bluuebunny/crossref_metadata_2025 huggingface dataset:
Improvement of the lasing performance of copper vapor laser by adding Sc atoms as energy donors
Authors: Kimura Hironobu , Chinen Masaru , Nayuki Takuya , Saitoh Hiroshi
Published: July 2002

The lasing performance of a copper vapor laser with a 60 mm diameter and 2000 mm discharge length has been improved by adding Sc atoms. As a typical result, a 28% increase of output power and electrical-optical conversion efficiency has been obtained. The result was qualitatively but reasonably interpreted as indicating that the upper laser level was enhanced by the collisional energy transfer from a response of Sc atoms to a resonance-excited state of Cu atoms.
Novel high temperature multilayer electrode-barrier structure for high-density ferroelectric memories
Authors: Bhatt H. D. , Desu S. B. , Vijay D. P. , Hwang Y. S. , Zhang X. , Nagata M. , Grill A.
Published: July 2002

This has been accomplished in the past using four/five separate electrode- and diffusion-barrier layers. In this letter, we report a novel Pt–Rh–Ox/Pt–Rh/Pt–Rh–Ox electrode-barrier structure which acts as an electrode as well as a diffusion barrier for integration of the ferroelectric capacitors directly onto silicon deposited using an in situ reactive rf sputtering process. The electrodes have a smooth and fine grained microstructure and are excellent diffusion barriers between the PbZr0.53Ti0.47O3 (PZT) and Si substrate and exhibit good thermal stability up to very high processing temperatures of 700 °C. The ferroelectric (PZT) test capacitors using these electrode barriers grown directly on Si, show well saturated hysteresis loops with Pr and Ec of 16 μC/cm2 and 30–40 kV/cm, respectively. The capacitors exhibit no significant fatigue loss (<5%) up to 1011 cycles and have low leakage currents (2×10−8 A/cm2 at 100 kV/cm). These electrode barriers can be used to directly integrate the thin film capacitors on the source/drain of the transistors of the memory cell structure for accomplishing large scale integration.
Low-temperature nitridation of silicon surface using NH3-decomposed species in a catalytic chemical vapor deposition system
Authors: Izumi Akira , Matsumura Hideki
Published: July 2002

This letter reports a procedure for low-temperature nitridation of silicon surfaces using species produced by NH3 catalytic decomposition on heated tungsten in a catalytic chemical vapor deposition system. The surface of Si(100) was nitrided at temperatures as low as 200 °C. Silicon oxinitride films are obtained with a stoichiometry Si:N:O=1:0.9:0.3, a maximum thickness as high as 4.8 nm and an electrical breakdown field of 6 MV/cm.
Biaxial moduli of coherent Si1−xGex films on Si (001)
Authors: Floro J. A. , Chason E. , Lee S. R. , Petersen G. A.
Published: July 2002

The biaxial moduli of coherently strained Si1−xGex thin films have been determined over the composition range x=0.15–0.6 from independent measurements of film stress and strain. Our results indicate that use of the rule of mixtures to determine the strained-alloy elastic constants from the bulk values for pure Si and Ge is valid, and that higher-order elastic effects are relatively unimportant over this composition range.
Buried tunnel contact junction AlGaAs-GaAs-InGaAs quantum well heterostructure lasers with oxide-defined lateral currents
Authors: Wierer J. J. , Evans P. W. , Holonyak N.
Published: July 2002

Al x Ga 1−x As-GaAs-In y Ga 1−y As quantum well heterostructure (QWH) lasers with p+-n+ GaAs–InyGa1−yAs reverse-biased tunnel junctions (hole sources) located in the upper cladding of standard lasers and in oxide-defined cavities (requiring lateral bias currents) are demonstrated. The tunnel junctions, introduced to aid lateral current spreading, are grown at different distances from the waveguide active region in a standard QWH structure to determine first the effect of heavily doped tunnel layers on laser threshold currents. Other QWH laser crystals are oxidized to form oxide-aperture devices with, in addition, either a top confining oxide or a top and bottom oxide confining layer. Hole injection is provided between the oxide layers with the aid of the tunnel contact junction and lateral electron current. The buried tunnel contact junction is shown to be an effective method to make possible hole injection via a lateral electron current, with only a modest increase (a small penalty) in voltage drop and series resistance compared to standard devices.
Critical-current measurements in planar Josephson junctions
Authors: Rzchowski M. S. , Hinaus B. M.
Published: July 2002

The properties of planar high-temperature superconducting Josephson junctions are not entirely consistent with low Tc models. Some of these disparities may be intrinsic, related to the unusual superconducting properties of the electrodes, while others are due to the nonstandard planar geometry. By comparing experimental measurements of a 24° bicrystal substrate Josephson junction with a simple model of nonuniform current flow in a planar geometry, we show that several unusual properties can be explained as extrinsic. We show that nonuniform current feed in a planar geometry leads to a reduced critical current, an unchanged Meissner field Hco, and a power-law dependence of the critical current on Hco different from that expected in an overlap geometry.
Simultaneous mapping of bulk and surface recombination in silicon
Authors: Ostendorf Hans-Christoph , Endrös Arthur L.
Published: July 2002

A method is presented which allows a fast, nondestructive, and laterally resolved separation of bulk and surface recombination of silicon samples. The method works without any assumptions on the values of diffusion length and surface recombination velocity. No special sample processing is necessary prior to the measurement. An extended Monte Carlo based sensitivity analysis shows that diffusion lengths below the sample thickness can be determined with an accuracy better than ±20%. The detection range for the surface recombination velocity is 102–105 cm/s with a maximum uncertainty of a factor of 2. Experimental data are presented that prove the applicability of the new scheme.
The effects of different interfacial environments on the optical nonlinearity of nanometer-sized CdO organosol
Authors: Wu Xiaochun , Wang Rongyao , Zou Bingsuo , Wu Pengfei , Wang Li , Xu Jiren , Huang Wei
Published: July 2002

The third-order optical nonlinearity χ(3) of nanometer-sized CdO with different interfacial environments has been measured using the Z-scan technique. The real and imaginary parts of χ(3) at 800 nm have been determined to be: −1.55×10−16 m2/W and 0.91 cm/GW for CdO–CTAB (cetyltrimethyl ammonium bromide) organosol, and −6.97×10−16 m2/W and 8.64 cm/GW for CdO–DBS (dodecylbenzene sulfonate) organosol. Origins of the optical nonlinearity and the effects of the interfacial conditions have been discussed. The optical Stark effect (OSE) and surface trapped states are the possible origins of the observed optical nonlinearity. The possible enhancement of optical nonlinearity of nanoparticles by intentional interfacial modification is suggested.
Influence of silicon-wafer loading ambients in an oxidation furnace on the gate oxide degradation due to organic contamination
Authors: Saga Koichiro , Hattori Takeshi
Published: July 2002

Organic contaminants adsorbed on the surface of silicon wafers do not always cause the degradation of gate-oxide integrity (GOI) degradation but very little information is available on the ambient atmosphere when wafers are loaded in an oxidation furnace. It has been found in this work that GOI is degraded when wafers having organic contamination are loaded in a nitrogen atmosphere, but that GOI degradation does not occur when the wafers are loaded in an oxygen-containing ambient. In a high-temperature nitrogen atmosphere, carbon remains in silicon dioxides, while in an oxygen-containing ambient, the organic contaminants will be oxidatively degraded and evaporated, so carbon does not remain on the surface.
Influence of carrier relaxation on the dynamics of stimulated emission in microcavity lasers
Authors: Hilpert M. , Klann H. , Hofmann M. , Ellmers C. , Oestreich M. , Schneider H. C. , Jahnke F. , Koch S. W. , Rühle W. W. , Wolf H. D. , Bernklau D. , Riechert H.
Published: July 2002

The influence of carrier relaxation on the emission dynamics of a semiconductor microcavity laser is investigated using femtosecond optical excitation. For moderate excitation intensities, the dynamics of the output laser pulse becomes significantly slower when the photon energy of the pump laser is tuned from the quantum well band-gap energy towards higher energies. Theoretical calculations reproduce this trend only if the interaction-induced dephasing of the polarization driven by the pump pulse, the formation, and relaxation of the nonequilibrium carrier distribution as well as the chirp of the excitation pulse are taken into account. Additionally, band-structure effects such as excitation of light holes influence the thermalization dynamics and lead to discontinuities in the general trend.
Recombination characteristics of minority carriers near the AlxOy/GaAs interface using the light beam induced current technique
Authors: Gebretsadik H. , Zhang K. , Kamath K. , Zhang X. , Bhattacharya P.
Published: July 2002

The light beam induced current (LBIC) technique was used to characterize the interface formed by the wet oxidation of AlAs and AlxGa1−xAs (x=0.98 and 0.95). LBIC scans were used to calculate the diffusion lengths of minority carriers both in the bulk and near these interfaces; and the corresponding interface recombination velocities were estimated. The interface recombination velocity at the oxide/semiconductor interface is 3.13×105 cm/s for AlAs, and 1.90×104 cm/s for Al0.98Ga0.02As. It is found that the addition of gallium in the AlAs can significantly improve this property.
Chemically assisted ion beam etching of submicron features in GaSb
Authors: Nagy G. , Ahmad R. U. , Levy M. , Osgood R. M. , Manfra M. J. , Turner G. W.
Published: July 2002

We describe the use of chemically assisted ion beam etching to realize smooth, highly anisotropic features in GaSb. The measured etch rates are comparable to those of GaAs, and are fitted to a model that assumes the formation of trichloride etch product species.
Homoepitaxy of 6H and 4H SiC on nonplanar substrates
Authors: Nordell N. , Karlsson S. , Konstantinov A. O.
Published: July 2002

Growth by vapor phase epitaxy around stripe mesas and in trenches formed by reactive ion etch on 6H and 4H SiC substrates has been investigated. The mesas were aligned with the low index 〈112̄0〉 and 〈11̄00〉 directions, as well as with the high index 〈1,1+∛,2+∛¯,0〉 directions, in order to reveal and study the growth habit. It was found that a low C:Si ratio gave a smooth growth and small differences in growth rate between lattice planes. A larger C:Si ratio gave more faceted growth, both limited by surface kinetics and surface diffusion, and the growth rate was 10% lower in the [11̄00] direction and 10% higher in the [112̄0] direction, than on the substrate. Growth on mesas oriented parallel to the substrate off-orientation shows clear step-flow growth, while growth on mesas oriented perpendicular to the off-orientation reveals the singular (0001) plane, where islands are observed, which might indicate Stranski–Krastanov growth.
Formation of BN nanoarches: Possibly the key to cubic boron nitride film growth
Authors: Collazo-Davila C. , Bengu E. , Leslie C. , Marks L. D.
Published: July 2002

The formation of epitaxial nanotubes (nanoarches) on the surface of hexagonal BN (h-BN) during electron irradiation is reported. In addition to implications in terms of understanding fullerene based structures, we suggest that these act as the nucleation sites for cubic BN (c-BN) growth and may lead to improved film growth. We also report a strong dependence upon the microscope vacuum, which may be critical in understanding irreproducibility in film growth.
Stabilization of two diode laser wavelengths using photorefractive gratings
Authors: Yang Changxi , Yokoyama S. , Honda T. , Seta K.
Published: July 2002

We propose to demonstrate a method of stabilizing the wavelengths of two diode lasers through the use of two photorefractive volume gratings. The two photorefractive gratings recorded at a visible line from an argon ion laser in one LiNbO3 crystal are designed to be Bragg matched for the counterpropagating reflections at infrared wavelengths. The two diode lasers are stabilized at the center wavelengths of the counterpropagating reflections of the two gratings. The stabilized wavelengths and the synthetic wavelength exhibit good short- and long-term stabilities. By using photorefractive crystal, we can effectively control the separation of the stabilized wavelengths. The thermal stability of the photorefractive gratings and the thermal stability of the synthetic wavelength are discussed.
Heterostructure optoelectronic switch with lightcontrollable S-shaped negative differential resistance
Authors: Guo Der-Feng
Published: July 2002

A heterostructure optoelectronic switch, grown by molecular beam epitaxy, has been fabricated. Owing to the carrier confinement and avalanche multiplication in the transport mechanism, S-shaped negative-differential-resistance performances are observed in the current–voltage (I–V) characteristics. The device shows a flexible optical function related to the potential barrier height and breakdown voltage controllable by incident light. The dependence of the I–V characteristics on illumination is attributed to the carrier confinement effect in the device operation.
A novel self-consistent simulator for current-density–voltage characteristics of semiconductor field emitters
Authors: DasGupta A. , Arslan D. , Sigurdardottir A. , Hartnagel H. L.
Published: July 2002

An efficient and reliable simulator has been developed which solves the Poisson, continuity, and Schrödinger equations self-consistently to obtain the current-density–voltage characteristics of n-type semiconductor field emitters of electrons. The one-dimensional simulator takes into account the multidimensional geometry dependent-field variation near the semiconductor tip. The results obtained show the effects of the semiconductor parameters such as electron affinity, effective mass, mobility, and dielectric constant on the emission characteristics. The doping concentration is found to have a strong influence on the emitted current. The emission characteristics show deviations from linearity in a Fowler–Nordheim-type plot especially at high currents.
Carbon doping of InSb using CBr4 during growth by gas-source molecular beam epitaxy
Authors: Schoenfeld W. V. , Antonell M. J. , Abernathy C. R.
Published: July 2002

Carbon doping of epitaxial InSb films grown by gas-source molecular beam epitaxy was studied using carbon tetrabromide as the carbon dopant source. Carbon was found to be a p-type dopant in InSb, yielding the highest as-grown acceptor concentrations to date, up to mid 1020 cm−3 as deposited. Room temperature mobilities ranged from 35 to 90 cm2/V s depending upon doping level. The hole concentration was found to be relatively insensitive to growth temperature between 325 and 400 °C. Higher growth temperatures required higher Sb fluxes in order to maintain a constant hole concentration. Hole concentration increased linearly with increasing CBr4 up to 5×1020 cm−3. Further increase in the dopant flow reduced the hole concentration and mobility and produced polycrystalline material.
Liquid source metal–organic chemical-vapor deposition of high-quality YBa2Cu3O7−x films on polycrystalline silver substrates
Authors: Studebaker D. B. , Zhang J. , Marks T. J. , Wang Y. Y. , Dravid V. P. , Schindler J. L. , Kannewurf C. R.
Published: July 2002

High-temperature superconducting YBa2Cu3O7−x films were grown by liquid delivery metal–organic chemical-vapor deposition on silver-coated stainless-steel substrates. The films are highly c-axis oriented, have a Tc above 90 K, and exhibit a surface resistance of 110 μΩ at 77 K and 3 GHz.
Differential gain and threshold current of 1.3 μm tensile-strained InGaAsP multi quantum well buried-heterostructure lasers grown by metalorganic molecular beam epitaxial growth
Authors: Itoh Masayuki , Sugiura Hideo , Yasaka Hiroshi , Kondo Yasuhiro , Kishi Kenji , Fukuda Mitsuo , Itaya Yoshio
Published: July 2002

The laser characteristics of 1.3 μm tensile-strained InGaAsP/InP multi quantum well (MQW) lasers were studied. The tensile strain of well layers ranged from 0.5% to 1.8%. The level of the strain dependence of the threshold current shows that the threshold current decreases drastically with increase in the tensile strain from 0.5% to 1.3%, while it stays almost constant in the 1.45%–1.8% range. Among all the samples, the 1.3% tensile-strained MQW laser shows superior performance in terms of minimum threshold current and maximum differential gain (∂g/∂N). The 1.3% tensile strain is the optimum level for the tensile-strained MQW buried-heterostructure lasers.
Acoustically driven bound exciton lifetimes in CdS crystals
Authors: Korotchenkov O. A. , Goto T.
Published: July 2002

The exciton lifetime has been found to be repeatedly tuned by a MHz frequency acoustic driving without degradation of the optical properties of CdS crystals. The increase in the lifetime, up to 5%, followed by its ∼20% decrease has been detected with increasing driving amplitude. The lifetime increase can now be understood as due to reduction in the electron-hole wave function overlap in electric fields generated by the driving. The decrease in the recombination lifetime is ascribed to a widening of the potential well trapping the exciton due to variations in the local-crystal environment at acoustic driving.
Mixing effect of chelate complex and metal in organic light-emitting diodes
Authors: Lee Jae-Gyoung , Kim Youngkyoo , Jang Sei-Hum , Kwon Soon-Nam , Jeong Kwangho
Published: July 2002

Organic light-emitting diodes using thin film dispersing a hole transport material into a soluble polyimide as a hole transport layer and the sublimed molecular film of a chelate complex as an emissive layer were fabricated. In order to improve the injection of electrons into the emissive layer as well as the durability of devices, we have attempted mixing the chelate complex and metal between the emissive layer and the cathodic electrode. The charge injection of the device with the mixed layer was initialized at an applied voltage of 4.19 V. It was observed from the electroluminescent spectra that the oscillator strength was dramatically enhanced with the applied voltage.
1.3 μm photoresponsivity in Si-based Ge1−xCx photodiodes
Authors: Shao Xiaoping , Rommel S. L. , Orner B. A. , Feng H. , Dashiell M. W. , Troeger R. T. , Kolodzey J. , Berger Paul R. , Laursen Thomas
Published: July 2002

Ge 1−x C x /Si heterostructure photodiodes with nominal carbon percentages (0⩽x⩽0.02), which exceed the solubility limit, were grown by solid source molecular beam epitaxy on n-type (100) Si substrates. The p-Ge1−xCx/n-Si photodiodes were fabricated and tested. The p-Ge1−xCx/n-Si junction exhibits diode rectification with a reverse saturation current of about 10 pA/μm2 at −1 V and high reverse breakdown voltage, up to −80 V. A significant reduction in diode reverse leakage current was observed by adding C to Ge, but these effects saturated with more C. Photoresponsivity was observed from these Si-based p-Ge1−xCx/n-Si photodiodes at a wavelength of ⩾1.3 μm, compatible with fiber optic wavelengths. External quantum efficiency of these thin surface-normal photodetectors was measured up to 2.2%, which decreased as the carbon percentage was increased.
Determination of thermal parameters of microbolometers using a single electrical measurement
Authors: Gu X. , Karunasiri G. , Chen G. , Sridhar U. , Xu B.
Published: July 2002

Accurate determination of thermal parameters of microbolometer-based sensors is of considerable interest for many applications. The most important parameters are thermal time constant, heat capacitance and thermal conductance. In this work, we have developed a technique to measure all three quantities using a single electrical measurement. The method involves the measurement of time dependent output voltage of a balanced Wheatstone bridge containing a microbolometer under pulse bias condition. The validity of the approach is verified experimentally using metal–film microbolometers. The experimental results are in excellent agreement with the theoretical analysis of the measurement technique.
Thermally-actuated reflection mode asymmetric Fabry–Perot modulator utilizing a thin transparent elastomeric film
Authors: Rogers John A. , Schueller Olivier J. A. , Whitesides George M.
Published: July 2002

This letter describes a thermally-actuated reflection mode asymmetric Fabry–Perot modulator that consists of a thin transparent elastomeric film bounded by partially and highly reflecting metallic mirrors. The thickness of the transparent layer determines the intensity of light reflected from the modulator; changes in its thickness modulate the reflectivity. Electrical current flowing through the highly reflecting mirror provides a source of heat for controlling, by thermal expansion, the thickness of the elastomeric film. Modulators with this design show contrast ratios >15 dB and insertion losses <0.3 dB.
Carrier capture into InGaAs/GaAs quantum wells via impurity mediated resonant tunneling
Authors: Dao L. V. , Gal M. , Tan H. , Jagadish C.
Published: July 2002

We have investigated the photoexcited carrier dynamics in In1−xGaxAs/GaAs quantum wells using the photoluminescence up-conversion technique. We found a unique capture process which was exceptional both in terms of the capture time and its temperature dependence. In the case of a specific quantum well with wide barriers, the photoluminescence rise time, a parameter which includes the overall capture time and the exciton formation time, was less than 600 fs instead of the expected few hundred picoseconds. We show in this work that this unusually rapid process is the result of the capture of the photoexcited carriers (or excitons) by impurities in the GaAs barriers, from where they resonantly tunnel into the quantum well.
Transverse magnetic field studies in ZnSe/BeTe resonant tunneling structures
Authors: Lunz U. , Keim M. , Waag A. , Faschinger W. , Landwehr G.
Published: July 2002

We report on resonant electron tunneling in ZnSe/BeTe double-barrier, single-quantum-well heterostructures under high magnetic fields. Current–voltage characteristics have been investigated in the presence of a magnetic field B perpendicular to the tunneling current (B⊥I). The effect of the field on the main resonance position as well as two additional features due to optical phonon assisted tunneling into the quantum well has been studied and analyzed. The peak bias voltage exhibits a quadratic shift with increasing magnetic field due to a Lorentz force acting on the tunneling electrons. The phonon peaks do not shift, because the transverse momentum is no longer conserved during this process.
A scanning tunneling microscopy study of atomic-scale clustering in InAsP/InP heterostructures
Authors: Zuo S. L. , Bi W. G. , Tu C. W. , Yu E. T.
Published: July 2002

We have used cross-sectional scanning tunneling microscopy to perform atomic-scale characterization of InAs0.35P0.65/InP strained-layer multiple-quantum-well structures grown by gas-source molecular-beam epitaxy. High-resolution (110) cross-sectional images reveal nanoscale clustering of As and P in the InAsxP1−x alloy layers. Boundaries between As-rich and P-rich regions in the alloy layers appear to be preferentially oriented along the [1̄12] and [11̄2] directions in the (110) plane, suggesting that boundaries between As-rich and P-rich clusters tend to form within {111} planes in the lattice. The nanoscale compositional variations within the InAsxP1−x alloy layers lead to an asymmetry in interface quality in the (110) cross section, with the InAsxP1−x-on-InP interfaces being much smoother and more abrupt than the InP-on-InAsxP1−x interfaces. Analysis of (11̄0) cross-sectional images suggests that the clusters formed within the InAsxP1−x alloy are elongated along the [110] direction in the crystal.
Doped organic light emitting diodes having a 650-nm-thick hole transport layer
Authors: Yamamori Asuka , Adachi Chihaya , Koyama Toshiki , Taniguchi Yoshio
Published: July 2002

We have succeeded in fabricating a thick-film organic light emitting diode having a doped hole transport layer (DHTL). The basic cell structure is anode DHTL/emitter layer/cathode. The DHTL is composed of a hole transporting polycarbonate polymer (PC-TPB-DEG) and tris(4-bromophenyl)aminium hexachloroantimonate (TBAHA) as a dopant. As an emitter, we used tris(8-hydroxyquinoline) aluminum (Alq). With a 650-nm-thick DHTL, the device showed considerable reduction in cell resistance compared with an anode/nondoped HTL/Alq/cathode device with the same HTL thickness. Although the electroluminescent quantum efficiency ΦL was rather low in the doped device, we should be able to increase it by interposing a thin tetraphenylbendidine (TPB) layer between the DHTL and the emitter layer while keeping the driving voltage low. The anode/DHTL (650 nm)/TPB(50 nm)/Alq(50 nm)/cathode showed luminance of more than 4004 cd/m2 at 10.0 V and 220 mA/cm2.
New buffer concept inherent to pulsed laser induced epitaxy
Authors: Guedj Cyril , Boulmer Jacques , Nouet Gérard , Godet C. , Roca i Cabarrocas P.
Published: July 2002

We demonstrate the growth of a 250 nm-thick graded buffer based on Si1−x−yGexCy. This buffer, with 0<x<0.25 and 0<y<0.004, looks entirely free from threading dislocation. Its original microstructural arrangement is inherent to the growth method: pulsed-laser induced epitaxy. After epitaxy, small amorphous precipitates are buried at the former amorphous/crystalline interface. They behave like buffers capable of storing elastic energy. With proper annealing parameters, no dislocation is seen by transmission electron microscopy. This result is obtained when the laser fluence is sufficient to melt the layer down to the substrate. This indicates that pulsed laser induced epitaxy is a promising method for new buffer concepts with low threading dislocation densities.
Recurrent local resistance breakdown of epitaxial BaTiO3 heterostructures
Authors: Watanabe Y. , Sawamura D. , Okano M.
Published: July 2002

Leakage current through epitaxial BaTiO3 films was investigated to clarify the difference between the characteristics of nanometer and millimeter-size metal contacts. SrTiO3:Nb bottom electrode revealed genuine properties of a single metal/BaTiO3 contact and demonstrated that breakdown voltage and leakage current density at both nanometer and millimeter-size contacts were controlled by the Schottky barrier. However, in marked contrast with millimeter-size contacts, nanometer-size contacts conducted little current below breakdown voltage and repeatedly exhibited abrupt breakdowns having a giant current density >10 A mm−2. The breakdown field was as high as 0.45 MV cm−1 at the forward bias, while no breakdown occurred up to 0.5 MV cm−1 at the reverse bias.
Correlation between electron mobility and silicon-hydrogen bonding configurations in plasma-hydrogenated polycrystalline silicon thin films
Authors: Kitahara K. , Murakami S. , Hara A. , Nakajima K.
Published: July 2002

This letter describes the relationship between electron mobility and Si-hydrogen bonding configurations in poly-Si thin films after plasma-hydrogenation treatment. A 50-nm-thick amorphous-Si film was crystallized by excimer laser irradiation followed by plasma hydrogenation. Measurements of the Hall effect and Raman scattering demonstrated that mobility increased under the Si-H dominant state and decreased under the Si-H2 dominant state, which were respectively caused by adjusted and excessive hydrogenation times. Mobility degradation was recovered by dissociation of excess H atoms by annealing. The origin of the correlation is discussed in terms of imperfections such as grain boundaries and in-grain defects.
Influence of boundary conditions on time-reversal focusing through heterogeneous media
Authors: Tanter Mickaël , Thomas Jean-Louis , Fink Mathias
Published: July 2002

This letter presents a way to overcome ultrasonic focusing degradations through strongly diffracting nondissipative layers. A first set of experiments shows that, using finite aperture transducer arrays, neither the time-reversal technique, nor other focusing techniques are able to achieve proper focusing through this kind of aberrator. These experimental results show the limits of a finite aperture time-reversal mirror compared to the theoretical behavior of a time-reversal cavity. To simulate a time-reversal cavity, totally reflecting walls are set between the time-reversal mirror and the aberrator. The experiments and numerical simulations presented in this letter show that as soon as we introduce these reflecting boundaries, the time-reversal focusing becomes optimal and the spatial resolution is strongly improved.
Silicon-based organic-inorganic microcavity and its dispersion curve from angle-resolved photoluminescence
Authors: Arena A. , Patanè S. , Saitta G. , Savasta S. , Girlanda R. , Rinaldi R.
Published: July 2002

We report an experimental study of a planar organic-inorganic microcavity consisting of a porous silicon distributed Bragg reflector, a single layer of acridina orange as active material and a top aluminum reflector. By tuning the cavity resonance energy around the maximum of the organic material photoluminescence, we found an intense emission and a spectral narrowing of the emission band to about 45 meV. The angle-resolved photoluminescence spectra enable us to determine the microcavity dispersion curve. The very good agreement with the theoretical dispersion provides a precise determination of the refractive index of the organic material.
Creation of [110]-aligned Si quantum wires encompassed by SiO2 using low-energy separation-by-implanted-oxygen on a V-groove patterned substrate
Authors: Ishikawa Yukari , Shibata N. , Fukatsu S.
Published: July 2002

Si quantum wires (QWRs) suspended in SiO2 are successfully created on a V-groove patterned Si(001) substrate by using low-energy oxygen ion implantation. A single Si QWR aligned to [110] is formed near the bottom center of the V groove, which has a hexagonal cross section with {111} and {001} lateral facets. The development of Si QWRs was found to be controlled by the oxygen ion dose and the formation mechanism is attributed to an oxygen ion enrichment near the V-groove corner which arises from lateral ion straggling.
Photoluminescence nonlinearities in mixed type I–type II quantum well heterostructures
Authors: Finkman E. , Planel R.
Published: July 2002

We report on nonlinear behavior of the intensities and the energies of photoluminescence lines in mixed type I–type II quantum well heterostructures. The structures under study consist of a single enlarged quantum well (SQW), embedded in type II short period superlattices (SPS) on both sides. The nonlinearities are interpreted considering a coupling between the electron levels in the SPS and the SQW, and a very efficient transfer of electrons from the whole structure to the well. The electron density in the SQW as well as the internal electric fields can be optically controlled to high values depending on input power intensities. The nonlinear effects, and the extension of light emission to higher energies in such structures, compared to traditional type I systems, may be of interest in potential applications.
Coulomb effects on charged, buried metal disks at room temperature
Authors: Wernersson L.-E. , Litwin A. , Montelius L. , Pettersson H. , Samuelson L.
Published: July 2002

Capacitance transients caused by capture and emission of electrons from buried metal disks are investigated. A single layer of tungsten disks, arranged in a square lattice, is introduced into GaAs by epitaxial overgrowth and a depleted layer is formed around the disks due to the metal–semiconductor Schottky barrier. The number of captured electrons on each disk is measured by the capacitance associated with the width of the depletion layer, whereas the capacitance transients reflect the changes in the number of excess electrons on the disks. By investigating the emission time constants for varying numbers of electrons in excess on the disks, the Coulomb effect is studied. In combination with a temperature-dependent capture, a Coulomb charging energy of only 4 meV is shown to shift the measured activation energies erroneously by hundreds of meV.
Low-level copper concentration measurements in silicon wafers using trace-element accelerator mass spectrometry
Authors: McDaniel F. D. , Datar S. A. , Guo B. N. , Renfrow S. N. , Zhao Z. Y. , Anthony J. M.
Published: July 2002

Accelerator mass spectrometry (AMS) is now widely used in over 30 laboratories throughout the world to measure ratios of the abundances of long-lived radioisotopes such as Be111, C14, CI36 and I127 to their stable isotopes at levels as low as 10−16. Trace-element AMS (TEAMS) is an application of AMS to the measurement of very low levels of stable isotope impurities. Copper concentrations as low as 1 part per billion have been measured in silicon wafers. In this letter, we demonstrate the use of TEAMS to measure previously unknown copper concentration depth profiles in As-implanted Si wafers at a few parts per billion. To verify the TEAMS technique, the samples from the same wafer were measured with secondary ion mass spectrometry, which showed the same profiles, albeit plateauing out at a concentration level six times higher than the TEAMS measurement. The ability to measure at these levels is especially significant in light of the recent moves towards the use of copper interconnects in place of aluminum in integrated circuits.
Metalorganic molecular beam epitaxial growth of semi-insulating GaInAsP(λg=1.05 μm):Fe optical waveguides for integrated photonic devices
Authors: Künzel H. , Albrecht P. , Ebert S. , Gibis R. , Harde P. , Kaiser R. , Kizuki H. , Malchow S.
Published: July 2002

Iron doping of InP and GaInAsP(λg=1.05 μm) layers grown by metalorganic molecular beam epitaxy was studied using elemental source material in combination with a conventional effusion cell. This study was aimed at the creation of semi-insulating optical waveguides under growth conditions compatible with selective area growth. Secondary ion mass spectroscopy measurements revealed a reproducible and homogeneous incorporation behavior of the iron dopant in the materials investigated. Resistivities in excess of 109 Ω cm were obtained for both compositions at medium doping levels. GaInAsP/InP waveguide structures grown at 485 °C—the minimum temperature necessary for selective deposition—exhibited averaged resistivities of 5×107 Ω cm in combination with optical losses of 2.5±0.5 dB/cm.
Fabrication and properties of all-refractory Nb/Al–AlOx–Ti junctions for microbolometers and microrefrigerators
Authors: Zhao S. P. , Du H. , Chen G. H. , Yang Q. S.
Published: July 2002

Fabrication of all-refractory Nb/Al–AlOx–Ti superconducting tunnel junctions using selective titanium etching process (STEP) is described. Results including anodization properties of Ti, and junction’s I–V characteristics and subgap currents measured in the temperature range of 0.4–9.2 K are presented. The junctions show fairly high quality with respect to their stability and reproducibility. Possible utilization of these junctions as superconductor–insulator–normal metal type devices operating around 100 mK and above for ultrasensitive microbolometer and electronic microrefrigerator applications is discussed.
Patterning the second-order optical nonlinearity of asymmetric quantum wells by ion implantation enhanced intermixing
Authors: Janz S. , Buchanan M. , van der Meer P. , Wasilewski Z. R. , Xu D.-X. , Piva P. , Mitchell I. V. , Akano U. G. , Fiore A.
Published: July 2002

The change in the second-order nonlinear susceptibility of an asymmetric quantum well (AQW) superlattice induced by ion beam-enhanced intermixing has been measured. The surface-emitted second-harmonic intensities radiated from implanted and masked areas of an AQW waveguide were measured and compared for incident wavelengths between λ=1480 and 1600 nm. Intermixing resulted in a 60 meV blueshift of the AQW band edge and a uniform suppression of the AQW second-order susceptibility, while the masked AQWs were unchanged.
Reduction of effects of Fabry–Perot fringing in wavelength modulation experiments
Authors: Dharamsi A. N. , Shea P. C. , Bullock A. M.
Published: July 2002

One of the factors limiting the sensitivity of wavelength modulation experiments is the fringing that is created by inadvertent multiple reflections between parallel optical surfaces in the apparatus. It is shown that the effects of this “étaloning” can be countered by using detection harmonic orders greater than the second. A theoretical basis for the effect is presented and compared with experimental results obtained.
Elastic and plastic deformation of diamondlike carbons
Authors: Stoneham A. M. , Godwin P. D. , Sutton A. P. , Bull S. J.
Published: July 2002

In exploiting tribological applications of diamondlike carbons (DLC, a-C:H), both elastic and plastic properties must be optimized. We use tight-binding molecular dynamics to generate realization of DLC, from which can be obtained properties and their dependence on the precursors used, and on the H/C ratio. Here we analyze the elastic properties and especially the rebonding events which occur under strain. Rebonding occurs only at rather large strains; in some cases, it is reversible. Hydrogen has a key role in determining the number of carbons with less than four carbon neighbors, since it is mainly these carbons which participate in the major plastic (rebonding) events.
Composition modulation in InxGa1−xAs nanocrystals embedded in SiO2 film by radio frequency magnetron cosputtering
Authors: Shi Jianzhong , Zhu Kaigui , Zhang Lide
Published: July 2002

We have succeeded in preparing InxGa1−xAs (0.2⩽x⩽0.8) nanocrystals with 3–5 nm in size embedded in SiO2 thin film by using the radio frequency magnetron cosputtering technique. The analyses of x-ray diffraction and Raman spectra strongly suggest the existence of InxGa1−xAs nanocrystals in the matrices. It has been found that the optical absorption edge, lattice constant and Raman shift can be modulated by composition of InxGa1−xAs by varying the effectively sputtered area ratio of InAs to GaAs on the target. The blueshift of the optical absorption edge is explained by the effective mass approximation method.
Basal plane oxygen vapor pressure of Co-doped YBa2Cu3O7−δ
Authors: Sydow J. P. , Buhrman R. A. , Moeckly B. H.
Published: July 2002

Transport data for YBa2Cu3−xCoxOz thin films, with x=0.3, 0.5, 0.75, and 1.0, are reported as a function of annealing history in O2 and O2/O3 at temperatures ranging from 200 to 500 °C. For x=0.3 and 0.5, O2/O3 anneals resulted in maximal Tc’s significantly higher than any previously reported, while in all cases the annealing substantially increased the film’s conductivity. Subsequent anneals in O2 resulted in oxygen loss, demonstrating that these materials have a much higher oxygen vapor pressure in the well-oxygenated state than YBa2Cu3O7−δ.
Room temperature photoinduced Faraday rotation in Hg1−xMnxTe alloys at 1550 nm
Authors: Ghislotti G. , Masseroni C. , Zappettini A. , Martinelli M. , Mycielski A.
Published: July 2002

Faraday rotation of the polarization for a 1550 nm probe beam induced by a pump beam at shorter wavelength is studied in Hg1−xMnxTe semimagnetic semiconductors. Photoinduced rotation decays in a nanosecond timescale and it is related to carrier-induced refractive index saturation. Observed decay is discussed in terms of photoexcited carrier dynamics.
Investigation of solid phase reaction of Ni with GaAs/Si(001)
Authors: Zhou T. C. , Jiang S. , Kirk W. P. , Hao P. H. , Wang L. C. , Chen P. J.
Published: July 2002

A Ni/GaAs/Si(001) structure was used to investigate solid-phase reactions of Ni with GaAs and Si. Cross-sectional transmission electron microscopy and secondary-ion-mass-spectrometry depth profile data reveal that a Ni/GaAs/Si(001) structure converts to a crystalline GaAs/amorphous NiSi/Si(001) after low temperature (⩽350 °C) annealing. We demonstrate that the reaction is driven by the decomposition of a NixGaAs intermediate which is induced by the proximity of the Si substrate. Two models are suggested to explain the mechanism of a crystalline GaAs layer nucleated from NixGaAs on the amorphous NiSi layer.
Hall mobility in poly(4,4′-dipentoxy-2,2′bithiophene) as a function of the doping level
Authors: Camaioni Nadia , Casalbore-Miceli Giuseppe , Geri Alessandro , Nicoletti Sergio
Published: July 2002

We report a systematic study of the Hall mobility and the carrier concentration of a conjugated polymer [poly(4,4′-dipentoxy-2,2′bithiophene)] as a function of the electrochemical doping level, over a wide range of the carrier concentration (from ∼1015 to ∼1019 cm−3). Very high values were obtained for the carrier mobility (from 102 to 10−1 cm2 V−1 s−1), when compared with those reported in the literature for organic materials. Furthermore, an inverse relationship between mobility and carrier concentration was found.
Growth of HgBa2Ca2Cu3O8 thin films using stable Re0.1Ba2Ca2Cu3Ox precursor by pulsed laser deposition
Authors: Kang W. N. , Meng R. L. , Chu C. W.
Published: July 2002

High quality c-axis oriented HgBa2Ca2Cu3O8 thin films have been fabricated with the stable Re-doped Ba2Ca2Cu3Ox precursor powder by pulsed laser deposition followed by postannealing without any special handling. As-grown films on (100) SrTiO3 exhibit a zero-resistance transition (Tc,zero) at ∼131 K with a narrow transition width ΔT∼1.5 K after oxygen annealing at 340 °C for 12 h. The critical current densities are observed 1.1×107 A/cm2 at 10 K and 1.2×105 A/cm2 at 120 K in zero field. The x-ray diffraction pattern indicates highly c-axis oriented thin films normal to the substrate plane containing a minor HgBa2CaCu2O6 phase. The scanning electron microscopy analysis shows that the surface morphology of the film is well connected platelike crystals but reveals Ba–Cu–Ox impurities are uniformly scattered across the film surface.
Thick lens model for self-focusing in Kerr medium
Authors: Chen Yu-Chuan , Lin Wei-Zhu
Published: July 2002

An asymmetric “thick-lens” model for self-focusing in Kerr medium of finite thickness is presented by introducing a complex curvature radius of a Gaussian beam in nonlinear medium and a transfer matrix for the transition from linear to nonlinear medium. With this model the linear ABCD-matrix formalism can be extended to nonlinear optical systems with a clear physical insight. The modulation of the cavity transverse mode of a resonator containing a Kerr medium is characterized by the asymmetry of the “thick lens.” The intracavity small-signal relative spot size variation outside as well as inside the Kerr medium can be calculated efficiently with the “thick-lens”-like matrix formalisms. Criteria for the design and optimization of a Kerr-lens mode-locked laser resonator with a hard or soft aperture are predicted.
Third harmonic generation through coupled second-order nonlinear optical parametric processes in quasiperiodically domain-inverted Sr0.6Ba0.4Nb2O6 optical superlattices
Authors: Zhu Yong-yuan , Xiao R. F. , Fu J. S. , Wong G. K. L. , Ming Nai-ben
Published: July 2002

A one-dimensional quasiperiodically domain-inverted optical superlattice has been designed and fabricated in a strontium barium niobate (Sr0.6Ba0.4Nb2O6) single-crystal plate. A third harmonic output generated through coupled second-order nonlinear parametric processes with a conversion efficiency of about 1.6% was obtained when both the second harmonic and the third harmonic were simultaneously quasiphase matched in the crystal.
Phase transition of C60 crystal in high temperature regime
Authors: Yan Feng , Wang Ye-Ning
Published: July 2002

The internal friction of the polycrystalline C60 films was measured in the temperature range of 320–620 K. Around 426 K, a λ-shaped internal friction peak was detected. The peak was interpreted in terms of another phase transition above the order-disorder phase transition temperature.
Impact excitation of the f–f emission in clusters Er–O in silicon
Authors: Gerchikov L. G. , Masterov V. F.
Published: July 2002

The Er2O3 quantum dot (cluster) with dimensions about 1.2 nm in silicon is discussed as a possible source of the Er-related emission in Si:Er, O, excited by hot carriers in the light-emitting diodes under reverse bias. This quantum dot is represented as a spherical quantum well 1 eV in depth. The electron resonance level with energy about 0.8 eV above the bottom of the silicon conduction band plays the role of an electron trap. The energy of 1.6 eV hot electrons trapped by the Er–O cluster is transferred to excitation of the f shell of erbium.
Application of δ-doped wide-gap collector structure for high-breakdown and low-offset voltage transistors
Authors: Liu Wen-Chau , Cheng Shiou-Ying , Chang Wen-Lung , Pan Hsi-Jen , Shie Yung-Hsin
Published: July 2002

An In0.5Ga0.5P/GaAs double heterojunction bipolar transistor with a δ-doped wide-gap collector structure has been fabricated and studied. Experimental results show that this device exhibits the advantages of a small offset voltage of 50 mV, a small saturation voltage of 1 V, and a large breakdown voltage of 20 V with a current gain of 20. These good characteristics are mainly due to the complete elimination of potential spike at emitter–base and base–collector heterojunctions. Consequently, the studied device shows a good promise for high-speed, high-power, lower-power consumption and large input signal circuit applications.
Coherent control of optical gain from electronic intersubband transitions in semiconductors
Authors: Hu Xuedong , Pötz Walter
Published: July 2002

We study electronic transitions between a subband and a lower subband doublet which is driven by a coherent microwave (MW) field in a semiconductor double well structure. Within a microscopic three-band model, we show that variation of the MW phase allows manipulation of the optical gain provided the probe pulse duration is shorter than the period of the MW-field-generated interband polarization in the doublet. Moreover, we find that optical gain without inversion can be achieved in spite of subpicosecond dissipative mechanisms provided by electron-phonon coupling and electron tunneling into and out of the double well.
Ultraviolet single-frequency pulses with 110 mW average power using frequency-converted passively Q-switched miniature Nd:YAG ring lasers
Authors: Bode M. , Spiekermann S. , Fallnich C. , Welling H. , Freitag I.
Published: July 2002

We demonstrate a compact source of ultraviolet single-frequency pulses with high average output power realized by subsequent single-pass frequency doubling and quadrupling of a diode-pumped passively Q-switched miniature Nd:YAG ring laser. Pulse widths of 2 ns (full width at half maximum), 20 μJ single pulse energy, and 10 kW peak power are achieved at a wavelength of 266 nm with kilohertz repetition rates. A single-pass energy conversion efficiency of 22% with respect to the fundamental light at 1064 nm and an overall efficiency of 2.8% with respect to the diode pump power are obtained.
Silicon di-interstitial in ion-implanted silicon
Authors: Lee Young Hoon
Published: July 2002

A new Si di-interstitial model is derived from the Si-P6 electron paramagnetic resonance spectrum observed in neutron-, proton-, or ion-implanted silicon. Two Si interstitials lie in the {100} plane at a position considerably off from two tetrahedral interstitial sites nearby, sharing one Si lattice atom. The di-interstitial disappears at 170 °C annealing and can form the 〈110〉 interstitial chains which are considered to be a “building block” of the {311} extended defects frequently observed in ion-implanted Si.