bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of recombination processes in multiple narrow asymmetric coupled quantum wells based on the dependence of photoluminescence on laser intensity
Authors: Ding Y. J. , Guo C. L. , Khurgin J. B. , Law K.-K. , Merz J. L.
Published: July 2002

Continuous-wave intensity-dependent photoluminescence spectra of multiple narrow asymmetric coupled quantum wells at room temperature have been measured. At low laser intensity, the total photoluminescence intensity is primarily proportional to the square of the laser intensity due to dominant nonradiative recombination of free carriers at nearly saturated interface traps. At high laser intensity, however, the total photoluminescence intensity approaches a level proportional to the laser intensity due to radiative recombination of free carriers. Based on this transition behavior, which has been observed for the first time to the best of our knowledge, and our simple theory, the transition intensity, the nonradiative decay time of the carriers, and the intensity-dependent carrier density and photoluminescence quantum efficiency have been determined.
Optically induced intersubband absorption in biased double quantum wells
Authors: Berger V. , Vodjdani N. , Vinter B. , Costard E. , Böckenhoff E.
Published: July 2002

We present a new all-optical infrared modulator, which is based on biased double quantum wells. The electric field separates the photogenerated electrons and holes and hence increases their lifetime τ: the photoinduced infrared absorption is therefore enhanced. An increase of the modulation efficiency by two or three orders of magnitude is predicted and an enhancement of at least 20 has been observed at 4 K. At high pump power (150 mW), the linear dependence of the absorption as a function of applied bias is observed and discussed. We have also observed photoinduced intersubband transitions in the valence band in both infrared polarizations.
Surface defect inspection of spherical objects by the resonant sphere technique
Authors: Hsieh C. P. , Khuri-Yakub B. T.
Published: July 2002

Ceramic materials, such as silicon nitride and silicon carbide, are important because of their high mechanical strength at high temperature and in nonlubricative environments. The weakness of these materials lies in their brittleness. Stress concentration caused by the existence of surface or subsurface cracks can lead to the total mechanical failure of parts. In this letter, we describe the application of the resonant-sphere technique to perform nondestructive evaluation of ceramic bearing balls. The technique had been shown to be capable of measuring various material properties, such as Vs (shear wave velocity) and ν (Poisson’s ratio). We use phase and amplitude measurements to simplify the evaluation of various resonance quality factors (Q), and we present, for the first time, the use of a resonance technique to propagate and detect surface waves on a sphere. We also show a decrease in Q for surface-wave modes due to the existence of surface cracks.
Intensity oscillations in reflection high-energy electron diffraction during disilane gas source molecular beam epitaxy
Authors: Hiroi Masayuki , Koyama Kazuhisa , Tatsumi Toru , Hirayama Hiroyuki
Published: July 2002

Reflection high-energy electron diffraction (RHEED) intensity oscillations during growth in disilane gas source Si molecular beam epitaxy (MBE) on Si(100) and (111) surfaces were observed under low substrate temperature and high disilane flow rate conditions. As has been observed in solid source Si MBE, these oscillations included periods corresponding to periods for monolayer and bilayer growth. On Si(100) surfaces, growth rate, which was estimated from the periods of the oscillations, was limited by a reaction process whose activation energy was 47 kcal/mol. This rate limitation is thought to stem from hydrogen desorption from monohydride phase on the Si(100). On Si(111) surfaces, oscillations in specular beam intensity were clearly observed. Although clear oscillations in the 7×7 diffraction spots could not be observed because of intensity weakness of the fractional order spots under disilane exposure. At high disilane flow rates, 7×7 diffraction spots almost disappeared and only fundamental spots were observed. The fundamental 1×1 RHEED pattern also indicated monohydride structure on Si(111) surface during the growth.
Spatial modes of a concentric-circle-grating surface-emitting, AlGaAs/GaAs quantum well semiconductor laser
Authors: Erdogan T. , King O. , Wicks G. W. , Hall D. G. , Dennis C. L. , Rooks M. J.
Published: July 2002

We demonstrate the fabrication and operation of an AlGaAs surface-emitting semiconductor laser, grown by molecular-beam epitaxy, that incorporates a circularly symmetric grating of period Λ=0.25 μm fabricated using electron-beam lithography. Azimuthal variations in the grating linewidth have a significant impact on the spatial modes of the laser.
Ambient gas effects on debris formed during KrF laser ablation of polyimide
Authors: Küper Stephan , Brannon James
Published: July 2002

The surface debris that results from KrF excimer laser ablation of polyimide has been investigated as a function of the pressure, and atomic or molecular weight of several ambient gases: H2, He, Ne, air, Ar, Kr, and Xe. A linear relation between the measured debris radius and the inverse third root of the ambient pressure was found to exist, consistent with the predictions of blast wave theory. No measurable debris could be observed using helium or hydrogen gases up to 1 atm, similar to previous reports on helium. The derived value of the blast energy, equal to about 5% of the incident pulse energy, was used to estimate a nascent blast pressure of approximately 150 atm. By making the assumption that surface debris will form if the ablation fragments are confined in a ‘‘small’’ volume for a ‘‘sufficient’’ time, conclusions from blast wave theory suggest how to decrease the amount of generated debris.
Dynamic charge storage in 6H silicon carbide
Authors: Gardner C. T. , Cooper J. A. , Melloch M. R. , Palmour J. W. , Carter C. H.
Published: July 2002

pn-junction storage capacitors have been fabricated in 6H silicon carbide. The charge decay is dominated by surface generation at the mesa edges, and the storage time strongly depends on the method of surface passivation. Charge recovery is thermally activated. Devices passivated by dry oxidation and by wet oxidation exhibit activation energies of 0.66 and 1.48 eV, respectively. As a figure of merit, extrapolation of the dry-oxide data gives a room-temperature storage time of 106 s, while extrapolation of the wet-oxide data gives a room-temperature storage time of 1014 s.
Structure of GaAs=GaSb incoherent interface after epitaxial growth
Authors: Bourret A. , Fuoss P. H.
Published: July 2002

The structure of GaAs=GaSb(001) incoherent interface has been studied by grazing incidence x-ray scattering. The interface is periodic with a square array of edge dislocations. It is shown that the interface is nonplanar with 2–4 GaAs monolayers protruding in the GaSb epilayer at the dislocation core. This corrugated interface does not increase the strain energy by a large factor. Two possible mechanisms are suggested for the interface formation of large misfit epitactic growth: a stress induced mechanism or the presence of an ordered intermediate 2D layer.
Experimental and theoretical surface acoustic wave analysis of thin-film lipid multilayers
Authors: Bianco Bruno , Cambiaso Andrea , Paradiso Rita , Tommasi Tullio
Published: July 2002

The leaky surface acoustic wave (LSAW) velocity of thin films of lipids on a glass substrate has been investigated, using a reflection acoustic microscope at a frequency of 1 GHz. Multilayers of ω-tricosenoic acid (28–220 nm in depth), collected with the Langmuir–Blodgett technique have been deposited on silanized glass. V(z) curves have been measured, and the LSAW velocity has been calculated from them. The results point out that the velocity decreases linearly as the lipid-layer thickness increases. A theory is also presented, which gives a linear dependence between the LSAW velocity and the layer thickness.
Novel seeding method for the growth of polycrystalline Si films with hemispherical grains
Authors: Sakai Akira , Tatsumi Toru
Published: July 2002

A novel method for the fabrication of hemispherical-grained polycrystalline Si (HSG-Si) films, which is applicable to high capacitance storage electrodes for dynamic random access memory (DRAM) cells, has been developed. This technique consists of first seeding a clean amorphous-Si (a-Si) surface with crystalline Si nuclei at an elevated substrate temperature using Si molecular-beam deposition. Upon subsequent isothermal annealing under ultrahigh vacuum conditions, it was found that the Si microcrystals act as nuclei for the formation of HSG-Si. Precise control of the grain size distribution of the HSG-Si structure was successfully demonstrated, which is key to the possible application of this material to the next generation of DRAM devices.
Use of Zn doping for tuning of the operating temperature of a bolometer based on the high T
c superconductor thin film of Y1Ba2Cu3O7−δ
Authors: Ogale S. B. , Vedawyas M. , Bendre G. S. T. , Kanetkar S. M.
Published: July 2002

A simple microbridge type of bolometer configuration is fabricated using high quality Zn doped Y1Ba2Cu3O7−δ superconducting thin film. It is shown that Zn doping lowers the Tco without affecting the transition width significantly. This feature is found to be useful in tuning the operating temperature of the bolometer to 77 K or to another convenient value.
Growth of the infinite layer phase of Sr1−xNdxCuO2 by laser ablation
Authors: Niu Chunming , Lieber Charles M.
Published: July 2002

Pulsed laser deposition (PLD) has been used to prepare tetragonal Sr1−xNdxCuO2 thin films that have the parent structure of the high Tc copper oxide superconductors. Low-temperature deposition using a single source target has been shown to kinetically trap c-axis oriented, infinite layer Sr1−xNdxCuO2 materials on 〈100〉SrTiO3 substrates. In addition, electrical measurements indicate that neodymium substitution drives the system from an insulating to a weakly metallic state.
Large and small signal dynamics of vertical cavity surface emitting lasers
Authors: Tauber D. , Wang G. , Geels R. S. , Bowers J. E. , Coldren L. A.
Published: July 2002

Continuous wave relative intensity noise (RIN) measurements and pulsed electrical gain switching measurements were performed on vertical cavity surface emitting lasers in order to investigate the high speed potential of these devices. A high resonance frequency–square root of power coefficient of 7.6 GHz/√mW was obtained from the RIN measurements. The gain switched pulses exhibited very fast relaxation oscillations with a maximum observed relaxation oscillation frequency of 71 GHz.
Photoluminescence study of radiative recombination in porous silicon
Authors: Wang C. , Perz J. M. , Gaspari F. , Plumb M. , Zukotynski S.
Published: July 2002

Photoluminescence in porous Si films has been studied in the temperature range from 15 to 250 K. The luminescence peak is found to shift to higher frequency with increasing temperature. Above 100 K the luminescence intensity shows strong thermal quenching with an activation energy of 60 meV. Below 100 K photoluminescence decay data obtained using quadrature frequency resolved spectroscopy are characterized by a single lifetime of about 300 μs. At 250 K several time constants are seen to contribute to the luminescence decay. We attribute the very intense low-temperature photoluminescence to recombination at localized extrinsic centers.
n-p-(p+-n+)-n AlyGa1−yAs-GaAs-InxGa1−xAs quantum-well laser with p+-n+ GaAs-InGaAs tunnel contact on n-GaAs
Authors: Sugg A. R. , Chen E. I. , Richard T. A. , Maranowski S. A. , Holonyak N.
Published: July 2002

Data are presented on the growth, by metalorganic chemical vapor deposition, and fabrication of n-p (n-up) AlGaAs-GaAs-InGaAs quantum-well heterostructure lasers using a p+-n+ GaAs-InGaAs reverse-biased tunnel junction to contact the n-type GaAs substrate. The lasers operate continuously at 300 K with a threshold of ∼37 mA for a 10-μm-wide native-oxide-defined gain-guided stripe (cavity length ∼375 μm). Comparison tunnel junctions similar to those used in the diode lasers are also fabricated and exhibit low reverse-biased series resistances (∼2.2 Ω, area ∼4.5×larger).
Thin-film CdS/CdTe solar cell with 15.8% efficiency
Authors: Britt J. , Ferekides C.
Published: July 2002

This letter describes the fabrication and characteristics of high-efficiency thin-film CdS/CdTe heterojunction solar cells. CdS films have been prepared by chemical bath deposition and p-CdTe films have been deposited by close-spaced sublimation. A CdS/CdTe solar cell of greater than 1 cm2 area with an AM1.5 efficiency of 15.8% is reported.
Average energy deposited per atom: A universal parameter for describing ion-assisted film growth?
Authors: Petrov I. , Adibi F. , Greene J. E. , Hultman L. , Sundgren J.-E.
Published: July 2002

The average energy deposited per atom, 〈Ed〉=Ei(Ji/JMe), where Ei is the ion energy and Ji/JMe is the ratio of the accelerated-ion to deposited-thermal-particle fluxes incident at the growing film, has been shown to be one of a set of parameters useful for describing the effects of low-energy ion irradiation on film microstructure during ion-assisted deposition. Recently, however, 〈Ed〉 has often been treated as if it were a fundamental, or universal, parameter. We have carried out experiments in which Ei (20–100 eV) and Ji/JMe (1–10) were varied independently during the deposition, at constant temperature, of polycrystalline Ti0.5Al0.5N films onto amorphous SiO2 substrates by ultrahigh vacuum reactive magnetron sputtering in pure nitrogen. Ion-irradiation-induced changes in film microstructure, texture, phase composition, and nitrogen-to-metal ratio were found to follow distinctly different mechanistic pathways depending upon whether Ei or Ji/JMe was varied, resulting in quite different properties for the same value of 〈Ed〉. Thus, 〈Ed〉 is clearly not a universal parameter.
Optical properties of Si/Si0.87Ge0.13 multiple quantum well wires
Authors: Tang Y. S. , Wilkinson C. D. W. , Sotomayor Torres C. M. , Smith D. W. , Whall T. E. , Parker E. H. C.
Published: July 2002

Nanometer-scale wires cut into a Si/Si0.87Ge0.13 multiple quantum well structure were fabricated and characterized by using photoluminescence and photoreflectance at temperatures between 4 and 20 K. It was found that, in addition to a low-energy broadband emission at around 0.8 eV and other features normally observable in photoluminescence measurements, fabrication process induced strain relaxation and enhanced electron-hole droplets emission together with a new feature at 1.131 eV at 4 K were observed. The latter was further identified as a transition related to impurities located at the Si/Si0.87Ge0.13 heterointerfaces.
Metalorganic vapor phase epitaxy of GaP1−xNx alloys on GaP
Authors: Miyoshi S. , Yaguchi H. , Onabe K. , Ito R. , Shiraki Y.
Published: July 2002

We demonstrate a successful growth of GaP1−xNx alloys on GaP by metalorganic vapor phase epitaxy (MOVPE). This alloy system is predicted to have an extremely large miscibility gap, ranging from x=0.0000003 to 0.9999997 at 700 °C. However, metastable alloys (x≤0.04) have been obtained at the growth temperature of 630–700 °C. We focused on the growth condition dependence of solid composition (x). The nitrogen incorporation increases with decreasing growth temperature. It also increases with increasing growth rate, possibly due to nonequilibrium circumstances in the MOVPE growth. Low-temperature photoluminescence (PL) measurements show that the band gap of GaP1−xNx shifts to lower energy with increasing x.
Spatially confined nickel disilicide formation at 400 °C on ion implantation preamorphized silicon
Authors: Erokhin Yu. N. , Hong F. , Pramanick S. , Rozgonyi G. A. , Patnaik B. K. , White C. W.
Published: July 2002

The localized formation of continuous silicide layers via solid state reaction of nickel atoms with ion implantation preamorphized silicon is described. Ni films 12 nm thick were evaporated on 65 nm deep amorphized surface layers. The silicidation reaction was induced by two stage thermal annealing at 360 and 400 °C, well below the solid phase epitaxial regrowth temperature for amorphous Si and the normal NiSi2 formation temperature. Rutherford backscattering with channeling, XTEM, and four-point-probe measurements were used to determine the structure, interfacial morphology, composition, and resistivity of the silicide films. After the lower temperature annealing stage a continuous layer of NiSi2 is formed with an underlying residual amorphous region located above the crystalline substrate. During a second annealing the residual amorphous areas recrystallize epitaxially with respect to the substrate via lateral silicide growth. The process leads to formation of a continuous 35 nm thick nickel disilicide layer completely confined within the original amorphous region. Silicide resistivity was 44 μΩ cm. The process may be viewed as a low-temperature process enhancement to self-aligned silicide (SALICIDE) technology since silicide growth proceeds only on preamorphized areas of the silicon substrate.
Wide range wavelength conversion experiments using a side-injection light-controlled bistable laser diode
Authors: Tsuda H. , Nonaka K. , Hirabayashi K. , Uenohara H. , Iwamura H. , Kurokawa T.
Published: July 2002

Wavelength conversion has been demonstrated using a distributed feedback side-injection light-controlled bistable laser diode with an input wavelength range of 1496–1597 nm. Insensitivity to input light wavelength and a large separation ratio of output from input (more than 30 dB) are advantageous for a wavelength converter.
SiO2/Si(100) interface studied by Al Kα x-ray and synchrotron radiation photoelectron spectroscopy
Authors: Lu Z. H. , Graham M. J. , Jiang D. T. , Tan K. H.
Published: July 2002

Both synchrotron radiation photoemission spectroscopy (PES) and Al Kα photoelectron spectroscopy (XPS) are used to determine the suboxide distribution at SiO2/Si (100) interfaces. High resolution PES measurements clearly resolved various suboxides with chemical shifts of 0.97, 1.80, and 2.60 eV for Si+1, Si+2, and Si+3, respectively. A total of 9.3×1014 atoms cm−2 of suboxide is found by PES measurements while only 4.2×1014 atoms cm−2 is measured by XPS on the same sample. This discrepancy is neither caused, as previously believed, by a difference in SiO2/Si (100) quality nor by a difference in methodology in data analysis. The possible factors, e.g., electron mean-free path and photoionization cross section, which contribute to the difference between PES and XPS data, are considered.
Growth of InP epitaxial layers by rapid thermal low pressure metalorganic chemical vapor deposition, using tertiarybutylphosphine
Authors: Katz A. , Feingold A. , Moriya N. , Nakahara S. , Abernathy C. R. , Pearton S. J. , El-Roy A. , Geva M. , Baiocchi F. A. , Luther L. C. , Lane E.
Published: July 2002

High-quality InP layers with low impurity backgrounds have been grown by means of the rapid thermal low pressure metalorganic chemical vapor deposition technique, using tertiarybutylphosphine as the phosphorus source. The films were grown at a P:In ratio of 75 or higher, temperatures between 500 and 525 °C, a pressure of 2 Torr and growth rates as high as 2 nm/s. The undoped films were defect-free with exhibited featureless morphologies, and minimum backscattering yields (Xmin) as low as 3.1%, measured by ion channeling. The electrical quality of the films (Nd=2.5×1016 cm−3, μ=4200 cm2/V s) was also excellent.
Observation of open-ended stacking fault tetrahedra in Si0.85Ge0.15 grown on V-grooved (001) Si and planar (11¯1) Si substrates
Authors: Howard David J. , Bailey William E. , Paine David C.
Published: July 2002

A new strain relief mechanism was observed in lattice mismatched epitaxial layers grown on (11¯1) surfaces. Thin films of Si0.85Ge0.15 were epitaxilly grown by rapid thermal chemical vapor deposition on patterned (001) and planar (11¯1) Si substrates. The (001) Si substrates were lithographically patterned and anisotropically etched to produce a line pattern of V-shaped grooves running in the [11¯0] direction where the walls of the grooves were the {111} crystal planes. Cross-section and plan-view transmission electron microscopy studies revealed the presence of open-ended stacking fault tetrahedra in Si0.85Ge0.15 grown both on (11¯1) Si wafers and the {111} side walls of the patterned (001) Si wafers. No defects were observed in the (001) portions of the films grown on nonplanar substrates.
30% external quantum efficiency from surface textured, thin-film light-emitting diodes
Authors: Schnitzer I. , Yablonovitch E. , Caneau C. , Gmitter T. J. , Scherer A.
Published: July 2002

There is a significant gap between the internal efficiency of light-emitting diodes (LEDs) and their external efficiency. The reason for this shortfall is the narrow escape cone for light in high refractive index semiconductors. We have found that by separating thin-film LEDs from their substrates (by epitaxial lift-off, for example), it is much easier for light to escape from the LED structure and thereby avoid absorption. Moreover, by nanotexturing the thin-film surface using ‘‘natural lithography,’’ the light ray dynamics becomes chaotic, and the optical phase-space distribution becomes ‘‘ergodic,’’ allowing even more of the light to find the escape cone. We have demonstrated 30% external efficiency in GaAs LEDs employing these principles.
Infrared radiometry for monitoring temperature of photoresist during dry etching
Authors: Dankner Yair , Simhony S. , Shneider Y. , Katzir A.
Published: July 2002

The temperature of a thin photoresist layer on a silicon wafer was measured in situ and controlled during a dry etching process by using a silver halide optical fiber noncontact thermometer. We were able to monitor and control the photoresist temperature to within 2 °C of a present value. This may be used to prevent cross linking and deterioration of the photoresist during dry processing of semiconductors.
Observation of 1.798 μm intersubband transition in InGaAs/AlAs pseudomorphic quantum well heterostructures
Authors: Hirayama Y. , Smet J. H. , Peng L. H. , Fonstad C. G. , Ippen E. P.
Published: July 2002

The well-width dependence of intersubband transition energies in InGaAs/AlAs pseudomorphic quantum well structures has been studied, and the shortest intersubband wavelength reported to date, 1.798 μm, has been observed for 6 monolayer wells. Both transverse electric and transverse magnetic optical polarizations are absorbed, with an energy splitting of 67 meV between them.
Influence of silver cladding on the formation and alignment of the (Bi2−xPbx)Sr2Ca2Cu3O10+δ phase
Authors: Luo J. S. , Merchant N. , Maroni V. A. , Riley G. N. , Carter W. L.
Published: July 2002

Cross-section transmission electron microscopy was used to investigate the interaction of silver with (Bi,Pb)-Sr-Ca-Cu-O phases during the formation of (Bi2−xPbx)Sr2Ca2Cu3O10+δ (Bi-2223) in a silver-sheathed wire containing a powder composed of (Bi,Pb)2Sr2CaCu2O8+δ (Bi-2212) plus second phases. Observations of the interfacial regions of samples quenched at different stages of conversion revealed that (1) Bi-2212 is initially in direct contact with silver, with the (001) planes parallel to the interface; (2) an amorphous layer between Bi-2212 and silver appears during the induction period that precedes the conversion reaction; and (3) Bi-2223 is detected at the silver/powder interface hundreds of minutes before it begins to appear in regions of the powder away from the interface. The implications of these results are presented and discussed.
On the origin of photoluminescence in spark-eroded (porous) silicon
Authors: Hummel R. E. , Morrone A. , Ludwig M. , Chang S.-S.
Published: July 2002

Photoluminescence measurements and high-resolution transmission electron microscopy studies on spark-treated (porous) silicon have been performed. Contrary to suggestions put forward by others, it has been found that spark erosion does not yield structures comparable to those obtained for irradiated, that is, damaged silica. Instead, evidence is given that spark treatment of single crystalline silicon wafers produces randomly oriented nanometer-sized silicon crystallites surrounded by a SiO2 matrix. This configuration is believed to be responsible for the observed room temperature visible photoluminescence.
Existence of persistent photoconductivity in C70
Authors: Hamed A. , Rasmussen H. , Hor P. H.
Published: July 2002

We have observed a persistent photoconductivity effect (PPC) in C70 films well above room temperature. The effect, which consists of a metastable increase in dark conductivity caused by brief exposure to light, exhibits characteristics very similar to the PPC previously observed in C60 films. These characteristics include a magnitude of the effect independent of the light exposure temperature, the existence of a PPC even at 520 K, and the inability of subgap illumination to create or quench PPC. A common origin for the PPC in C70 and C60 seems plausible, and may be related to the distortions the fullerene molecules experience when charged.
Maskless InP wire formation on planar GaAs substrates
Authors: Ahopelto J. , Lezec H. , Ochiai Y. , Usui A. , Sakaki H.
Published: July 2002

Maskless growth of InP wires on planar (100)GaAs substrates by hydride vapor phase epitaxy is demonstrated. The selectivity of the growth was achieved by using focused ion beam to modify locally the substrate surface. The nucleation of deposited InP is enhanced on the exposed areas leading to the selectivity. Continuous 200 μm long wires with submicron cross-sectional dimensions were obtained in a single growth process. Cross-sectional transmission electron microscope micrographs show that the number of dislocations in the wires is relatively low, indicating the suitability of the present method for fabrication of nanoscale structures, e.g., quantum wires.
Subpicosecond switching in a current injected GaAs/AlGaAs multiple-quantum-well nonlinear directional coupler
Authors: Lee S. G. , McGinnis B. P. , Jin R. , Yumoto J. , Khitrova G. , Gibbs H. M. , Binder R. , Koch S. W. , Peyghambarian N.
Published: July 2002

We have demonstrated ultrafast switching behavior in a current injected GaAs/AlGaAs multiple-quantum-well nonlinear directional coupler at room temperature. The results show low crossover pulse energy (10 pJ) and full recovery within 1 ps.
Formation of β-SiC nanocrystals by the relaxation of Si1−yCy random alloy layers
Authors: Powell A. R. , LeGoues F. K. , Iyer S. S.
Published: July 2002

In this work we consider the relaxation behavior of Si1−yCy random alloys grown epitaxially on Si, with 0.005≳y≳0.05. The Si1−yCy layers are under tensile strain as grown and at annealing temperatures below 900 °C the relaxation of strain is achieved by dislocation formation, in a fashion similar to SiGe relaxation. However, at temperatures in excess of 900 °C the C, which at lower temperatures remained in substitutional sites, precipitates out of the lattice, this removes all of the tensile strain from the layer. The nature of this precipitation is to form single crystal, nanoparticles of β-SiC with the same lattice orientation as the Si lattice in which they are created. These nanoparticles are of uniform diameter (3±1 nm for y=0.005 Si1−yCy material) and randomly dispersed throughout the original Si1−yCy region. This ability to produce nanocrystals of wide band-gap material within the Si matrix should enable the exploration of mesoscopic phenomena. The nanoparticles once formed also block the movement of dislocations, thus locking in any strain fields associated with the dislocations.
Direct high-resolution electron microscopy observations of sputtered a-axis oriented YBa2Cu3O7 films prepared by a self-template method on SrTiO3 substrates
Authors: Wen J. G. , Mahajan S. , Ito W. , Morishita T. , Koshizuka N.
Published: July 2002

A-axis oriented YBa2Cu3O7 films grown on a SrTiO3 substrate with and without the template layer have been studied by high-resolution electron microscopy. The self-template layer was found to be very effective to obtain highly crystalline a-axis oriented YBa2Cu3O7 film. A disordered cubic perovskite structure with a lattice parameter of 3.85 Å was found in the template layer which could be a good seed for further growth of a-axis film. In the film without the self-template layer, YBa4Cu3Ox cubic perovskite with lattice parameter 4.08 Å was observed to have grown at the interface as an island growth. Moreover, some faulted c-axis film at the very beginning of the template layer was observed even at the rather lower deposition temperature of 640 °C.
Scanning tunneling microscopy using a ZnO whisker tip
Authors: Yoshida T. , Naito H. , Okuda M. , Ehara S. , Takagi T. , Kusumoto O. , Kado H. , Yokoyama K. , Tohda T.
Published: July 2002

A zinc oxide (ZnO) whisker crystal has been examined as a probing tip for scanning tunneling microscopy (STM). Atomic resolution images of the surfaces of highly oriented pyrolytic graphite and Si(111)-7×7 structures are successfully observed by STM using a ZnO whisker tip, demonstrating that the ZnO whisker crystal is applicable to a STM tip.
Highly tetrahedral, diamond-like amorphous hydrogenated carbon prepared from a plasma beam source
Authors: Weiler M. , Sattel S. , Jung K. , Ehrhardt H. , Veerasamy V. S. , Robertson J.
Published: July 2002

A highly tetrahedral, diamond-like form of hydrogenated amorphous carbon (a-C:H) with density of 2.9 g cm−3, sp3 fraction of 0.75, and hardness of 61 GPa, the highest values so far attained from a hydrocarbon source gas, has been deposited from acetylene in a novel plasma beam source. The ion energy for highest sp3 fraction is measured to be about 100 eV per C atom, similar to that for a-C, indicating that the subplantation deposition model of a-C also describes a-C:H.
Ultrafast carrier trapping and slow recombination in ion-bombarded silicon on sapphire measured via THz spectroscopy
Authors: Brorson Stuart D. , Zhang Jucheng , Keiding So/ren R.
Published: July 2002

We have performed two different types of femtosecond pump and probe measurements on THz transmitting antennas fabricated on ion-bombarded silicon-on-sapphire chips. We find evidence that the decay of the photoexcited current occurs on a time scale of less than 1 ps. Simultaneously, we observe unambiguous evidence of screening originating from carriers trapped in long-lived trap states. A simple model of carrier transport and screening in the presence of fast trapping and slow recombination is discussed.
Micrometer scale visualization of thermal waves by photoreflectance microscopy
Authors: Pottier L.
Published: July 2002

We propose a novel approach of photoreflectance microscopy that provides a direct visualization of the phase contour lines of the thermal wave. The method is applicable to (possibly heterogeneous) samples of mediocre polish. In a locally homogeneous region it yields the local thermal diffusivity.
Periodic pin array at the fluxon lattice scale in a high-field superconducting wire
Authors: Cooley L. D. , Lee P. J. , Larbalestier D. C. , O’Larey P. M.
Published: July 2002

A periodic pin array has been made at dimensions approaching the diameter and spacing of the fluxon cores in an ‘‘island’’-type of artificial pinning center superconducting composite wire. Gun-barrel drilling was used to precisely incorporate a hexagonal array of Nb 1.3 wt. % Ti pinning centers into an ingot of Nb 46.5 wt. % Ti, before extrusion and wire drawing. Transmission electron microscopy images showed little evidence of pin geometry alteration down to 100 nm pin diameter. At ∼30 nm effective pin diameter, the aspect ratio of the pins was 3–5, and the pin array retained its hexagonal geometry. Bulk pinning force curves had temperature-independent structure down to 15 nm effective pin diameter, suggestive of matching between fluxons and pins. Because of the uniform pin geometry, the maximum bulk pinning force exceeded that of the best conventional composites, even though the upper critical field and the volume fraction of pins were significantly lower.
Thermal stability of titanium hydride thin films
Authors: Chatbi H. , Vergnat M. , Marchal G.
Published: July 2002

The thermal stability of titanium hydride thin films prepared by reactive evaporation is reported. The release of hydrogen is monitored by the effusion method. The gas evolution spectrum shows two peaks corresponding to the hydrogen effusion from the titanium hydride phase and to the crystallographic transformation from fcc to hcp structure, respectively.
High modulation efficiency of intracavity contacted vertical cavity lasers
Authors: Scott J. W. , Thibeault B. J. , Mahon C. J. , Coldren L. A. , Peters F. H.
Published: July 2002

A very high current modulation efficiency of 5.7 GHz/√(mA) has been demonstrated in a low threshold (0.85 mA) InGaAs vertical-cavity surface-emitting laser. These top surface emission devices have been fabricated with intracavity contacts on semi-insulating substrates to realize their high speed potential. Data is presented for various laser diameters. Modulation bandwidths up to 9.3 GHz at a bias of only 4.5 mA have been measured for 7 μm diameter lasers. Derived parameters indicate that considerably higher bandwidths should be possible with better heat dissipation and modified cavity designs.
Femtosecond wave mixing experiments in ZnCdSe/ZnSe quantum wells
Authors: Kim D. S. , Fischer A. J. , Hays J. , Shan W. , Song J. J. , Eason D. B. , Ren J. , Schetzina J. F.
Published: July 2002

Extreme high order nonlinear diffracted signals are found in ZnCdSe/ZnSe quantum wells in two beam, self-diffraction geometry. Diffracted signals of all observed orders are shown to originate predominantly from excitonic resonances. Using four-wave mixing, an indication of hole-longitudinal optical phonon scattering between the heavy and the light hole states is found, and exciton-phonon interaction is studied.
Reaction induced texture of (Bi,Pb)2Sr2Ca2Cu3O10+δ /Ag composite conductors
Authors: Merchant N. , Luo J. S. , Maroni V. A. , Riley G. N. , Carter W. L.
Published: July 2002

A considerable body of evidence collected on silver-sheathed (Bi,Pb)2Sr2Ca2Cu3O10+δ  (Bi-2223/Ag) composite conductors heat treated without any additional rolling or pressing (beyond fabrication of the initial composite) has revealed that significant texturing of the Bi-2223 grains occurs as the Bi-2223 formation reaction takes place. During heat treatment, Bi-2223 is produced via a reaction between Bi-2212 and second phases in the core of the composite. As the Bi-2223 forms, it develops texture by what appears to be a grain growth mechanism. These concurrent processes ultimately result in a well-textured, single-phase conductor even when no additional rolling or pressing is done to the initial composite. This observation raises important questions about the relative contributions of the heat treatment and deformation steps to texture development during conventional oxide-powder-in-tube processing of Bi-2223/Ag composite conductors.
Terahertz four-wave mixing in semiconductor optical amplifiers: Experiment and theory
Authors: Uskov A. , Mo/rk J. , Mark J. , Tatham M. C. , Sherlock G.
Published: July 2002

Highly nondegenerate four-wave mixing processes in bulk semiconductor optical amplifiers are analyzed by comparing experimental data at detuning frequencies up to 3 THz with numerical calculations based on semiclassical density-matrix equations. Carrier heating and spectral holeburning are found to be dominant in mediating wave mixing in the THz region and lead to comparable contributions to nonlinear gain suppression in semiconductor lasers.
Antenna-coupled high-T
c air-bridge microbolometer on silicon
Authors: Rice J. P. , Grossman E. N. , Rudman D. A.
Published: July 2002

An antenna-coupled high-Tc superconducting microbolometer on a silicon substrate, operating at infrared wavelengths, is described. This detector incorporates a silicon-micromachined yttria-stabilized zirconia air bridge at the feed of a planar lithographic antenna to simultaneously minimize the thermal conductance and the heat capacity of the bolometer. At an operating temperature of 87.4 K, the optical responsivity measured using a 300-K blackbody source over a 0.2–2.9 THz bandwidth is 2900 V/W, the optical noise-equivalent power (NEP) is 9×10−12 W/Hz1/2, and the time constant is <10 μs. This NEP is nearly a factor of 2 lower than the previous record for a liquid-nitrogen-cooled thermal detector, and the time constant is several orders of magnitude shorter.
Dominant photogenerated valley current in a double-barrier resonant-tunneling diode
Authors: Li H. S. , Chen L. P. , Chen Y. W. , Wang K. L. , Pan D. S. , Liu J. M.
Published: July 2002

Dominant photogenerated valley current has been observed in an optically-excited InGaAs/AlAs double-barrier resonant-tunneling diode. The photogenerated valley current in the resonant-tunneling diode varies with the optical power level. Under intense illumination, the photogenerated valley current increases to such a high level that it becomes dominant over the peak current. As a consequence, the negative differential resistance of the device is removed. The observed photogenerated valley current is described by photogenerating electron-hole pairs in the depletion region adjacent to the double-barrier structure. Transient behavior of the photogenerated carriers is also studied. The observed dominant photogenerated valley current may have useful applications.
Spectral modulation of luminescence of strained Si1−xGex/Si quantum wells in a vertical cavity with air/Si and Si/SiO2 interface mirrors
Authors: Fukatsu S. , Nayak D. K. , Shiraki Y.
Published: July 2002

Integration of strained Si1−xGex/Si quantum wells (QWs) in a vertical cavity is demonstrated on a Si substrate with a buried-oxide using gas source Si molecular beam epitaxy. Spontaneous emission from the SiGe QW is found to be spectrally coupled to the longitudinal modes of a vertical cavity with buried oxide/Si and top Si/air interface mirrors, which is in excellent agreement with separate reflectance measurements. In addition, clear oscillations were observed in photoluminescence excitation spectra for photon energies even above the Si band gap, demonstrating cavity modulation of the incident light absorption.
Wet oxidation of AlAs grown by molecular beam epitaxy
Authors: Lee Yong-Soo , Lee Yong-Hyun , Lee Jung-Hee
Published: July 2002

A 1 μm thick n-type GaAs layer with Si doping density of 1×1017/cm3 and a 1000 Å thick undoped AlAs layer was subsequently grown by molecular beam epitaxy on the n+ GaAs substrate. To perform selective oxidation of the AlAs layer, the wafer was oxidized in N2 bubbled H2O vapor ambient at 370 °C, 400 °C, and 430 °C, each for 3 hours. It is found that the defect-free selective oxidation of AlAs is very critically dependent on oxidation temperature. Both GaAs and AlAs layers were oxidized at the oxidation temperature of 430 °C, and some defects were found by scanning electron microscopy (SEM) on the surface oxidized at 370 °C. Oxidation was, however, stopped at the AlAs/GaAs interface at the oxidation temperature of 400 °C, and no defects were found on the surface. By the slow ramp rate (5 mV/sec) high frequency (100 kHz) C-V measurement, the fixed charge density was estimated to be about 1×1011/cm2 for the metal-oxide-semiconductor (MOS) capacitor fabricated from the oxidized sample at 400 °C.
Theoretical performance of very long wavelength InAs/InxGa1−xSb superlattice based infrared detectors
Authors: Grein C. H. , Cruz H. , Flatté M. E. , Ehrenreich H.
Published: July 2002

Optimal detectivities of very long wavelength (11–19 μm) photovoltaic infrared detectors based on ideal InAs/InGaSb superlattices are calculated. Accurate K⋅p band structures are used to obtain radiative, electron–electron and hole–hole band-to-band Auger, and for the first time shallow acceptor level assisted Auger recombination rates for n-on-p photodiodes. The suppression of band-to-band Auger by ‘‘band gap engineering’’ is predicted to lead to improved background-limited operating temperatures just as it does in long-wave InAs/InGaSb infrared detectors.
High p-type doping of ZnSe using Li3N diffusion
Authors: Lim S. W. , Honda T. , Koyama F. , Iga K. , Inoue K. , Yanashima K. , Munekata H. , Kukimoto H.
Published: July 2002

We have achieved a highly doped p-type ZnSe layer using a Li3N diffusion technique. The hole concentration of the p-type ZnSe layer, grown on a GaAs substrate by metalorganic vapor phase epitaxy, reached a level as high as 1017 cm−3. With the diffusion temperature of 470 °C, the resistivity of the layer is as low as 0.4 Ω cm, with hole concentration p≳9×1017 cm−3 and hole mobility μp=17 cm2/V s. We made an ohmic contact by using this p+-type ZnSe as a contact layer for p-ZnSe epilayers.
Low resistance ohmic contacts on nitrogen ion bombarded InP
Authors: Ren F. , Pearton S. J. , Lothian J. R. , Chu S. N. G. , Chu W. K. , Wilson R. G. , Abernathy C. R. , Pei S. S.
Published: July 2002

Nonalloyed Ti/Pt/Au contacts deposited in situ onto nitrogen ion bombarded n-type InP show contact resistivities as low as 3.4×10−6 Ω cm2. Acceleration voltages of 100–300 V and exposure times of 3–11 min were used to remove InP native oxide and produce a shallow (≤300 Å) disordered donor layer on which ohmic contacts were deposited. Electron diffraction patterns matching those of polycrystalline InN were identified in this degenerately doped surface layer, which was further characterized by secondary ion mass spectrometry and ion channeling. Similar layers produced by Ar ion bombardment under the same conditions showed much higher contact resistivities (∼10−4 Ω cm2), indicating that the InN formation is beneficial for contact properties.
Organometallic vapor phase epitaxial growth of AlP/GaP monolayer superlattice using tertiarybutylphosphine
Authors: Wang Xue-Lun , Wakahara Akihiro , Sasaki Akio
Published: July 2002

The growth interruption time in the organometallic vapor phase epitaxial growth of AlP/GaP layers using tertiarybutylphosphine is optimized for the realization of an AlP/GaP monolayer superlattice. In the growth interruption, there exists an optimum time (2 s) beyond which the full width at half-maximum (FWHM) of the x-ray diffraction satellite peaks of an (AlP)5/GaP)5 superlattice becomes broader. The monolayer (AlP)1/(GaP)1 superlattice is realized for the first time in a AlP/GaP system. An average heterointerface roughness of as small as 0.12 Å is estimated from the FHWM of the (001) diffraction peak of the (AlP)1/(GaP)1 superlattice.
Fabrication of p-channel polycrystalline Si1−xGex thin-film transistors by ultrahigh vacuum chemical vapor deposition
Authors: Lin Horng-Chih , Jung Tze-Guei , Lin Hsiao-Yi , Chang Chun-Yen , Chen L. P.
Published: July 2002

In this report, we present a novel approach for fabricating polycrystalline silicon-germanium thin-film transistors at low temperatures (≤550 °C). A bottom gate configuration is used for this approach, and an i-Si1−xGex/i-Si/p+-Si1−yGey multilayer is deposited sequentially on the gate oxide using an ultra-high vacuum chemical vapor deposition technique. The i-Si1−xGex serves as the channel while the i-Si is used as a buffer layer for allowing p+-Si1−yGey to be etched selectively on. p-channel thin-film transistors with a field-effect mobility of 13 cm2/V s were achieved using this method, which is superior to those grown by low pressure chemical vapor deposition. Our results indicate that the deposition of poly-Si1−xGex/poly-Si multilayer structure would be a promising way for polycrystalline thin-film device applications.
Epitaxial growth of C60 and KI(001) surface
Authors: Yanagi H. , Sasaki T.
Published: July 2002

Epitaxial growth of C60 is observed for vacuum-deposited crystals on the KI(001) cleavage surface. When the KI surface is kept at 240 °C and the deposition rate is controlled to be less than a monolayer min−1 (∼0.5 nm min−1), rectangular platelike crystals of C60 grow epitaxially. Transmission electron micrographs and electron diffraction patterns of the crystals exhibit that the (002) planes of the face-centered cubic C60 crystal orient in parallel to the KI(001) surface. This epitaxial orientation is explained in terms of thec(2×2) commensurate lattice matching.
Extraction of the minority carrier recombination lifetime from forward diode characteristics
Authors: Vanhellemont J. , Simoen E. , Claeys C.
Published: July 2002

A simple procedure is proposed to calculate the minority carrier recombination lifetime from forward diode I/V characteristics. By using diodes with strongly different perimeter to area ratio and by taking into account the diode ideality, more accurate lifetime values are obtained. The thus obtained values are in excellent agreement with the ones obtained from microwave absorption measurements of photoconductive decay as is illustrated on Czochralski substrates with different oxygen densities and pretreatments.
Efficient optical parametric generation in an organomineral crystal
Authors: Samuel I. D. W. , Villacampa B. , Josse D. , Khodja S. , Zyss J.
Published: July 2002

Organomineral crystals are engineered to combine the favorable properties of organic and inorganic materials. High gain parametric emission and amplification at telecommunications wavelengths are demonstrated in an organomineral crystal, 2-amino-5-nitropyridinium-dihydrogen phosphate. A novel angle-noncritical type-II phase-matching configuration is observed in parametric emission, and parametric amplification is demonstrated at 1.5 μm.
Stable phase locking in a two-cell ladder array of Josephson junctions
Authors: Larsen B. H. , Benz S. P.
Published: July 2002

The stability of the periodic solution of the two-cell ladder array has been numerically investigated in order to explore intrinsic phase-locking mechanisms relevant to arrays and stacked junction oscillators. In zero magnetic field the periodic in-phase solution of the system is neutrally stable. However, this solution is stable over a finite voltage range when an applied control current exceeds a critical value. The dependence upon system parameters of the boundaries of the stable range and the critical control current is investigated. Finally, the influence of the control current on the microwave power in a typical range of stability is calculated.
Determination of the intersubband lifetime in Si/SiGe quantum wells
Authors: Heiss W. , Gornik E. , Hertle H. , Murdin B. , Knippels G. M. H. , Langerak C. J. G. M. , Schäffler F. , Pidgeon C. R.
Published: July 2002

A direct pump and probe lifetime determination in the ps regime has been made in quantum wells of Si/Si1−xGex. We have used an rf linac-pumped free-electron laser to determine the relaxation time associated with intersubband absorption in Si/SiGe quantum wells with a subband separation smaller than the optical phonon energy. This measurement yields a lifetime of T1=30 ps.
TFTR vertical x-ray imaging system
Authors: Johnson L. C. , Bitter M. , Chouinard R. , von Goeler S. , Hill K. W. , Liew S.-L. , McGuire K. , Paré V. , Sauthoff N. R. , Young K. M.
Published: July 2002

A vertically viewing x-ray imaging system (XIS) has been designed to complement the existing 64-channel horizontal system on the tokamak fusion test reactor (TFTR) and enhance measurements of soft x-ray emissivity, plasma (major) radial position, and magnetohydrodynamic (MHD) phenomena. System parameters have been selected to provide adequate signal strength and spatial resolution while permitting a substantial size and cost reduction with respect to the horizontal system. The compact, helium filled x-ray camera employs four eight-channel silicon detector modules and views the plasma through a 3-mil-thick beryllium window, providing 6-cm position resolution at the center. An x-ray absorber foil changer permits energy selection to match the horizontal XIS. Lead and hydrogenous shielding reduce noise from thermonuclear neutrons and associated gamma rays.