bluuebunny/crossref_metadata_2025 huggingface dataset:
Improved dosimetry for metalorganic vapor phase epitaxy from a solution of trimethylindium
Authors: Frigo D. M. , van Mier G. P. M. , Wilkie J. H. , Gal A. W.
Published: July 2002

A novel precursor system for metalorganic vapor phase epitaxy of indium-containing layers, solid trimethylindium (TMI) partly dissolved in N, N-dimethyldodecylamine, is described. Used in a conventional bubbler, the output concentration of TMI entrained by H2 carrier gas from this source was measured using an ultrasonic cell (Epison) and compared with that from a conventional TMI source. Initially the output stability from both sources was found to be virtually identical; after approximately 50% depletion the output from the solution source was substantially more stable. The solution source was used to deposit InP and lattice-matched InGaAs/InP, with excellent optical and electrical properties (μ77=181 000 and 44 000 cm2/V s, respectively). With only 5 g solid TMI remaining, the continued stability of the solution source was shown by growing a lattice-matched GaInAs/InP layer having an x-ray diffraction peak of 26 arcsec.
New method to improve the adhesion strength of tungsten thin film on silicon by W2N glue layer
Authors: Kim Yong Tae , Lee Chang Woo , Min Suk-Ki
Published: July 2002

When the partial pressure ratio of WF6:NH3:H2 is 2:1:50, (111) and (200) oriented tungsten nitride (W2N) thin films can be deposited by plasma enhanced chemical vapor deposition and the resistivity of as-deposited films is 95–100 μm cm. In order to improve the adhesion of chemical vapor deposited tungsten (W) thin films, this W2N glue layer is interposed between W and Si. The acoustic emission-load graphs obtained by the scratch test method show that the adhesion strengths of W films on the W2N glue layers are apparently improved from 1–2 to 9–11 N. The more adhesive contact can be attributed to the introduction of nitrogen interstitials because these nitrogen interstitials are expected to modify the structural properties such as porosity and vacancies in the W2N films.
Temperature dependence of damping in high-speed quantum-well lasers
Authors: Ishikawa Masayuki , Fukushima Toru , Nagarajan Radhakrishnan , Bowers John E.
Published: July 2002

The temperature dependence of damping in quantum-well lasers has been investigated. The lasers with large K factors at room temperature show a rapid increase of the K factor with temperature. The temperature dependence of the K factor is larger for lasers with wider separate confinement heterostructure region, fewer wells, and narrower quantum-well width. The carrier transport in quantum-well structures is responsible for the excess increase of the K factor at high temperatures.
Interface states in regrown GaAs p-n junctions by selective molecular beam epitaxy
Authors: Ikossi-Anastasiou K. , Johnstone D. K. , Stutz C. E. , Evans K. R. , Ezis A.
Published: July 2002

We report the first evaluation of interface states present in GaAs p-n junctions regrown on a SiO2 masked substrate by selective molecular beam epitaxy. A constant-capacitance deep-level transient spectroscopy (CC-DLTS) method is extended to the regrown p-n junction case, and a technique to distinguish the DLTS signal emerging from bulk and interface states is employed. The extracted interface state density is in good agreement with predictions based on the unified disorder-induced gap state model.
On-axis dc magnetron sputtering of large area high quality YBa2Cu3O7 superconducting thin films
Authors: Zhang Y. Z. , Li L. , Zhao Y. Y. , Zhao B. R. , Li J. W. , Sun J. R. , Su Q. X. , Xu P.
Published: July 2002

It is demonstrated by our experiment that using the in situ dc magnetron sputtering method, it is possible to prepare high quality YBa2Cu3O7 (YBCO) thin films with substrates facing the region of plasma ring. The effect of oxygen resputtering can be greatly reduced with a high argon-oxygen working gas ratio and a large target to substrate distance. It is shown that high quality YBCO thin films of more than 60 mm in diameter, that is about the same size of the diameter of the YBCO target, can be prepared with this process. The thin films were characterized by x-ray diffractometry, and the critical temperatures were determined by both resistive and ac susceptibility techniques.
Degradation by electromigration in passivated Al–1 wt% Si thin films
Authors: Li Z. , Bauer C. L. , Mahajan S. , Milnes A. G.
Published: July 2002

Time evolution of the fractional change of electrical resistance of passivated Al–1 wt% Si thin-film conductors is characterized by five distinct stages: (1) undetectable change during an incubation period, (2) subsequent linear increase, (3) saturation, (4) abrupt decrease when applied current is interrupted or reversed, and (5) erratic fluctuations at extended times. Results are interpreted in terms of generation of localized tensile and compressive stress by electromigration, resulting in (reversible) hole formation at grain boundary triple junctions, followed by complex combinations of hole movement, coalescence, and annihilation.
Carrier capture and unipolar avalanche multiplication in quantum well heterostructures
Authors: Lefebvre Kevin R. , Anderson Neal G.
Published: July 2002

The influence of carrier capture on unipolar carrier multiplication in quantum well photomultipliers is investigated. General considerations regarding gain and carrier capture in quantum wells are discussed, and it is suggested that capture efficiencies need not be unexpectedly high to quench gain from intraband multiplication in some structures. This is investigated quantitatively through gain calculations which include the effects of electron capture via optical phonon emission in symmetric Al0.32Ga0.68As-GaAs quantum wells. Our results are discussed in the context of previous work on quantum well avalanche photodiodes, and some implications for the design of such devices are detailed.
Damage saturation during high-energy ion implantation of Si1−xGex
Authors: Holland O. W. , Haynes T. E.
Published: July 2002

Saturation of radiation damage during MeV Si+-ion implantation of unstrained Si1−xGex (x=0.15,0.50) alloy layers, as well as bulk Ge, was investigated. First observed in self-ion irradiated Si, damage saturation is distinguished by a low concentration of lattice defects in the near-surface region ahead of the ions’ end-of-range which remains constant over an extended range of implantation dose. A previously proposed model accounted for saturation by assuming that damage nucleates homogeneously during ion irradiation. Different mechanisms for nucleation of damage are discussed and substrate conditions are specified under which each dominates. A characteristic temperature is defined for each substrate above which damage nucleates primarily by a homogeneous mechanism. Results are presented which show the damage saturation occurs above this characteristic temperature but not below, thus establishing homogeneous nucleation as a necessary condition for the occurrence of damage saturation, as previously suggested.
Optical investigation of the one-dimensional confinement effects in narrow GaAs/GaAlAs quantum wires
Authors: Birotheau L. , Izrael A. , Marzin J. Y. , Azoulay R. , Thierry-Mieg V. , Ladan F. R.
Published: July 2002

We show optical data obtained at 8 K on narrow GaAs/GaAlAs quantum wires, with width down to 15 nm, fabricated by reactive ion etching and metal organic chemical vapor deposition overgrowth. Lateral confinement energies (up to 23 meV) and polarization effects are evidenced in the photoluminescence excitation spectra. These experimental results are in good agreement with calculated absorption spectra, which include the effects of wire width fluctuations, yielding, for our fabrication technique, a value of ±5 nm for these size fluctuations.
Switching and memory phenomena in Langmuir–Blodgett films with scanning tunneling microscope
Authors: Takimoto K. , Kawade H. , Kishi E. , Yano K. , Sakai K. , Hatanaka K. , Eguchi K. , Nakagiri T.
Published: July 2002

The current-voltage characteristic has been measured for a probe/Langmuir–Blodgett (LB) film/metal structure with the scanning tunneling microscope (STM). The rapid increase of current and substantial increase in conductance have been found when a critical positive voltage was applied to the probe. A bright spot in the STM image has been observed at the position where the increase in the conductance occurred. The changes in the STM images are attributed to the change in the conductance of LB films themselves rather than the surface topography, and may be associated with the switching phenomena in LB films.
Kinetics of nucleation and growth of Si on SiO2 in very low pressure SiH4 chemical vapor deposition
Authors: Dana S. S. , Liehr M. , Anderle M. , Rubloff G. W.
Published: July 2002

The initial growth kinetics for SiH4 chemical vapor deposition of Si on SiO2 at low temperature (500–600 °C) have been revealed using rapid thermal UHV-CVD, together with in situ H2 thermal desorption spectroscopy to titrate the amount of exposed Si surface. In the few mTorr pressure range, the reaction is heterogeneous, i.e., dominated by surface reaction. Below ∼0.7 monolayer Si coverage, the growth kinetics is rapid (∼t4), indicating spontaneous generation of new nuclei, while at higher coverage Si island growth dominates.
Improved inhibit patterning of YBa2Cu3O7 thin films
Authors: Copetti C. A. , Gassig U. , Zander W. , Schubert J. , Buchal Ch.
Published: July 2002

We present an improved reaction patterning technique to fabricate very stable thin film devices of YBaCuO on various substrates. Our approach includes in situ patterning and completely avoids the contact between YBaCuO superconductor and chemical or physical etchants. Very thin, high quality YBaCuO structures are grown on ridges or in trenches and in situ protected by passivating layers, demonstrating excellent long term stability.
Iron acceptor level in ZnTe
Authors: Meyer B. K. , Omling P. , Linke H. , Salk B. , Benz K.-W.
Published: July 2002

The iron acceptor, FeZn, in as-grown ZnTe has been investigated by electron-paramagnetic resonance (EPR) and by photo-EPR. The photo-EPR investigation shows that the Fe+ EPR signal is enhanced by optical illumination, and the threshold energy for enhancement, at ≊1.75 eV, suggests that the acceptor level is located at 0.65 eV below the conduction band. The energy dependence of the optical cross-section for hole ionization, σp0, was determined from an analysis of the time dependent EPR signals. This first determination of the Fe+ acceptor energy level in a II-VI semiconductor allows us to predict the positions of the acceptor level in other II-VI materials. In particular, for Cd-based II-VI materials it is suggested that the acceptor level of iron is located degenerate with the conduction band.
Spectral and intensity dependence on dipole localization in Fabry–Perot cavities
Authors: Huang Z. , Lei C. , Deppe D. G. , Lin C. C. , Pinzone C. J. , Dupuis R. D.
Published: July 2002

Data is presented on the characteristics of light emitted from localized dipoles contained in Fabry–Perot cavities. The cavities consist of AlGaAs semiconductor with the dipole localization achieved using GaAs quantum wells. Experimental data shows that the standard assumption of the spectral width of a cavity mode as having some fixed relationship to the photon lifetime in the cavity is an approximation which only becomes valid for dipoles throughout the cavity. Also, intensity differences are measured out either side of a cavity even when symmetrical mirrors are used. The intensity difference depends on the precise dipole position. Both the spectral and intensity differences can be derived from theory using a model which accounts for interference between coherent spontaneous wavepackets emitted in opposite directions from individual emission events.
Isotopically pure diamond anvil for ultrahigh pressure research
Authors: Vohra Yogesh K. , Vagarali Suresh S.
Published: July 2002

Large gem quality type IIa crystal of isotopically pure 12C diamond (364 mgm) was evaluated for applications as an anvil in ultrahigh pressure research. Raman microprobe and photoluminescence studies on 12C diamond were compared with a typical type Ia natural diamond anvil used in high pressure research. Visible fluorescence in the isotopically pure diamond is an order of magnitude lower as compared to natural diamond and is ideal for spectroscopic studies in diamond cell devices. Low intrinsic strain, high purity and crystal perfection of 12C diamond anvil offer better performance under extreme stresses.
Large third-order optical nonlinearity of nanometer-sized amorphous semiconductor: Phosphorous colloids formed in SiO2 glass by ion implantation
Authors: Hosono Hideo , Abe Yoshihiro , Lee Ying L. , Tokizaki Takashi , Nakamura Arao
Published: July 2002

This article reports large nonlinear susceptibility χ(3) of nanometer-sized particles of amorphous phosphorus. Nanocomposites of amorphous red phosphorous colloid particles (3–5 nm in diameter) and SiO2 glasses have been fabricated by ion implantation technique. Silica glasses implanted at an acceleration voltage of 180 keV to a dose of 5×1017 P+ ions/cm2 shows χ(3) of ∼1×10−6 esu, which is comparable to quantum-sized crystals of semiconductors such as CuCl and CdS1−xSex. This is the first finding that quantum dots of amorphous semiconductors embedded in dielectrics exhibits such a large χ(3).
Wavelength-selectable laser emission from a multistripe array grating integrated cavity laser
Authors: Soole J. B. D. , Poguntke K. R. , Scherer A. , LeBlanc H. P. , Chang-Hasnain C. , Hayes J. R. , Caneau C. , Bhat R. , Koza M. A.
Published: July 2002

We report laser operation of a multistripe array grating integrated cavity (MAGIC) laser in which the wavelength of the emission from a single output stripe is chosen by selectively injection pumping a second stripe. We demonstrate a device that lases in the 1.5 μm fiber band at 15 wavelengths, evenly spaced by ∼2 nm. The single-output/wavelength-selectable operation, together with the accurate predefinition of the lasing wavelengths, makes the MAGIC laser a very attractive candidate for use in multiwavelength networks.
Programmable electro-optic waveguide filter
Authors: Okayama H. , Kawahara M.
Published: July 2002

Programmable filters with multisection electro-optic mode converter structures are proposed, with which wavelength tuning without increasing the drive voltage and simultaneous selection of multiple wavelengths can be realized.
Preparation of polymeric metal-tetracyanoquinodimethane film and its bistable switching
Authors: Gong Jianping , Osada Yoshihito
Published: July 2002

Metal salts of charge transfer complex such as CuTCNQ, LiTCNQ and others have been found to dissolve in water when mixed with polyethyleneimine (PEI). From electronic spectra it was supposed that metal salts of organic complex form trilateral complex with PEI in water. Homogeneous and continuous polymeric thin film was prepared by casting this solution. The film with a thickness of 150–200 nm showed field-induced bistable switching from low to high impedance regime at a field strength of 4×104 V/mm. A possible switching mechanism was briefly discussed.
Control of selectivity during chemical vapor deposition of copper from copper (I) compounds via silicon dioxide surface modification
Authors: Jain A. , Farkas J. , Kodas T. T. , Chi K.-M. , Hampden-Smith M. J.
Published: July 2002

The selective chemical vapor deposition of the compounds, (hfac)CuL, where hfac=1,1,1,5,5,5-hexafluoroacetylacetonate and L=trimethylphosphine (PMe3); 1,5-cyclooctadiene (1,5-COD); vinyltrimethysilane (VTMS), and 2-butyne onto W in the presence of SiO2 has been studied as a function of surface pretreatment. Cleaning the substrates with hot aqueous H2O2, followed by washing and drying resulted in blanket copper deposition (except for L=PMe3). In contrast, the nucleation of copper onto SiO2 can be controlled by reacting the SiO2 surface with chlorotrimethylsilane regardless of the nature of L. Transmission FTIR studies of (hfac) Cu(VTMS) adsorbed on a model (Cab-O-Sil) SiO2 surface in the presence and absence of chlorotrimethylsilane suggested that the chlorotrimethylsilane interacted with the surface hydroxl groups to reduce the number of sites at which (hfac) Cu(VTMS) can adsorb and react, therefore providing selectivity.
Si band-gap shrinkage caused by local strain at Si/SiO2 edge
Authors: Takeuchi Kan , Aoki Masakazu
Published: July 2002

This letter describes Si band-gap shrinkage caused by local strain at the local oxidation of silicon (LOCOS) edge. The local band-gap shrinkage of 20–30 meV is shown to exist at the LOCOS edge by measuring the forward-biased junction current of square n+ regions on a p substrate for various junction sizes. The junction current is observed to be proportional to the peripheral length rather than the area of the square n+ regions at liquid-nitrogen temperatures. It is also likely that the shrinkage would degrade the current gain of bipolar transistors, especially at low temperatures.
Desorption properties of amine species during atomic layer epitaxy of GaAs using amino-As
Authors: Fujii Kazuyuki , Suemune Ikuo , Yamanishi Masamichi
Published: July 2002

The substantial expansion of the temperature range for atomic layer epitaxy (ALE) was reported using triethyl-gallium by K. Fujii, I. Suemune, T. Koui, and M. Yamanishi [Appl. Phys. Lett. 60, 1498 (1992)]. This was observed by replacing arsine with an amino-As, tris-dimethylamino-arsenic {As[N(CH3)2]3}. The self-limiting mechanism was attributed to the adsorption of amine species on the Ga as well as As surfaces. The time constants and the activation energies for the desorption of the amine species were measured using transient quadrupole mass spectrometry. It is shown that the adsorption properties of the amine species on the Ga surfaces are intermediate between those of methyl and ethyl species.
Picosecond time-resolved measurements of electroabsorption in an InGaAs/GaAs multiple quantum well p-i-n modulator
Authors: Mahgerefteh Daniel , Yang Ching-Mei , Chen Li , Hu Kezhong , Chen Wei , Garmire E. , Madhukar A.
Published: July 2002

We report the first picosecond time-resolved measurements of electroabsorption in a strained InGaAs/GaAs multiple quantum well p-i-n structure as a function of applied bias at various optical excitation densities. The data above 4 V are explained by a model which assumes a rise time dominated by a single carrier sweep-out time and a decay dominated by lateral diffusion. A bias independent electro-absorption rise time of 10±2 ps is obtained and appears to be limited by the transit time of carriers across the structure. The decay time is also ≊10 ps. Below 4 V the decay time increased to 80 ps as the bias was reduced to 0 V. This increase may be related to the change in depletion length with bias in the intrinsic region.
Synthesis and properties of a-axis and b-axis oriented GdBa2Cu3O7−δ high T
c thin films
Authors: Nakamura O. , Guimpel J. , Sharifi F. , Dynes R. C. , Schuller Ivan K.
Published: July 2002

We report the growth and properties of a-axis oriented GdBa2Cu3O7−δ high Tc thin films on (100) SrTiO3 substrates by dc magnetron sputtering. It is found that GdBa2Cu3O7−δ films on (100) SrTiO3 exhibit a-oriented growth at higher substrate temperatures compared with YBa2Cu3O7−δ films. By utilizing low-temperature-grown a-axis GdBa2Cu3O7−δ films (200 Å in thickness) as a self-template, pure a-axis films can be grown at elevated temperatures. The growth of b-axis film on vicinal (100) SrTiO3 under similar growth conditions is also reported.
Double-wavelength laser array with InGaAsP/InGaAsP multiple quantum well grown by Ar ion laser-assisted metalorganic molecular beam epitaxy
Authors: Yamada T. , Iga R. , Sugiura H.
Published: July 2002

This letter reports a laser diode array of InGaAsP/InGaAsP multiple quantum well (MQW) lasers, emitting at different wavelengths, grown by Ar ion laser assisted metalorganic molecular beam epitaxy. A separate confinement heterostructure MQW laser film was locally irradiated during well growth with an Ar ion laser and processed into a laser diode array having a 6 μm stripe width and 300 μm pitch. The laser diode with an irradiated MQW active layer operated at 1.40 μm; the laser diodes with nonirradiated MQW active layers operated at 1.28 μm. The threshold currents of the 300 μm-long laser diodes were 23 mA for the irradiated diode and 55 mA for the nonirradiated diodes.
Superconductive tunneling through semiconductor heterostructures
Authors: Waung Raymund , Feng Shechao
Published: July 2002

We investigate the characteristics of Cooper pair tunneling through a system of two superconductors separated by a double-barrier semiconductor quantum well. The zero-voltage critical supercurrent is calculated for a select range of well widths and doping concentrations, and is found to depend sensitively on these parameters. Resonance effects arising from an optimal alignment between the Fermi level and the subband eigenenergies in the well are shown to enhance the current by up to four orders of magnitude.
Symmetry properties of Er3+ related centers in In1−xGaxP with low alloy compositions
Authors: Buyanova I. A. , Neuhalfen A. J. , Wessels B. W.
Published: July 2002

The symmetry properties of Er3+-related centers in InP and In1−xGaxP (x=0.08) epitaxial layers are determined using the method of polarized excitation spectroscopy. It is shown that the Er3+-related luminescence is strongly polarized under polarized excitation. The polarization measurements indicate the low symmetry of these centers. Two transition mechanisms are proposed to explain the polarized luminescence. The first mechanism involves excitation of the intra-4f-shell electron into higher lying excited states of the Er3+ ion. A second mechanism involves the recombination of an exciton bound to an Er-related trap with a subsequent Auger excitation of the 4f shell.
Transform of dynamic heat equation in anisotropic media and its application in laser-induced temperature rise
Authors: Lu Yong-Feng
Published: July 2002

Scanning cw laser-induced temperature rise in anisotropic substrates has been investigated by simplifying and solving the dynamic heat equation in anisotropic media. It is found that the heat equation in anisotropic media can be simplified to a heat equation in isotropic media by coordinate transformation. The anisotropy of the media can then be reflected by heat source transformation. A general model was derived to calculate the scanning laser-induced temperature rise in anisotropic substrates. The result reveals that the substrate anisotropy affects both the peak temperature rise and the peak position.
Single mode broad area distributed Bragg reflector ring oscillators
Authors: Dzurko Kenneth M. , Scifres Donald R. , Hardy Amos , Welch David F. , Waarts R. G.
Published: July 2002

A large aperture, spatially coherent, single frequency semiconductor ring laser is demonstrated for the first time. Two diffraction gratings oriented orthogonally to each other are used to uniquely select a single broad area mode which oscillates at a single wavelength. Spatial coherence across a 411 μm output aperture is observed, giving a diffraction limited output beam measuring 0.2°×0.135°. The surface emitting ring oscillators contain strained InGaAs/GaAs quantum well active regions and operate at 1012 nm to pulsed output powers exceeding 500 mW with threshold current densities under 300 A/cm2.
Negative differential conductance observed in a lateral double constriction device
Authors: Wu J. C. , Wybourne M. N. , Berven C. , Goodnick S. M. , Smith Doran D.
Published: July 2002

Lateral double point contact devices were fabricated using a split-gate high electron mobility transistor. The low-temperature source-drain characteristics show pronounced S-shaped negative differential conductance that can be independently controlled by an applied gate bias. The mechanism for the observed switching behavior is believed to be similar to that proposed for heterostructure hot electron diodes.
Quantum well infrared photodetectors with bi-periodic grating couplers
Authors: Lee C. P. , Chang K. H. , Tsai K. L.
Published: July 2002

Multiple quantum well infrared photodetectors (QWIPs) with bi-periodic grating couplers have been demonstrated. The bi-periodic grating consists of two gratings with different periods. The response linewidths of such QWIPs are found to be much wider than those of conventional grating coupled QWIPs. By using bi-periodic gratings for coupling the radiation into QWIPs, the influence of variation of material and grating quality on the performance of QWIP can be largely eliminated.
Four-port guided-wave nonsymmetric Mach–Zehnder interferometer
Authors: Wang W. J. , Honkanen S. , Najafi S. I. , Tervonen A.
Published: July 2002

A four-port guided-wave nonsymmetric Mach–Zehnder interferometer based on two hybrid optical couplers is proposed. A potential application of the device is a 0.98 μm/1.55 μm wavelength multiplexer in connection with an optical ring resonator. The proposed device is designed by using the effective indices of the guided modes in a silver ion-exchanged waveguide. The device is fabricated in glass substrate by a two-step ion-exchange process, and it is characterized using a continuous source as well as lasers at λ=1.06, 1.3, and 1.523 μm.
In situ study of relaxation of SiGe thin films by the modified Frank–Read mechanism
Authors: LeGoues F. K. , Ott J. A. , Eberl K. , Iyer S. S.
Published: July 2002

We have studied the dynamics of thermal relaxation of highly metastable films of SiGe/Si(100) in situ in the transmission electron microscope (TEM). This makes it possible to study the early stages of strain relaxation, and thus obtain information about the nucleation of dislocations. We find that, when care is taken not to introduce artifacts during sample preparation, relaxation occurs by the multiplication of ‘‘precursor dislocations’’ through a mechanism similar to the Frank–Read mechanism. An individual nucleation site is observed, confirming the model previously proposed.
Observation of strong Si/Si1−xGex narrow quantum-well near-edge luminescence under applied hydrostatic pressure
Authors: Northrop G. A. , Morar J. F. , Wolford D. J. , Bradley J. A.
Published: July 2002

We report the first measurements of band-gap energy versus applied hydrostatic pressure in the Si1−xGex system, a result achievable only with the recent availability of high-quality alloys. The Si/Si1−xGex (x=0.05–0.25) quantum wells used here were prepared by molecular beam epitaxy, and produced relatively intense photoluminescence (PL). Indeed, this PL emission from just two 25-Å-thick quantum wells was found to be comparable to that from high-optical quality, ultrahigh-purity bulk Si. A clear no-phonon emission line is found in the low-temperature (6 K) PL which displays a strictly linear PL energy dependence with pressure. The alloy and Si pressure dependencies (−1.50 and −1.52 meV/kbar) were found to be virtually identical thus proving the luminescence is from a ‘‘shallow’’ electronic state and associated with the X band gap of the pseudomorphically strained alloy.
DCM-polyimide system for triple-stack poled polymer electro-optic devices
Authors: Ermer S. , Valley J. F. , Lytel R. , Lipscomb G. F. , Van Eck T. E. , Girton D. G.
Published: July 2002

We report development of the first all-polyimide system (cladding/core/cladding) suitable for fabrication of electro-optic waveguide devices on silicon substrates. The cladding layers are spun from a low optical loss, commercially available polyimide that is suitable for multilayer stacks. The electro-optic material consists of this same polyimide as host to a commercially available guest chromophore and is based upon our prior work on thermoplastic polyimides [J. F. Valley, J. W. Wu, S. Ermer, M. Stiller, E. S. Binkley, J. T. Kenney, G. F. Lipscomb, and R. Lytel, Appl. Phys. Lett. 60, 160 (1992)]. We present the materials and process development methodology with the results for this polymer system and demonstrate it by fabrication of an all-polyimide Mach–Zehnder modulator operating at 830 nm.
Large area, low voltage, transit time limited InGaAs metal semiconductor metal photodetectors
Authors: Ralph Stephen E. , Hargis M. C. , Pettit G. D.
Published: July 2002

We demonstrate the efficacy of a method for reducing the effects of charge associated with the InP substrate-InGaAs interface. By incorporating an AlInAs buffer layer we have dramatically improved the performance of InGaAs metal-semiconductor-metal-photodetectors grown by molecular beam epitaxy. The buffer layer reduces the parasitic capacitances and also reduces the carrier concentration in the absorbing InGaAs layer. This allows complete depletion at low bias, giving rise to a more uniform field strength. The relatively large, 50-μm-diam detectors, operating at 5 V, have an extremely linear response, and a 3 dB power bandwidth of ∼30 GHz. Low frequency gain was not observed for bias voltages to 20 V.
Effect of sub-band-gap illumination on β-FeSi2/n-type Si diodes under reverse bias
Authors: Leibovitch M. , Shapira Yoram , Regolini J. L.
Published: July 2002

A recently reported decrease of the reverse current in β-FeSi2-n-type Si diodes under sub-band-gap illumination is theoretically considered. It is shown that this effect can be explained through a reduction of the generation component of the reverse current, which is caused by a decrease in the width of the space charge region due to illumination-induced charging of deep impurities. Physical modeling of the effect is also presented.
Growth morphology of epitaxial ErAs/GaAs by x-ray extended range specular reflectivity
Authors: Miceli P. F. , Palmstro/m C. J. , Moyers K. W.
Published: July 2002

The growth morphology of ErAs on [001] GaAs with thicknesses ranging from 2 atomic layers to 400 Å is investigated using x-ray specular reflectivity. This epitaxial system displays rich morphological behavior and we observe the evolution from discontinuous to continuous layers at just a few monolayers and qualitative changes occur in layer thickness fluctuations for thicker films having high dislocation densities. We also demonstrate that the reflectivity of a heteroepitaxial system can be measured and modeled over an extended angular range, starting from grazing angles and continuing through the regions of Bragg scattering at higher angles. Disorder in epitaxial layers typically gives a mosaic line broadening transverse to the reflectivity and we show that transverse line shape considerations are crucial to these measurements.
Magnetization studies of the influence of fast neutron irradiation on critical current density of melt-textured YBa2Cu3O7−x
Authors: Puźniak R. , Wiśniewski A. , Szymczak H. , Wang Jingrong , Zhang Pingxiang , Zhou Lian
Published: July 2002

The decrease of the magnetization hysteresis loop proportional to the decrease of the sample size was found for unirradiated and fast neutron irradiated bulk samples obtained from a powder melting process (PMP). This fact indicates that the superconducting current flows throughout the whole sample even when the magnetic field is applied. Thus, the critical current is not limited by field induced decoupling of the weak links. This is a consequence of specific microstructure of PMP samples. The increase of the critical current density by the factor of about 3 was observed after irradiation in magnetic field of 1 T in the examined temperature range from 60 to 85 K. The highest critical current density of the irradiated sample determined from magnetic measurements was equal to 5×104 A/cm2 in 1 T at 77 K.
Oxidizer partial pressure window for YBa2Cu3O7−x thin film formation by metalorganic chemical vapor deposition
Authors: Chern C. S. , Zhao J. , Norris P. E. , Garrison S. M. , Yau K. , Li Y. Q. , Gallois B. M. , Kear B. H.
Published: July 2002

We have conducted a systematic study of oxidizer partial pressure effects on both the superconducting transport properties and structural properties of YBa2Cu3O7−x (YBCO) films grown by conventional metalorganic chemical vapor deposition (MOCVD). Superconducting YBCO thin films were grown in partial N2O pressures ranging from 0.4 to 45 Torr and at substrate temperatures of 500 and 700 °C. We have observed a window in oxidizer partial pressure within which YBCO thin films can be formed in the as-deposited state by the MOCVD process. A trend of increasing b-axis orientation as the oxidizer partial pressure increased was revealed by detailed x-ray diffraction. The reduction of superconducting properties for films grown at high oxidizer partial pressure might result from the lack of surface mobility. Oxygen deficiency in the films was ruled out as the cause of the degraded properties.
Analysis of distributed-feedback lasers: A recursive Green’s function approach
Authors: Kahen K. B.
Published: July 2002

A recursive Green’s function method is introduced for obtaining the exact modal characteristics of aperiodic distributed-feedback lasers. Additionally, based on scaling arguments, a new expression for the coupled-mode theory coupling coefficient, κ, is derived, resulting in increased accuracy for coupled-mode calculations.
Enhanced breakdown voltages in strained InGaAs/GaAs structures
Authors: David J. P. R. , Morley M. J. , Wolstenholme A. R. , Grey R. , Pate M. A. , Hill G. , Rees G. J. , Robson P. N.
Published: July 2002

The breakdown voltage (VBD) in a semiconductor is usually proportional to its band-gap (Eg) through the dependence of the impact ionization process on the threshold voltage (Eth). It has recently been suggested that strain can cause Eth to increase even when Eg decreases, raising the possibility of narrow band-gap materials with large VBD. By growing a range of strained InGaAs/GaAs multiple quantum well (MQW) pin diode structures and measuring VBD, we show that the presence of strained InGaAs increases VBD confirming that it has a larger Eth than GaAs.
Observation of polarization independent electric field effect in InGaAs/InP tensile strained quantum well and its proposal for optical switch
Authors: Ravikumar K. G. , Aizawa T. , Suzaki S. , Yamauchi R.
Published: July 2002

We have experimentally observed the polarization independent electric field induced absorption coefficient variation in an InGaAs/InP tensile strained quantum well (QW) structure for the first time. We have also found that the field induced absorption coefficient/refractive index variation of strained QW for the transverse electric (TE) mode does not change appreciably from that of an unstrained one. Based on these results, we propose tensile strained QW for polarization independent optical switch/modulator.
Evidence for state filling effect on high speed modulation dynamics of quantum well lasers
Authors: Zhao B. , Chen T. R. , Yamada Y. , Zhuang Y. H. , Kuze N. , Yariv A.
Published: July 2002

By using different separate confinement structures for otherwise identical quantum well lasers, we find experimentally that the differential gain can vary over a factor of three, which significantly affects the high speed modulation bandwidth in such lasers. These observations are in agreement with the predictions of a theory of modulation dynamics which accounts for the carrier population in the optical confining region of the separate confinement structure (state filling effect) in quantum well lasers.
Frequency stabilization, linewidth reduction, and fine detuning of a semiconductor laser by using velocity-selective optical pumping of atomic resonance line
Authors: Kozuma M. , Kourogi M. , Ohtsu M. , Hori H.
Published: July 2002

A novel optical feedback technique for a semiconductor laser has been used successfully in stabilizing the laser frequency to a hyperfine transition frequency of the Rb87-D2 line (F=2–3) and simultaneously reducing the laser field spectral linewidth 20-times that of the free-running laser. The locking range of this feedback was 200 MHz. The possibility of continuous detuning of the stabilized frequency as large as ±γ/2 (half of the natural linewidth of the atomic resonance) was demonstrated.
Optical properties of the buried waveguide in a bistable InGaAsP semiconductor laser
Authors: Joindot I.
Published: July 2002

In this letter, we first examine the power reflection coefficient at the interface between InGaAsP active and passive waveguides in a bistable laser and the optical losses of the passive waveguide. An original method is used for carrier density investigations: the spontaneous emission from the uncleaved sides of the active region is analyzed. With the experimental results and from a simple model we then calculate the carrier density difference and the reflection coefficient at the interface. After that we examine the ratio of the output power from each uncoated cleaved facet and deduce the spectrally resolved modal attenuation.
Influence of 180° domains on ferroelectric properties of BaTiO3 single crystal
Authors: Nakao Osamu , Tomomatsu Kazuhiko , Ajimura Shoji , Kurosaka Akihito , Tominaga Haruo
Published: July 2002

Mechanical poling was applied to a BaTiO3 single crystal grown by the top-seeded solution growth (TSSG) method to remove its 90° domain walls, and then four-step electrical poling was applied to rearrange the 180° domain configuration. In each of these steps, the dielectric constant (from 50 kHz to 10 MHz) was measured by using an impedance analyzer, and the 180° domains were observed by the etching method. The dielectric spectra were confirmed to vary with rearrangement in 180° domain configuration. Dielectric constant εc in the 〈001〉 direction was 130 at 100 kHz and 58 at 10 MHz. Dielectric constant εa in the 〈100〉 direction was 4700 at 100 kHz and 1900 at 10 MHz.
Pattern effects in time jitter of semiconductor lasers
Authors: Sapia Adalberto , Spano Paolo , Mirasso Claudio R. , Colet Pere , San Miguel Maxi
Published: July 2002

The effect of fast repetitive pulse modulation on the value of time jitter affecting the optical pulses emitted by semiconductor lasers is studied both experimentally and by numerical simulations. The results show that the modulation also induces pattern effects that increase the value of time jitter to non-negligible values for bias above threshold.
Phase controlled all-optical switching in rocking filter fibers
Authors: Krautschik C. G. , Stegeman G. I. , Stolen R. H.
Published: July 2002

We demonstrate experimentally that all-optical switching of a strong beam can be controlled by the phase of a weak beam in a rocking rotator fiber.
n- and p-type in-plane gated field effect transistors directly written on a semi-insulating GaAs substrate
Authors: Hirayama Y.
Published: July 2002

A new type in-plane gated field effect transistor where the semi-insulating substrate itself is used as a gate insulator region is proposed. n- and p-type in-plane gated field effect transistors are fabricated on a semi-insulating GaAs substrate by focused ion beam scanning of Si++ and Be++, respectively. These in-plane gated field effect transistors are found to operate well at room temperature.
Effects of 300 MeV Au+24 ion irradiation on superconductivity in YBa2Cu3O7 epitaxial films
Authors: Budhani R. C. , Zhu Y. , Suenaga M.
Published: July 2002

We report the effects of 300 MeV gold ion irradiation on the transition temperature (Tc) and critical current density (Jc) of YBa2Cu3O7 epitaxial films. The radiation at a dose as low as 5.6×1010 ions/cm2 decreases the zero field Tc and Jc. However, the response of the mixed state in 1–8 T field remains relatively unchanged up to a dose of ∼9×1010 ions/cm2. We argue that the stiffness of the flux lines in a film geometry and the pinning sites distributed at a length scale much smaller than that of the ion-induced defects are responsible for this null result.
Comparison between ruthenium-based and other ohmic contact systems to p-type GaAs
Authors: Barnard W. O. , Myburg G. , Auret F. D.
Published: July 2002

A conventional furnace annealed Ru/Au ohmic contact system on p-GaAs has been investigated. Electrical and morphological characteristics of this contact system were compared with other systems such as Cr/Au, Ti/Pt, and Mn/Au. The Ru/Au contact system has been shown to have superior surface morphology and a comparable specific contact resistance value, even after annealing at 485 °C. The advantages of utilizing Ru as contact material to GaAs are that it forms high quality, thermally stable Schottky contacts to n-GaAs and thermally stable ohmic contacts with low specific contact resistance to p-GaAs. This dual nature of Ru contacts to GaAs makes them extremely important for future use in devices such as heterojunction bipolar transistors (HBTs) and solid state lasers.
Low-temperature (490 °C)GaAs epitaxial growth on (100)Si by molecular beam epitaxy
Authors: Chiang T. Y. , Yiin D. H. , Liu E. H. , Yew T. R.
Published: July 2002

Low-temperature (490 °C)GaAs epitaxial growth on (100) silicon by molecular beam epitaxy is reported in this letter. Silicon wafers were cleaned by spin-etch technique to passivate silicon surface with hydrogen, by which the conventional high-temperature (≳850 °C) oxide desorption step for pre-epitaxial substrate preparation is eliminated. The possibility of epitaxial growth on such a passivated surface to obtain good quality epitaxy is investigated. Epitaxial films are characterized by cross-sectional transmission electron microscopy (XTEM), plan-view transmission electron microscopy, and double crystal diffraction (DCD).
Room temperature 10 MHz electro-optic modulation in ferroelectric liquid crystals
Authors: Liu Jian-Yu , Johnson Kristina M. , Robinson Michael G.
Published: July 2002

We report high frequency (≳10 MHz) electro-optic (EO) modulation using a chiral smectic C* ferroelectric liquid crystal (FLC). Results indicate that the r32 coefficient of the commercially available chiral smectic FLC SCE9 is ≊3 pm/V.
Cobalt self-diffusion during cobalt silicide growth
Authors: Diale M. , Challens C. , Zingu E. C.
Published: July 2002

The flux of atoms during Si/Co interdiffusion has been investigated by means of thin tantalum marker layers imbedded in the deposited Co layer. The silicide phase CoSi is found to grow in the Si/CoSi/Co structure without any conversion of CoSi to Co2Si. Cobalt is found to be the dominant diffusing species in CoSi during its growth in Si/CoSi/Co structures. Cobalt atoms are also found to diffuse in the unreacted Co layer from the Co surface towards the CoSi/Co interface. These results present evidence that some of the Co vacancies in the metal silicide layer are annihilated at the Co surface.
Evidence for an alternative, hole-trapping related random telegraph signal mechanism in n-channel silicon-on-insulator metal-oxide-semiconductor transistors
Authors: Simoen E. , Claeys C.
Published: July 2002

In this letter, evidence will be given for an alternative random telegraph signal (RTS) mechanism in silicon-on-insulator (SOI) metal-oxide-semiconductor transistors (MOSTs). It will be demonstrated that anomalous RTS behavior is observed in floating-film operated SOI nMOSTs. The experimental results strongly suggest that the origin of the drain current switching is related to trapping of holes, most likely by a defect center in the Si overlayer. This is in contrast to the normal RTSs which are caused by electron trapping by an interface near-oxide trap.
100 GHz oscillations on monolithic high T
c chip
Authors: Edstam J. , Nilsson P-Å. , Stepantsov E. A. , Olsson H. K.
Published: July 2002

We have coupled 80–180 GHz oscillations from a HTc Josephson junction onto an on-chip YBa2Cu3O7/SiO/Au microstrip resonator. Efficient coupling was achieved at the resonance frequencies and both resonance frequency and Q value could be measured from the I-V curve. The use of a superconductor in the microstrip gave negligible dispersion (<4%) from 80 to 180 GHz, whereas the attenuation of 4–8 dB/nm originated mainly from the normal metal groundplane.
Submicron niobium junctions for submillimeter-wave mixers using optical lithography
Authors: Dierichs M. M. T. M. , Panhuyzen R. A. , Honingh C. E. , de Boer M. J. , Klapwijk T. M.
Published: July 2002

High-current density, submicron-sized superconductor-insulator-superconductor niobium junctions are made with optical lithography. With a novel process junctions as small as 0.8 μm2 are routinely made using a controlled under-etch with the quality parameter Vm up to 67 mV. The junction quality is found to be independent of the amount of under-etch. Used in a 345 and 490 GHz waveguide mixer, noise temperatures have been obtained as low as 131 K double-side band (DSB) and 120 K (DSB), respectively.
Planar optical waveguides formed by erbium ion exchange in glass
Authors: Zheng X. H. , Mears R. J.
Published: July 2002

We report the use of erbium ion as the sole dopant in the formation of planar optical waveguides on glass substrates through a simple ion exchange process. Index differences of more than 0.04 have been achieved. This offers the prospect of designing active optical waveguides free from the unwanted side effects of additional index-raising dopants currently used in the ion exchange process.
Simple in-line method to measure the dispersion of an optical system
Authors: Yao X. Steve , Feinberg Jack
Published: July 2002

We describe a simple in-line method to measure the dispersion of an optical system. The light beam passing through the optical system interferes with a reference beam in a spectrometer, and the resulting spectrum yields the quadratic and cubic dispersion terms of the system. We demonstrate this technique on an optical system made of grating pairs.
Perfectly selective Si epitaxial growth due to synchrotron radiation irradiation during disilane molecular beam epitaxy
Authors: Utsumi Yuichi , Akazawa Housei , Nagase Masao , Urisu Tsuneo , Kawashima Izumi
Published: July 2002

Perfect selectivity in Si epitaxial growth has been achieved by irradiating SR during molecular beam epitaxy (MBE) using disilane. No Si nucleation occurs on SiO2 irrespective of growth time, in contrast to conventional selective growth by MBE using disilane. At a given disilane pressure, higher temperatures are preferable for SR-induced selective growth, whereas lower temperatures are preferable for conventional selective growth. It is proposed that perfect selectivity results from SR-stimulated SiO2 evaporation which expels Si atoms with dangling bonds, i.e., Si nucleation sites, from the SiO2 surface.
Hydrogen interactions with delocalized spin centers in buried SiO2 thin films
Authors: Warren W. L. , Schwank J. R. , Shaneyfelt M. R. , Fleetwood D. M. , Winokur P. S.
Published: July 2002

Defect centers have been investigated in bonded and etchback silicon-on-insulator materials following irradiation using electron paramagnetic resonance (EPR). Three different EPR centers are created in the top 0.1 μm of the SiO2 dielectric by either x-ray irradiation or vacuum ultraviolet (VUV) illumination. Two of the defects are the classic E′ center (⋅Si≡O3) and the amorphous silicon center (⋅Si≡Si3). The third EPR active defect center is characterized by g=2.0025 with an effective line width of 1.1 G. Longer irradiation times transform this new center into a hydrogen-related defect as observed by its two hyperfine lines split by 23.1 G. It appears that this defect is positively charged when EPR active. Using conventional capacitance versus voltage techniques, it is also found that irradiation leads to the generation of positive charge in the dielectric. This charge is located near the bottom Si/SiO2 interface, opposite the interface at which the paramagnetic centers are located.
InGaAsP monolithic extended-cavity lasers with integrated saturable absorbers for active, passive, and hybrid mode locking at 8.6 GHz
Authors: Hansen P. B. , Raybon G. , Koren U. , Iannone P. P. , Miller B. I. , Young G. M. , Newkirk M. A. , Burrus C. A.
Published: July 2002

Active, passive, and hybrid mode locking of a monolithic extended-cavity semiconductor laser with an integrated saturable absorber have been demonstrated. Actively mode locked at a repetition rate of 8.6 GHz, 6.2 ps pulses were measured. Hybrid mode locking resulted in 4.4 ps pulses. The extended-cavity laser also exhibits self-starting passive mode locking at a repetition rate of 8.57 GHz with 5.5 ps pulses. A broad spectrum allows wavelength selectivity over a range of 15 nm with little change in the pulse width.