bluuebunny/crossref_metadata_2025 huggingface dataset:
Image formation in a superresolution phase conjugate scanning microscope
Authors: Johnson K. M. , Cathey W. T. , Mao C. C.
Published: July 2002

Analytical and experimental results of a new type of optical scanning microscope, which uses a phase conjugate mirror and pinholes to achieve superresolution, are presented. This phase conjugate scanning microscope has a higher Rayleigh resolution limit than conventional, single-pass, and double-pass scanning microscopes.
Plasma-enhanced photoemission as a discharge lamp diagnostic
Authors: Schulman M. B. , Woodward D. R.
Published: July 2002

We describe our application of plasma-enhanced photoemission as an in situ electrode diagnostic for operating discharge lamps. The method uses focused low-power laser beams of various wavelengths to investigate emission properties of cathodes in fluorescent lamps. When a pulsed laser beam is directed onto the cathode, the photoemission effect will cause electrons to be ejected if hν is greater than the effective work function of the surface over the area illuminated. This burst of photoelectrons can be monitored, as well as the optogalvanic signal which results as they enter the surrounding discharge and produce additional ionization. The photon energy at which photoemission is observed places an upper limit on the local effective work function, which is influenced by the electric field at the cathode surface.
Investigation of hydrogenated amorphous carbon coatings for magnetic data storage media by atomic force microscopy
Authors: Meyer E. , Heinzelmann H. , Grütter P. , Jung Th. , Scandella L. , Hidber H.-R. , Rudin H. , Güntherodt H.-J. , Schmidt C.
Published: July 2002

Thin films of hydrogenated amorphous carbon for magnetic data storage media have been examined by atomic force microscopy. The topography of several coatings has been imaged with a lateral resolution of a few nanometers. Histograms of the height distribution and rms values have been calculated to characterize the roughness of the surfaces quantitatively. Variations of these microscopic properties could be related to changes in the macroscopic behavior like friction and wear.
Strain-induced confinement of carriers to quantum wires and dots within an InGaAs-InP quantum well
Authors: Kash K. , Bhat R. , Mahoney Derek D. , Lin P. S. D. , Scherer A. , Worlock J. M. , Van der Gaag B. P. , Koza M. , Grabbe P.
Published: July 2002

We describe a novel method of confining carriers by deliberately creating large inhomogeneous strain patterns in a quantum well. The strain modulates the band gap to provide lateral quantum confinement for excitons. Here, we generate strain confinement in an InGaAs quantum well by reactive ion beam assisted etching through an overlying compressed pseudomorphic quaternary layer using etch masks patterned by electron beam lithography. Photoluminescence spectra of arrays of wires and dots show red-shifted band gaps in direct evidence of lateral confinement. We compare our results to finite element calculations of the inhomogeneous strain in an InP substrate from a compressed overlayer patterned into rectangular wires.
Anisotropy effects on fracto-emission from MgF2 single crystals
Authors: Yoo K. C. , Rosemeier R. G. , Dickinson J. T. , Langford S. C.
Published: July 2002

An important component of fracto-emission is the emission of electrons (EE) accompanying the fracture of materials. In this letter we present measurements of EE accompanying the fracture of MgF2 single crystals loaded in three-point bend. In particular, we examine the effect of changing the crystal orientation relative to the loading direction on emission intensity. We find that fracture surfaces with different crystal orientations yield significantly different EE. We propose that this is due to differences in the density of defects produced by such a fracture.
Electron-phonon relaxation rate in single-crystal lanthanum cuprate
Authors: Doll G. L. , Eesley G. L. , Brorson S. D. , Dresselhaus M. S. , Dresselhaus G. , Cassanho A. , Jenssen H. P. , Gabbe D. R.
Published: July 2002

We report the results of phonon relaxation processes obtained from picosecond transient thermoreflectance measurements of single-crystal La2CuO4+y (y∼0.06). Nonequilibrium heating was found to occur on a picosecond time scale. The time scale of the nonequilibrium heating is a sensitive measurement of the modest electron-phonon interaction (λ≤0.1) in the nonsuperconducting La2CuO4+y.
Broader spectral width InGaAsP stacked active layer superluminescent diodes
Authors: Mikami Osamu , Yasaka Hiroshi , Noguchi Yoshio
Published: July 2002

Fabrication and characteristics of broader spectral width 1.3 μm and 1.5 μm InGaAsP superluminescent diodes having a novel stacked active layer (STAC-SLDs) structure are reported. The emission spectral width is successfully broadened as much as twice that of conventional SLDs, yielding spectral widths of 80 and 140 nm for the 1.3 μm and the 1.5 μm SLD, respectively.
Improvement on the current-voltage characteristics of polycrystalline silicon contacted n+-p junctions with high-field stressing
Authors: Wu S. L. , Lee C. L. , Lei T. F.
Published: July 2002

Improvement on the current-voltage characteristics of polycrystalline silicon contacted n+-p junctions after they were applied a high-field scanned stressing is reported. For the stressed diodes, the leakage current decreased as much as two orders, the breakdown voltage shifted from −45 to −60 V, and the forward ideality factor also decreased. Scanning electron microscopy photographs on the cross-sectional view of the junctions revealed that local melting might have occurred during stressing to cause the improvement.
Nonlinear optical properties of benzimidazobenzophenanthroline type ladder polymers
Authors: Lindle J. R. , Bartoli F. J. , Hoffman C. A. , Kim O.-K. , Lee Y. S. , Shirk J. S. , Kafafi Z. H.
Published: July 2002

Third-order optical susceptibilities (χ(3)) of poly{(7-oxo-7, 10H-benz[de]imidazo[4′,5′:5,6]benzimidazo [2,1-a]isoquinoline-3,4:10,11-tetrayl)-carbonyl}, referred to as BBL, and poly(6,9-dihydro-6,9-dioxobisbenzimidazo[2,1b:1′,2′j] benzo[1mn]-[3,8]phenanthroline-3,12-diyl), known as BBB, have been determined using the technique of degenerate four-wave mixing (DFWM) at 1.064 μm. BBL has a χ(3)xxxx=(1.5±0.4)×10−11 esu, three times as large as that of BBB and 38 times as large as that of CS2. Electrochemical doping led to a small (<30%) increase in the third-order susceptibility of BBL.
Electroabsorption effects in InxGa1−xAs/GaAs strained-layer superlattices
Authors: Niki S. , Kellner A. L. , Lin S. C. , Cheng A. , Williams A. R. , Chang W. S. C. , Wieder H. H.
Published: July 2002

Electroabsorption of strained-layer Inx Ga1−x As/GaAs superlattice structures grown by molecular beam epitaxy on GaAs substrates was experimentally investigated. Its spectral characteristics were found to be similar to those of Franz–Keldysh electroabsorption of bulk semiconductor materials, and suggest that the widths of ground-state electron and hole minibands might be larger than the maximum tilt of the potential well caused by an applied voltage. We attribute the electroabsorption of such superlattices to photon-assisted tunneling between ground-state electron and heavy hole minibands.
Nonequilibrium electron transport in heterostructure bipolar transistors probed by magnetic field
Authors: Nottenburg R. N. , Levi A. F. J. , Jalali B. , Sivco D. , Humphrey D. A. , Cho A. Y.
Published: July 2002

We show that the static current-voltage characteristics of a heterojunction bipolar transistor are dramatically influenced by application of a magnetic field. Nonequilibrium base transport has a strong influence on collector/emitter breakdown voltage, VCEB. With a magnetic field applied perpendicular to the direction of the injected emitter current VCEB increases from 2.6 V at 0 T to 8 V at 8 T. In the same device with a magnetic field applied parallel to the current flow, the current gain increases by a factor of 2 over the same magnetic field range. Transistors which exploit nonequilibrium base and collector transport have qualitatively different behavior compared to conventional devices which use diffusive and drift-diffusive transport.
Direct correlation between reflection electron diffraction intensity behavior during the growth of AlxGa1−xAs/GaAs quantum wells and their photoluminescence properties
Authors: Deparis C. , Massies J. , Neu G.
Published: July 2002

The reflection high-energy electron diffraction (RHEED) intensity level behavior during the growth of AlxGa1−xAs/GaAs quantum wells (QWs) is compared to the photoluminescence characteristics. The correlation between a decrease of the RHEED intensity level and the linewidth broadening of the excitonic QW transitions allows the unambiguous association of such a decrease with a roughening of the growth interface.
Transmission spectra of substrate-free ZnTe-ZnSe superlattices
Authors: Yang H. , Ishida A. , Fujiyasu H.
Published: July 2002

Transmission spectra of ZnTe-ZnSe strained-layer superlattices grown on GaAs (001) have been measured for the first time and step-like optical-absorption spectra between conduction and valence subbands have been observed. The GaAs substrates with a narrower band gap than the superlattices were partially removed by a chemical etching method. For the ZnTe-ZnSe superlattices with a type II band structure, the transmission spectra provide a powerful tool for determining the effective band gap and band offset, because the spatial indirect transition of separately confined electrons and holes is very weak and therefore difficult to observe in photoluminescence measurements. The absorption thresholds observed in the transmission spectra agree very well with the exciton emissions that appeared in photoluminescence data.
Realization of high mobilities at ultralow electron density in GaAs-Al0.3Ga0.7As inverted heterojunctions
Authors: Kim Dojin , Madhukar A. , Hu Ke-Zhong , Chen Wei
Published: July 2002

We report the first realization of extremely low free-carrier concentration (≤4×1010 cm−2) and high LN2 electron mobilities (∼1.8×105 cm2/V s) in the dark in inverted Al0.3Ga0.7As /GaAs(100) modulation-doped structures. The obtained results are all the more remarkable since the structures do not involve any superlattice or graded barrier, δ doping, or large spacer layer thicknesses. We attribute the observed properties to the high quality of the ambient in the molecular beam epitaxy system and the use of optimized growth kinetics and procedure as determined from reflection high-energy electron diffraction intensity behavior.
Relaxed GexSi1−x films grown by rapid thermal processing chemical vapor deposition
Authors: Jung K. H. , Kim Y. M. , Kwong D. L.
Published: July 2002

High quality, epitaxial, relaxed GexSi1−x layers have been grown by rapid thermal processing chemical vapor deposition. Relaxation is believed to be due primarily to the high deposition temperature of 1000 °C and occurred through the formation of an asymmetric misfit dislocation network aligned along the 〈110〉 directions and confined to the interface. The only other defects observed were single threading dislocations at the ends of misfit dislocations.
Ion channeling investigation of the lattice location of Sn atoms in GaAs thin films grown by molecular beam epitaxy
Authors: Yu Kin Man , Lee Henry P. , Wang S.
Published: July 2002

We have investigated the lattice location of Sn atoms in Sn-doped GaAs thin films grown by molecular beam epitaxy using ion channeling techniques. Accumulation of ≊2×1014 atoms/cm2 of Sn on the GaAs surface was detected. These surface Sn atoms were determined to be randomly distributed within ≊20 Å of the surface of the GaAs. Angular scans of the Ga Kα, As Kβ, and Sn L x rays across the 〈100〉, 〈110〉, and 〈111〉 axial channels indicated that the Sn atoms in the GaAs layer are mostly substitutional. No displacement of the Sn atoms larger than 0.14 Å from the substitutional sites was detected.
Structural and chemical stability in nonrandom silver-YBa2Cu3O7 composites in the presence of water
Authors: Veretnik D. , Reich S.
Published: July 2002

Accelerated water and moisture degradation of YBa2Cu3O7(YBCO)-silver nonrandom composites is studied. Oxygen evolution for these composites immersed in water at 65 °C was compared with that for regular YBCO ceramic material prepared under similar sintering conditions. Time evolution of the decay of crystalline structure was followed by x-ray diffraction for the composite material and for the regular YBCO ceramic. We find that the nonrandom Ag-YBCO composite exhibits high chemical and structural stability in the presence of water; this advantageous property is probably due to the encapsulation of the YBCO grains with silver in this composite material.
Neutron-induced microwave loss in ceramic YBa2Cu3O7−δ
Authors: Cooke D. W. , Jahan M. S. , Brown R. D. , Ott K. C. , Gray E. R. , Smith J. L. , Willis J. O. , Bennett B. L. , Maez M. A. , Peterson E. J. , Hults W. L. , Coulter J. Y. , Portis A. M. , Piel H. , Klein N. , Müller G. , Hein M.
Published: July 2002

An increase by over three orders of magnitude from 0.58 mΩ to 1.17 Ω was observed at 4.0 K in the 3 GHz microwave surface resistance of ceramic YBa2Cu3O7−δ following exposure to neutrons. The transport resistivity of an unirradiated pellet was linear in temperature down to Tc with a room-temperature value of 2.13 mΩ cm and a resistivity extrapolated to 4.0 K of 0.53 mΩ cm. Following irradiation, the resistivity rose with decreasing temperature from a room-temperature value of 1.5 Ω cm to a maximum at around 45 K with little change evident at Tc . These results, in conjunction with eddy current, susceptibility, iodometric titration, and thermally stimulated luminescence measurements on irradiated and unirradiated samples, collectively suggest that the effect of neutron irradiation has been to decrease intergranular coupling without the development of an insulating phase.
Sharp angular sensitivity of pinning due to twin boundaries in Ba2YCu3O7
Authors: Gyorgy E. M. , van Dover R. B. , Schneemeyer L. F. , White A. E. , O’Bryan H. M. , Felder R. J. , Waszczak J. V. , Rhodes W. W. , Hellman F.
Published: July 2002

We have measured the pinning force due to twin boundaries by measuring the magnetic torque produced when a field is applied perpendicular to the c axis and rotated with respect to the ab axes. At 76 K, the torque increases roughly fourfold, when the field is within 2° of the parallel to the twin boundaries. This peak is absent at 27 K. Irradiation with 5×1016 cm−2 3.5 MeV protons increases the overall critical current and eliminates the peaks observed at 76 K.
Improved contacts to semi-insulating GaAs photoconductive switches using a graded layer of InGaAs
Authors: Kuchta D. , Whinnery J. R. , Smith J. S. , Woodall J. M. , Pettit D.
Published: July 2002

High performance photoconductive switches are demonstrated using a molecular beam epitaxy grown graded layer of InxGa1−xAs to make an ohmic contact to semi-insultating GaAs. It is found that the graded layer results in a peak signal amplitude that is more than a factor of 2 larger than what is obtained using conventional alloyed AuGeNi contacts.
Miniaturized total-reflection ferroelectric liquid-crystal electro-optic switch
Authors: Bawa S. S. , Biradar A. M. , Saxena K. , Chandra Subhas
Published: July 2002

A total internal reflection (TIR) ferroelectric liquid-crystal optical switch has been described using a larger value of birefringence and higher extraordinary refractive index (ne) of FLC than the refractive index (ng) of glass. The off-axis orientations of voltage selected optic axes directions provide a convenient matching of transmission and reflection characteristics. This enables one to decrease the critical angle for TIR. The electro-optic switch can be miniaturized and a large switch array (1×4; 4×4) architecture is feasible.
Novel modulation method for bidirectional transmissions on a single optical fiber
Authors: Goedgebuer J. P. , Hamel A.
Published: July 2002

A novel method of simultaneous two-way transmission over one fiber is described. Only one optical source is required. Transmission of signals exhibiting the same modulation speeds along the two directions of a single fiber is demonstrated using a coherence-modulated light source. The first experimental results of a version of this system operating over 1 km of a multimode fiber are presented.
Electron/hole energy shifts in narrow GaAs/AlAs quantum wells: Inhomogeneous broadening due to half-monolayer well-width fluctuations
Authors: Fu W. S. , Olbright G. R. , Owyoung A. , Klem J. F. , Biefeld R. M. , Hadley G. R.
Published: July 2002

We use absorption, photoluminescence, and x-ray diffraction spectra of two GaAs/AlAs type II heterostructures, whose GaAs well thicknesses differ by ≂4 Å to obtain a direct measurement of the individual quantum confinement energy shifts of the heavy hole, light hole, and electron levels. We find that excitonic absorption linewidths are dominated by inhomogeneous broadening that arises from half-monolayer well-thickness fluctuations. For self-consistency these shifts are applied to separately determine the individual valence-band and conduction-band offsets.
Ultraclean, integrated processing of thermal oxide structures
Authors: Offenberg M. , Liehr M. , Rubloff G. W. , Holloway K.
Published: July 2002

Ultraclean, integrated metal-oxide-semiconductor oxide fabrication has been investigated for the first time by combining (i) surface cleaning in inert ambient, (ii) wafer transfer through ultrahigh vacuum, and (iii) thermal oxidation in an ultrahigh vacuum-based reactor. Device quality oxide structures are obtained (evidenced by dielectric breakdown characteristics for Al gate capacitors) under suitable conditions, while under other circumstances chemical mechanisms severely degrade electrical performance; even in ultraclean environments, impurity-related Si etching reactions before oxidation degrade oxide quality, but this can be avoided by appropriate use of passivating oxide films which prevent roughness associated with etching.
Magnetization of (100) Cu-Ni, (100) Cu-Co, and (100) Ni-Co superlattices deposited on silicon using a Cu seed layer
Authors: Chang Chin-An
Published: July 2002

The magnetization of (100)Cu-Ni, (100)Cu-Co, and (100)Ni-Co superlattices has been studied. The structures were grown on the (100)Cu/Si substrates, with the (100)Cu epitaxially grown on the (100)Si as the seed. The (100)oriented superlattices show different magnetization curves from the (111) structures and from bulk (100)Ni and Co films. A much enhanced magnetization is observed for the (100)Cu-Ni superlattice with the field perpendicular to the film plane. The remanence is larger than that for the field parallel to the film plane. Negative remanence and coercivity are observed for the (100)Cu-Co and Ni-Co structures. The magnetization curve for the (100)Ni-Co superlattice is further shown to resemble a superposition of the Cu-Ni and Cu-Co ones. Upon heating the Ni-Co structure to 400 °C to consume more Ni than Co, a magnetization curve similar to that of the Cu-Co one is observed.
Mechanisms for the emission of visible light from GaAs field-effect transistors
Authors: Zappe Hans P. , As Donat J.
Published: July 2002

The emission of visible light from GaAs metal-semiconductor field-effect transistors under high electric field conditions is studied in detail in order to learn more about the luminescence mechanism. The electroluminescence spectrum is examined for energies both greater and less than the energy gap. It is seen that the form of the subgap spectrum can be explained by a Bremsstrahlung mechanism. However, the prominence of a voltage-dependent band-gap peak indicates that recombination processes also contribute to visible photon emission. A strongly polarized component of electroluminescence further substantiates the existence of radiative elastic collisions (Bremsstrahlung) and may provide insights into the scattering behavior of electrons in the channel.
Extremely thin and defect-free Si-on-insulator fabrication by tunnel epitaxy
Authors: Ogura Atsushi , Fujimoto Yuki
Published: July 2002

A novel technique for extremely thin and defect-free Si-on-insulator (SOI) fabrication, called tunnel epitaxy, is demonstrated. A lateral/vertical growth ratio of 20 is achieved with precisely controlled SOI film thickness, where the minimum thickness for the fabricated SOI is 0.05 μm. No defect was observed in the fabricated SOI with 〈001〉 lateral growth direction. The growth front is a flat (001) plane. The lateral growth length is limited to 1–2 μm by tunnel clogging, due to poly-Si grain growth. The tunnel epitaxy, however, has a potential for larger area SOI fabrication, because the fabricated tunnel length is 10 μm.
Studies of silicon photoelectrochemical cells under high injection conditions
Authors: Kumar Amit , Lewis Nathan S.
Published: July 2002

The behavior of Si/CH3OH-dimethylferrocene+/0 junctions has been investigated under high injection conditions. Open circuit voltages of (626±5) mV were obtained at short circuit photocurrent densities of 20 mA/cm2 for samples with an n+-diffused back region, point contacts on the back surface, and with a base of thickness 390 μm and a 1 ms hole lifetime. The diode quality factor and recombination current density were 1.8±0.1 and (2.6±1.5)×10−8 A/cm2, respectively. These data are consistent with recombination dominated by the base and back contact regions, and not at the Si/CH3OH interface.
Quantitative characterization of physical processes during nanometer surface modification
Authors: McBride S. E. , Wetsel G. C.
Published: July 2002

A scanning tunneling microscope developed for microscopy, spectroscopy, and lithography has been used for modification of metallic surfaces exposed to the atmosphere. We report here the first quantitative characterization of a submicrometer area of a metallic sample before and after pulsing the tip-sample voltage using both tunneling spectroscopy determination of the apparent mean barrier potential (φ) and imaging of the area in constant tunneling current mode. The before and after images show that the form of the created features ranges from craters to mounds. The current wave form recorded during a surface modification is indicative of the form of the feature. Diminution of the contamination layer often associated with surfaces exposed to the atmosphere is inferred from the values of φ before and after modification. Analysis of the results indicates that the observed features were caused by high electric fields and not by high temperatures.
Mode locking and frequency tuning of a laser diode array in an extended cavity with a photorefractive phase conjugate mirror
Authors: Segev Mordechai , Ophir Yoav , Fischer Baruch , Eisenstein Gadi
Published: July 2002

We demonstrate active mode locking and a tunable narrow spectrum under cw conditions in an extended cavity laser which uses an AlGaAs/GaAs array gain medium and an external feedback from a self-pumped photorefractive phase conjugate mirror. The mirror ensures self-aligned, spatially matched feedback. The mode-locked pulses are 92 ps wide. The tuning, obtained by an intracavity grating, has a range of 70 Å under cw conditions.
Dual-side contact formation on isolated diamond films
Authors: Engemann J. , Keller H. , Reinhard D. K. , Huang B. , Asmussen J.
Published: July 2002

A method is described for transferring deposited diamond films to a second substrate, thereby providing access to the diamond film back surface and also allowing post-deposition contact formation to both surfaces of the film. The availability of both sides of the diamond film allows increased experimental control and flexibility for investigation of electrical properties and contact phenomena. The films are deposited in a microwave plasma disk reactor onto silicon substrates and transferred to epoxy substrates. Also presented is a comparison of the roughness of the top and bottom film surfaces, a Raman spectrum of the transferred film, and current-voltage characteristics of samples with dual-side contacts.
Use of black diamond-like carbon films as a contrast enhancement layer for liquid-crystal displays
Authors: Singh B. , McClelland S. , Tams F. , Halon B. , Mesker O. , Furst D.
Published: July 2002

We report development of single-layer, highly durable, pinhole-free, abrasion-resistant, chemically inert ‘‘black coating’’ suitable for use as a contrast enhancement layer for liquid- crystal display devices. The single layer is a diamond-like carbon coating that has a high extinction coefficient and appears black due to optical absorption. The optical transmittance is less than 2% over the visible spectrum, and the reflectance is about 20%. Furthermore, this coating is easy to deposit onto large-area substrates at high deposition rates. The coating is sufficiently durable, electrically insulating, and chemically compatible with liquid-crystal display materials. Its hardness exceeds that of SiC (9+ on Mohs scale), and it is resistant to abrasion and most common solvents and acids. It exhibits good adhesion to glass, silicon, metal, and oxide substrates. Films of this material have been used to provide an increased contrast enhancement ratio in liquid-crystal displays. Details on the synthesis of these films are presented. Also, data on the optical and mechanical properties of these films as well as their use as contrast enhancement layers for liquid-crystal displays are presented.
Behavior of charged particles in an electron cyclotron resonance plasma chemical vapor deposition reactor
Authors: Nakayama Yoshikazu , Kondoh Mitsuru , Hitsuishi Kohji , Zhang Mei , Kawamura Takao
Published: July 2002

This letter presents the behavior of electrons and ions in an electron cyclotron resonance (ECR) plasma chemical vapor deposition (CVD) reactor. The reactor consists of an ECR chamber with a hydrogen plasma and a CVD chamber into which a source gas of SiH4is fed. It is found that electrons and ions of H+ extracted from the ECR chamber by a divergent magnetic field move along the magnetolines of force and play respective roles in the production of the film precursor from SiH4 and in the relaxation of the silicon network. The precursor for films on the substrate perpendicular to the magnetic flux is mainly produced on the growing surface.
Photoluminescence of quantum well structures with modulated layers grown by an alternating source supply
Authors: Hashimoto A. , Sugiyama N. , Tamura M.
Published: July 2002

The photoluminescence (PL) spectra from modulated quantum well structures were observed. The modulated quantum well structure comprised a 4 monolayer (ML) modulated layer and an 18 ML GaAs layer between AlAs barrier layers. The modulated layer was grown by incorporating As into a Ga and Al mixture on an AlAs surface. The main peak energy of the PL spectra at 77 K showed a growth temperature dependence; a remarkable red shfit of the main peak energy was observed for samples grown at low temperature. The red shift of the PL peak energy indicates an increase in the effective width of the GaAs well. A rearrangement model of Ga and Al atoms on the AlAs surface during growth with As incorporation into the Ga and Al mixture is proposed to explain the growth temperature dependence of the PL peak energy.
Anomalies of hypersonic velocity and attenuation in vinylidene fluoride-trifluoroethylene copolymer from Brillouin scattering
Authors: Liu Zhimin , Schmidt V. Hugo
Published: July 2002

The hypersonic behavior of a vinylidene fluoride and trifluoroethylene (70/30 mol %) copolymer has been investigated by Brillouin scattering without using index matching liquid. Both the glass and ferroelectric transitions are clearly seen in the acoustic behavior. The home-prepared sample has excellent optical properties and let us obtain sound attenuation information in the temperature range of 23–123 °C, which another investigator did not discuss because of the bad optical properties of the sample surface. Anomalies of sound attenuation near the transition point have been observed.
Low-threshold vertical cavity surface-emitting lasers with metallic reflectors
Authors: Schubert E. F. , Tu L. W. , Kopf R. F. , Zydzik G. J. , Deppe D. G.
Published: July 2002

Continuous-wave room-temperature operation is reported for the first time of vertical cavity current injection semiconductor lasers with a metallic reflector. The GaAs/(AlGa)As lasers have low-threshold currents of 8 mA for 8-μm-diam contacts and threshold current densities of 9.5 kA/cm2. Single longitudinal mode and bimodal operation are obtained for short and long Fabry–Perot étalons, respectively. The spectral width of the single-mode laser line is 0.1 Å. The laser structures have a very small series resistance which results in a voltage drop of 1.8 V along the diodes at lasing threshold.
Polar optic phonon and Γ→L intervalley scattering times in GaAs from steady-state hot-electron luminescence spectroscopy
Authors: Hackenberg W. , Fasol G.
Published: July 2002

We deduce the Γ→L intervalley and polar optic phonon scattering times of hot electrons in bulk GaAs from cw hot (e,A0) luminescence spectra at low excitation densities and their dependence on electron kinetic energy. We obtain the lifetime broadening due to these two processes from comparison with line shape calculations using a 16×16 k⋅p Hamiltonian, a full integration over k space, and a dipole model for the optical matrix elements. We find for the LO-phonon emission time τLO=(132±10)fs. The threshold for Γ→L scattering is determined as 330±10 meV, above which a distinct decrease in total lifetime is observed. Γ→L scattering times of 150–200 fs are deduced, and we discuss a corresponding deformation potential.
GaInAs/GaAs thermally actuated optical switch
Authors: Partain L. D. , Schultz J. C. , Virshup G. F. , Ladle Ristow M.
Published: July 2002

A Ga0.8In0.2As/GaAs thermally actuated optical switch has been demonstrated for unpolarized 1.08 μm light. Its measured on:off contrast ratio of 4.7 was produced electrically by changing the applied voltage from 0 to 3.2 V on a device with a 2.25-μm-thick Ga0.8In0.2As active layer. The ‘‘on’’ insertion loss was 3.8 dB. The on:off change in Ga0.8In0.2As absorption coefficient was 6660 cm−1. The switching current density was 9.7 A/cm2. The thermal switching energy can be supplied optically for an all-optical switch.
Low-threshold surface-emitting laser diodes with distributed Bragg reflectors and current blocking layers
Authors: Shimada M. , Asaka T. , Yamasaki Y. , Iwano H. , Ogura M. , Mukai S.
Published: July 2002

AlGaAs/GaAs surface-emitting laser diodes (SELDs) with distributed Bragg reflectors (DBRs) and current blocking layers are fabricated with the combination of a two-step epitaxial growth and the reactive ion beam etching (RIBE) technique. An Al0.1Ga0.9As/Al0.7Ga0.3As multilayer and an amorphous silicon (a-Si)/silicon dioxide (SiO2) multilayer are employed for the lower and upper mirrors, respectively. The active region has a 5×5 μm or 4 μm φ area and a 0.8 μm thickness. The minimum threshold current is 3.3 mA under pulsed condition and 4.1 mA under continuous wave (cw) operation at 12 °C with junction-side-up configuration. Stable single longitudinal mode is observed, and far-field pattern (FFP) indicates higher transverse mode operation.
In situ etching depth monitoring for reactive ion etching of InGaAs(P)/InP heterostructures by ellipsometry
Authors: Müller Roland
Published: July 2002

In situ ellipsometry at a wavelength of 1300 nm is used to control the etching depth in InGaAs(P)/InP heterostructures. A rotating analyzer ellipsometer, adapted to a parallel-plate reactor for reactive ion etching (RIE), monitors the decreasing layer thickness during the dry etching process. The momentary etching depth is determined with an accuracy of ±10 nm. Using a methane/hydrogen gas mixture for RIE a characteristic surface modification of the semiconductor material is observed.
Picosecond on-off switching using a pair of picosecond-on/nanosecond-off GaAs étalons
Authors: Lowry C. W. , Gibbs H. M. , Pon R. M. , Khitrova G.
Published: July 2002

An architectural approach that decreases the pair on-off time to much less than the individual device recovery time is presented. Two GaAs Fabry–Perot étalons, each having a 30 ns recovery time, were connected in series, defining a logic function with a fast turn-on time and a fast turn-off time. Either of two data pulses, spaced 40 ps apart, was extracted by appropriately delaying a pair of switching pulses spaced 40 ps apart. This approach has application to data generation, multiplexing and demultiplexing, self-routing, and bit permutation.
Optical properties of SnOx thin films: Theory and experiment
Authors: Stjerna B. , Granqvist C. G.
Published: July 2002

Transparent and conducting SnOx thin films were made by reactive rf magnetron sputtering of Sn in Ar+O2 onto unheated glass. Optical and electrical properties were reconciled with a quantitative model for wide band-gap semiconductors. The theory is based on heavy n doping by doubly ionized oxygen vacancies and ionized impurity scattering of the free electrons.
Critical current enhancement in multilayered Y1Ba2Cu3O7−y/Y1Ba2(Cu1−xNix)O7−y structures
Authors: Witanachchi S. , Lee S. Y. , Song L. W. , Kao Y. H. , Shaw D. T.
Published: July 2002

Multilayers of YBaCuO superconductors and Ni-doped YBaCuO superconductors have been grown by the laser ablation technique to study the flux pinning properties of the nonmagnetic/magnetic superconducting heterostructures. Even though Ni doping depressed the superconducting properties of the single layer films, when sandwiched between high quality YBaCuO films, the composite showed high critical temperatures. Three-layer and five-layer structures of the YBaCuO/YBaCuNiO system become superconducting around 87 K when the doped layer thickness was below 100 Å. Three-layer structures grown on ZrO2(100) showed critical current densities of 3×106 A/cm2 at 77 K, which is about three times larger than the reported results in the literature. Epitaxial layer growth between the two superconductors was indicated by x-ray diffraction measurements, which showed complete c-axis orientation with full width at half maximum of 0.45° in a (006) line scan. Behavior of the critical current up to 0.85 T and temperatures down to 66 K has been studied. Critical current densities close to 4.5×106 A/cm2 in 0.85 T fields perpendicular to the films have been obtained at 67 K.
New family of high Tc superconductors in the (Tl1−x
M
x)Sr2(Ca1−yYy)Cu2O7−δ system (M=IVA and VA elements)
Authors: Liu R. S. , Zhou W. , Edwards P. P.
Published: July 2002

A new family of high Tc superconductors with superconducting transition temperatures ranging from 40 to 100 K have been synthesized in the (Tl1−xMx)Sr2 (Ca1−yYy)Cu2O7−δ (M=Ti, Zr, Hf, V, Nb, and Ta) system. Here, we use as an example, vanadium and yttrium substitution into the thallium and calcium sites, respectively, in the parent compound TlSr2CaCu2O7 to demonstrate the substitutional chemistry, crystal structure, and superconductivity for these new superconductors.
Observation of solid-state amorphization in the immiscible system Cu-Ta
Authors: Sakurai Kenji , Yamada Yuh , Ito Masahisa , Lee Chung Hyo , Fukunaga Toshiharu , Mizutani Uichiro
Published: July 2002

The Cu-Ta system has been known to be immiscible and never amorphized by the conventional rapid quenching technique. The possibility of solid-state amorphization of Cu30 Ta70 during mechanical alloying (MA) was examined by the local structure observation using extended x-ray absorption fine structure (EXAFS). It was found that long-range order around Cu and Ta atoms gradually disappeared as a result of MA. These results are also important to an understanding of the reaction mechanism of amorphization during MA.
Effect of oxidation gases on the formation of Bi2Sr2CuO6 thin films
Authors: Kanai Masaki , Horiuchi Ken , Kawai Tomoji , Kawai Shichio
Published: July 2002

Three kinds of oxidation gases, O2, N2O, and NO2, have been used during the deposition of Bi2Sr2CuO6 thin films, and the effect of the gases on the film formation has been compared. Ambient N2O with substrate irradiation by ArF excimer laser is effective for lowering the substrate temperature to form an as-grown film. The as-grown film formed in N2O, however, has a higher resistivity due to the lower oxygen concentration in the film. The mixed gas of N2O and O2 gives the best result. NO2 is very effective for film formation under low-pressure conditions, and makes it possible to form a crystallized as-grown film at such a low pressure of 1×10−4 Torr even in a conventional laser ablation experiment.
Critical current density of strained multilayer thin films of Nd1.83Ce0.17CuOx/YBa2Cu3O7−δ
Authors: Gross R. , Gupta A. , Olsson E. , Segmüller A. , Koren G.
Published: July 2002

The superconducting transport properties of strained multilayer thin films of YBa2Cu3O7−δ/ Nd1.83Ce0.17CuOx, grown heteroepitaxially by laser ablation deposition, are reported. For individual layer thicknesses below a critical layer thickness of about 250 Å, coherency strain removes the orthorhombic distortion in the YBa2Cu3O7−δ layers and makes them twin-free. Zero-field critical current densities as high as 1.1×107 A/cm2 at 77 K have been measured for the YBa2Cu3O7−δ layers. Flux pinning energies at zero temperature and zero magnetic field in the range of 80–140 meV have been found.
Magnetization hysteresis and flux pinning in twinned and untwinned YBa2Cu3O7−δ single crystals
Authors: Welp U. , Kwok W. K. , Crabtree G. W. , Vandervoort K. G. , Liu J. Z.
Published: July 2002

Measurements of the magnetization hysteresis of the same crystal in the twinned and untwinned state reveal that pinning due to twinning planes may contribute a substantial, anisotropic fraction of the observed critical currents. A linear scaling between magnetization hysteresis and sample dimension shows that the twinned and untwinned crystal does not exhibit any subgranular effects.
Mode locking of laser diodes by picosecond optical pulse synchronous pumping
Authors: Kawaguchi Hitoshi , Iwata Hideyuki , Tan-no Naohiro
Published: July 2002

Short optical pulse generation from an external-cavity laser diode (LD) by optical pulse pumping has been investigated for the first time. An optical pulse train (pulse duration ∼40 ps) generated by a gain-switched LD was injected into a LD with an external cavity (slave LD) which was biased just below the laser threshold. The wavelength of the injected optical pulse was chosen to be slightly shorter than that of the slave LD. When the repetition rate of the optical injection pulse was nearly equal to the round trip time of the external cavity, the slave LD showed stable mode locking with the shorter pulse duration (∼22 ps) than that of the pumping pulse. At both the upper and lower repetition rates, the pulse duration of the slave LD also became shorter than that of the pumping pulse.
Strained-layer multiple quantum well distributed Bragg reflector lasers with a fast monitoring photodiode
Authors: Koren U. , Miller B. I. , Young M. G. , Chien M. , Gnauck A. H. , Magill P. D. , Woodward S. L. , Burrus C. A.
Published: July 2002

We describe a photonic integrated circuit composed of a distributed Bragg reflector laser and a fast monitoring photodiode operating at 1.54 μm wavelength. The integrated waveguide photodiode has a 3 dB bandwidth of 2 GHz with 1.2 mA/mW responsivity. We demonstrate ‘‘on chip’’ monitoring of a digitally modulated laser signal at 2 Gbit/s.
Photon-assisted resonant tunneling through variably spaced superlattice energy filters
Authors: Larsson A. , Borenstain S. I. , Jonsson B. , Andersson I. , Westin J. , Andersson T. G.
Published: July 2002

We report on the observation of photon-assisted resonant tunneling in a multiple quantum well structure composed of doped quantum wells separated by variably spaced superlattice energy filters. Electrons confined in the quantum wells are excited to the second quantized state by intersubband absorption of incident infrared radiation and are subsequently emitted through the filters under appropriate bias conditions. This is manifested by a distinct peak, with an associated negative differential photoconductance, in the photocurrent versus bias voltage characteristic at low temperatures.
Analysis of pseudomorphic GaAs/InGaAs/AlGaAs modulation-doped field-effect transistor structures by secondary-ion mass spectrometry and ion channeling
Authors: Chan K. T. , Kirschbaum C. L. , Yu K. M.
Published: July 2002

Secondary-ion mass spectrometry has been used to analyze the Al and In depth profiles in pseudomorphic GaAs/InGaAs/AlGaAs modulation-doped field-effect transistor structures. Surface segregation of In was found on the upper interface of the strained InGaAs layer under a moderate growth temperature of 510 °C. The segregation effect was found to be suppressed when the As4 overpressure was doubled. Ion channeling measurements are capable of differentiating the coherency of the strained InGaAs layer in the samples studied. A correlation was found between the coherency of the layer and its electrical transport property.
Experimental measurement of bulk and edge generation in Al0.4Ga0.6As PiN structures
Authors: Neudeck P. G. , Cooper J. A. , Melloch M. R.
Published: July 2002

A study of reverse-bias leakage due to thermal generation in Al0.4Ga0.6As PiN junctions was conducted using the charge recovery transient technique on PiNiP storage capacitors. The relative importance of bulk generation and generation at the etched device periphery is documented, and the temperature dependence of both leakage mechanisms is presented. The experimental data suggest that the majority of bulk generation occurs at centers energetically near the middle of the band gap. In contrast, the temperature performance of the perimeter generation rate suggests that it is governed by surface states whose energy is 0.5 eV above or below midgap.
Modeling superconductor degradation using magnetic levitation
Authors: Sriram M. A. , Ponce Laura , Murr L. E.
Published: July 2002

Corrosion of YBa2Cu3O7−x pellets has been studied using magnetic levitation. Pellets compressed at green compaction pressures of 120–200 MPa were exposed to water and air and the levitation heights were measured over a period of more than a month. A model based on diffusion as a rate-controlling step has been proposed. Levitation height normalized with respect to the initial levitation height was used as the modeling parameter. The experiments indicate that the normalized levitation height decreased with time up to a certain level called the saturation leviation, beyond which there is no change in the levitation height. Samples in air degraded faster than samples in water. The initial period of degradation before saturation fits the proposed model well and therefore appears to be diffusion controlled. The saturation levitation shows a dependence on the green compaction pressure. It has been proposed that corrosion (degrading reactions) is due to open porosities which are closed by the reaction products, thus causing a saturation in the levitation height dependent on the porosities.
Transmission electron microscopy investigation of the recrystallization of an amorphous layer in Si+-implanted silicon
Authors: Nabert G. , Habermeier H.-U.
Published: July 2002

The recrystallization of a buried amorphous layer in p-type (111) float zone silicon implanted at room temperature with a dose of 2×1015 cm−2 100 keV Si+ ions is studied between room temperature and 1200 °C by transmission electron microscopy. A 150-nm-thick amorphous layer is created by ion implantation below a 25-nm-thick surface layer, which remains crystalline. Below the amorphous layer small defects are observed, which form well-resolved dislocation loops after annealing at higher temperatures. At 700 °C, one nearly defect-free layer grows from the microcrystalline surface layer up to a depth of 40 nm and another nearly defect-free layer grows from the crystalline-amorphous interface up to a thickness of 25 nm. Between these two layers the sample recrystallizes by forming a 110-nm-thick layer containing a high density of microtwin lamellae. In the top layer up to a depth of 40 nm some stacking-fault tetrahedra are formed by epitaxial regrowth from the surface. After annealing at higher temperatures only the sizes of the structural defects increase.
Fabrication of wedge-shaped silicon field emitters with nm-scale radii
Authors: Liu D. , Ravi T. S. , Gmitter T. , Chen C. Y. , Marcus R. B. , Chin K.
Published: July 2002

Wedge-shaped field emitters may have some advantages over conical tip emitters as electron sources in vacuum microelectronic devices. A method has been developed to make atomically sharp wedge-shaped silicon through use of dry etching and dry oxidation. Transmission electron microscopy studies show that silicon wedge emitters can be made with wedge radius and angle at 1 nm and 60°, respectively, by repeated oxidation in oxygen at 950 °C.  
Epitaxial growth and crystallographic analyses of (Pb, La)TiO3 thin films by a multi-ion-beam reactive cosputtering technique
Authors: Xiao Dingquan , Xiao Zhili , Zhu Jumu , Wan Derui , Guo Huachong , Xie Bizheng , Yuan Hong
Published: July 2002

Epitaxial thin films of lead titanate(PbTiO3) and lanthanium-modified lead titanate [(Pb, La)TiO3] have been successfully grown on (0001) sapphire substrates for the first time by the recently developed multi-ion-beam reactive cosputtering (MIBRECS) technique. The deposition processes and the thin-film analyses studied by x-ray diffraction (XRD), electron probe x-ray microanalyzer (EPMA), and reflection high-energy electron diffraction (RHEED) are reported. The experiments show that the multi-ion-beam reactive cosputtering process is very suitable for deposition of multicomponent oxide thin films with high reproducibility.
Parallel and perpendicular hole transport in heterostructures with high AlAs mole-fraction barriers
Authors: Kiehl R. A. , Shtrikman Hadas , Yates J.
Published: July 2002

The potential advantages of high-barrier quantum well structures for p-channel field-effect transistors are investigated in measurements of parallel and perpendicular hole transport in high AlAs mole fraction heterostructures. The hole mobility in GaAs and (In,Ga)As quantum wells confined by (Al,Ga)As barriers and current-voltage characteristics of metal-(Al,Ga)As/GaAs diodes are examined in structures with AlAs mole fractions as high as 0.85. Hole mobilities of nearly 5000 cm2/V s with a density of 1.0×1012 cm−2 are obtained at 77 K and reductions in perpendicular currents by several orders-of-magnitude are obtained at 300 and 77 K.
Possibility of a new phase transition in 7×7 structure on clean Si(111) surfaces
Authors: Ishizaka Akitoshi , Doi Takahisa , Ichikawa Masakazu
Published: July 2002

Temperature dependences of reflection high-energy electron diffraction intensities are measured for Si(111)-7×7 clean surfaces. The temperature dependences of diffraction intensities for both 7×7 super spots and specular spots change above 830 K. These show the possibility of two states in the 7×7 structure. The high-temperature phase of the 7×7 structure is stable up to 1090 K, following the well known phase transition between 7×7 and 1×1 structures.
Infrared photoconductor fabricated with a molecular beam epitaxially grown CdTe/HgCdTe heterostructure
Authors: Yuan Shixin , He Li , Yu Jinbi , Yu Meifang , Qiao Yiming , Zhu Jianmei
Published: July 2002

Infrared photoconductors fabricated with a CdTe/Hg0.64Cd0.36Te abrupt heterostructure grown on a GaAs substrate by molecular beam epitaxy are described here for the first time. The growth procedure, device fabrication, and measurement results are described. The results show that the devices have relatively high detectivity and uniformity. The observed enhancement in device performance attributed essentially to the large reduction in interface states and surface contamination by a subsequent growth of a lattice-matched semi-insulating CdTe epilayer for the passivation of HgCdTe surface.