surface of YBCO (001) 1×1 is produced by annealing at around 500 °C. The surface structure is discussed in terms of the blocking and the nonblocking effects caused by the desorption of O(4) atoms. We conclude that the (001) surfaces are stabilized by Cu(1)-O chains.
Ohmic heating and series resistance of a vertical-microcavity surface-emitting laser
Authors: Du Guotong , Lin J. , Gamelin J. K. , Wu B. , Talghader J. J. , Wang S. , Yang Y. J. , Dziura T. G. , Wang S. C.
Published: July 2002

We report the results of investigations on the transient heating and series resistance of a vertical-microcavity surface-emitting (VMSE) laser with an air-bridge structure. Transient temperature broadening of the lasing spectrum and chirping of the current versus voltage characteristic are analyzed experimentally and theoretically. We believe that the experiments provide us valuable information on the severity of the heating problems in VMSE laser.
Laser-induced fluorescence studies of pulsed uranium ablation by a Nd:YAG Q-switched laser
Authors: Qu Jianan , Zhou Zhiyao , Zhu Lizhou , Lin Fucheng
Published: July 2002

A high-resolution laser spectroscopy method is used to analyze the time-of-flight (TOF) distribution of uranium atoms photoablated by a Nd:YAG Q-switched laser in real time. The velocity distribution of an individual pulsed beam of ablated particles was derived from the TOF spectrum. The velocity of the neutral atoms ranged from 1 to 10 km/s in our experiments.
Ultrafast energy relaxation phenomena of photoexcited minority electrons in p-GaAs
Authors: Furuta Tomofumi , Yoshii Akira
Published: July 2002

Energy relaxation processes for minority electrons in p-GaAs are investigated by time-resolved photoluminescence (PL) measurements using an up-conversion technique with a high time resolution of 130 fs. By measuring the time evolution of PL intensity, the energy relaxation time of electrons is obtained directly. Moreover, electron distribution created by laser excitation which is in a thermally nonequilibrium state is successfully observed. With increasing hole concentration, the time response in PL intensity becomes fast. This implies that electron-hole interaction plays a key role in energy relaxation in high hole concentration. By detailed analyses of PL intensity, it can be found that the relaxation time by electron-hole interaction is approximately 500 fs or less, and electrons which are in a nonequilibrium state just after excitation are thermalized rapidly within about 200 fs at the first stage by electron-hole interaction.
Etchant dependence of surface reconstructions of GaAs surfaces prepared by ultrasonic-running de-ionized water treatment
Authors: Hirota Y. , Homma Y. , Sugii K.
Published: July 2002

(001) GaAs surfaces treated with ultrasonic-running de-ionized water (U-RDIW) after NH4OH/H2O2/H2O etching are investigated by reflection high-energy electron diffraction (RHEED) and by x-ray photoelectron spectroscopy (XPS). RHEED observations show a spotty (1×1) pattern lying on the 0-th Laue circle at room temperature, a (2×4) streaky pattern at 310 °C, and a spotty (3×6) pattern after annealing at 370 °C. We discuss the difference in surface stoichiometry after U-RDIW between the H2SO4- and NH4OH-etched surfaces based on the results of XPS. The experimental results indicate the possibility of controlling the surface stoichiometry of the U-RDIW-treated GaAs surfaces by varying the etching solution.
Thermal stresses in square-patterned GaAs/Si: A finite-element study
Authors: Lingunis E. H. , Haegel N. M. , Karam N. H.
Published: July 2002

The effect of free edges on the thermal stress distribution in square-patterned GaAs/Si (100) is studied by three-dimensional finite-element elastic analysis. The results are discussed in comparison with previous analytical and numerical calculations. Finally the stress in the most important central portion of the square is calculated as a function of width to thickness ratio in the range 1 to 40. Results are presented in a form appropriate for interpretation of 4.2-K photoluminescence (PL) measurements and device optimization.
Fermi level pinning at epitaxial Si on GaAs(100) interfaces
Authors: Silberman J. A. , de Lyon T. J. , Woodall J. M.
Published: July 2002

GaAs Schottky barrier contacts and metal-insulator-semiconductor structures that include thin epitaxial Si interfacial layers operate in a manner consistent with an unpinned Fermi level at the GaAs interface. These findings raise the question of whether this effect is an intrinsic property of the epitaxial GaAs(100)-Si interface. We have used x-ray photoemission spectroscopy to monitor the Fermi level position during in situ growth of thin epitaxial Si layers. In particular, films formed on heavily doped n- and p-type substrates were compared so as to use the large depletion layer fields available with high impurity concentration as a field-effect probe of the interface state density. The results demonstrate that epitaxial bonding at the interface alone is insufficient to eliminate Fermi level pinning, indicating that other mechanisms affect the interfacial charge balance in the devices that utilize Si interlayers.
Thermal stability of Schottky barriers at Au and Ag/InP(110) interfaces with Sb interlayers
Authors: Yamada Masao , Green Albert M. , Herrera-Gomez Alberto , Kendelewicz Tom , Spicer William E.
Published: July 2002

Schottky barriers at Au and Ag/InP(110) interfaces with Sb interlayers show an unusually low Fermi level pinning position of about 0.52 eV above the valence-band maximum (VBM) at room temperature using photoemission spectroscopy. Thermal stability of these interfaces have been first studied. Strong clustering is observed by annealing these interfaces, suggesting less reaction between overlayers and substrates. Change in Fermi level positions due to annealing is <0.1 eV up to 300 °C at these interfaces including measurement errors. However, segregation of In atoms into the Ag overlayer is observed above 300 °C for 10 min at Ag/Sb/InP interfaces, and a small pinned component with a level 0.9 eV above the VBM appears above 200 °C for 10 min at Au/Sb/InP interfaces. These Schottky barriers are stable up to at least 200 °C.
Effect of structural disorder on electronic states in GaAs/AlGaAs quantum wires
Authors: Singh Jasprit
Published: July 2002

Perfect quantum wire structures are attractive candidates for low threshold lasers and high speed electronic devices because of the nature of the density of states and eigenfunctions. In this letter, we discuss the effect of structural disorder on the density of states as well as on the localization length of these eigenstates. We find that significant changes in the density of states and eigenfunctions occur with a small random disorder along the wire axis. Consequences for devices based on quantum wires are discussed.
InGaAs/InP multiple quantum well tunable Bragg reflector
Authors: Blum O. , Zucker J. E. , Chiu T. H. , Divino M. D. , Jones K. L. , Chu S. N. G. , Gustafson T. K.
Published: July 2002

We demonstrate a voltage-tunable distributed Bragg reflector grown by chemical beam epitaxy that utilizes 31 periods of alternating InGaAs/InP multiple quantum well and bulk InP quarter-wave layers. We obtain a differential change in transmission of 14% at 1570 nm wavelength for an applied field of 2.25×104 V/cm. We find good agreement between the experimental results and transmission spectra calculated using the optical transmission matrix method.
Molecular beam epitaxial growth of ultrathin CdTe–CdMnTe quantum wells and their characterization
Authors: Waag A. , Schmeusser S. , Bicknell-Tassius R. N. , Yakovlev D. R. , Ossau W. , Landwehr G. , Uraltsev I. N.
Published: July 2002

We report the growth and optical characterization of CdTe/CdMnTe single quantum wells with well thicknesses ranging from 60 down to 6 Å. The single quantum wells were grown by standard molecular beam epitaxy without growth interruption and investigated by reflection, photoluminescence (PL), and excitation PL. All structures including the 6-Å-thick quantum well exhibit extraordinarily narrow photoluminescence lines. From an analysis of linewidth and Stokes shift of the photoluminescence lines informations on the structure of the CdTe/CdMnTe interfaces are derived. The good quality of those structures made it possible to identify for the first time recombination of two-dimensional free exciton magnetic polarons.
Visible spectrum native-oxide coupled-stripe In0.5(AlxGa1−x)0.5P–In0.5Ga0.5P quantum well heterostructure laser arrays
Authors: Kish F. A. , Caracci S. J. , Holonyak N. , Maranowski S. A. , Dallesasse J. M. , Burnham R. D. , Smith S. C.
Published: July 2002

Data are presented demonstrating the continuous (cw) operation (10–50 °C) of coupled-stripe In0.5(AlxGa1−x)0.5P–In0.5Ga0.5P multiple quantum well heterostructure (QWH) visible (λ∼655 nm) laser arrays. The ten stripe QWH arrays (3 μm emitters on 4 μm centers) are defined by ‘‘wet’’ oxidation (H2O vapor in N2 carrier gas, 550 °C) of the high gap In0.5(AlxGa1−x)0.5P upper confining layer outside of the active stripes. The gain-guided arrays exhibit relatively low cw 20 °C threshold current densities (∼1.6 kA/cm2, ∼450 μm cavity) and high output powers of 25 mW per uncoated facet (cw, 20 °C). Optical coupling between stripes results in a near diffraction-limited single-lobe far-field pattern indicative of oscillation in the lowest order supermode of the array (in-phase operation).
Improvements in the heteroepitaxy of GaAs on Si by incorporating a ZnSe buffer layer
Authors: Lee M. K. , Horng R. H. , Wuu D. S. , Chen P. C.
Published: July 2002

Heteroepitaxy of GaAs on Si with a ZnSe interlayer by low-pressure metalorganic chemical vapor deposition is reported. The structural and electrical properties of the GaAs epilayers grown on ZnSe/Si substrates were found to be superior to those of the GaAs directly on Si. The surface dislocation density of the GaAs/ZnSe/Si film can be reduced to 2×105 cm−2, which is one order of magnitude lower than that of GaAs/Si. The planar Schottky diode fabricated on the GaAs/ZnSe/Si sample shows a reverse breakdown voltage as high as 30 V, whereas the diode on GaAs/Si has a breakdown voltage of about 12 V. In addition, the residual stress in the GaAs heteroepilayers calculated from photoluminescence peak shifts was 8.2×108 dyn/cm2 for the GaAs/ZnSe/Si structure, as compared to 2.7×109 dyn/cm2 for the GaAs directly on Si. This indicates that the ZnSe intermediate layer is also effective in reducing the residual stress in the GaAs film grown on Si.
In-plane anisotropic transport properties observed in epitaxial Bi2(Sr,Ca)3Cu2Ox films grown on tilted (001)SrTiO3 substrate
Authors: Fujita J. , Yoshitake T. , Satoh T. , Miura S. , Tsuge H. , Igarashi H.
Published: July 2002

We report on large in-plane anisotropic transport properties observed in epitaxial Bi2(Sr,Ca)3Cu2Ox films grown on tilted (001)SrTiO3 substrate. By tilting the surface normal axis about 4° toward [111]SrTiO3, regular steps and terraces were formed on the substrate surface and perfect alignment of film b axis with incommensurate modulation along [110]SrTiO3 was realized. The film c axis was perpendicular to the (001)SrTiO3 terrace, thus the film c axis grew tilted 4° toward [111] from surface normal due to the surface inclination. In those epitaxial configurations, the in-plane resistivity along the step direction(ρ[110]) involved the contribution from the c-axis(ρc) component, and we observed the large resistivity anisotropy between a- and b- direction of the film. The transport along a axis(ρa) showed a low resistivity with metallic temperature dependence while the resistivity along the step direction(ρ[110]) was higher and semiconductive. The ratio of ρc/ρa ≊ 104 estimated in this experiment agrees well with the anisotropy observed in the bulk single crystal.
Micrometer patterning of phthalocyanines by selective chemical vapor deposition
Authors: Sekiguchi A. , Pasztor K. , Shimo N. , Masuhara H.
Published: July 2002

Micrometer size patterns of copper phthalocyanine derivatives were fabricated from 1,2,4,5-tetracyanobenzene (TCNB) by a selective chemical vapor deposition method. Copper films were patterned on silicon wafers by photolithography and wet etching techniques, sealed in a glass tube with TCNB, and heated at different temperatures. Controlling the treatment temperature, selective chemical vapor deposition was achieved to produce copper phthalocyanine thin films on the copper patterns. After thermal annealing of the deposited film in vacuum, the films were converted to a polymer of the copper phthalocyanines.
Role of trimethylgallium exposure time in carbon doping and high temperature atomic layer epitaxy of GaAs
Authors: Reid K. G. , Urdianyk H. M. , Bedair S. M.
Published: July 2002

The window for the ALE self limited growth of GaAs can be expanded by reducing the gas phase decomposition. We found that the exposure time to TMGa flux is critical and has to be reduced for ALE to be achieved at high growth temperature. An ALE reactor was used which allows minimum gas heating, short exposure time, and sudden termination of the gas exposure without relying on the diffusion of gases away from the substrate surface. ALE was achieved in the 450–700 °C temperature range. Carbon doping in the 1015–1020/cm3 range was also achieved by adjusting the exposure time and the growth temperature. The combined role of gas phase decomposition and surface reaction are proposed to explain these results.
Evidence for pair-breaking in (R1−xPrx)Ba2Cu3O7−y (R=Er, Y, Dy, Gd, Eu) systems
Authors: Xu Yunhui , Guan Weiyan
Published: July 2002

We observed that the superconducting critical temperature Tc(x) of the oxides (R1−xPrx)Ba2Cu3O7−y (R=Er, Y, Dy, Gd, Eu) decreases monotonically with increasing Pr concentration x. Using the reduced parameters Tc/Tc(0) and x/xcr all the experimental data for five studied systems fall onto the theoretical universal curve of Abrikosov and Gor’kov over the reduced Pr concentration regime, x/xcr<0.6, where xcr is the critical concentration of Pr for the complete suppression of superconductivity and Tc(0) is the Tc for undoped material. The consistency of these results suggests a pair-breaking mechanism which plays a role in depressing superconductivity in these high Tc oxides.