bluuebunny/crossref_metadata_2025 huggingface dataset:
Prebreakdown conduction in zinc oxide varistors: Thermionic or tunnel currents and one-step or two-step conduction processes
Authors: Castro M. S. , Aldao C. M.
Published: July 2002

This letter is aimed at understanding the intergranular conduction in zinc oxide varistors. In particular, we have studied current-voltage and Arrhenius plots of the resistive current for the prebreakdown conduction. A current-temperature (I-T) relation has been found to present two breaks at ∼370 and ∼240 K. Although this result can be interpreted as a consequence of distinct regimes, we found that experimental I-T curves can be theoretically reproduced by calculating currents for a double Schottky barrier. Experimental results were fitted with one- and two-step transport process models. It was found that a two-step model better reproduces the electrical properties of these devices.
Nature of P
b-like dangling-orbital centers in luminescent porous silicon
Authors: Rong F. C. , Harvey J. F. , Poindexter E. H. , Gerardi G. J.
Published: July 2002

The Pb-like dangling-orbit centers in luminescent porous silicon (LPSi) have been enhanced to very high concentration (1015 cm−2) by gentle oxidation. High signal-to-noise ratio and very sharp lines enable the g-value maps, and 29Si hyperfine and superhyperfine structures to be clearly resolved by ordinary EPR. Only one Pb-like center is observed, and it is proven to be of the Pb0 variety (⋅Si≡Si3). The relative EPR signal strengths from different g limbs indicate that the LPSi crystallite morphology is not dominated by needles or platelets.
Control of interface stoichiometry in InAs/GaSb superlattices grown by molecular beam epitaxy
Authors: Bennett Brian R. , Shanabrook B. V. , Wagner R. J. , Davis John L. , Waterman J. R.
Published: July 2002

The InAs/GaSb materials system, with different species for both cations and anions, allows one to envision the construction of heterojunctions with either InSb- or GaAs-like interfaces. As a result, this system provides a unique opportunity to explore the limits of interfacial control that can be achieved at the monolayer level by vapor phase growth techniques. Using migration-enhanced epitaxial techniques, we have prepared a series of InAs/GaSb superlattices with both types of interfaces. The large differences in bond lengths and vibrational properties of InSb and GaAs interfaces allow x-ray diffraction and Raman spectroscopy to be sensitive probes of interfacial structure. The x-ray and Raman measurements reveal that it is possible to grow superlattices with almost pure InSb-like or GaAs-like interfaces.
Effects of microstructure on transport properties of undoped hydrogenated amorphous silicon films
Authors: Dawson R. M. A. , Fortmann C. M. , Gunes M. , Li Y. M. , Nag S. S. , Collins R. W. , Wronski C. R.
Published: July 2002

Electronic transport properties have been investigated in undoped hydrogenated amorphous silicon (a-Si:H) materials whose microstructure and void fraction are changed by deposition temperature (Ts). The hydrogen content in these materials decreases from 15 to 5 at. % and the void fraction by 14% as Ts is raised from 200 to 350 °C. The photo and dark conductivities are measured from 40 to 190 °C and extended state electron mobilities are derived from a self-consistent analysis. The room temperature mobilities are found to increase from 0.8 to 30 cm2/V s and become less temperature dependent as Ts increases. These temperature activated mobilities explain the Meyer–Neldel rule [Z. Tech. Phys. 18, 588 (1937)] in a-Si:H materials whose dark conductivity activation energies are greater than 0.4 eV where it cannot be explained by the statistical shift of the Fermi level.
Properties of superconductive bandpass filters with thermal switches
Authors: Nagai Y. , Hebert D. F. , Van Duzer T. , Michikami O.
Published: July 2002

This letter reports experimental results on frequency tuning and switching in superconductive bandpass filters with thermal switches. The four-pole microstrip filters with frequency of 1.5 GHz and bandwidth of 1.5% were fabricated using Nb or EuBaCuO films. The addition of thermal switches around conductors did not affect the filter characteristics. A negative frequency shift of −2 MHz was confirmed at 8 K in the Nb filter with loss of less than 0.7 dB. In contrast, a positive shift of +5 MHz was observed at 77 K in the EuBaCuO filter. Furthermore, switching with a large difference of approximately 50 dB in loss was achieved in the Nb filters.
Anomalous photoluminescence behavior of porous Si
Authors: Stevens P. D. , Glosser R.
Published: July 2002

We have investigated the photoluminescence (PL) behavior of porous Si and have found that the PL intensity rises with time under exposure to continuous laser light at high power densities (≳50 W/cm2). Samples exposed to lower power density laser light exhibit the well-known degradation of its PL intensity. As the power density is raised, the PL intensity increases with time and shows a ‘‘window’’ effect in which the PL intensities will again degrade at higher power density. Micro-Raman studies were performed on the sample and no apparent change in crystalline structure could be found for differing power densities. We correlate this anomalous PL effect with porous Si samples etched with different HF acid concentrations and show that this effect occurs only for porous Si samples etched with a relatively high acid concentration (≳30%).
Strained-layer InSb/GaSb quantum wells grown by metalorganic vapor phase epitaxy
Authors: Qian L. Q. , Wessels B. W.
Published: July 2002

InSb/GaSb quantum well structures have been prepared by atmospheric pressure metalorganic vapor phase epitaxy. Strong sharp photoluminescence emission peaks with a full width at half- maximum of 6–11 meV were obtained for the quantum well structures with well thicknesses of 0.35–0.88 nm, suggesting nearly atomically planar interfaces. The observed photoluminescence transition energies are in excellent agreement with the calculated values using a standard finite square well model taking into account strain. A broadening of the predominant photoluminescence emission peak was observed for quantum well structures with well thicknesses above 1 nm, indicating nonplanar growth.
Below band-gap electroabsorption in bulk semi-insulating GaAs
Authors: Adams J. C. , Capps C. D. , Falk R. A. , Ferrier S. G.
Published: July 2002

Electroabsorption measurements of bulk semi-insulating GaAs using a pulsed applied voltage are presented for the wavelength range 890–920 nm and compared with results of the same measurement using a dc applied voltage. In the latter case, field inhomogeneities in the GaAs gives a spatially dependent absorption which thwarts extraction of the absorption coefficient versus electric field. We circumvent this problem by transiently measuring the absorption during a pulsed bias voltage when the field in the sample is nearly uniform.
Velocity modulation in focused-ion-beam written in-plane-gate transistors
Authors: Bever T. , Klitzing K. v. , Wieck A. D. , Ploog K.
Published: July 2002

The mobility of a one-dimensional electron gas can be changed markedly by moving the electron path from the high-mobility channel toward the low-mobility focused ion-beam-implanted regions. This can be done simply by applying different biases to the two adjacent in-plane gates. When the bias voltage on one gate is fixed, we increase the other gate potential and force the current path close to the ion-implanted region. In this way the mobility rather than the density of the carriers is controlled, which is the key feature of the velocity modulation transistors with inherently fast response.
Photoemissions related to the kink effect in GaAs metal-semiconductor field-effect transistors with an Al0.2Ga0.8As/GaAs buffer layer
Authors: Haruyama Junzi , Goto Norio , Nashimoto Yasunobu
Published: July 2002

Photoemissions related to the ‘‘kink’’ effect are observed in GaAs metal-semiconductor field-effect transistors with an Al0.2Ga0.8As/GaAs heterostructure buffer layer. In drain voltage (VDS) regions lower than the kink VDS, the photoemission mainly results from the bremsstrahlung radiation because the energy spectrum is broad between 1.1 and 1.8 eV. Near the kink VDS, photoemission results from the direct recombination process of holes generated by the impact ionization because it has a peak near at 1.4 eV. In addition, at VDS’s higher than the kink VDS, the photo intensity, as well as the drain current, saturates. It is explained by the equilibrium of the hole generation/recombination, the accumulation, and the hole current flow into the substrate.
Low-voltage vertical-cavity transmission modulator for 1.06 μm
Authors: Fritz I. J. , Brennan T. M. , Hammons B. E. , Howard A. J. , Worobey W. , Vawter G. A. , Myers D. R.
Published: July 2002

We present results on the first all-semiconductor, vertical Fabry–Perot-cavity optical transmission modulator. This device combined mechanically stable strained and unstrained (In,Al,Ga)As multilayers to achieve operation at 1.06 μm. Transmission-mode operation allows the resonant wavelength of the cavity to be finely tuned by varying the angle of incidence, providing, for the first time, a means of compensating for small inaccuracies in growth parameters. Using the modulator in double-pass operation with a corner-cube retroreflector, we demonstrate a tunable reflectance modulator with a fractional modulation of 25% at 3-V bias, suitable for applications in free-space communication.
Simultaneous synthesis of well-separated buried and surface silicides using a single ion implantation step
Authors: Wu M. F. , De Wachter J. , Hendrickx P. , Van Bavel A.-M. , Pattyn H. , Langouche G. , Vanhellemont J. , Bender H. , Maenhoudt M. , Bruynseraede Y.
Published: July 2002

An unusual Ni distribution with two completely separated buried and surface silicide layers has been observed after Ni ion implantation in Si(111) kept at a temperature of 300 °C, with a dose of 1.1×1017/cm2 and at a fixed energy of 90 keV. RBS/channeling, AES, and cross-sectional TEM have been used to study this phenomenon as a function of the substrate temperature and Co co-implantation. A model is presented, based on the diffusion of the transition metal, the defect annealing during the implantation, and the gettering power of the surface and the end of range defects.
Measurement of magnetic fields using the magneto-optic Kerr effect
Authors: Oliver S. A. , DiMarzio C. A. , Lindberg S. C. , McKnight S. W. , Kale A. B.
Published: July 2002

A technique for measuring small magnetic fields using a thin amorphous magnetic film and the magneto-optic Kerr effect has been developed. A thin film having in-plane uniaxial anisotropy is aligned such that an external magnetic field rotates the film magnetization in a controllable manner. This magnetization rotation is ‘‘read’’ optically by a coherent homodyne measurement of the amount of polarization rotation caused by the magneto-optic Kerr effect during reflectance of polarized light from the film surface, using one polarization as the local oscillator. The resulting signal is linear in magnetic field. Initial noise equivalent magnetic field sensitivity measurements of the technique yield 2 mOe/Hz1/2 at a frequency of 8 mHz. Calculations indicate that sensitivities of order 10−6 Oe/Hz1/2 are obtainable using this technique.
Influence of separate-confinement layer band structure on the transport-limited modulation bandwidth in quantum well lasers
Authors: Wu T. C. , Kan S. C. , Vassilovski D. , Lau K. Y.
Published: July 2002

We analyze the influence of band-structure design of the SCH region on the transport-limited modulation bandwidth in quantum well (QW) lasers. By properly grading the SCH region, limitations due to physical-space transport can largely be removed. Limitations due to intrinsic quantum capture (state-space transport) then becomes the dominant one for GRINSCH QW lasers, though this, too, can be alleviated (but only completely removed) by proper band-structure design.
Nearly resonant two-photon absorption of C60 thin film at 633 nm
Authors: Han Y. N. , Zhang W. J. , Gao X. M. , Cui Y. B. , Xia Y. X. , Gu G. , Zang W. C. , Yang P. , Du Y. W. , Feng D.
Published: July 2002

We present an absolute measurement of a two-photon absorption (TPA) coefficient of C60 thin film at 633 nm. Large values of β≊4.4 cm/W were determined. A nearly resonant TPA transition around the 3.76 eV absorption region was discussed.
Hydrogen incorporation in the early stages of hydrogenated amorphous silicon deposition evaluated by real time infrared reflectance spectroscopy
Authors: Katiyar M. , Feng G. F. , Yang Y. H. , Abelson J. R. , Maley N.
Published: July 2002

We use real time, high sensitivity infrared reflectance spectroscopy to quantitatively study hydrogen incorporation during the growth of hydrogenated amorphous silicon by magnetron sputtering. For the range of deposition conditions studied (substrate temperature between 120 and 270 °C and H2 partial pressure between 0.1 and 1.0 mTorr, which result in film hydrogen content between 10 and 30 at. %), hydrogen incorporation reaches steady state for film thickness, d≳25 Å. Deviations from uniform growth for d<25 Å are attributed to plasma-substrate interactions due to energetic hydrogen implantation tens of angstroms beneath the growing surface and changes in the surface area during nucleation and coalescence.
Epitaxial lead zirconate-titanate thin films on sapphire
Authors: Braun W. , Kwak B. S. , Erbil A. , Budai J. D. , Wilkens B. J.
Published: July 2002

Pb(Zr1−xTix)O3 thin films covering the whole compositional range x=0 to x=1 have been grown for the first time on the sapphire (11̄02) plane using the metalorganic chemical vapor deposition technique. The films are three-dimensionally epitaxial and exhibit single crystal properties. The structural transitions, examined by x-ray diffraction, are shifted slightly from the bulk single crystal values. Ferroelectric P-E hysteresis curves and the dielectric constant of the films were investigated using interdigitated electrodes fabricated by photolithography.
Measurements of barium photocathode quantum yields at four excimer laser wavelengths
Authors: Van Loy M. D. , Young A. T. , Leung K. N.
Published: July 2002

The electron quantum yields from barium cathodes excited by excimer laser radiation at 193, 248, 308, and 351 nm have been determined. Experiments with different cathode surface preparation techniques reveal that deposition of barium film a few microns thick on a clean copper surface under moderate vacuum conditions achieves relatively high quantum efficiencies. Quantum yields measured from surfaces prepared in this manner are 2.3×10−3 at 193 nm, 7.6×10−4 at 248 nm, 6.1×10−4 at 308 nm, and 4.0×10−4 at 351 nm. Other preparation techniques, such as laser cleaning of a solid barium surface, produced quantum yields that were at least an order of magnitude lower than these values.
Intersubband transitions in high indium content InGaAs/AlGaAs quantum wells
Authors: Chui H. C. , Lord S. M. , Martinet E. , Fejer M. M. , Harris J. S.
Published: July 2002

We report the first observation of intersubband transitions in InyGa1−yAs(y=0.3,0.5)/ AlGaAs quantum wells. These quantum wells were grown on a GaAs substrate with a linearly graded InGaAs buffer to achieve strain relaxation before growth of the quantum wells. Measured intersubband transition energies of 316 and 350 meV are among the largest ever reported. Asymmetric step In0.5Ga0.5As/AlGaAs quantum wells designed for second harmonic generation measurements also demonstrate strong intersubband absorption at 224 meV corresponding to the 1-2 transition. With the large conduction band offsets (larger than 800 meV) available in this material system, extension to larger intersubband transitions energies for quantum well photodetector and nonlinear optics applications should be possible.
Light-controlled beam deflector in semiconductor doped glasses
Authors: Ma H. , de Araújo Cid B.
Published: July 2002

We report on the operation of an all-optical beam deflector whereby the deflected signal beam can be more powerful than the driving beam. Therefore, we have transferred the modulation of the driving beam to the signal beam with power gain and angular deflection rate of 10 mrad/kW. The main component of our deflector is a sample of Cd(S,Se) doped glass and its operation is based on the cross-bending effect.
Diode-laser isotope enrichment of rubidium with a polarized atomic beam
Authors: Mei Gang-hua , Zhang Yuan , Huang Gui-long , Zhu Xi-wen , Tan Yong-fang , Liu Jin-ting
Published: July 2002

Diode-laser isotope enrichment of rubidium by magnetic deflection of a polarized atomic beam has been experimentally studied with laser-induced fluorescence detection. The abundance of 85Rb was enhanced from the natural value of 72.8% to 97% and that of 87Rb, from 27.2% to 83%. The results were compared with those with hot-wire detection.
AlGaInP visible vertical cavity surface emitting lasers operating with gain contributions from the n=2 quantum well transition
Authors: Lott J. A. , Schneider R. P. , Zolper J. C. , Malloy K. J.
Published: July 2002

We report the characteristics of visible vertical cavity surface emitting laser diodes. Wafers are grown such that the Fabry–Perot resonance wavelength changes with position from 690 to 620 nm, overlapping to varying degrees with the n=1 and n=2 quantum well gain peaks at ∼670 and 650 nm. Gain guided devices are tested across the entire wafer, and pulsed room temperature lasing is observed from 634.6 to 663.2 nm. Our results suggest that gain contributions from the second quantized state are required to overcome high cavity losses in order to achieve lasing.
Effect of synchrotron radiation on electrical characteristics of SiOxNy thin films formed by rapid thermal processing in a N2O ambient
Authors: Arakawa Tomiyuki , Yamashita Yoshio , Hoga Hiroshi , Noda Shuichi , Fukuda Hisashi
Published: July 2002

The synchrotron radiation durability of SiOxNy films (about 10 nm) formed by rapid thermal processing in a N2O ambient was studied. No significant difference between the flat-band voltage of SiOxNy-metal-oxide semiconductors (MOS) capacitors patterned by synchrotron radiation lithography (SR-MOS) and that of capacitors patterned by conventional optical lithography (OP-MOS) was observed. The midgap interface state density of the SR-MOS was approximately one order of magnitude larger than that of the OP-MOS. The differences between the SR-MOS and the OP-MOS were nearly independent of the SR dose in the range of 540–2700 mJ/cm2, and were eliminated by annealing in a hydrogen ambient at 400 °C for 30 min.
Precursor-mediated epitaxial growth of GaAs(001) from triethylgallium: Where is the gallium released?
Authors: Shitara Tomoya , Kaneko Tadaaki , Vvedensky Dimitri D.
Published: July 2002

A model is described for the morphological evolution of GaAs(001) during metalorganic molecular-beam epitaxy (MOMBE) with triethylgallium (TEG) and solid-As sources. The model includes the migration and attachment/detachment kinetics of atomic Ga and the migration and decomposition kinetics of a more mobile precursor (not necessarily TEG). By biasing the decomposition of the precursor to sites with low coordination, we are able to account for two important observations concerning MOMBE and molecular-beam epitaxy under nominally the same growth conditions: the reflection high-energy electron diffraction (RHEED) specular intensity oscillations on a singular surface show higher amplitude and are less damped during MOMBE, but on a vicinal surface, there is no discernible difference in the RHEED measurements for the two techniques.
Additivity of ballistic electrons
Authors: Sakamoto T. , Nihey F. , Nakamura K.
Published: July 2002

The additivity of ballistic electron beams is confirmed in the mesoscopic regime. Two ballistic electron beams are injected simultaneously from different injectors and cross each other at a collector. The voltage drop at the collector is proven to be equivalent to the algebraic sum of those separately obtained when each electron beam is individually injected from a corresponding injector. The additivity is considered to be valid based on the fact that the mean distance between the ballistic electrons is much larger than the screening length. Confirming of additivity is essentially important in designing new functional devices such as a synapse for neural networks in the ballistic regime. The quantum interference effect is also observed in the same sample.
Activation energy and mechanism of CO desorption from (100) diamond surface
Authors: Frenklach M. , Huang D. , Thomas R. E. , Rudder R. A. , Markunas R. J.
Published: July 2002

An apparent activation energy for CO desorption from (100) diamond surfaces exposed to atomic oxygen was determined by thermal desorption spectroscopy performed in ultrahigh vacuum and found to be equal to 45.0 kcal/mol. A minimum potential-energy reaction path was identified by semiempirical quantum chemical calculations. Starting with an O-on-top radical site, the reaction proceeds through a β-scission of the C—CO bond, formation of a dimer C—C bond, and finally cleavage of the second C—CO bond. The largest barrier along this pathway is that of the final desorption step; it is equal to 38.4 kcal/mol, in reasonable agreement with the experimental activation energy. Taken together, the broad experimental desorption-peak feature and the multitude of possible desorption sites with differing potential-energy barriers, suggests the existence of a distribution of CO sites on diamond surfaces.
94-GHz phase modulation of light by organic MNA (2-methyl-4-nitroaniline) crystal
Authors: Wah C. K. L. , Iizuka K. , Freundorfer A. P.
Published: July 2002

Success in 94-GHz electro-optic phase modulation using the nonlinear organic MNA (2-methyl-4-nitroaniline) crystal is reported. We believe this to be the highest electro-optic modulation frequency ever achieved in a controlled manner. Dielectric constant, loss tangent, and electro-optic constant of the MNA crystal were also measured at 94 GHz, εr′=2.2, tan δ=0.09, and r11=30±10 pm/V.
High efficiency ZnS:Mn ac thin film electroluminescent device structure
Authors: Thomas C. B. , Cranton W. M.
Published: July 2002

A method for improving the luminous efficiency of a ZnS:Mn ac thin film electroluminescent device by modifying the structure to include thin, 100 Å, barrier layers of a Y2O3 is presented, with experimental comparisons of devices showing a fourfold increase in efficiency. The results are discussed in terms of electron tunneling and field redistribution as the mechanisms responsible for the enhancement of efficiency.
Generation of 425-nm light by waveguide frequency doubling of a GaAlAs laser diode in an extended-cavity configuration
Authors: Risk W. P. , Kozlovsky W. J. , Lau S. D. , Bona G. L. , Jaeckel H. , Webb D. J.
Published: July 2002

A blue output power of 1.2 mW at 425 nm was generated using a periodically poled KTP waveguide for frequency doubling of a grating tuned, extended-cavity laser containing an antireflection-coated GaAlAs SQW-GRINSCH laser diode as the gain element. A normalized conversion efficiency of 127%/W cm2 was achieved in the extended-cavity configuration.
Diamond deposition from halogenated methane reactants in a hot-filament chemical vapor deposition reactor
Authors: Chau-Nan Hong Franklin , Liang Gou-Tsau , Wu Jih-Jen , Chang Dawson , Hsieh Jing-Chuang
Published: July 2002

The growth behavior of diamond films synthesized from halomethane reactants is studied in a hot-filament chemical vapor deposition reactor. The growth characteristics of methane and several chloromethane reactants (CH2Cl2, CHCl3, and CCl4) are examined over a number of reactant concentrations, substrate temperatures (700–900 °C), reactor pressures, and filament temperatures. The results indicate that in comparison to methane, chloromethane reactants generally yield higher rates of diamond film growth, with this difference becoming more pronounced at lower substrate temperatures. As a result, chloromethane reactants possess potential in facilitating diamond growth at low growth temperatures. Possible explanations for this behavior involving gas phase and surface reaction mechanisms of chloromethane reactants are proposed.
Effect of rapid thermal annealing on gate induced drain leakage in a n-channel metal-oxide-semiconductor field effect transistor
Authors: Hsieh J. C. , Fang Y. K. , Chen C. W. , Tsai N. S. , Lin M. S. , Tseng F. C.
Published: July 2002

Significant gate induced drain leakage caused by post-oxide rapid thermal annealing (RTA) was studied in this letter in comparison with the non-RTA process for n-channel metal-oxide- semiconductor field effect transistor. It is found that the sub-breakdown leakage increases with increasing RTA temperature. We proposed that interface states and recombination centers generated after RTA are the dominant factors in the enhancement of the leakage current. In addition, it is found that RTA has no effect on the avalanche breakdown voltage.
New insight into proton-induced latchup: Experiment and modeling
Authors: Levinson J. , Akkerman A. , Victoria M. , Hass M. , Ilberg D. , Alurralde M. , Henneck R. , Lifshitz Y.
Published: July 2002

A combination of irradiation experiments (using energetic protons and heavy ions) and a theoretical analysis was used, for the first time, to study proton induced single event latchup (SEL) in electronic devices. A significant difference between SEL and single event upset (SEU) was found. For SEU the device sensitivity can be predicted by a model assuming the collection of the majority of the charge carriers generated in the sensitive volume by the nuclear fragments of the (p,Si) reactions. For SEL, the measured sensitivities are much lower than predicted by prompt charge collection. Recombination of charge carriers (generated by the heavier fragments) due to a track electric field reasonably explains the SEL data.
Grating-coupled surface-emitting lasers with integrated corner reflectors
Authors: Hagberg Mats , Kjellberg Torgil , Eriksson Niklas , Larsson Anders G.
Published: July 2002

Grating-coupled surface-emitting InGaAs/AlGaAs lasers with a single large area output coupler were fabricated by integrating a second order surface grating with corner reflectors. The grating as well as the corner reflectors were fabricated using electron beam lithography and chemically assisted ion beam etching, producing a uniform rectangular grating and high quality corner facets. A thin etch-stop layer incorporated in the epitaxial structure made it possible to combine precise control of the grating position with a strained layer SQW-GRINSCH structure. Well behaved lateral modes were observed in 70-μm-wide lasers, emitting narrow beams in both the lateral and the longitudinal direction. Threshold current densities as low as 99 A/cm2 were measured for 1200-μm-long lasers.
Transient dynamics in a self-starting passively mode-locked fiber-based soliton laser
Authors: Abraham D. , Nagar R. , Mikhelashvili V. , Eisenstein G.
Published: July 2002

We describe measurements of spectrally resolved turn-on and turn-off dynamics in a self-starting passively mode-locked fiber soliton laser. An intracavity quantum well optical amplifier whose bias is modulated changes the cavity losses, thereby switching the laser between continuous wave and mode-locked states. We show that during the transients, the laser undergoes a period of self Q switching lasting a few hundreds of microseconds (as determined by the relaxation oscillation frequency in the fiber gain medium) before it reaches steady state.
High specific laser output energy at 157 nm from an electron beam pumped He/Ne/F2 gas mixture
Authors: Lankhorst F. T. J. L. , Bastiaens H. M. J. , Peters P. J. M. , Witteman W. J.
Published: July 2002

The output energy and the temporal behavior of a molecular F*2 laser pumped by a coaxial electron beam have been measured in gas mixtures of He/F2 and He/Ne/F2. The highest output energy of 172 mJ has been obtained in a mixture of He/Ne/F2 (19.9%/80%/0.1%) at a pressure of 12 bar, corresponding to a specific output energy of 10.8 J/ℓ and an intrinsic efficiency of 2.6%.
Temperature dependent gain of the atomic xenon laser
Authors: Hebner Gregory A. , Shon Jong W. , Kushner Mark J.
Published: July 2002

Measured and calculated gain of the 1.73 μm [5d(3/2)1–6p(5/2)2] and 2.03 μm [5d(3/2)1–6p(3/2)1] atomic xenon transitions for gas temperatures between 290 and 590 K are presented. Fission-fragment excitation was used to generate the gain in Ar/Xe, He/Ar/Xe, and Ne/Ar/Xe gas mixtures at a pump power of 8 W/cm3. For constant gas density, the gain exhibits an approximate Tgas−n dependence with n between 2 and 3. The primary reactions responsible for the temperature dependence of the gain have been identified as dimer formation, dissociative recombination, and enhanced electron collisional mixing of the laser manifold due to an increased electron density.
Stress induced pattern formation preceding crystallization of Te3Se4(I) thin films
Authors: Blatter A. , Ortiz C.
Published: July 2002

Amorphous Te3Se4 and Te3Se4I thin films, prepared by rf sputtering, were crystallized by thermal treatment. The relaxation of residual stresses upon heating the films produced a macroscopic strain pattern in the amorphous phase prior to crystallization. This pattern determined the growth of a preferred crystallographic orientation which led to the evolution of a macroscopic branching crystalline morphology. Interference of transformation stresses between neighboring surface spherulites (sometimes called cylindrites) resulted in the development of shared morphological domains.
Critical current density and microstructure of screen-printed (Bi,Pb)2Sr2Ca2Cu3Ox thick film sandwiched between Ag substrates
Authors: Oota A. , Matsui H. , Funakura M. , Iwaya J. , Maeda J.
Published: July 2002

A process of combined rolling and uniaxial pressing with intermediate sintering steps for fabrication of screen-printed (Bi,Pb)2Sr2Ca2Cu3Ox thick films sandwiched between Ag substrates yields c-axis-oriented microstructures with a high critical current density (Jc) of 1.5×104 A/cm2 (77 K, 0 T) and 9.0×104 A/cm2 (23 K, 0 T). The measured Jc anisotropy at 77 K, as a function of the angle θ between B and c axis, is pronounced. An increase in B sharpens a peak at θ=90° (i.e., B⊥c) in the Jc vs θ curve, together with enhancement of the anisotropy ratio defined as Jc(B⊥c)/Jc(B∥c). In high fields above 0.5 T, the half-height angular width of the peak approaches an average misalignment angle (4°–6°) between the grains with increasing B.
Superconductivity in ultrathin films consisting of Bi2Sr2CaCu2O8+δ/Bi2Sr2CuO6+δ heterostructures
Authors: Watanabe H. , Tsukada I. , Kobayashi S. , Koyama I. , Terasaki I. , Uchinokura K.
Published: July 2002

Superconductivity of a one-primitive-cell-thick Bi2Sr2CaCu2O8+δ layer was investigated in ultrathin films consisting of Bi2Sr2CaCu2O8+δ/Bi2Sr2CuO6+δ heterostructures. Films were prepared directly on substrates of SrTiO3(001) with a molecular beam epitaxy technique. The number of CuO2 planes is fixed at six in all films, in which the one-primitive-cell-thick Bi2Sr2CaCu2O8+δ layer is located at various positions with respect to the Bi2Sr2CuO6+δ layers, from the surface of films to the interface between films and substrates. We observed that the one-primitive-cell-thick Bi2Sr2CaCu2O8+δ layer shows superconductivity when it is surrounded by Bi2Sr2CuO6+δ layers. Superconductivity of the Bi2Sr2CaCu2O8+δ layers is, however, destroyed if it is located at the surface or at the interface between films and substrates.
Pseudomorphic separate confinement heterostructure blue-green diode lasers
Authors: Grillo D. C. , Fan Y. , Han J. , He L. , Gunshor R. L. , Salokatve A. , Hagerott M. , Jeon H. , Nurmikko A. V. , Hua G. C. , Otsuka N.
Published: July 2002

The growth and performance of pseudomorphic separate confinement heterostructure blue-green laser diodes are described. The devices incorporate the (Zn,Mg)(S,Se) quaternary as cladding layers surrounding a Zn(S,Se) waveguiding layer, and having single or multiple quantum wells of (Zn,Cd)Se. Devices have been operated at room temperature under pulsed conditions (∼1 μs, 10−3 duty cycle) for periods up to 1 h. X-ray rocking curve full width at half-maxima as low as 44 arcsec were obtained for a laser structure employing quaternary cladding layers (Mg=9%, S=12%), consistent with transmission electron microscope observations showing no dislocations or stacking faults. The Zn(Se,Te) graded contact was adapted to form an ohmic contact to the top p-type quaternary layer.
Novel amorphous silicon doping superlattice device with bidirectional S-shaped negative differential characteristics
Authors: Liu C. R. , Fang Y. K. , Chen K. H. , Hwang J. D. , Kuo L. C.
Published: July 2002

A novel amorphous silicon doping superlattice device with bidirectional S-shaped negative-differential characteristics has been fabricated and investigated experimentally. The occurrence of the S-shaped switching phenomenon is caused by the potential redistribution due to the avalanche multiplication process. The experimental results are demonstrated and the electronic transport theory is proposed in this letter.
Low-temperature rapid thermal low pressure metalorganic chemical vapor deposition of Zn-doped InP layers using tertiarybutylphosphine
Authors: Katz A. , Feingold A. , Pearton S. J. , Moriya N. , Baiocchi C. J. , Geva M.
Published: July 2002

High purity Zn doped InP layers were grown by rapid thermal low pressure metalorganic chemical vapor deposition technique, using tertiarybutylphosphine as the phosphorus source. The best quality layer, which was grown at P:In ratio of 75, temperature as low as 525 °C, pressure of 2 Torr and growth rate of 2 nm/s, exhibited electron mobility of 80 cm2 V−1 s−1 and Hall carrier concentration of 3.5×1018 cm−3 at room temperature. The stoichiometry of the InP Zn-doped layer was excellent, regardless of the Zn content in the reactive gas mixture. The crystallographic defect density and the surface morphological particle concentration, however, were found to be strongly dependent on the Zn concentration.
Electronic states studies of alkali-metal-doped C60 superconductors by nuclear magnetic resonance
Authors: Kosaka Mayumi , Tanigaki Katsumi , Ebbesen Thomas W. , Nakahara Yoshifumi , Tateishi Kazuo
Published: July 2002

The density of states at the Fermi level [N(EF)] of alkali-metal-doped C60 superconductors having a wide range of Tc from Na2Rb1C60 (Tc=3.5 K) to Rb1Cs2C60 (Tc=33 K) is systematically studied using spin-lattice relaxation times (T1) by NMR spectroscopy. The obtained N(EF) values suggest that the phonon modes associated with superconductivity are high and that the electron-phonon coupling constant is responsible for the large decrease in Tc in the small lattice parameter region.
Dynamic mode force microscopy for the detection of lateral and vertical electrostatic forces
Authors: Watanabe S. , Hane K. , Ito M. , Goto T.
Published: July 2002

In this letter, a variant of scanning force microscope for detecting attractive forces is reported. The force gradients of the attractive forces acting in two orthogonal directions were detected simultaneously from the resonant frequency shifts of a cantilever oscillating in two directions. Using the fine electrode sample, the distributions of the electrostatic forces acting in lateral and vertical directions were visualized separately.
Photoluminescence of hydrogenated GaAs/AlGaAs quantum wells grown by metalorganic vapor phase epitaxy
Authors: Botha J. R. , Leitch A. W. R.
Published: July 2002

The incorporation of hydrogen into an undoped GaAs/Al0.3Ga0.7As quantum well (QW) structure (containing wells of varying thickness) grown by metalorganic vapor phase epitaxy has been studied by photoluminescence (PL) in the temperature range 12–200 K. Hydrogenation is shown to reduce the PL linewidths. This is attributed to a passivation of impurities in the wells and heterointerfaces. In addition, the influence of hydrogenation on the radiative efficiency of each QW as a function of temperature is discussed in terms of a passivation of grown-in defects as well as a depth distribution of plasma-induced defects.
Can n-type doping of diamond be achieved by Li or Na ion implantation?
Authors: Prawer S. , Uzan-Saguy C. , Braunstein G. , Kalish R.
Published: July 2002

The electrical conductivity of Na- and Li-implanted diamond is investigated. The highest conductivities are obtained for high dose implantations followed by thermal graphitization of the heavily damaged layer and chemical removal of the graphitized layer. The temperature dependence of the resistivity is measured, yielding activation energies of 0.2 eV for Li (400<T<680 K) and for Na 0.13 eV (220<T<400 K) and 0.21 eV (415<T<670 K). Analysis of the data shows that the conduction may be understood in terms of variable range hopping between implant sites in the crystal rather than due to thermal activation.
Giant optical bistable behavior using triple-barrier resonant tunneling light-emitting diodes
Authors: Van Hoof C. , Genoe J. , Raymond S. , Borghs G.
Published: July 2002

By achieving electrostatic feedback due to hole accumulation in an asymmetric triple-barrier resonant tunneling light-emitting diode, inverted bistability is obtained in the current-voltage characteristics. In the low current state, the resonant electron current is suppressed, resulting in the absence of quantum-well light emission. When switching to the high current state, the sudden increase in electron population causes a steplike increase in luminescence which yields an optical on–off ratio larger than 104:1. This improvement by a least a factor of 1000 with respect to the existing double-barrier resonant tunneling light-emitting diodes makes the new triple-barrier structure drastically more appealing for bistable switching applications.
15.9% efficiency solar cells on electromagnetic cold crucible cast multicrystalline silicon
Authors: Elgamel H. E. , Ghannam M. Y. , Murti M. R. , Nijs J. , Mertens R.
Published: July 2002

Hydrogen passivation is found very effective in improving the quality of electromagnetically cased (EMC) multicrystalline silicon from Osaka Titanium Co. (OTC), now Sumitomo Sitix Corp.), due to its small grain size and low oxygen content. A top efficiency of 15.9% is achieved for a 4 cm2 solar cell fabricated on hydrogen passivated EMC-OTC multicrystalline silicon. Such a result is comparable to the top efficiencies achieved on high quality conventionally casted material and represents the maximum efficiency ever reported for EMC multicrystalline silicon. Fourier transform infrared measurements confirm the low oxygen content in the EMC-OTC material and spectral response as well as contactless lifetime measurements confirm the role of the plasma hydrogen passivation in substantially improving the diffusion length in this material.
Effect of high temperature processing of Si/SiO2/Si structures on their response to x-ray irradiation
Authors: Paillet P. , Hervé D. , Leray J. L. , Devine R. A. B.
Published: July 2002

The radiation response of Si/SiO2/ Si structures subjected to x-ray irradiation in the presence and absence of applied electric field has been studied as a function of accumulated dose. High temperature annealing of sandwiches involving thermally grown oxide results in a softening of the radiation response, evidence for both hole and electron trapping is found. Similar behavior is found in buried oxide layers produced by O+ implantation, then subjected to high temperature annealing. Evidence for majority hole trapping is found in unannealed, thermal oxide. It is suggested that high temperature annealing results in a reduction of the oxide which is driven by the Si/SiO2 interface, resulting in electron and hole trap generation.
Theoretical optimization of quantum wire array lasers for low threshold current density and high modulation frequency
Authors: Vurgaftman Igor , Singh Jasprit
Published: July 2002

We show that as one decreases the cross-sectional area of quantum wire lasers, the threshold current decreases, but the carrier relaxation time increases. Since the electron relaxation time sets the upper limit on the modulation frequency, there is a tradeoff between speed and efficiency in quantum wire lasers. We derive the optimal wire cross-sectional area for a one-dimensional array of quantum wire lasers based on a balance between an acceptably high maximum modulation frequency and a desirably low threshold current density. We find that for a relaxation time of 60 ps, the quantum wire of 150×150 Å cross section has the lowest threshold current density of 560 A/cm2. If high-speed operation is not needed, the optimal choice for the quantum wire cross-sectional area is 100×50 Å with the threshold current density of 420 A/cm2. For optimized quantum wells with the same cavity losses, the threshold current density is ≊620 A/cm2. We also present the results for the threshold current density and the relaxation time that allow one to find the optimal quantum wire structure weighing the speed and efficiency considerations in accordance with their relative importance.
Magnetization process observation of a CoNiCr film in the field of a weakly excited objective lens in transmission electron microscope
Authors: Tang Li , Thomas Gareth
Published: July 2002

Dynamic observation of the magnetization process of a fcc CoNiCr thin film has been made by tilting the specimen in the magnetic field of a weakly excited objective lens in a transmission electron microscope. Domain wall motion, magnetization direction rotation, and pinning effect due to surface NaCl contamination have been clearly revealed by this method for the film.
Multiresonance tunneling effect in double-well potentials
Authors: Khuat-duy D. , Leboeuf P.
Published: July 2002

We prove that one-dimensional asymmetric double-well potentials of degree four have the property that, at a fixed energy, the classical period is the same in both wells. Quantum mechanically this reflects in a simultaneous occurrence, or alignment, of the spectral quasidegeneracies at certain values of the parameters controlling the shape of the potential. Experimental applications of this property, like multiresonance tunneling effect, are discussed.
Phonon-electron interactions in the two-dimensional electron gas in InGaAs-InAlAs modulation-doped field-effect transistor structures studied by Raman scattering
Authors: Maslar J. E. , Dorsten J. F. , Bohn P. W. , Agarwala S. , Adesida I. , Caneau C. , Bhat R.
Published: July 2002

Raman scattering by coupled longitudinal optic phonons and two-dimensional electron gas electrons in In0.53Ga0.47As-In0.52Al0.48As δ-doped heterostructures provides a powerful probe of electronic properties in these In-based structures. The two highest frequency modes, of the three coupled electron-phonon modes expected in this system, were observed, with the highest frequency mode being identified in InGaAs-based systems. The large dispersion of this mode makes it a particularly sensitive probe for changes in such properties as carrier concentration and subband energy. For structures with higher carrier concentrations coupling of the longitudinal optic phonon to multiple electron intersubband transitions is resolved. These measurements are particularly useful for heavily doped structures for which room-temperature Hall measurements cannot distinguish channel electrons from those in parallel conduction paths.
On resolving hot carrier induced degradation mechanisms in silicon-on-sapphire metal-oxide-semiconductor field-effect transistors
Authors: Chao E. Y. , Li G. P.
Published: July 2002

Hot carrier induced damage in silicon-on-sapphire (SOS) metal-oxide-semiconductor field-effect transistors (MOSFETs) are reported. Various experimental techniques—the peak linear-region transconductance change, extrapolated threshold voltage shift, exponent in time dependence of transconductance, and charge pumping current—are employed to explore the degradation mechanisms. Hot light holes alone in silicon-on-sapphire MOSFETs are found ineffective in generating interface states, but their interaction with trapped electrons are.
Nanosize structures connectivity in porous silicon and its relation to photoluminescence efficiency
Authors: Teschke O. , Alvarez F. , Tessler L. , Kleinke M. U.
Published: July 2002

Transmission electron microscopy is used to reveal the existence of an interconnected nanosize structure in porous silicon films. The interconnections of this nanostructure determine the photoexcited electron-hole pair separation and consequently the luminescence efficiency of the material. Efficient photoluminescence is obtained from structures which shows no connectivity.
Electron spin resonance investigations of oxidized porous silicon
Authors: Meyer B. K. , Petrova-Koch V. , Muschik T. , Linke H. , Omling P. , Lehmann V.
Published: July 2002

The defect properties of rapidly thermally oxidized porous silicon are studied by electron paramagnetic resonance. Two different types of defects can be distinguished. One is very similar to the defects observed in damaged crystalline or amorphous Si, whereas the second one is closely related to the Pb center. A maximum defect density of 8×1018 cm−3 is observed for samples annealed at about 600 °C. The intensity of the photoluminescence band at 1.7 eV anticorrelates with the density of the defects.
Photovoltaic effect and its polarity in Si doping superlattices
Authors: Luo C. P. , Jiang D. S. , Zhuang W. H. , Li F. , Li Y. Z.
Published: July 2002

We have studied the photovoltaic effects in Si doping superlattices (nipi) under different excitation conditions with and without additional cw optical biasing using a He-Ne laser. On the basis of the photovoltaic theory of carrier spatial separation in superlattices, we propose the concept of spatial fixity of the photovoltage polarity in type-II superlattices and examine the experimental results. The photovoltaic effect in Si nipi is found mainly from the direct transitions related with shallow impurities in real space, not the electron-hole band-to-band process as in GaAs nipi.
Electron beam-enhanced etching of InAs in Cl2 gas and novel in situ patterning of GaAs with an InAs mask layer
Authors: Miya S. , Yoshida T. , Kadoya Y. , Akamatsu B. , Noge H. , Kano H. , Sakaki H.
Published: July 2002

We propose and demonstrate a novel in situ patterning process of GaAs and GaAs/AlGaAs heterostructures in which a thin InAs layer is used as an electron-beam resist layer for Cl2 gas etching in ultrahigh vacuum environment. It has been found that the etch rate of InAs by Cl2 gas is far lower (by a factor of 500) than that of GaAs but this etch rate can be enhanced by electron beam irradiation by a factor of 20, allowing the pattern formation in the InAs mask layer. By delineating a stripe pattern in the InAs resist and subsequently etching in situ the GaAs underneath, we have successfully formed a fine V groove. Since this process is clean and damage free, it is suited for the fabrication of quantum structures in which high-quality etch/regrowth interfaces are required.
Analytical results of the switch on statistics in distributed feedback laser diodes by short triangular pulses
Authors: Balle Salvador , Mirasso Claudio R. , Sapia Adalberto , Spano Paolo
Published: July 2002

The results of a theoretical analysis of the first passage time statistics in single mode diode lasers are reported. A fast triangular current pulse is used to drive a semiconductor laser in order to approximate working conditions close to those obtained when the transmission rate is limited by the parasitics of the driving circuit. The results show a very good agreement with numerical simulations of the nonlinear evolution of the dynamical system demonstrating the accuracy of the approximations involved in our theory.