bluuebunny/crossref_metadata_2025 huggingface dataset:
4.3 terahertz four-wave mixing spectroscopy of InGaAsP semiconductor amplfiers
Authors: D’Ottavi A. , Iannone E. , Mecozzi A. , Scotti S. , Spano P. , Dall’Ara R. , Guekos G. , Eckner J.
Published: July 2002

A four-wave mixing experiment in a bulk InGaAsP traveling-wave semiconductor amplifier is reported. The maximum pump-probe detuning is 4.3 THz. The equivalent time resolution of 37 fs is high enough to measure with good accuracy the time constant of spectral-hole burning (100 fs in our case). The simultaneous presence of spectral-hole burning and of an instantaneous, within our time resolution, saturation process is clearly displayed.
High quality 4H-SiC epitaxial layers grown by chemical vapor deposition
Authors: Kordina O. , Henry A. , Bergman J. P. , Son N. T. , Chen W. M. , Hallin C. , Janzén E.
Published: July 2002

High quality, homoepitaxial layers of 4H-SiC have been grown by chemical vapor deposition in a hot-wall reactor. The residual doping concentration obtained by capacitance versus voltage measurements was as low as 2×1014 cm−3. The high quality is confirmed by photoluminescence measurements performed at low temperatures (1.8–4.2 K) showing strong free exciton related luminescence and by the fact that optically detected cyclotron resonance signals could be observed (at 6 K), as a result of the highest mobility reported in SiC.
Crystalline quality analysis of YBaCuO ultrathin films by high resolution ion backscattering and channeling spectrometry
Authors: Hüttner D. , Meyer O. , Reiner J. , Linker G.
Published: July 2002

Medium energy ion scattering combined with channeling was applied to study the crystalline quality of ultrathin YBaCuO films on (100) SrTiO3 and MgO substrates. Films with thicknesses between 3 and 6 nm were deposited by inverted cylindrical magnetron sputtering. Under optimized growth conditions c-axis oriented growth was obtained with minimum yield values of 2%–12% (depending on thickness) for films on SrTiO3 and 23% on MgO. On the surface of the films a disordered region with a thickness of about 0.6 nm independent of substrate, film thickness, and storage time under ambient conditions was observed. During etching experiments an Y-oxide layer was formed on the surface. For films on SrTiO3 at thicknesses above 4 nm an abrupt increase in the minimum yield was found indicating pseudomorphic growth up to this thickness. In contrast, for films on MgO it was found that a critical film thickness of about 3.6 nm is necessary for the formation of a homogeneous film.
Polarization of lasing emission in microdisk laser diodes
Authors: Frateschi N. C. , Kanjamala A. P. , Levi A. F. J. , Tanbun-Ek T.
Published: July 2002

TE polarization of optical emission from microdisk laser diodes of radius R=5 μm, thickness L=0.3 μm, is found to dominate both below and above room-temperature lasing threshold current, Ith=2 mA. TE emission in the lasing mode at λ=1560 nm wavelength is due to higher optical gain for TE modes in the quantum well device. In our device geometry, the intrinsic whispering gallery resonances have essentially no polarization selectivity.
Deep-oxide planar buried-channel AlGaAs–GaAs quantum well heterostructure waveguides with low bend loss
Authors: Krames M. R. , Chen E. I. , Holonyak N. , Crook A. C. , DeTemple T. A. , Besse P.-A.
Published: July 2002

Data are presented on planar S-bend waveguides fabricated in an AlxGa1−xAs–GaAs p-n quantum well heterostructure (QWH) crystal by a self-aligned process combining Si impurity-induced layer disordering and ‘‘wet’’ native oxidation. In the process, a deep, low-index (n∼1.7) oxide cladding structure is formed, creating a buried channel in the QWH core layers and defining the routing properties of ∼2.5-μm-wide guides. Deep-oxide S-bend waveguides with 100 μm offsets exhibit low excess bend losses with a 3 dB transition distance less than 140 μm for transverse electric polarization. These bend losses are significantly lower than those measured for oxide-only and disordered-only guides. Excellent optical isolation of the guided signal is observed, indicating very little crosstalk occurs between adjacent guides.
Femtosecond carrier dynamics in low-temperature-grown indium phosphide
Authors: Kostoulas Y. , Waxer L. J. , Walmsley I. A. , Wicks G. W. , Fauchet P. M.
Published: July 2002

Up-conversion luminescence and pump-probe spectroscopy are used to determine the energy distribution and recombination kinetics of photoexcited carriers in low-temperature-grown InP. The samples used are two unannealed InP films grown at 200 and 300 °C. The photoexcited carriers undergo fast trapping in less than 1 ps with recombination taking place on a much longer time scale. The carrier trapping time is found to be 500±100 fs for the 200 °C sample and 1.6±0.05 ps for the 300 °C sample and the trap photoionization cross section is estimated to be 10−16 cm2.
Transient current study of low-temperature grown GaAs using an n-i-n structure
Authors: Fujioka H. , Weber E. R. , Verma A. K.
Published: July 2002

The electrical properties of molecular beam epitaxy (MBE) grown low-temperature GaAs (LT-GaAs) by current transient spectroscopy (CTS) has been investigated. At least three deep traps have been observed in LT-GaAs grown at 250 °C and annealed at 600 °C. The deepest level is dominant and has an activation energy of 0.82 eV, which is the same as that of the midgap donor, EL2. This is consistent with the activation energy of resistivity of this sample (0.77 eV), which is close to that for bulk nondoped semi-insulating wafers. These results indicate that the Fermi level of annealed LT-GaAs grown at 250 °C is pinned by the deep level at the midgap that is generally ascribed to AsGa antisite defects.
Effective mass and band nonparabolicity in remote doped Si/Si0.8Ge0.2 quantum wells
Authors: Whall T. E. , Plews A. D. , Mattey N. L. , Phillips P. J. , Ekenberg U.
Published: July 2002

The effective masses in remote doped Si/Si0.8Ge0.2/Si quantum wells having sheet densities, Ns in the range 2×1011–1.1×1012 cm−2 have been determined from the temperature dependencies of the Shubnikov–de Haas oscillations. The values obtained increase with magnetic field and Ns. This behavior is taken as evidence for the nonparabolicity of the valence band and accounts for the discrepancies in previously reported masses. Self-consistent band structure calculations for a triangular confinement of the carriers have also been carried out and provide confirmation of the increase in mass with Ns. Theory and experiment give extrapolated Γ point effective masses of 0.21 and 0.20 of the free-electron mass, respectively.
Formation of a strongly coupled YBa2Cu3Ox domain by the melt-joining method
Authors: Shi Donglu
Published: July 2002

A method was developed to melt join two YBa2Cu3Ox domains together. After melt joining, the scanning electron microscopy analysis did not reveal any interfaces near the original domain contact surfaces. Both samples with equal geometry and orientation before and after the melt-joining process exhibited the same magnetic hysteresis, indicating that the melt-joined sample was strongly coupled. Also discussed is a possible domain growth mechanism during the melt-joining process.
Linewidth and α-factor in AlGaAs/GaAs vertical cavity surface emitting lasers
Authors: Kuksenkov D. , Feld S. , Wilmsen C. , Temkin H. , Swirhun S. , Leibenguth R.
Published: July 2002

Measurements of the α-factor, the linewidth-power product, and the differential gain in AlGaAs/GaAs vertical cavity surface emitting lasers are presented. The linewidth power product of 95 MHz mW which results in the α-factor of 3.7 is obtained. The α-factor as a ratio of the refractive index and gain derivatives with respect to the carrier density is also estimated. From the small signal modulation measurements of the resonance frequency, a differential gain of 3.7×1016 cm2 is obtained. The estimate of differential effective index is made difficult by an anomalously strong dependence of the emission wavelength on injection current.
Study of exciton dynamics in InGaAs/InP quantum wells using a femtosecond optical parametric amplifier
Authors: Nisoli M. , Magni V. , De Silvestri S. , Svelto O. , Campi D. , Coriasso C.
Published: July 2002

We investigated the exciton dynamics in InGaAs/InP quantum wells using a novel infrared tunable femtosecond laser source, based on an optical parametric frequency converter pumped by a femtosecond Ti:sapphire laser. The wide tuning range of this source allowed to excite three different excitonic resonances in the absorption spectrum of the sample. The n=1 heavy-hole excitons are approximately eight times more efficient than free electron-hole plasma in the absorption saturation. This value is much higher than that measured in GaAs quantum wells. The exciton ionization time constant of the n=1 and n=2 heavy-hole excitons has been measured to be 170 and 100 fs, respectively. No evidence of the n=1 light-hole exciton dynamics was found in the measurements. The study of the dynamics at the n=2 heavy-hole resonance allowed the measurement of a n=2 to n=1 intersubband relaxation time of 1 ps.
Silicon on insulator photoelastic optical waveguide and polarizer
Authors: Yu L. S. , Guan Z. F. , Liu Q. Z. , Lau S. S.
Published: July 2002

Single-mode silicon on insulator photoelastic waveguides and polarizers have been investigated. It was found that waveguides induced by the photoelastic effect can be low loss (1.5 dB/cm at 1.53 μm) and can serve as polarizers as well. A polarization distinction ratio of 14 dB for both TE and TM mode has been obtained.
Heavy phosphorus doping in molecular beam epitaxial grown silicon with a GaP decomposition source
Authors: Lippert G. , Osten H. J. , Krüger D. , Gaworzewski P. , Eberl K.
Published: July 2002

Doping with phosphorus in solid source silicon molecular beam epitaxy is possible using a GaP decomposition source. This source evaporates solid GaP and is combined with an efficient mass separator system. Homogeneous P doping up to concentrations higher than 1019 cm−3 was realized. Surface accumulation of phosphorus was not observed for the low growth temperature of 400 °C used in this study. The parasitic Ga incorporation is about three orders of magnitudes below the P concentration. This new phosphorus doping technique is suitable for n-type doping in the range of 1017–1020 cm−3.
Measurement of photoemission oscillations during molecular beam epitaxial growth of (001) GaAs, AlAs, AlGaAs, InAs, and AlSb
Authors: Zinck J. J. , Chow D. H.
Published: July 2002

Photoemission oscillations are observed from (001) GaAs, AlAs, AlGaAs, InAs, and AlSb. The periodicity of the oscillations corresponds to that of reflection high-energy electron diffraction oscillations measured using the same growth conditions. For both methods, the oscillation amplitude is strongly dependent on the substrate temperature, III/V flux ratio, and the nature of the surface on which growth is nucleated for the oscillation measurement.
Observation of dressed-exciton oscillating emission over a wide wavelength range in a semiconductor microcavity
Authors: Cao H. , Jacobson J. , Björk G. , Pau S. , Yamamoto Y.
Published: July 2002

We have observed the dressed-exciton oscillating emission in the time domain and the associated spectral splitting in the frequency domain from a GaAs single quantum well microcavity over a very broad range of cavity resonant wavelengths. The spectral splitting and temporal oscillation period have been measured to be nearly constant over two orders of magnitude variation of pump intensity, which confirms the linear bosonic feature of Wannier excitons in the weak excitation regime.
Practical laser-activated photoemissive electron source
Authors: Lee Chunghsin , Oettinger Peter E. , Sliski Alan , Fishbein Marvin
Published: July 2002

The design and performance of a laser-excited cesium antimonide (Cs3Sb) photoemissive electron source operating in an electron-gun configuration is described. Such an electron source has advantages of higher brightness, beam shapeability, low-temperature operation, external modulability, and ease of service compared with conventional thermal and field emission sources. With an uncooled photoemissive source operating at 2.9 A/cm2, cathode life exceeded 50 h without degradation. Photoemissive electron sources should be especially useful in applications requiring high-resolution imaging or high-frequency pulsed operation.
Conduction mechanism in arsenic implanted GaAs
Authors: Fujioka H. , Weber E. R. , Verma A. K.
Published: July 2002

We have investigated the electrical properties of heavily arsenic implanted GaAs, which has structural properties similar to low temperature GaAs. The electrical conduction in the lateral direction is dominated by hopping in a defect band and the resistivity after a 600 °C anneal is on the order of 103 Ω cm. However, the resistivity measured on an n-i-n structure in the direction perpendicular to the surface is on the order of 109 Ω cm. This huge difference in resistivity can be explained by the lack of an electrical contact to the defect band in the n-i-n structure. The activation energy of the resistivity in the n-i-n structure is 0.74 eV. This value is close to that for bulk undoped semi-insulating wafers, in which the Fermi level is pinned at the midgap donor, EL2. A current transient spectroscopy study of this material reveals an electron trap with an activation energy of 0.82 eV, identical to the EL2.
Lateral patterning of arsenic precipitates in GaAs by a surface stress structure
Authors: Kiehl R. A. , Saito M. , Yamaguchi M. , Ueda O. , Yokoyama N.
Published: July 2002

Lateral patterning of arsenic precipitates in GaAs is reported. The positions of near-surface precipitates in a GaAs layer grown by molecular beam epitaxy at low temperature are controlled by InGaAs stressors 45 nm in width covered by a SiO2 film. The stressors form a surface grating which governs the precipitate position by modulating the strain in the GaAs near the surface. Electron microscopy clearly reveals the formation of precipitates about 15 nm in diameter aligned with the stressors at a depth of ∼50 nm. It is suggested that this capability to control the position of nanometer-size metallic particles within a semiconductor could open up new possibilities for novel devices.
Modification of excitonic emission in a GaAs bulk microcavity
Authors: Tredicucci A. , Chen Y. , Pellegrini V. , Deparis C.
Published: July 2002

We report the observation of cavity-induced modifications of the three-dimensional bulk exciton emission in a planar GaAs microcavity, in which the entire cavity layer is an active material. We have performed standard photoluminescence measurements at various emission angles, obtaining evidence of coupling between the exciton and the cavity mode. The modified density of photon states available for the exciton decay shows up in the angle dependence of the emission lineshape, as well as of the photoluminescence peak intensity. The experimental results are qualitatively clarified with theoretical calculations performed with an adapted transfer-matrix approach.
Kinetics of interdiffusion in strained nanometer period Si/Ge superlattices studied by Raman scattering
Authors: Dettmer K. , Freiman W. , Levy M. , Khait Yu. L. , Beserman R.
Published: July 2002

Intermixing time ti and interdiffusion coefficients D of nanometer periods Si/Ge strained layer superlattices (SLSs) were measured by Raman scattering technique. Si12Ge12 and Si19Ge9 SLSs have been annealed in the temperature range 760–900 °C during various time intervals. The observed D and ti follow the Arrhenius-like behavior with different activation energies ΔE=1.78±0.15 eV and 3.94±0.15 eV and pre-exponential factors D=2×10−10 cm2 s−1 and 0.7 cm2 s−1, respectively, for the Si12Ge12 and Si19Ge9 SLSs. D, ti, ΔE, and D0 are strongly affected by the changes of the SLS layer thickness, and strain. An explanation of the experimental observations is proposed in terms of the kinetic electron-related theory of atomic diffusion in solids. The observed variations of ΔE and D0 are related to the material parameters, which are characterized by picosecond atomic and electronic phenomena in nanometer regions, in good agreement with the observations.
A high-voltage, short-risetime pulse generator based on a ferrite pulse sharpener
Authors: Seddon N. , Thornton E.
Published: July 2002

A high-voltage, short-risetime pulse generator is described. The generator consists of a Marx bank, which produces an initial high-voltage pulse, and a ferrite pulse sharpener that reduces the risetime of the pulse. The generator delivers 70-kV, 350-ps risetime pulses into a 50-Ω load.
Enhanced hot-carrier spontaneous and stimulated recombination in a photopumped vertical cavity AlxGa1−xAs–GaAs quantum well heterostructure with multiple top and bottom native oxide mirrors
Authors: Richard T. A. , Maranowski S. A. , Holonyak N. , Chen E. I. , Ries M. J. , Neff J. G. , Grudowski P. A. , Dupuis R. D.
Published: July 2002

Data (300 and 77 K) are presented on the photopumped laser operation of AlxGa1−xAs–GaAs vertical cavity quantum well heterostructure crystals that exhibit enhanced hot-carrier recombination. The mirrors defining the vertical cavity are formed by selective lateral oxidation (H2O+N2, 425 °C, 30 min) of quadruple AlAs layers separated by lower composition AlxGa1−xAs ‘‘stop’’ layers in order to create upper and lower high-index-step oxide-semiconductor distributed Bragg reflector mirrors. The Q of the compact vertical-cavity (a microcavity) enhances the spontaneous and stimulated recombination of hot carriers, making possible single mode laser operation at an energy corresponding to the second state of the quantum well. The laser operation can be shifted to the first state by cooling to 77 K and shifting the energy gap towards the vertical cavity resonance.
Enhanced electron emission from n-type porous Si field emitter arrays
Authors: Takai M. , Yamashita M. , Wille H. , Yura S. , Horibata S. , Ototake M.
Published: July 2002

Tip surfaces of n-type Si field emitter arrays (FEAs) have been anodized to obtain n-type porous layers on the top surfaces of the Si emitters. The gate voltage required for emission could be lowered by tip anodization and the emission current was enhanced by a factor of up to 10. Fowler–Nordheim plots for the FEAs before and after tip anodization revealed that the work function of the tip could be decreased and the field conversion factor could be increased by the process.
Optical constants for coated thin films in the soft x-ray region
Authors: Kihara N. , Nagata H. , Nakagiri N. , Fujisaki H. , Miyahara T.
Published: July 2002

We present optical constants for Ti, V, and Ni in the 2–4.5 nm wavelength region. The reflected synchrotron radiation intensity was measured at more than 30 incident angles for each wavelength. A protective layer of carbon was sputtered onto each sample to prevent surface oxidization. A three-phase model was used to analyze the data. Instead of replacing some of the parameters by values determined by other experimental methods, eight parameters were simultaneously used in the least squares fitting. A 5-nm layer of carbon was found to be thin enough not to cause significant errors in the derived optical constants of the test materials.
Imaging domains in Co/Pt multilayers by magnetic force microscopy
Authors: Valera M. S. , Farley A. N. , Hoon S. R. , Zhou L. , McVitie S. , Chapman J. N.
Published: July 2002

The magnetic microstructure in a Co/Pt multilayer has been imaged by magnetic force microscopy employing a novel tip structure. Magnetic tips have been fabricated by evaporating a thin film onto a single facet of the pyramidal tip of a silicon nitride cantilever. Nanolithographically defined elements have been used to simulate the micromagnetic structure of the tip and have been investigated by the Lorentz mode of electron microscopy. We demonstrate that stray fields from the Co/Pt multilayer can be sensed by the tip producing images of the magnetic microstructure with a fine structure on a scale of 30–40 nm.
Measurement of H− ion density by laser photodetachment in a cesium–hydrogen plasma
Authors: Elizarov L. I. , El Balghiti F. , Bacal M.
Published: July 2002

The standard photodetachment method was applied for the diagnostic of negative ions in a cesium–hydrogen plasma. The plasma generator studied is a steady-state source of hydrogen negative ions with a cesium hollow cathode and a radial magnetic field. We demonstrate the possibility of using the photodetachment method for the diagnostics of cesium–hydrogen plasma.
Intercascade annihilation of freely migrating defects
Authors: Iwase A. , Rehn L. E. , Baldo P. M. , Funk L.
Published: July 2002

To characterize putative interactions between freely migrating defects (FMD) and remnants of energetic displacement cascades, radiation-induced segregation (RIS) in Cu-1 at. % Au was measured by Rutherford backscattering during separate and simultaneous irradiation at 400 °C with 1.5 MeV He and 800 keV Cu ions. The strong RIS observed during only He irradiation was greatly reduced under simultaneous Cu irradiation at approximately the same displacements per atom rate; increasing the Cu flux by a factor of 5 suppressed the RIS from the He beam almost completely. The suppression of RIS at 400 °C disappeared quickly when the Cu irradiation ceased. These results demonstrate that a transient population of interstitial and/or vacancy clusters from the Cu irradiation greatly reduces the survival rate of FMD produced by the He.
Further developments of series-connected superconducting tunnel junction to radiation detection
Authors: Kurakado Masahiko , Ohsawa Daisuke , Katano Rintaro , Ito Shin , Isozumi Yasuhito
Published: July 2002

One of the promising radiation detection devices for various practical applications is the series-connected superconducting tunnel junction (STJ) detector. In this article, interesting topics of the detectors are described since our previous work: e.g., more than two order higher detection efficiency compared with single STJ detectors, high count rate detection, and position resolution. Detectors were cooled to 0.35–0.4 K by means of a convenient He3 cryostat. The 5.9 and 6.5 keV x rays from Fe55 are separated by a detector specially designed for x-ray detection. The possible count rate of the series-junction detector estimated from the shaping-time constant applied in the measurements is high, e.g., over 104 counts per second. A series-junction detector equipped with a position sensing mechanism has shown a position resolution of about 35 μm in a sensing area with a radius of 1.1 mm. The position resolution of series junctions improves the energy resolution. A new type series-connected STJ detector is also proposed, i.e., the dispersed multitrap series-junction detector, for further improvement of detection efficiency and energy resolution.
Suppression of dislocation formation in silicon by carbon implantation
Authors: Simpson T. W. , Goldberg R. D. , Mitchell I. V.
Published: July 2002

We have examined the role of carbon co-implantation in the formation of secondary defects in self-ion-irradiated Si(100). Implantation of Si ions (540 keV energy, 1015 ions/cm2 at 1.3×1011 ions/cm2/s, Ti=90 °C) followed by a 900 °C, 15 min anneal leads to the growth of an extended defect band at the end of range. Range matched-carbon co-implantation (300 keV energy, 1015 ions/cm2 plus 500 keV energy 1015 ions/cm2 of 1.5×1011 ions/cm2/s, Ti=90 °C) can be used to modify this defect development dramatically. While direct co-implantation of carbon and silicon ions to similar concentrations has no apparent effect on the formation of extended defects, such formation is suppressed when the implanted C is incorporated substitutionally into the silicon lattice. These results are discussed in the context of recent reports on C suppression of the transient enhanced diffusion of boron.
Resistless high resolution optical lithography on silicon
Authors: Kramer N. , Niesten M. , Schönenberger C.
Published: July 2002

In this letter, we report on the high resolution patterning of a silicon surface without using a resist layer. A hydrogen passivated silicon surface is chemically modified by illumination with ultraviolet light (UV, λ=350.7 nm) in air. Auger electron spectroscopy (AES) revealed that silicon oxide was formed at the illuminated areas. A light interference pattern was made on the silicon surface by two UV laser beams, oxidation occurred only at the maximum intensity, but not at the minimum. In this way oxide lines were fabricated with a width below 200 nm on a 500 nm period. The oxide lines were used as a wet etch mask to etch more than 25 nm into Si(110) without affecting the oxide. The advantage of this technique is that it is a very simple process which allows the high resolution patterning over large areas of silicon without using a resist.
Single pulse selection from a cw mode-locked laser
Authors: Nampoothiri A. V. V. , Kundu T. , Singh Bhanu P.
Published: July 2002

A low cost, high performance single pulse switch-out system based on the high speed Pockels cell shutter, is presented. The circuit uses commonly available fast transistor transistor logic circuit elements for control logic and chains of bipolar junction transistors 2N2222A connected in avalanche mode for high-voltage switching of the Pockels cell. The system provides high contrast ratio pulses free from amplitude and timing jitter, and has been tested for more than 50 000 000 shots.
A fast atomic oxygen beam facility with in situ testing/analysis capabilities
Authors: Kinoshita H. , Ikeda J. , Tagawa M. , Umeno M. , Ohmae N.
Published: July 2002

A fast atomic oxygen beam facility consisting of a beam source, a mass spectrometer, an Auger electron spectroscope, a scanning tunneling microscope, and a friction tester has been developed to investigate interaction of energetic atomic oxygen with solid surfaces. The fast atomic oxygen beam has been characterized by time of flight distribution, quadrupole mass spectrometry, and quartz crystal microbalance. The time of flight distribution of the beam has shown that the average translational energy of the atomic oxygen beam reaches 4.7 eV and that the full width at half-maximum is 5.5 eV. A flux of the atomic oxygen is calculated from the frequency shift of the quartz crystal microbalance with silver electrodes, and typical flux of the atomic oxygen beam being 4.0×1012 atoms/cm2 s. The flux of atomic oxygen of this source is fairly low, but is corresponding to that in the altitude of 500 km in low Earth orbit. The surface sensitive analysis methods equipped with the facility, such as Auger electron spectroscopy and scanning tunneling microscopy, have provided changes in the surface composition and morphology caused by the atomic oxygen exposure, without receiving any effect of ambient air. The ultrahigh vacuum friction tester especially designed for this facility is used to measure tribological properties of solid lubricants under the atomic oxygen exposures. Such in situ testing capability of this facility enables fundamental research for understanding the reaction scheme of atomic oxygen as well as engineering-oriented research for obtaining high reliability of the space systems.
Step flow growth of (La,Ca)MnOδ thin films on (110)NdGaO3
Authors: Zeng X. T. , Wong H. K. , Xu J. B. , Wilson I. H.
Published: July 2002

Step flow growth patterns have been observed on single-crystal (La,Ca)MnOδ (LCMO) thin films by atomic force microscopy. These films were grown on (110) NdGaO3 substrates by a simple facing-target sputtering method. The steps, of monolayer height (0.2 nm), are surprisingly straight and evenly spaced. The best sample has an average step width of about 400 nm which is comparable to that found on the molecular beam epitaxially grown GaAs. The step edges are parallel to the LCMO [001] direction indicating that the growth rates are anisotropic.
Growth of 1.3 μm InAsP/InGaAsP laser structures by gas source molecular beam epitaxy
Authors: Thiagarajan P. , Bernussi A. A. , Temkin H. , Robinson G. Y. , Sergent A. M. , Logan R. A.
Published: July 2002

The optimization of growth conditions for high quality 1.3 μm InAsP/InGaAsP laser structures by gas source molecular beam epitaxy is reported. Measurements of photoluminescence intensity and threshold currents of highly strained InAsP/InGaAsP multiple quantum well (MQW) lasers indicate an optimum growth temperature substantially lower than that for conventional 1.3 μm InGaAsP quaternary lasers. Broad-area laser structures grown under the optimum conditions exhibited threshold current densities as low as 400 A/cm2. Buried heterostructures with uncoated facets exhibited threshold currents as low as 5.0 mA and internal losses of 8.0 cm−1.
A fast moving diagnostic system on the RFX experiment
Authors: Desideri D. , Serianni G. , Antoni V. , Bagatin M. , Pitcher C. S. , Tramontin L.
Published: July 2002

A fast rotating graphite arm equipped with two Langmuir probes has been developed to investigate the temperature, density, and plasma potential profiles at the edge in the reversed field pinch experiment RFX. The system, driven by an electromagnetic torque, allows a 5 cm radial insertion in about 20 ms with a magnetic field of 0.3 T. The motion of the arm takes place on a plane having an angle of 45° with respect to the direction of the poloidal magnetic field. The probe collecting area is constant during the movement. The initial and final positions of the graphite arm are monitored by electrical contacts. To reconstruct the motion of the equipment, an equivalent lumped-constant network has been developed. The equivalent resistance and inductance are measured before each discharge. By this system radially resolved measurements of edge plasma parameters in a single RFX plasma discharge have been obtained.
Chirp of passively and actively mode-locked semiconductor lasers
Authors: Schell M. , Yu J. , Tsuchiya M. , Kamiya T.
Published: July 2002

The experimental observation of blue-chirped pulses for passive mode-locking and red-chirped pulses for active mode-locking is theoretically explained as a consequence of different α parameters in the gain and absorber section. The influence of nonlinear gain due to carrier heating is also discussed. The knowledge of the chirp is crucial for the optimization of passively mode-locked lasers for spectrally narrow emission or for the emission of linearly chirped pulses.
High T
c step-edge Josephson junctions on silicon substrates
Authors: Linzen S. , Schmidl F. , Dörrer L. , Seidel P.
Published: July 2002

The epitaxial buffer system CeO2/YSZ was used to prepare YBCO films of high crystalline quality on silicon substrates by laser deposition. An advanced technique of step preparation in the YSZ buffer layer preserved the critical current densities of jC (77 K)∼106 A/cm2 for 30 nm thick YBCO films also in the etched parts of the substrate. Further, a homogeneous growth over the 35 to 45 nm deep steps was observed. So we were able to realize step-edge Josephson junctions with critical temperatures up to 77 K. Our dc SQUIDs on silicon substrates showed voltage modulation up to 74 K.
Critical currents and pinning forces in a-axis oriented EuBa2Cu3O7/PrBa2Cu3O7 superlattices
Authors: Vélez M. , Martín J. I. , Vicent J. L.
Published: July 2002

a-axis oriented EuBa2Cu3O7/PrBa2Cu3O7 (EBCO/PBCO) superlattices have been grown by dc sputtering. The critical current (JC) behavior is modified by the pinning force arising from the insulating PrBa2Cu3O7 layers, which in a-axis oriented superlattices are perpendicular to the Cu–O planes. Depending on the EBCO and PBCO layer thicknesses the pinning forces deviate from the usual scaling laws as a function of temperature observed in single films. When B is perpendicular to the sample, an exponential dependence of JC(B) appears as the PBCO thickness is increased (coupling is reduced), and also as the thickness of the EBCO layer is reduced.
Vortex dynamics at microwave frequencies in patterned YBa2Cu3O7−δ thin films
Authors: Willemsen Balam A. , Sridhar S. , Derov John S. , Silva José H.
Published: July 2002

YBa2Cu3O7−δ thin films patterned in the form of a meander line resonant structure, are used as a sensitive probe of vortex dynamics at microwave frequencies. The experiments enable highly sensitive measurements of the complex microwave surface impedance Zs(ω,T,H) of YBa2Cu3O7−δ as a function of applied dc magnetic field, temperature, and frequency. The Zs(H,T) versus H data yield direct experimental results for the vortex viscosity and pinning force constant, which are compared with microscopic theory.
Nitridation of GaAs surfaces using nitrogen through a hot tungsten filament
Authors: Makimoto Toshiki , Kobayashi Naoki
Published: July 2002

This letter reports the nitridation of GaAs surfaces using N2 through a hot tungsten filament. After nitridation, GaAs cap layers were grown by molecular beam epitaxy to form GaAs/GaN/GaAs structures. For these structures, we determine the sheet nitrogen atom concentration by secondary ion mass spectrometry analysis. The sheet nitrogen atom concentration is proportional to the square root of the N2 pressure, indicating that N2 molecules are decomposed into nitrogen atoms to adsorb on the GaAs surfaces. The activation energy of this decomposition process is 3.6±0.4 eV.
Electroluminescence from spark-processed silicon
Authors: Yuan J. , Haneman D.
Published: July 2002

We have fabricated spark-processed silicon so as to produce electroluminescence which is readily visible in semidark conditions. There are three emission peaks at around 1.3, 1.6, and 1.9 eV. The photoluminescence spectrum shows only one peak at around 1.9 eV. The electroluminescence is polarity dependent. Although the average efficiency over areas of several mm2 is low, the emission is concentrated at various spots which are bright and have a much higher efficiency.
Fabrication of ZnO thin films using charged liquid cluster beam technique
Authors: Ryu Choon Kun , Kim Kyekyoon
Published: July 2002

A thin-film deposition technique utilizing a charged liquid cluster beam was applied in the fabrication of ZnO thin films on silicon substrates with a thin layer of native oxide. The liquid precursor was prepared by dissolving Zn-trifluoroacetate in methanol. The film was very uniform, densely packed, and predominantly c-axis oriented. The initially resistive ZnO thin film became conductive after annealing in a hydrogen atmosphere for 5 min. The electrical resistivities of the annealed films ranged from 7.99×10−3 to 1.60×10−2 Ω cm. The electron carrier concentrations were in the range of 3.33–5.35×1019 cm−3 and the mobilities were 7.30–19.07 cm2 V−1 s−1. The refractive index varied from 1.89 to 1.96 as the growth temperature increased from 340 to 440 °C.
Absence of Stark shift in strained Si1−xGex/Si type-I quantum wells
Authors: Miyake Y. , Kim J. Y. , Shiraki Y. , Fukatsu S.
Published: July 2002

Excitonic photoluminescence in a transverse electric field has been studied in strained Si1−xGex/Si type-I quantum wells (QWs) in the weak field regime. With increasing electric field, a steady blue-shift of the free exciton emission energies has been observed, thereby suppressing the anticipated downward shift due to a quantum confined Stark effect. It is revealed that a field-driven decrease of the exciton binding energies gives a good account of the experimental blue-shift for a wide range of well widths, which is also in good agreement with variational calculations. We also find that the extremely small conduction band offset characteristic of stained Si1−xGex/Si type-I QWs is responsible for the absence of the Stark red-shift and the mixed dimensionality.
Diffusion velocity of magnetic fields through high-T
c sintered superconducting rings
Authors: Matsuzawa Hidenori , Matsushita Atsushi , Hayashi Yutaka , Suganomata Shinji
Published: July 2002

By regarding intense electron beams (∼340 keV, ∼2 kA, ∼10 ns) of a single pulse mode as a magnetic field source, we observed diffusion velocities of self-magnetic fields of the beams through a 1.5 mm thick wall of a sintered superconducting Bi(2223) tube. Contrary to our prediction, fields of about 900 G out of the self-magnetic fields diffused through the wall with an average diffusion velocity of 4×104 m/s, almost independently of the operation temperatures for the range from Tc(∼103 K) to 80 K. Such a slow, viscous diffusion process accounts for effective functioning of superconducting tubes as lenses (Supertrons) for the short electron beams.
Direct observation of ultraviolet laser induced photocurrent in oxygen deficient silica and germanosilicate glasses
Authors: Bagratashvili Victor N. , Tsypina Svetlana I. , Chernov Pavel V. , Rybaltovskii Aleksey O. , Zavorotny Yuriy S. , Alimpiev Sergey S. , Simanovskii Yaroslav O. , Dong Liang , Russel Philip St. J.
Published: July 2002

UV laser induced inonization of silicon oxygen deficient centers (SODC) in silica glasses and germanium oxygen deficient centers (GODC) in germanosilicate glasses has been studied by direct displacement photocurrent measurements. For both SODC and GODC the two-photon (two-step) nature of photoionization has been established. The cross sections of transitions from first excited to upper (ionizable) states were estimated as σ12=6×10−18 cm2 for SODC and (0.5–1.0)×10−19 cm2 for GODC. The effect of pulse-to-pulse degradation of the photocurrent signal caused by the screening effect is applied to estimate the lifetimes and ranges of the free carriers. The conclusion was drawn, that ionized SODC and GODC play the key role for free charge trapping.
The ordered–disordered transition in Si delta-doped GaAs
Authors: Buyanov A. V. , Holtz P. O. , Chen W. M. , Monemar B. , Anderson T. G. , Thordson J.
Published: July 2002

We report results for Si layers embedded in GaAs, extending from the delta-doped (δ-doped) range up to 6 monolayers (MLs) derived by means of variable temperature resistivity and Hall effect measurements, secondary ion mass spectrometry (SIMS), and high resolution x-ray diffractometry (HRXRD) techniques. The conductivity transition from free carrier transport in ordered δ-layers (<1 ML) to strongly localized two-dimensional variable range hopping (2D-VRH) transport under potential fluctuation disordered conditions (≳4 ML) is clearly observed. This observation is in good agreement with the SIMS and HRXRD data. Results from the intermediate case with 2–3 MLs are also discussed.
The effect of thermal processing on polycrystalline silicon/SiO2/6H–SiC metal-oxide-semiconductor devices
Authors: Xie W. , Shenoy J. N. , Sheppard S. T. , Melloch M. R. , Cooper J. A.
Published: July 2002

Thermal processing of polycrystalline silicon (polysilicon)/SiO2/SiC metal-oxide-semiconductor (MOS) devices following polysilicon deposition can have an adverse effect on the electrical properties of the SiO2/SiC interface. The primary effect is a negative shift in flatband voltage caused by an increase in fixed oxide charge and interface state density. These effects can be minimized or eliminated by restricting processing temperatures to 900 °C or below following polysilicon gate deposition.
Diffusion cooling mechanism in a hot-electron NbC microbolometer mixer
Authors: Karasik B. S. , Il’in K. S. , Pechen E. V. , Krasnosvobodtsev S. I.
Published: July 2002

The crossover between the electron–phonon relaxation and the diffusion transport of hot electrons in an NbC microbolometer has been studied. At least an 80 ps relaxation time can be achieved in 0.2 μm long bridges of the material with a diffusivity of 8 cm2/s. The high diffusivity is accompanied by a large sheet resistance (≊10 Ω) that simplifies the match of the mixer device made of NbC to planar antenna at terahertz frequencies. The intrinsic noise mechanisms imply a very low mixer noise temperature of the order of a few tens of Kelvin, independent on the radiation frequency.
A low-noise micromachined millimeter-wave heterodyne mixer using Nb superconducting tunnel junctions
Authors: de Lange Gert , Jacobson Brian R. , Hu Qing
Published: July 2002

A heterodyne mixer with a micromachined horn antenna and a superconductor-insulator- superconductor (SIS) tunnel junction as mixing element is tested in the W-band (75–115 GHz) frequency range. Micromachined integrated horn antennas consist of a dipole antenna suspended on a thin Si3N4 dielectric membrane inside a pyramidal cavity etched in silicon. The mixer performance is optimized by using a backing plane behind the dipole antenna to tune out the capacitance of the tunnel junction. The lowest receiver noise temperature of 30±3 K (without any correction) is measured at 106 GHz with a 3-dB bandwidth of 8 GHz. This sensitivity is comparable to the state-of-the-art waveguide and quasi-optical SIS receivers, showing the potential use of micromachined horn antennas in imaging arrays.
Influence of mole fraction on normal incidence bound-free absorption in p-doped InxGa1−xAs/GaAs strained quantum wells
Authors: Tadić M. , Ikonić Z.
Published: July 2002

Bound-free absorption in strained InxGa1−xAs/GaAs p-doped quantum wells is calculated for various values of the mole fraction x. The position dependence of Luttinger parameters is taken into account. Values of absorption exceeding those in unstrained structures by a factor of 2 are found. Also, it is shown that in symmetric structures it suffices to calculate the wave functions of only one block of the Luttinger-Kohn Hamiltonian. © 1996 American Institute of Physics.
Infrared light emission from semiconductor double wells
Authors: Pötz W.
Published: July 2002

A microscopic theoretical analysis of coherent charge oscillations in optically excited GaAs- AlxGa1−xAs double wells and resulting infrared light emission is presented. Our non-phenomenological study is based on generalized Boltzmann–Bloch equations which account for the laser field within the rotating-wave approximation, the dynamics of interacting electron-hole pairs in the heterostructure, excitonic effects, and the destruction of phase coherence by the inter-carrier Coulomb interaction. Emitted THz electromagnetic pulses are analyzed.
Quasiresonance due to electron–electron interaction in coupled quantum dots
Authors: Ugajin Ryuichi
Published: July 2002

Quasiresonant tunneling between states of multiple electrons is caused by electron–electron interaction in coupled quantum dots. The effect of the quasiresonance on optical transition is investigated using the effective mass approximation. The peaks in the optical transition coefficients of two electrons confined in a pair of coupled quantum dots are due to this kind of resonance.
Effect of boron doping on the crystal quality of chemical vapor deposited diamond films
Authors: Won J. H. , Hatta A. , Yagyu H. , Jiang N. , Mori Y. , Ito T. , Sasaki T. , Hiraki A.
Published: July 2002

Boron doping of chemical vapor deposited (CVD) diamond films plays an important role for modification of their electrical properties, as well as it improves crystallinity of the resulting films. A comparative study of crystalline quality has been made for boron doped and undoped CVD diamond. It is also found that the edge emission near 240 nm in cathodoluminescence (CL) is significantly intensified by boron incorporation. It is observed that the hydrogen plasma etching rate of B-doped CVD diamond is much smaller than the etching rate of undoped diamond. This proves the fact, that boron incorporation during CVD growth of diamond films can lead to better crystal quality.
Low energy ion beam mixing as a tool for multilayer x-ray mirror fabrication
Authors: Schlatmann R. , Keppel A. , Bultman S. , Weber T. , Verhoeven J.
Published: July 2002

We present low energy ion beam mixing as a tool for the fabrication of composite layers with smooth interfaces. Using this tool we make a stack of alternating layers of Si and MoxSiy. We measure composition and interfacial roughness (σ) and find x/y≊5/3 and σ≊4 Å. The method can be applied to reduce absorption losses in x-ray multilayer mirrors for high-resolution dispersive purposes, and to increase thermal stability of multilayers. The thickness of the mixed layers is found to be equal to the ion range.
High oxygen and carbon contents in GaAs epilayers grown below a critical substrate temperature by molecular beam epitaxy
Authors: Goo C. H. , Lau W. S. , Chong T. C. , Tan L. S. , Chu Paul K.
Published: July 2002

By quantitative secondary ion mass spectroscopy (SIMS) analyses, oxygen and carbon contents in GaAs epitaxial layers grown by molecular beam epitaxy (MBE) were found to increase significantly when the growth temperature was reduced below a critical value at about 450 °C. The concentrations of oxygen and carbon in GaAs epilayers grown below the critical temperature were about 4×1017 cm−3 and 3×1016 cm−3, respectively. Meanwhile, impurity accumulation during growth interruption became faster resulting in even higher interfacial impurity concentrations. Oxygen and carbon will affect the electrical properties of the GaAs epilayers, especially those grown between 350 °C and 450 °C where defects related to excess As may not be dominating.
Time resolved four-wave mixing technique to measure the ultrafast coherent dynamics in semiconductor optical amplifiers
Authors: Hofmann M. , Brorson S. D. , Mo/rk J. , Mecozzi A.
Published: July 2002

A femtosecond four-wave mixing technique is used to measure the ultrafast coherent dynamics of the optical polarization in semiconductor optical amplifiers. A heterodyne detection scheme enables us to measure a background-free quasi-degenerate four-wave mixing signal even without spatial separation of the pump and probe beam. First results indicate that the polarization dephasing time close to the transparency point is on the order of 100 fs.
Dependence of ZnTe-based contact structure properties on nitrogen concentration
Authors: Taike A. , Momose M. , Kawata M. , Gotoh J. , Mochizuki K. , Nakatsuka S.
Published: July 2002

The effect of nitrogen concentration on the properties of ZnTe-based contact structures, which consist of p-ZnTe layers, ZnSe/ZnTe graded superlattices and p-ZnSe layers is described. The nitrogen concentration of the ZnTe layer was varied by using a modulation doping method. Ohmic I–V characteristics were observed when the nitrogen concentration of the ZnTe layer was as low as 3×1018 cm−3. When the nitrogen concentration rose above 1×1019 cm−3, however, no current was observed in the I–V curves. Nitrogen diffusion from the ZnTe layer to the superlattice and the ZnSe layer was observed by SIMS analysis and PL measurement. The ZnSe layers became highly resistive, probably because deep donors were induced by the nitrogen diffusion.
Low resistance graded contacts to n-type ZnSe
Authors: Lazzarino M. , Ozzello T. , Bratina G. , Paggel J. J. , Vanzetti L. , Sorba L. , Franciosi A.
Published: July 2002

The specific resistance of metal contacts to Cl-doped, n+-type ZnSe can be lowered by over one order of magnitude for comparable doping by fabricating a Zn1−xCdxSe ternary layer of the interface. Photoemission studies of the Al/Zn1−xCdxSe Schottky barriers, and current–voltage measurements indicate that the decrease in the specific contact resistivity reflects the grading of the conduction band discontinuity across the heterostructure.
Femtosecond violet light generation by quasi-phase-matched frequency doubling in optical superlattice LiNbO3
Authors: Lu Yan-Qing , Lu Ya-Lin , Xue Chen-Chen , Zheng Jian-Jun , Chen Xiang-Fei , Luo Gui-Peng , Ming Nai-Ben , Feng Bao-Hua , Zhang Xiu-Lan
Published: July 2002

We report the 390 and 385 nm violet light generation by frequency doubling of a tunable 90 fs, 82 MHz Ti:sapphire laser in two optical superlattice LiNbO3 samples through third-order quasiphase matching (QPM). With the average incident infrared light power of 770 mW, 9.7 and 2.9 mW output second-harmonic lights were obtained without photorefractive damage. The QPM wavelength acceptance bandwidth measurement indicates that violet light generation with higher efficiency is possible.