bluuebunny/crossref_metadata_2025 huggingface dataset:
Low-temperature growth of high resistivity GaP by gas-source molecular beam epitaxy
Authors: Ramdani J. , He Y. , Leonard M. , El-Masry N. , Bedair S. M.
Published: July 2002

GaP films were epitaxially grown on GaP substrates at a low temperature ∼200 °C using gas source molecular beam epitaxy (MBE). The lattice constant of these LT GaP films was found to be larger than that of both the GaP substrate and films grown at high temperatures. These results can be explained by excess phosphorus present in these LT films. The resistivity of these films is comparable to that of the semi-insulating (SI) GaP substrate. These results are considered the first demonstration of high resistivity, semi-insulating LT GaP films.
Optical gain and ultrafast nonlinear response in GaAs/AlAs type-II quantum wells
Authors: Fu W. S. , Olbright G. R. , Klem J. F. , Harris J. S.
Published: July 2002

We describe the femtosecond optical gain nonlinearities for the unusual case of electrons which are distributed between the direct-GaAs and indirect-AlAs layers in a GaAs/AlAs type-II multiple quantum-well (MQW) structure. Due to the spatial separation of electrons from the holes, we observe a significant increase in the gain lifetime (≳150 ps) in type-II MQWs, as compared to type -I MQWs (∼50 ps). In addition, we investigate the effect of a longitudinal electric field on Γ-X energy splitting in type-II structures. Finally, at early times we observe an ultrafast nonlinear optical response in the gain/absorption spectra which we attributed to electron-hole scattering without carrier loss.
Excitonic electroabsorption in type II superlattices
Authors: Li Shaozhong , Khurgin Jacob B.
Published: July 2002

Electric field dependence of the exciton absorption in the ZnSe0.35Te0.65-ZnTe type II superlattice has been studied theoretically. Large effective blue shift of the absorption edge and strong modulation of the absorption prove that type II structures can be used in visible spatial light modulators and switches.
Room temperature, local tailoring of electronic properties of Hg0.3Cd0.7Te by applying an external electric field
Authors: Gartsman Konstantin , Chernyak Leonid , Gilet Jean Marc , Cahen David , Triboulet Robert
Published: July 2002

Electronic properties of initially homogeneous (Hg,Cd)Te samples have been modified on a local scale, in a stable manner at room temperature, by reverse biasing of small-area Schottky contacts on them. This was shown, after the bias voltage had been lifted, by current-voltage measurements and by electron beam-induced current scans. The creation of a clear diodelike structure in the vicinity of the Schottky contact on a scale of about hundred μm could be explained by electromigration of electrically active ions and/or by generation of point and line defects. The latter type of defect was revealed by chemical etch after application of the field.
Growth of InAs on diamond (001) by molecular beam epitaxy
Authors: Williams K. E. , Tarsa E. J. , Speck J. S.
Published: July 2002

Highly oriented InAs films have been grown on natural diamond by MBE. InAs growths were carried out on diamond and on lattice-matched III–V substrates at 250, 300, and 470 °C. The highest quality films (smoothest surface and highest degree of crystallinity) were obtained at 300 °C. X-ray diffraction data indicate that the films have a strong [111] surface normal orientation. RHEED data indicate that the InAs forms a polyvariant thin film with alignment parallel to the interface of one of the 〈110〉InAs directions with one of the 〈110〉diamond directions.
Diamond growth by laser-driven reactions in a CO/H2 mixture
Authors: Rebello J. H. D. , Subramaniam V. V. , Sudarshan T. S.
Published: July 2002

Diamond growth is observed on diamond-abraded single crystal Si(111) substrates from a 99.3%H2/0.7%CO gas mixture at a total pressure of 8 Torr. The gas mixture is reacted by using 193 nm irradiation from an ArF excimer laser. Multiphoton dissociation of CO takes place via the a3Π state, with subsequent chemical reactions between C and O fragments and hydrogen. Of importance is the fact that we observe significant diamond particle growth within a period of 1 h on unheated substrates. This research represents the first known effort where diamond growth is observed at room temperature.
Distributed nature of quantum-well lasers
Authors: Tessler N. , Eisenstein G.
Published: July 2002

In this letter, we show that a quantum-well laser should be modeled as a distributed, rather than a lumped, device. Using a detailed model of current injection which analyzes electron and hole distribution in space as well as in energy, we demonstrate that the static and dynamic laser responses are not uniform along the growth axis.
Phase locking between light pulses and a resonant tunneling diode oscillator
Authors: Lann A. F. , Grumann E. , Gabai A. , Golub J. E. , England P.
Published: July 2002

We report the phase locking of an oscillating GaAs/AlGaAs resonant tunneling diode (RTD) to a train of optical pulses. Locking was achieved by direct illumination of a specially designed RTD with a diode laser pulse train. Locking occurs at all rational frequency ratios and with excitation energies as low as 0.1 pJ/pulse for the principle lock.
Wideband electronically tunable integrated magneto-optic frequency shifter at X band
Authors: Pu Y. , Tsai C. S.
Published: July 2002

A new wideband integrated optical frequency shifter that utilizes noncollinear guided-wave magneto-optic (MO) Bragg diffraction from magnetostatic-forward-volume waves (MSFVW) in a bismuth-doped yttrium-iron-garnet/gadolinium-gallium-garnet (YIG/GGG) waveguide, 6×10 mm2 in size, is reported. Constancy in the output angle of the frequency-shifted light beam, irrespective of the amount of frequency shift, is facilitated by synchronous tuning of the carrier frequency of the MSFVW and the bias magnetic field using an electronic synchronizer. The device operating at the optical wavelength of 1.302 μm and the carrier frequency centered at X band has demonstrated desirable characteristics including large frequency shift, very large tunable bandwidth, large dynamic range, and fast tuning speed. Specifically, bandwidths of 1.61 and 2.35 GHz and dynamic ranges of 35 and 32 dB at the center carrier frequencies of 6.035 and 11.025 GHz, respectively, and a tuning speed of 50 μs have been accomplished.
Dislocation imaging using ion beam induced charge
Authors: Breese M. B. H. , King P. J. C. , Grime G. W. , Wilshaw P. R.
Published: July 2002

The recently developed ion beam induced charge technique has been used to image bands of misfit dislocations in a 4 μm thick epitaxial layer of Si0.875Ge0.125 grown on a Si substrate. The smallest resolvable bandwidth is 0.8 μm under present conditions. The factors which presently limit this value, and methods for improving it are discussed.
Time resolved photoluminescence of porous silicon: Evidence for tunneling limited recombination in a band of localized states
Authors: Tessler L. R. , Alvarez F. , Teschke O.
Published: July 2002

Time resolved photoluminescence of porous silicon at room temperature was measured for several emission energies under 2 ns nitrogen laser excitation. For each emission energy studied there is a broad distribution of lifetimes extending over a few decades. The mean value of the distribution varies with the emission energy, from 3 (2.77 eV) to 50 μs (1.96 eV). The results can be explained by assuming a tunneling limited recombination mechanism between bands of localized states. We associate this behavior with a superficial disordered Si:O:H compound rather than with quantum confinement effects.
Electroluminescence in oxygen co-doped ZnS:TmF3 and ZnS:Tm, Li thin-film devices
Authors: Sohn S. H. , Hamakawa Y.
Published: July 2002

The effects of oxygen co-doping in ZnS:TmF3 and ZnS:Tm, Li thin-film electroluminescent devices are reported. Active layers are deposited in oxygen atmosphere at substrate temperatures of 200 and 300 °C. It is found that by oxygen codoping the luminance of ZnS:TmF3 and ZnS:Tm, Li devices increases, and that this phenomenon becomes marked in the films prepared at a higher substrate temperature.
Microstructure of c-axis oriented lead titanate thin films by pulsed laser ablation
Authors: Ghonge Subodh G. , Goo Edward , Ramesh R.
Published: July 2002

Epitaxial ferroelectric PbTiO3/YBa2Cu3O7−x heterostructures have been fabricated on [001] LaAlO3 by pulsed laser ablation. X-ray diffractometer scans showed only the (00l) peaks from the lead titanate and YBa2Cu3O7−x film indicating c-axis growth. Transmission electron microscopy on planar and cross-sectional samples revealed a single domain film. The c-axis orientation in the lead titanate film is ascribed to the good lattice match of the a-axis of lead titanate with the a- or b-axes of the YBa2Cu3O7−x film. A cubic lead titanate film is deposited above the Curie point. Compressive stresses arise in the lead titanate film due to lattice mismatch. The c-axis orientation is favored since it reduces the compressive residual stresses.
Fabrication of GaAs arrowhead-shaped quantum wires by metalorganic chemical vapor deposition selective growth
Authors: Tsukamoto S. , Nagamune Y. , Nishioka M. , Arakawa Y.
Published: July 2002

We fabricated GaAs arrowhead-shaped quantum wires utilizing both the selective growth technique and the difference in the stabilized crystal facet between GaAs and Al0.4Ga0.6As; the stabilized facet of the GaAs layer is (111)A and that of the Al0.4Ga0.6As layer is (311)A. A systematic change in the size of the quantum wire exhibits blue shifts of the photoluminescence peak, which is due to enhancement of the two-dimensional quantum confinement effect.
Nanoindentation of a supported Au cluster
Authors: Schaefer D. M. , Patil A. , Andres R. P. , Reifenberger R.
Published: July 2002

An atomic force microscope has been used in the attractive (noncontact) force mode to image individual nanometer-size Au clusters preformed in the gas phase and deposited on a variety of atomically flat substrates. Using this technique, it is possible to reliably image preformed clusters in their as-deposited positions. This capability allows nanoindentation studies to measure the mechanical properties of individual nanometer-size clusters supported on atomically flat substrates. We find that the elastic modulus of a 3.1-nm Au cluster is 56−19+33 GPa. This should be compared to a bulk value of 80 GPa for polycrystalline Au and 120 GPa for crystalline Au in the [111] direction.
Fractal growth of silver nanoclusters in a polymer medium
Authors: Mukherjee M. , Saha S. K. , Chakravorty D.
Published: July 2002

Fractal growth of metallic silver within a polymer matrix has been induced by chemical reduction of a suitable sol. A fractal dimension of 1.73±0.01 over a length scale 100–10 000 nm has been estimated. The fractal structure consists of an aggregation of nanosized silver particles having diameters of the order of 15 nm. Electrical conductivity of these nanoparticles shows a lowering of the effective Debye temperature as the particle size is reduced.
Carrier dynamics and emission-line narrowing in n- and p-type molecular-beam grown ZnSe epilayers
Authors: Bolger J. A. , Kar A. K. , Wherrett B. S. , Prior K. A. , Simpson J. , Wang S. Y. , Cavenett B. C.
Published: July 2002

Carrier recombination processes in thin-film epitaxial ZnSe are investigated using a transient-grating technique. For photoexcitation levels in the 1017–1018 cm−3 range the dominant recombination mechanism is found to be radiative, described by a rate coefficient of 8×10−9 cm3 s−1. For densities exceeding approximately 2×1018 cm−3 ultrafast grating recovery is observed, accompanied by line narrowing of the near-band-edge blue photoluminescence; this is interpreted as being due to stimulated radiative recombination.
Voltage tunable three-color quantum well infrared photodetector
Authors: Tidrow M. Z. , Choi K. K. , Lee C. Y. , Chang W. H. , Towner F. J. , Ahearn J. S.
Published: July 2002

A voltage tunable three-color quantum well infrared photodetector (QWIP) consisting of asymmetric GaAs/AlGaAs double quantum wells has been demonstrated. The detector uses electron intersubband transitions in a coupled asymmetric double quantum well superlattice. The infrared photocurrent spectrum characterized using a blackbody monochromator source shows three prominent peaks appearing at 8.4 μm, 9.6 μm, and 10.3 μm under different biases. The three detection peaks are well resolved and can be independently selected by tuning the applied voltage. The responsivity and the detectivity of the detector at different biases and operating temperatures are characterized and found to be sufficient for detector operation at temperatures ∼60 K.
Optical properties of two-dimensional photonic lattices fabricated as honeycomb nanostructures in compound semiconductors
Authors: Gourley P. L. , Wendt J. R. , Vawter G. A. , Brennan T. M. , Hammons B. E.
Published: July 2002

We have experimentally studied two-dimensional photonic lattices, honeycomb nanostructures, fabricated by electron beam lithography with (Al,Ga)As materials. Surface normal optical properties were investigated by measuring reflectance to determine the effective index of refraction and lattice stability against degradation. Also, continuous wave and time-resolved luminescence spectroscopy was used to assess electron-hole recombination. Finally, light scattering was employed to study photon coupling and propagation through the lattice. These measurements show that the structures are stable, that nonradiative surface recombination is present, and that resonant coupling of light into/out of the lattice occurs at selected wavelengths satisfying a Bragg condition.
Enhanced gain and output power of a sealed-off rf-excited CO2 waveguide laser with gold-plated electrodes
Authors: Heeman-Ilieva M. B. , Udalov Yu. B. , Hoen K. , Witteman W. J.
Published: July 2002

The small-signal gain and the laser output power have been measured in a cw sealed-off rf-excited CO2 waveguide laser for two different electrode materials, gold-plated copper and aluminum, at several excitation frequencies, gas pressures and mixture compositions. In the case of the gold-plated electrodes an enhancement of the gain up to a factor of 2 and the output power up to a factor of 1.4 with time at a frequency of 190 MHz and 60 Torr of 1:1:5+5% (CO2:N2:He+Xe) mixture is observed. This is believed to be the result of the gold catalytic activities which are favored by increased electrode temperatures and helium rich gas compositions.
Effective mass and quantum lifetime in a Si/Si0.87Ge0.13/Si two-dimensional hole gas
Authors: Whall T. E. , Mattey N. L. , Plews A. D. , Phillips P. J. , Mironov O. A. , Nicholas R. J. , Kearney M. J.
Published: July 2002

Measurements of Shubnikov de Haas oscillations in the temperature range 0.3–2 K have been used to determine an effective mass of 0.23 m0 in a Si/Si0.87Ge0.13/Si two-dimensional hole gas. This value is in agreement with theoretical predictions and with that obtained from cyclotron resonance measurements. The ratio of the transport time to the quantum lifetime is found to be 0.8. It is concluded that the 4 K hole mobility of 11 000 cm2 V−1 s−1 at a carrier sheet density of 2.2×1011 cm−2 is limited by interface roughness and short-range interface charge scattering.
High brightness slab waveguide carbon monoxide laser
Authors: Colley A. D. , Villarreal F. , Baker H. J. , Hall D. R.
Published: July 2002

Near diffraction limited output from a slab waveguide carbon monoxide gain medium using a hybrid confocal unstable resonator is described. A device producing a cw output of 80 W in a beam with M2=1.5 has been demonstrated operating with 12% efficiency at −30 °C.
High temperature operation of 1.3 μm ridge waveguide lasers using lattice matched and strained multiple quantum wells
Authors: Lu H. , Blaauw C. , Makino T. , Gallant M.
Published: July 2002

We report the high temperature operation of 1.3 μm ridge waveguide Fabry–Perot lasers utilizing a double-carrier-confinement heterostructure, with an active region containing an n-type lattice-matched multiple quantum well (MQW) as well as a p-type strained MQW. All devices with a cavity length of 400–1000 μm and as-cleaved uncoated facets operated beyond 100 °C in the cw mode with an optical power in excess of 8 mW. T0 was found to be in the range of 65–75 and 72–98 K, for uncoated devices and devices with one high-reflectivity-coated facet, respectively.
Evidence for population inversion in excited electron states of a double barrier resonant tunneling structure
Authors: Cockburn J. W. , Skolnick M. S. , Whittaker D. M. , Buckle P. D. , Willcox A. R. K. , Smith G. W.
Published: July 2002

We report evidence for a population inversion between excited electron states of the quantum well of a GaAs-AlGaAs double barrier resonant tunneling structure (DBRTS). The relative populations of the states are determined by photoluminescence spectroscopy of the tunneling electrons in the structure. When the DBRTS is biased at the fourth electron resonance, the population of the n=4 confined level is found to be greater than that of the n=3 state. We show that such a population inversion is consistent with a rate equation analysis of the relative populations of the two levels when electrons tunnel into n=4.
Determination of the composition and thickness of borophosphosilicate glass films by infrared ellipsometry
Authors: Ossikovski R. , Blayo N. , Drévillon B. , Firon M. , Delahaye B. , Mayeux A.
Published: July 2002

A quantitative analysis of IR ellipsometry spectra of borophosphosilicate glass (BPSG) thin films deposited on silicon wafers is presented. The film thickness is determined with a standard deviation of 5.8 nm using a fitting procedure based on only two free parameters. A simple linear analysis of the dependence of the ellipsometric measurements upon film composition provides standard deviations of 0.04 and 0.12 wt % on boron and phosphorus content, respectively.
ZnMgSeTe light emitting diodes
Authors: Faschinger W. , Krump R. , Brunthaler G. , Ferreira S. , Sitter H.
Published: July 2002

The MBE growth of light emitting diodes based on junctions between n-ZnMgSe and p-ZnMgSeTe is reported. For optimized compositions of the n- and p-layer, doping levels as high as n=p=2×1018 cm−3 were obtained. The p contacts of these diodes are ohmic, and the voltage needed to achieve a given current density is comparable to that of the best ZnSe based p-n junctions reported in the literature. The diodes show green electroluminescence up to room temperature.
Electrical properties of epitaxially grown CdTe passivation for long-wavelength HgCdTe photodiodes
Authors: Bahir G. , Ariel V. , Garber V. , Rosenfeld D. , Sher A.
Published: July 2002

Results of experimental measurements and theoretical analysis are presented for the TiAu/ZnS/CdTe/HgCdTe metal–insulator–semiconductor heterostructure. The passivation of HgCdTe is provided by a double layer consisting of a dielectric ZnS placed on top of an epitaxial CdTe layer. Both HgCdTe and CdTe were grown by metalorganic chemical vapor deposition. Two types of CdTe layers were investigated: one was grown directly, in situ, immediately following the growth of HgCdTe; the second was grown indirectly using previously grown HgCdTe samples. It is shown that directly grown CdTe layers lead to low fixed interface charge, which is a good condition for passivation. The indirectly grown samples are still acceptable, but not as good as the directly grown samples. We demonstrate, on the basis of theoretical considerations, that the dielectric ZnS improves the flatband condition at the CdTe/HgCdTe interface.
Short wavelength (5.36–1.85 μm) nonlinear spectroscopy of coupled InGaAs/AlAs intersubband quantum wells
Authors: Martinet E. L. , Chui H. C. , Woods G. L. , Fejer M. M. , Harris J. S. , Rella C. A. , Richman B. A. , Schwettman H. A.
Published: July 2002

We report short wavelength second-harmonic generation (SHG) spectroscopy of asymmetric coupled In0.6Ga0.4As/AlAs quantum wells (QWs). The QW is designed to show maximum second-order nonlinear susceptibility χ(2) for SHG of 4 and 2 μm wavelengths by single and double resonance effects, respectively. SHG spectroscopy across the midinfrared is measured using both a CO2 and a free electron laser as pumps. The χ(2) of the QW is extracted from interference of the second-harmonic fields from the QW and GaAs substrate, determined by the azimuthal dependence of the SHG power. We measure χ(2) of the QW for harmonic wavelengths between 5.36 and 1.85 μm. This is the shortest wavelength SHG to date by any QW intersubband interaction. Good agreement of experiment with theory for the dispersion of χ(2) for both singly and doubly resonant conversion is observed throughout the midinfrared.
Epitaxial growth of optical Ba2NaNb5O15 waveguide film by pulsed laser deposition
Authors: Liu J. M. , Zhang F. , Liu Z. G. , Zhu S. N. , Shi L. J. , Wu Z. C. , Ming N. B.
Published: July 2002

The waveguiding Ba2NaNb5O15 films have been prepared on KTiOPO4 substrates by pulsed laser deposition technique. Characterizations of the as-grown films by the x-ray θ–2θ scan and β scan and the scanning electron microscopy revealed that epitaxial (110)-oriented Ba2NaNb5O15 films with small surface roughness were achieved on (100)-oriented KTiOPO4 plates. The x-ray photoelectron spectrometer was employed to probe the chemical constitution of the as-grown films. Favorable optical waveguiding properties were demonstrated by m-line measurement and evaluation of propagation loss on the order of 1.0 dB/cm of TM and TE multimodes.
Fluorine enhanced oxidation of silicon at low temperatures
Authors: Kazor A. , Jeynes C. , Boyd Ian W.
Published: July 2002

We report the oxidation of silicon at and below 550 °C in a mixture of oxygen and fluorine. Introduction of small concentrations of fluorine (<0.1%) in the oxygen ambient increases the oxide growth sharply to rates in excess of 8 Å/min where the average fluorine concentration in the oxide can exceed 6 at. %. For each oxidation temperature there was a unique fluorine concentration at which the oxidation rate was at its highest. Fluorine depth profiles in the film were determined by high depth resolution nuclear reaction analysis, and high interface concentrations of fluorine were observed.
Annealing behavior of AlxGa1−xAs:C grown by metalorganic molecular beam epitaxy
Authors: MacKenzie J. D. , Abernathy C. R. , Pearton S. J. , Chu S. N. G.
Published: July 2002

The effects of rapid thermal annealing on the materials properties of the carbon-doped AlxGa1−xAs system have been systematically studied. The hole concentration in GaAs and AlGaAs layers doped up to 1021 cm−3 drop severely after annealing for 5 min at temperatures above 650 °C. The decrease in hole concentration produces a minimum of 8×1019–1020 cm−3 free carriers. The hole concentration for heavily doped AlAs is relatively stable up to 950 °C in material with p∼1020 cm−3. Unlike GaAs, AlAs with a low hole concentration but a substantially higher total carbon background, exhibits a substantial drop in activation for annealing temperatures above 650 °C. High resolution x-ray diffraction studies show that the lattice parameter of both the AlAs and GaAs becomes less strained relative to the GaAs substrate as the annealing temperature is increased. In both materials, the changes observed with annealing are believed to be due to pairing of the carbon atoms on the As sublattice, resulting in a decrease in the electrically active carbon and the strain in the layer.
Simultaneous blue- and red-shift of light-hole and heavy-hole band in a novel variable-strain quantum well heterostructure
Authors: Zhou Weimin , Shen H. , Pamulapati J. , Cooke P. , Dutta M.
Published: July 2002

We have designed and studied a new type of strained semiconductor quantum well structure, variable-strain quantum well. The strain within the quantum well is graded from compressive to tensile in order to obtain mutually opposing slopes for the heavy- and light-hole band edges, causing the heavy and light holes to experience opposite fields created by the same strain. A unique bias controlled crossover with a simultaneous red and blue quantum confined Stark shift for the heavy- and light-hole transitions, respectively, has been observed by electroreflectance spectra. This results in a bias controlled change of the polarization properties and the transition energies suitable for polarization controllable photonic devices.
Josephson effects in YBa2Cu3Oy grain boundary junctions on (100)MgO bicrystal substrates
Authors: Lee Kiejin , Iguchi Ienari
Published: July 2002

The grain boundary YBa2Cu3Oy(YBCO) Josephson junctions are fabricated on (100)MgO bicrystal substrates with a misorientation angle of 24° and the microwave properties of Josephson effects are studied up to millimeter-wave range. Strong [100]//[010] and [010]//[100] in-plane orientations are observed at the junction interface of a YBCO film, whose microscopic geometries are discussed in connection with the observed Josephson effects. The directly observed maximum Josephson microwave self-radiation powers from the junction at receiver frequencies of fREC=22 GHz and 47 GHz are 3.2×10−12 W and 5.6×10−14 W, respectively. The observed characteristic voltage (Vc) is 4.4 mV, corresponding to the frequency of about 2 THz at 4.2 K.
Low temperature device creation in Si via fast Li electromigration
Authors: Chernyak Leonid , Lyakhovitskaya Vera , Cahen David
Published: July 2002

Micrometer-sized homojunction structures can be formed by local application of strong electric fields (∼106 V/cm) at ambient temperatures to Si which was homogeneously doped n-type by Li. Such junctions show electroluminesence and two such junctions, arranged back to back, act as transistors, as evidenced by electron beam induced current, current-voltage and capacitance-voltage measurements. These results are explained by thermally-assisted electromigration of Li.
Design and use of a gridded probe in a low-pressure rf argon discharge
Authors: Ingram S. G. , Annaratone B. M. , Ohuchi M.
Published: July 2002

Low-pressure rf discharges can be investigated experimentally using many diagnostic techniques. In many cases the simple Langmuir probe can be used to make reliable measurements of basic plasma parameters. In the work reported here, this technique has been extended by employing a gridded Langmuir probe in a parallel-plate rf discharge for the first time. Design considerations and construction of the probe are discussed. It was found that optimum performance could be achieved using a construction based on two independent grids with a nonzero potential difference between them. The probe was used to measure plasma parameters in a low-pressure argon discharge excited at 13.56 MHz between two planar parallel electrodes. Results obtained for different probe orientations along the discharge axis show the electron energy distribution to be approximately Maxwellian in the plasma bulk. However, there is evidence for anisotropy in the electron energy distribution in the region of the plasma nearest to the driven electrode. In fact the high-energy tail observed can be attributed to secondary electron emission from the electrode surface.
Investigation of fast diffusing impurities in silicon by a transient ion drift method
Authors: Zamouche A. , Heiser T. , Mesli A.
Published: July 2002

Transient ion drift in a depletion region of a Schottky barrier has been used to investigate Cu diffusion in boron or aluminum doped silicon. It is shown that in the investigated temperature range, the Cu-boron pairing is negligible, while for the other acceptors it is well described by a Coulombic interaction. In order to test the validity of the model used to extract the diffusion coefficient, the method has been applied to the well-known Li diffusion in silicon. For both Li and Cu ions, an excellent agreement with literature diffusivity data was obtained.
Above-threshold behavior of high-power, single-mode antiresonant reflecting optical waveguide diode lasers
Authors: Mawst L. J. , Botez D. , Nabiev R. F. , Zmudzinski C.
Published: July 2002

Above-threshold analysis of antiresonant reflecting optical waveguide (ARROW) diode lasers has been performed. One key finding is that preferential pumping of the (central) low-index core region dramatically enhances the device single-mode power capability, as a result of defocusing and subsequent radiation-loss increase for the first-order spatial mode. Stable, single-mode operation to drive levels ≳10× threshold is predicted for 6-μm wide core devices, in excellent agreement with experiment. Similar performance is found to hold true for ARROW devices with cores as wide as 10 μm, although due to gain spatial hole burning, the far-field beam pattern experiences mild broadening. Study of triple-core ARROW structures of 20-μm-wide aperture shows stable fundamental-mode operation to ≳10× threshold, thus raising the prospect for stable, single-mode reliable operation to power levels as high as 1 W cw.
Characterization of resonant tunneling paths in current–voltage characteristics line shapes
Authors: Rivera P. H. , Schulz P. A.
Published: July 2002

We analyze the current density-voltage characteristics of double-barrier tunneling diodes, with different spacer layers, within the framework of a Poisson solver together with a coherent tunneling approximation for transmission probabilities. We show that varying the spacer layer thickness, together with barrier heights, changes dramatically the current density-voltage characteristics line shape, which is revealed to be an important qualitative signature of the tunneling paths involved in the double-barrier diodes under operation.
Strong blueshift of the excitonic transition in the InGaAs/InP/InAsP antisymmetric coupled quantum wells
Authors: Huang Yimin , Chen Yimin , Lien Chenhsin
Published: July 2002

A new strained InGaAs/InP/InAsP antisymmetric coupled-quantum-well (CQW) structure with significant enhancement of the blue and red Stark effects in the first heavy-hole-to-electron excitonic transition is proposed in this letter. The calculated amount of blueshift is about 48 meV as the applied electric field varied from 0 to 90 kV/cm and the red Stark shift of about 56 meV can be achieved with an applied electric field in the 0 to −90 kV/cm range. The results of the strong Stark effect in the antisymmetric CQW structure may have potential applications in sophisticated new electronic devices, such as optical switching devices and tunable lasers.
Avalanche transients in shallow p-n junctions biased above breakdown
Authors: Lacaita A. , Spinelli A. , Longhi S.
Published: July 2002

We have studied the avalanche dynamics in shallow junction avalanche diodes designed for detection and timing of single photons. Space charge effects have been correctly taken into account, and both electron and hole transport were considered. Based on the results of the detailed computer simulation we have developed a simplified model of the detector which can be used for studying the avalanche transient in these devices and for optimizing the detector structure for the best timing performance. The results are in good agreement with the experiments.
Au–Sn solder bumps with tungsten silicide based barrier metallization schemes
Authors: Pittroff W. , Reiche T. , Barnikow J. , Klein A. , Merkel U. , Vogel K. , Würfl J.
Published: July 2002

A homogeneous melting eutectic Au/Sn solder bump for flip-chip application has been developed. The underbump metallization consists of a WSi0.4N0.2-layer and a Ni-wetting layer. The solder is deposited as a sequence of alternating Au and Sn layers. The bump can be exposed to multiple fluxless reflow cycles. The reflow of the solder as deposited starts with a phase forming process in the solid state which results in an eutecticlike phase and the near eutectic δ and ζ phases. The δ and ζ phases dissolve during the liquid state stage of the reflow at temperatures between 300 and 350 °C.
Desegregation of boron at the grain boundaries of the in situ boron doped diamond films
Authors: Huang J. T. , Hu C. S. , Hwang J. , Chang H. , Lee L. J.
Published: July 2002

High quality in situ boron doped polycrystalline diamond films were grown on the scratched Si (100) substrate. A saturated deionized water solution of boron acid was chosen as a dopant source. The concentration profiles of boron, tantalum, and oxygen were examined by using scanning Auger nanoprobe and secondary ion mass spectroscopy. The boron atoms are uniformly distributed inside each diamond grain. However, no Auger signal from boron was observed at grain boundaries within the detection limit. In contrast, tantalum atoms are uniformly distributed across diamond grains and grain boundaries. A simple model was proposed in explaining the boron desegregation.
Improved thermal stability of AlGaAs–GaAs quantum well heterostructures using a ‘‘blocking’’ Zn diffusion to reduce column-III vacancies
Authors: Krames M. R. , Minervini A. D. , Chen E. I. , Holonyak N. , Baker J. E.
Published: July 2002

Data are presented on the reduction of layer intermixing (disordering) in AlGaAs–GaAs quantum well heterostructures (QWH) during high-temperature anneals by an initial low-temperature ‘‘blocking’’ Zn diffusion. Room-temperature photoluminescence measurements of the increase in the lowest electron-to-heavy-hole transition energy in the QW are used to characterize the extent of layer intermixing. Doped (C and Si) samples annealed (850 °C, 12 h) after a low-temperature blocking Zn diffusion (480 °C) exhibit reductions in energy shift from ∼177 meV to as little as ∼18 meV. Similar effects are also observed, but to a lesser extent, for undoped samples. The improved thermal stability is attributed to a Zn-diffusion induced reduction in the number of column-III vacancies in the active layers and is confirmed by secondary-ion mass spectroscopy measurements.
Real time analysis of tokamak discharge parameters
Authors: Ferron J. R. , Strait E. J.
Published: July 2002

The techniques used in implementing two applications of real time digital analysis of data from the DIII-D tokamak are described. These tasks, which are demanding in both the speed of data acquisition and the speed of computation, execute on hardware capable of acquiring 40 million data samples per second and executing 80 million floating point operations per second. In the first case, a feedback control algorithm executing at a 10 kHz cycle frequency is used to specify the current in the poloidal field coils in order to control the discharge shape. In the second, fast Fourier transforms of Mirnov probe data are used to find the amplitude and frequency of each of eight toroidal mode numbers as a function of time during the discharge. Data sampled continuously at 500 kHz are used to produce results at 2 ms intervals.
Comparative analysis of the optical quality of single In0.1Ga0.9As/Al0.33Ga0.67As quantum wells grown by molecular beam epitaxy on (100) and (311) GaAs substrates
Authors: Brandt O. , Kanamoto K. , Tsugami M. , Isu T. , Tsukada N.
Published: July 2002

We investigate the room-temperature photoluminescence of single In0.1Ga0.9As/Al0.33Ga0.67As quantum wells grown simultaneously on (100), (311)A, and (311)B GaAs substrates. The measurements, taken under both steady state and transient conditions, evidence that nonradiative (Shockley-Read-Hall) recombination dominates the emission of both the [100] and [311]B oriented samples at low injection levels, and is still important up to injection levels approaching those in lasers. The emission of the [311]A oriented sample is, in contrast, dominated by radiative recombination already at modest injection levels. The origin of this remarkable feature of the [311]A oriented sample is traced back to the reduced incorporation of deep recombination centers at the (311)A In0.1Ga0.9As/Al0.33Ga0.67As interface.
Eu-doped CaF2 grown on Si(100) substrates by molecular beam epitaxy
Authors: Fang X. M. , Chatterjee T. , McCann P. J. , Liu W. K. , Santos M. B. , Shan W. , Song J. J.
Published: July 2002

Eu is incorporated into CaF2 films grown on Si(100) by molecular beam epitaxy using elemental Eu evaporation. Eu doping as high as 4.05 at. % does not significantly degrade the surface morphology, indicating a relatively high solubility of Eu in CaF2. Photoluminescence spectra from Eu-doped CaF2 show strong blue emissions from Eu2+ ions in cubic sites. The inhomogeneous broadening of the zero-phonon line near 24 190 cm−1 is reduced by ∼20% upon in situ annealing at 1100 °C.
A low-noise high-speed diode laser current controller
Authors: Libbrecht K. G. , Hall J. L.
Published: July 2002

We describe a new diode laser current controller which features low current noise, excellent dc stability, and the capacity for high-speed modulation. While it is simple and inexpensive to construct, the controller compares favorably with the best presently available commercial diode laser current controllers.
Ultrahigh Q pendulum suspensions for gravitational wave detectors
Authors: Blair D. G. , Ju L. , Notcutt M.
Published: July 2002

Pendulum suspensions for laser interferometer gravitational wave detectors need to have an extremely high Q factor to minimize Brownian motion noise. In this paper we analyze the limits to the Q factor of the compound pendulum. We show that the observed acoustic loss of niobium can allow pendulum Q factors of 1010 to be achieved. This should enable a 3 km terrestrial laser interferometer detector to achieve strain sensitivity of 10−22/√Hz at frequencies as low as 10 Hz. At cryogenic temperatures Q factors up to 1012 should be achievable.
Influence of the molecular conformation on the charge transport of irradiated P(VDF/TrFE) copolymers
Authors: da Cunha H. N. , Faria R. M.
Published: July 2002

In this letter we show that upon irradiation a poly(vinylidene fluoride)-trifluorethylene copolymer exhibits a molecular-dependent radiation-induced conductivity. It was observed that at room temperature, under which P(VDF/TrFE) is ferroelectric and possesses a transplanar conformation, the carrier recombination is negligible. Above the Curie temperature (TGTG′ conformation), the radiation-induced conductivity (RIC) is three orders of magnitude higher, and recombination becomes an important process as the trapping time is considerably reduced. The experimental results were analyzed using a modified multiple-trapping model usually applied to disordered materials. Important charge transport parameters were determined for the P(VDF/TrFE) copolymer for both ferro- and paraelectric phases.
Amorphous Ni50Nb50/C multilayers for soft x rays made by pulsed laser deposition
Authors: Vitta Satish , Metzger T. H. , Mai H. , Peisl J.
Published: July 2002

Amorphous Ni50Nb50/C multilayers with a repeat period of 2.39 nm, suitable for the water window region of soft x rays, have been prepared by pulsed laser deposition. The interface and in-plane structure of these multilayers was studied by low angle hard x-ray diffraction. It was found that the interfaces are very sharp with a typical lateral correlation length of the order of 180 nm.
A novel miniature spectrometer using an integrated acousto-optic tunable filter
Authors: Wang Xiaolu , Vaughan Derek E. , Pelekhaty Vladimir , Crisp Joy
Published: July 2002

In this paper, a novel miniature spectrometer is described which employs an integrated-optic acousto-optic tunable filter (IAOTF) as the monochromatic wavelength selective element. The performance of the system is highlighted by measuring the absorption spectra of two samples in the region of 1400 to 1600 nm. In the experiment, a light emitting diode (LED) centered at a wavelength of 1530 nm, is used as the light source and spectral filtering is achieved using an IAOTF that is tunable over more than 260 nm. The device exhibits a FWHM resolution of 1.2 nm, measures 25×3×1 mm3, weighs under 1 g and requires less than 70 mW of rf drive power. This miniature spectrometer offers several attractive design features that have utilities in a variety of applications, particularly for portable analysis and operation in harsh environments.
Low energy vacuum arc ion source
Authors: Brown Ian G. , Anders Simone , Dickinson Michael R. , Fojas Paul B. , MacGill Robert A.
Published: July 2002

We have developed a version of vacuum arc ion source that produces a metal ion beam with energy of order 1 keV. The ion beam extractor is a three-grid, multiaperture configuration with a low accel–decel ratio so that ions are extracted from the plasma at a relatively high energy and then decelerated to the desired net beam energy. We have tentatively given this ion source the name leva, for low energy vacuum arc ion source. The leva source is cylindrical in shape with diameter about 6 cm and length about 16 cm and is located completely within the vacuum system; it is constructed from metal and alumina only and can be baked. We have operated it at net extraction voltages in the range 0.5–10 kV and produced a titanium ion beam current of up to 120 mA. Here we describe the source construction details and its performance.
Oscillations at liquid-nitrogen temperatures in the transconductance of a silicon metal-oxide-semiconductor field-effect transistor with a neck in the middle
Authors: Takeuchi Kan , Hisamoto Dai , Aoki Masaaki
Published: July 2002

The conductance of a silicon metal-oxide-semiconductor field-effect transistor, the gate of which has a neck in the middle, was measured at liquid-helium temperatures and liquid-nitrogen temperatures. The channel width in the neck region configured by SiO2 isolation regions is below 50 nm. The transconductance at liquid-nitrogen temperatures shows periodic oscillations that are accentuated by negative substrate bias. We explain the results based on the one-dimensional subbands formed in the neck region.
Extended function of a high-T
c transition edge bolometer on a micromachined Si membrane
Authors: Neff H. , Laukemper J. , Hefle G. , Burnus M. , Heidenblut T. , Michalke W. , Steinbeiss E.
Published: July 2002

The bolometric performance of a high-Tc transition edge bolometer has been evaluated within the temperature range 80 K<T<300 K. The detectivity D* of the device is peaking at transition midpoint and remains at moderate levels up to room temperature. The bolometric time constant of the device increases from 0.33 ms at transition midpoint to 1.55 ms at ambient temperature. The noise pattern displays 1/f  behavior at low frequency and is scaling with bias current and the thermal resistance coefficient β of the superconducting film.
Effects of finite temporal duration on spatial solitons in a planar optical waveguide
Authors: Liu Shan-liang , Wang Wen-zheng , Xu Jing-zhi
Published: July 2002

The effects of finite temporal duration on the spatial solitons in a planar optical waveguide are analyzed. The results show that (i) the self-trapped pulses with finite temporal duration are unstable and collapse at higher peak power in a planar optical waveguide with the anomalous group velocity dispersion (GVD), but the collapse does not occur in a planar optical waveguide with the normal GVD; (ii) the spatial soliton with finite temporal duration has a transverse velocity which is proportional to the spatial width and inversely proportional to the temporal duration of the soliton, and the bright spatiotemporal solitons do not form multiple soliton bound states; and (iii) the peak power required for self-trapping of the pulse in a planar optical waveguide with the normal GVD is less than the critical peak power for collapse of the pulses in a planar optical waveguide with the anomalous GVD.
InGaAsP/GaAs elastically strained quaternary solid solutions with high critical thicknesses grown by liquid phase epitaxy
Authors: Bolkhovityanov Yu. B. , Jaroshevich A. S. , Nomerotsky N. V. , Revenko M. A. , Trukhanov E. M.
Published: July 2002

Highly elastically strained films of InGaAsP solid solutions in 1.4–1.8 eV interval of band gaps were grown on GaAs(111)B substrates by liquid phase epitaxy. Elastic strains close to 1% are achieved. The determined critical thicknesses exceed the predictions of the energy equilibrium theory by Matthews and Blakeslee by as much as an order of magnitude.
Room-temperature operation of intermixed GaAs/AlGaAs gain coupled distributed feedback lasers
Authors: Kaden C. , Gauggel H.-P. , Prins F. E. , Burkard M. , Adler F. , Schweizer H. , Smith G. W.
Published: July 2002

Room-temperature gain coupled distributed feedback (GC-DFB) lasers have been realized by implantation induced intermixing in the GaAs/AlGaAs material system. The implantation dose has been systematically varied to realize GC-DFB lasers with different gain coupling coefficients due to different band-gap modulation of the active quantum wells. It is demonstrated that a band-gap modulation of 7 meV is sufficient to achieve a high single mode yield at room temperature. The results are discussed on the basis of calculations with the optical matrix theory.
A photothermal beam deflection apparatus for the time-resolved kinetic study of fast photophysical and photochemical processes
Authors: Laman David M. , Falvey Daniel E.
Published: July 2002

Photothermal beam deflection (PBD) is a highly sensitive technique for monitoring the time-dependent heat release resulting from fast (μs time scale) photophysical and photochemical processes. A PBD apparatus which has been developed for use in the time-resolved kinetic study of fast photophysical and photochemical processes is described here. This instrument uses a pulsed excimer laser as the excitation source and a cw He–Ne laser as the probe beam in a counterpropagating geometry. The probe beam deflection is detected with a segmented fast photodiode (bi-cell) and a wideband differential amplifier. This PBD system has been used to study second-order (nongeminate back electron transfer) and complex-exponential (decay of molecular triplet states in the presence of oxygen) processes in solution. The kinetic information obtained with this PBD system has been shown to compare favorably with the same kinetic information obtained by time-resolved transient absorption spectroscopy.
Improved uniformity of multielement thin films prepared by off-axis pulsed laser deposition using a new heater design
Authors: Cillessen J. F. M. , de Jong M. J. M. , Croizé X.
Published: July 2002

A new compact substrate heater for the pulsed laser deposition (PLD) technique has been developed. The heater is built up of a radiation part, consisting of two quartz halogen lamps, and a rotating absorber, made of a SiC disk, to which the substrate is attached. The advantage of this system in comparison to conventional heaters is its suitability for substrate temperatures up to 800 °C in any ambient (vacuum as well as corrosive gases). The heater is applied for the deposition of thin, multielement films with improved thickness uniformity using off-axis PLD. This technique makes use of a rotating substrate which is off-centered from the depositing plasma plume. The thickness profile is modeled using predetermined stationary thickness distributions. For a variety of multielement materials good experimental uniformities in terms of thickness (in close agreement with the calculations) and of chemical composition are obtained. A relation is found between the value of experimental parameters and the achievable uniformity area within a large pressure range.