bluuebunny/crossref_metadata_2025 huggingface dataset:
High-power single-mode strained single quantum well InGaAs/AlGaAs lasers grown by molecular beam epitaxy on nonplanar substrates
Authors: Arent D. J. , Brovelli L. , Jäckel H. , Marclay E. , Meier H. P.
Published: July 2002

Strained single quantum well InGaAs/AlGaAs graded-index separate confinement heterostructure lasers have been grown by molecular beam epitaxy over nonplanar substrates. In addition to the low threshold currents provided in situ by lateral current blocking pn junctions obtained by plane-dependent doping of the amphoteric Si dopant, we observe variations in lasing wavelength, efficiency, and internal absorption as a function of the central (100) facet length. These variations are associated with increased indium composition in the strained quantum well which arises from incorporation of adatoms migrating from the low-growth (311)A side facets to the preferential growth (100) active area facets. Uncoated devices (750 μm×4 μm) have been found to have threshold currents as low as 6 mA (Jth=320 A/cm2) and exhibit single-mode behavior to greater than 100 mW at a wavelength of ∼1.0 μm when reflectivity modified (90%/10%).
Low series resistance vertical-cavity front-surface-emitting laser diode
Authors: Yoo Hoi-Jun , Hayes J. R. , Andreadakis N. , Paek E. G. , Chang G. K. , Harbison J. P. , Florez L. T. , Kwon Young-Se
Published: July 2002

We have fabricated a front-surface-emitting laser diode (FSELD) using a technique which relies on a double ion implant of oxygen and beryllium. The laser had a low operating voltage at the lasing threshold, a low series resistance, and a relatively small threshold current of 6 mA for a 25-μm-diam device. The lasing wavelength was 971 nm and the spectral width above threshold was 5 Å. Since the light comes from the front surface of the wafer, the fabrication technique described here for realizing a FSELD can be used for the fabrication of vertical-cavity visible surface-emitting lasers.
Imaging metal atoms in air and water using the atomic force microscope
Authors: Manne S. , Butt H. J. , Gould S. A. C. , Hansma P. K.
Published: July 2002

Gold atoms in an epitaxial film on mica are clearly visible in images obtained with an atomic force microscope (AFM). The measured lattice spacing of 3.0± 0.3 Å is consistent with previous scanning tunneling microscope images obtained in air and vacuum. Atoms are visible even if the sample surface, tip, and cantilever are submerged in water in a closed cell. Electrochemical studies of metal electrodes at atomic resolution may now be possible with the AFM.
Orientation-dependent doping in organometallic chemical vapor deposition on nonplanar InP substrates: Application to double-heterostructure lasers and lateral p-n junction arrays
Authors: Bhat R. , Zah C. E. , Caneau C. , Koza M. A. , Menocal S. G. , Schwarz S. A. , Favire F. J.
Published: July 2002

In this letter we show that the orientation dependence of dopant incorporation can be used to obtain lateral patterning of doping by growing on nonplanar substrates. Specifically, organometallic chemical vapor deposition has been used to obtain lateral p-n junction arrays and selective deposition of alternating p-n layers of InP. The latter technique has been used to grow double-heterostructure lasers with current confinement layers in a single step.
Fabrication of thin-film-type Josephson junctions using a Bi-Sr-Ca-Cu-O /Bi-Sr-Cu-O/Bi-Sr-Ca-Cu-O structure
Authors: Mizuno K. , Higashino K. , Setsune K. , Wasa K.
Published: July 2002

Thin-film Josephson junctions with normal metal barriers using a Bi-based high Tc oxide superconductor were successfully fabricated. Bi2Sr2Ca1Cu2Ox films were used for both superconducting electrodes and Bi2Sr2Cu1Oy for the barrier layer. The junction area of 20×40 μm2 was defined by photolithography and Ar ion milling. These S/N/S-type junctions clearly exhibited the ac Josephson effect under the irradiation of radio frequency waves of 12 GHz and more than 20 Shapiro steps were observed.
Hydrogenated multiple stripe high-power long-wavelength (1.06 μm) continuous (10–50 °C) AlyGa1−yAs-GaAs-InxGa1−xAs quantum well heterostructure lasers
Authors: Major J. S. , Plano W. E. , Sugg A. R. , Hall D. C. , Holonyak N. , Hsieh K. C.
Published: July 2002

High-power operation of hydrogenated AlyGa1−yAs-GaAs-InxGa1−xAs ten-stripe arrays operating at λ∼1.06 μm is described. Continuous (cw) operation of arrays with uncoated facets that are stabilized in temperature at 10 °C has produced output powers as high as 375 mW/facet at 1.4 A. The optical coupling of the gain-guided arrays is shown to be significantly different from otherwise similar arrays fabricated in the AlyGa1−yAs-GaAs system. Limited ‘‘lifetesting’’ (168 h) of these strained layer diodes, stabilized at 50 °C and a cw output power of 100 mW/facet (200 mW total), indicates good operating stability.
Ultraviolet-induced defect creation in amorphous SiO2 exposed to an O2 plasma
Authors: Devine R. A. B. , Francou J-M. , Inard A. , Pelletier J.
Published: July 2002

The creation of paramagnetic defects in plasma chemical vapor deposited amorphous SiO2 exposed to a rf oxygen plasma has been studied as a function of exposure time for two plasma power densities. Unpaired Si dangling bond defects (oxygen-vacancy or oxygen-vacancy like) have been observed in densities attaining ∼4×1017 cm−3 after more than 20 min exposure. These defect levels are equivalent to 10 Mrad of 60 Co γ radiation. Ultraviolet photons in the wavelength range 250≤λ≤300 nm are shown to be responsible for the defect creation. The 130 nm O* emission is found not to be important.
High structural quality epi/oxide boundaries of selective epitaxy grown by SiH4/H2 chemical vapor deposition using growth-sputter cycles
Authors: Yew Tri-Rung , Reif Rafael
Published: July 2002

This letter presents results of high structural quality epi/oxide boundaries of selective epitaxy grown on (100) oxide patterned Si wafers by ultralow pressure chemical vapor deposition from SiH4 /H2 at 800 °C using growth-sputter cycles. The epitaxial films were characterized by cross-sectional transmission electron microscopy and Nomarski optical microscope. About 2.1 μm silicon epitaxy was grown on the exposed silicon windows with about 0.27 μm lateral epitaxial growth over the oxide near {011} epi/oxide sidewalls. Almost no lateral epitaxial overgrowth was observed near {010} sidewalls. The epi/oxide boundary and the epitaxy grown over the oxide were found to be of high structural quality and defect-free.
Low-temperature i
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u formation of Y-Ba-Cu-O high T
c superconducting thin films by plasma-enhanced metalorganic chemical vapor deposition
Authors: Zhao J. , Noh D. W. , Chern C. , Li Y. Q. , Norris P. , Gallois B. , Kear B.
Published: July 2002

Highly textured, highly dense, superconducting YBa2Cu3O7−x thin films with mirror-like surfaces have been prepared, in situ, at a reduced substrate temperature as low as 570 °C by a remote microwave plasma-enhanced metalorganic chemical vapor deposition process (PE-MOCVD). Nitrous oxide was used as the oxidizer gas. The as-deposited films grown by PE-MOCVD show attainment of zero resistance at 72 K. PE-MOCVD was carried out in a commercial scale MOCVD reactor.
Epitaxial tendencies of ReSi2 on (001) silicon
Authors: Mahan John E. , Geib Kent M. , Robinson Gary Y. , Long Robert G. , Xinghua Yan , Bai Gang , Nicolet Marc-A. , Nathan Menachem
Published: July 2002

ReSi2 thin films were grown on (001) silicon wafers by vacuum evaporation of rhenium onto hot substrates in ultrahigh vacuum. The preferred epitaxial relationship was found to be ReSi2 (100)/Si(001) with ReSi2 [010]∥Si〈110〉. The lattice matching consists of a common unit mesh of 120 Å2 area, and a mismatch of 1.8%. Transmission electron microscopy revealed the existence of rotation twins corresponding to two distinct but equivalent azimuthal orientations of the common unit mesh. Although the lateral dimension of the twins is on the order of 100 Å, MeV He+ backscattering spectrometry revealed a minimum channeling yield of 2% for a ∼1500-Å-thick film grown at 650 °C. There is a very high degree of alignment between the ReSi2 (100) and the Si(001) planes.
Correlations between deposition parameters and structural and electrical properties of YBa2Cu3O7−δ thin films grown i
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u by sequential ion beam sputtering
Authors: Kittl J. A. , Nieh C. W. , Lee D. S. , Johnson W. L.
Published: July 2002

We have studied the correlations between deposition parameters and structural and electrical properties of YBa2Cu3O7−δ thin films grown in situ by sequential ion beam sputtering. Epitaxial, c-axis oriented YBa2Cu3O7−δ films were grown both on (100) SrTiO3 and on (100) MgO substrates following the stacking sequence of the ‘‘123’’ compound, with deposited layer thicknesses nominally equal to 1 monolayer. The c-axis lattice parameters obtained were larger than the corresponding lattice parameter in bulk samples, even after low-temperature anneals in O2. The transition temperatures were found to decrease with the enlargement of the c-axis lattice parameter. A clear correlation between growth temperature and the value of the c-axis lattice parameter was observed. The c-axis lattice parameter and the x-ray linewidth of Bragg reflections with the G vector along the c-axis were also found to be correlated. This suggests a relationship between the c-axis lattice parameter and the structural coherence of the epitaxial films.
Critical currents in proton-irradiated single-crystal Ba2YCu3O7−δ
Authors: van Dover R. B. , Gyorgy E. M. , White A. E. , Schneemeyer L. F. , Felder R. J. , Waszczak J. V.
Published: July 2002

Irradiation with 3.5 MeV protons creates defects in Ba2YCu3O7−δ, which can act as strong pinning sites, comparable to those produced by neutron irradiation. Indeed protons as well as neutrons undergo momentum-transferring collisions that result in atomic displacements; the additional electronic proton-solid interaction does not appear to yield defects which contribute to pinning. Under optimized conditions we have obtained Jc(T→0, H=1 T)∼2×107 A/cm2 in single crystals. At 77 K the value is still Jc∼1.7×105 A/cm2, decreasing only threefold in a field of 6 T. The fluence and temperature dependence of Jc suggest a model, in which spatially uncorrelated defects pin vortex cores.
Thin films of the Bi2Sr2Ca2Cu3Ox superconductor
Authors: Mei Yu , Luo H. L. , Hu Roger
Published: July 2002

Using rf sputtering technique, thin films of near single phase Bi2Sr2Ca2Cu3Ox were successfully prepared on SrTiO3(100), MgO(100), and LaAlO3(012) substrates. Zero resistance of these films occurred in the range of 90–105 K.
I
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u growth of superconducting Nd-Ce-Cu-O thin films
Authors: Terashima T. , Bando Y. , Iijima K. , Yamamoto K. , Hirata K. , Hayashi K. , Matsuda Y. , Komiyama S.
Published: July 2002

Superconducting Nd-Ce-Cu-O thin films were epitaxially grown on SrTiO3  (100) by activated reactive evaporation. As-grown films showed the metallic temperature dependence of the resistivity and superconducting transition at 12.5 K (R=0). The remarkable parallel shift of the onset temperature of the resistive transition in the magnetic fields was observed. Ginzburg–Landau coherence lengths along the c axis and in the basal plane are 7 and 96 Å, respectively.
Rapid chemical vapor deposition of superconducting YBa2Cu3Ox
Authors: Lackey W. J. , Carter W. B. , Hanigofsky John A. , Hill D. N. , Barefield E. Kent , Neumeier Galina , O’Brien David F. , Shapiro Michael J. , Thompson John R. , Green Andrew J. , Moss Thomas S. , Jake R. A. , Efferson K. R.
Published: July 2002

A process has been developed that enables the rapid chemical vapor deposition of superconducting YBa2Cu3Ox. In this process a finely ground mixture of Y(tmhd)3, Ba(tmhd)2, and Cu(tmhd)2 (tmhd=2,2,6,6-tetramethyl-3,5-heptanedionate) is slowly fed, and pneumatically transported, directly into the chemical vapor deposition furnace. Because vaporizers are not used, the number of process parameters that must be controlled is greatly reduced. Deposition rates are at least an order of magnitude greater than those achieved by reagent sublimation. Films have been characterized by scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction, and resistance versus temperature measurements. Films produced on planar MgO substrates have Tc values that are significantly higher than previously reported for MgO.
Low-threshold (≤ 92 A/cm2) 1.6 μm strained-layer single quantum well laser diodes optically pumped by a 0.8 μm laser diode
Authors: Zah C. E. , Bhat R. , Cheung K. W. , Andreadakis N. C. , Favire F. J. , Menocal S. G. , Yablonovitch E. , Hwang D. M. , Koza M. , Gmitter T. J. , Lee T. P.
Published: July 2002

To explore the ultimate threshold current limit in long-wavelength semiconductor lasers, InxGa1−xAs/InP strained-layer single quantum well laser diodes were studied for the first time by optically pumping with a 0.8 μm laser diode. Low-threshold (≤92 A/cm2) cw operation was obtained and the lasing wavelength (1.62 μm) corresponding to the transition from the first quantization state of a 25 Å In0.8Ga0.2As well was observed. By taking the carrier collection efficiency (≤77%) into account, the actual threshold current density could be as low as 70 A/cm2.
Analysis of a cascade-pumped 16 μm CO2-N2 downstream-mixing gasdynamic laser
Authors: Chakravarty Purandar , Reddy N. M. , Reddy K. P. J.
Published: July 2002

The generation of a 16 μm laser beam through cascading in a downstream-mixing CO2 gasdynamic laser is studied. To simulate actual lasing action, a generalized, two-dimensional, flow-radiation-coupled power extraction model for a gasdynamic laser is used. Also, to model the cascade process a new four-mode CO2-N2 vibrational kinetic model has been proposed. The steady-state intensity obtained for an exclusive 9.4 μm transition is of the order of 5×107 W/m2. In the cascade mode of operation the steady-state intensities for 9.4 and 16 μm transitions of the order of 5×107 W/m2 and 1.0×106 W/m2, respectively, have been obtained.
Silicon implantation into GaAs: Observations of dose rate dependent electrical activation and damage
Authors: Moore F. G. , Dietrich H. B. , Dobisz E. A. , Holland O. W.
Published: July 2002

The electrical activation of ion-implanted silicon in GaAs has been studied as a function of dose rate (i.e., ion-current density). For a fluence of 1014 cm−2, the Hall sheet carrier activation is shown to depend strongly on the dose rate at which the implant was carried out. Carrier concentrations of 7×1018 cm−3 were produced at a 50×10−9 A/cm2 ion-current density. The variation in electrical activation is believed to be the result of a dose rate dependence of the ion-induced damage of GaAs which can be clearly seen in Rutherford backscattering (RBS) channeling measurements of 1015 cm−2 implants.
Linewidth enhancement factor for InGaAs/InP strained quantum well lasers
Authors: Dutta N. K. , Temkin H. , Tanbun-Ek T. , Logan R.
Published: July 2002

The linewidth enhancement factor α in an InGaAs/InP strained-layer multiple quantum well (MQW) laser emitting near 1.55 μm has been determined from the spontaneous emission spectra below threshold. The active layers in the MQW structure in this device are under 0.7% compressive strain. The measured α at the lasing wavelength is 2.0. The calculation of α using interpolated bandstructure parameters shows that it varies rapidly with injected carrier density and the calculated value for our device is close to the measured value. The small α for strained MQW InGaAs lasers should result in performance improvement that are advantageous for lightwave system application.
Lateral quantum well wires fabricated by selective metalorganic chemical vapor deposition
Authors: Fukui Takashi , Ando Seigo , Fukai Yoshino K.
Published: July 2002

GaAs quantum wires of a new type are fabricated on {1̄10} crystallographic facets perpendicular to the (1̄1̄1̄)B substrates by selective area growth using metalorganic chemical vapor deposition. First, rectangular-shaped AlGaAs layers are grown on a SiO2 stripe-masked GaAs (1̄1̄1̄)B substrate at a high growth temperature. Next, n-AlGaAs/GaAs modulation-doped structures are laterally grown on {1̄10} sidewalls at a low growth temperature. The channel width of the one-dimensional electron gas can be exactly controlled by the thickness of the first rectangular AlGaAs layer. The existence of the quasi-one-dimensional electron gas on {1̄10} sidewalls is confirmed by the orientation dependence of the Shubnikov-de Hass oscillations. The advantage of this quantum wire structure is that there is no size fluctuation which is usually present when dry etching processes are used. Other applications of this selective growth on masked substrates, such as lateral superlattices, are also discussed.
Analysis of buried GaAs layers in 〈100〉 silicon by electron energy loss spectroscopy, Rutherford backscattering spectroscopy, and ion channeling
Authors: Madakson Peter , Bruley John
Published: July 2002

Detailed analysis of a buried layer of GaAs in 〈100〉 Si was carried out using electron energy loss spectroscopy, Rutherford backscattering spectroscopy, and ion channeling. The layer was formed by 200 keV dual ion implantation of Ga plus As ions, followed by furnace annealing at 600 and 950 °C. It consists of GaAs particles which are surrounded by fully recrystallized silicon. Beneath it is a dislocation network, made up of a mixture of edge and screw dislocations.
Dislocation constrictions at a Si/SixGe1−x interface
Authors: Rajan Krishna
Published: July 2002

Direct evidence of the constriction of dissociated partial dislocations at SiGe epitaxial interfaces is presented for the first time. The spacing between the dislocation constrictions is similar to that observed in deformed in bulk silicon. The importance of these observations to the interpretation of strain relaxation measurements in strained-layer heterostructures is discussed.
Effect of F co-implant during annealing of Be-implanted GaAs
Authors: Hallali P. E. , Baratte H. , Cardone F. , Norcott M. , Legoues F. , Sadana D. K.
Published: July 2002

F+ co-implantation at different doses and energies was performed into GaAs already implanted with Be+ at high dose (1015 cm−2) and low energy (20 keV), in order to reduce the beryllium diffusion during post-implant annealing. The redistribution behavior of Be and associated electrical effects were studied by secondary-ion mass spectrometry, transmission electron microscopy (TEM), Hall effect measurements, and current-voltage profiling. Be outdiffusion was reduced by co-implantation of F; more than 80% of the implanted Be was retained during rapid thermal annealing up to 850 °C. The dose and energy of the F implant strongly influenced Be electrical activation efficiency. High activation, up to 48.5%, was obtained when F was co-implanted at high dose (1015 cm−2) and low energy (10 keV). Hole profiles shown reduced electrical activation in the region where F and Be profiles overlapped and TEM studies indicated the formation of {111} coherent plates, possibly BeF2 precipitates, in the same region. The reduction of Be outdiffusion in F co-implanted samples led to high activation after annealing, and was believed to be due to chemical interaction between Be and F.
Carbon concentration dependence of charged point-defect density in semi-insulating GaAs as observed by nuclear magnetic resonance
Authors: Suemitsu Maki , Nishijima Masaaki , Miyamoto Nobuo
Published: July 2002

A newly developed method [J. Appl. Phys. 66, 3178 (1989)] in nuclear magnetic resonance (NMR) spin-echo measurements, which allows us a precise determination of the quadrupolar interaction magnitude in crystals, has been applied to a series of undoped, liquid-encapsulated Czochralski GaAs crystals. By varying the carbon concentration from 6×1014 to 1.4×1016 cm−3, it was verified that the quadrupolar interaction magnitude is proportional to the density of charged point defects in the crystal. The NMR method provides a feasible tool to detect ionized point defects of the order of as low as 1014 cm−3.
Selective chemical vapor deposition of tungsten using WF6 and GeH4
Authors: van der Jeugd C. A. , Leusink G. J. , Janssen G. C. A. M. , Radelaar S.
Published: July 2002

Germane (GeH4) has, for the first time, been used as a reducing agent for tungsten hexafluoride in selectively depositing tungsten on silicon. As shown by x-ray diffraction, films deposited below 400 °C consist of the β-W phase with A15 cubic crystal structure. This A15 structure proved to be stabilized by germanium which is probably incorporated in the film as a hitherto unknown W3Ge compound. Annealing for 1 h at 575 °C did not change the β-W structure to the low-resistivity body-centered-cubic α phase of tungsten. The superconducting transition temperature of the films is ≊3 K. The growth rate dependence on temperature, total pressure, and WF6, GeH4, and H2 partial pressure has been investigated. At deposition temperatures above 400 °C the deposited films consist of a mixture of the β and α-W phase.
Void formation, electrical activation, and layer intermixing in Si-implanted GaAs/AlGaAs superlattices
Authors: Lee S.-Tong , Chen Samuel , Braunstein G. , Ko Kei-Yu , Ott Mary L. , Tan T. Y.
Published: July 2002

Direct experimental evidence is presented for the correlation between void formation, dopant electrical activation, and layer intermixing in GaAs/AlGaAs superlattices (SLs). Maximum layer intermixing is observed in the regions of maximum carrier concentration and no or little void formation in Si-implanted and annealed SLs. In SLs implanted at room temperature, Si activation and layer intermixing enhancement are severely inhibited in the near-surface region where voids are formed. However, when implantation is carried out at 250 °C, both the suppression of Si activation and layer intermixing enhancement in the near-surface region are reduced, concurrent with a decrease in void density.
Uniaxial lattice expansion of self-ion-implanted Si
Authors: Holland O. W. , Budai J. D. , White C. W.
Published: July 2002

Lattice strain in self-ion-implanted Si is investigated. Under certain irradiation conditions, a unique strain field is shown to form over the range of the ions. This strain field is one-dimensional and expands the lattice along the direction normal to the surface of the crystal. This phenomena is investigated over a wide range of ion energy (100 keV and 1.25 MeV) and at different implantation temperatures. The presence of uniaxial strain is shown to correlate with a particular damage morphology in Si. This ion-induced morphology and the irradiation conditions under which it forms are discussed, as well as the mechanism which leads to uniaxial, lattice strain. Both ion channeling and x-ray diffraction analyses are used to characterize the strain field.
Conduction-band minima of InP: Ordering and absolute energies
Authors: Zollner Stefan , Schmid Uwe , Christensen Niels E. , Cardona Manuel
Published: July 2002

Since the conduction-band structure of InP is still controversial, we perform an ab initio linear muffin tin orbital (LMTO) band structure calculation to obtain the valence bands with high accuracy. The LMTO is based on the local density approximation (LDA) which suffers from the well known ‘‘band-gap problem.’’ We therefore combine our calculated valence-band energies with carefully evaluated optical data from the literature and confirm the interconduction-band separation energies ΔEΓL=0.86±0.02 eV and ΔEΓX=0.96±0.02 eV. We also give new empirical local pseudopotential form factors adjusted to reproduce these experimental values.
Nucleation rate and glide velocity of misfit dislocations in Si1−xGex/(100) Si heterostructures
Authors: Houghton D. C.
Published: July 2002

Expressions are presented for the rate of strain relaxation, misfit dislocation nucleation, and propagation in strained Si1−xGex/(100)Si heterostructures. Independent measurements of misfit dislocation nucleation and 60° type a/2 〈110〉 dislocation glide velocity in the temperature range 450–1000 °C have led to a model which characterizes the kinetics of strain relaxation for 0<x<0.25. The generalized force or effective stress τeff, which drives strain relaxation, is defined for an arbitrary strain profile and strained-layer geometry. New experimental data for misfit dislocation glide velocity (V in cm s−1) have been fitted to a semi-empirical relation found to be appropriate for all Si1−xGex/(100)Si heterostructures, V=(4±2)⋅1013(τeff /μ)2 exp−[(2.25±0.05)/kT]. An analogous expression for the nucleation rate of new misfit dislocation segments was determined from experimental data, dN(t)/dt=BN0(τeff /μ)2.5 exp−[2.5±0.2)/kT], where N0 is the density of heterogeneous nuclei and B is a material constant ∼1018 s−1 for Si1−xGex. These expressions are combined in a kinetic model which is then used to predict the rate of strain relaxation in Si1−xGex/Si heterostructures.
Bias-lead monitoring of ultrafast nonlinearities in InGaAsP diode laser amplifiers
Authors: Hall K. L. , Ippen E. P. , Eisenstein G.
Published: July 2002

In this letter we report the first femtosecond measurements of gain and loss dynamics in InGaAsP diode laser amplifiers using optically induced changes in diode junction voltage. Our results confirm that previously observed optical pump-probe signals are related to carrier dynamics in the active region of the amplifiers.
I
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u doping in silicon selective epitaxial growth at 800 °C by ultralow-pressure chemical vapor deposition
Authors: Yew Tri-Rung , Reif Rafael
Published: July 2002

I n situ doping capabilities, n and p type, in silicon selective epitaxial growth by ultralow-pressure chemical vapor deposition are presented in this letter. Selective epitaxial layers were grown at 800 °C after an in situ Ar/H2 plasma sputter clean. The n- and p-type dopant sources were 1000 ppm arsine and 1000 ppm diborane, respectively, in silane mixed with pure silane for dilution. It was found that high structural quality in situ doped selective epitaxial layers with n- or p-type dopant concentration of 1018 cm−3 can be obtained.
Spatially addressable light transducer using an organic electroluminescent diode combined with amorphous silicon carbide film as an electron photoinjecting electrode
Authors: Hiramoto Masahiro , Miyao Tomoya , Yokoyama Masaaki
Published: July 2002

A new type of light transducer has been designed consisting of an organic electroluminescent (EL) diode on a photoconductive amorphous silicon carbide (a-SiC:H) film as an electron photoinjecting electrode. Input light received by a photosensitive a-SiC:H film is transduced to the output light with a different wavelength emitted from an EL diode in the layered configuration. The input-light pattern was well kept spatially in the output. The EL output light was controllable with dc voltage applied to the device and input-light intensity. These features are suggested to be potentially applicable for a new type of the spatial light modulator.
Electronic surface states confined to the boundary of periodic multiple quantum wells
Authors: Huang F. Y.
Published: July 2002

A semi-infinite stratified multiquantum well structure with the boundary connected to a homogeneous medium is suggested. Electronic surface states are found to exist under certain conditions. These surface states have an interesting feature that the eigenenergy may even exceed the confinement potential of the periodic substrate. Possible application of this structure in optoelectronic devices is discussed.
Photodarkening and bleaching in amorphous silicon nitride
Authors: Seager C. H. , Kanicki J.
Published: July 2002

UV-induced enhancement of the subgap optical absorption has been observed in thin films of chemically vapor deposited silicon nitride. The threshold for this process is ∼4 eV. Visible light bleaches out much of the enhanced absorption and 200–400 °C thermal anneals remove the rest, leaving the optical properties of the nitride in the ‘‘as-grown’’ state. The characteristics of this creation and bleaching process suggest that UV light ‘‘optically dethermalizes’’ the distribution of carriers in localized band tail states. Correlation of our data with recent electron spin resonance results suggests that many of the trapped carriers may be singly occupied silicon dangling bonds.
Quantum-limited heterodyne detection of millimeter waves using superconducting tantalum tunnel junctions
Authors: Mears C. A. , Hu Qing , Richards P. L. , Worsham A. H. , Prober D. E. , Räisänen A. V.
Published: July 2002

We have made accurate measurements of the noise and gain of heterodyne mixers employing small-area (1 μm2) Ta/Ta2O5/Pb0.9Bi0.1 superconductor-insulator-superconductor tunnel junctions. These junctions have very low subgap leakage current and an extremely sharp current rise at the sum gap. We have measured an added mixer noise of 0.61±0.31 quanta at 95.0 GHz, which is within 25% of the quantum limit of 0.5 quanta for a single-sideband mixer. Values of the imbedding admittances are deduced from the shapes of I-V curves pumped at the upper and lower sideband frequencies. Using these admittances, the mixer performance calculated from the quantum theory is in good agreement with the experiment.
Origin of surface roughness for c-axis oriented Y-Ba-Cu-O superconducting films
Authors: Chang C. C. , Wu X. D. , Ramesh R. , Xi X. X. , Ravi T. S. , Venkatesan T. , Hwang D. M. , Muenchausen R. E. , Foltyn S. , Nogar N. S.
Published: July 2002

One problem with the growth of high quality c-axis oriented YBa2Cu3O7−x films is the tendency of the film surface to become rough. We studied the film growth mechanism as a function of deposition rate using pulsed laser deposition. These films form by the classic nucleation and growth process; the thickness at which the nucleated islands coalesce increased with decreasing deposition rate. The film has pinholes prior to coalescence and nucleates outgrowths during coalescence. The outgrowths enlarge rapidly because they contain materials and crystallographic directions with growth rates faster than that of the c-axis film. A smooth surface is obtained if the substrate temperature and deposition rate are chosen such that coalescence is just completed at the final film thickness. We observed the outgrowths nucleating at coalescence and propose that certain defects, related to the c-axis growth habit, may be the fundamental cause of outgrowth formation. Outgrowths have not been observed in a-axis films. Outgrowths are easily confused with the particulate deposition problem associated with laser deposition. In these experiments, the particulate problem was essentially eliminated by using freshly polished targets for each run.
180° surface domain wall magnetization profiles: Comparisons between scanning electron microscopy with polarization analysis measurements, magneto-optic Kerr microscopy measurements and micromagnetic models
Authors: Scheinfein M. R. , Ryan P. J. , Unguris J. , Pierce D. T. , Celotta R. J.
Published: July 2002

We compare measurements of magnetization profiles across a 180° surface domain wall in a 0.24-μm-thick of Permalloy (Ni81Fe19), obtained with scanning electron microscopy with polarization analysis (SEMPA) and longitudinal magneto-optic (MO) Kerr microscopy with the predictions of a bulk micromagnetic theory. Both measurement techniques yield wall profiles in accordance with the predictions of micromagnetic theory. We conclude that for micromagnetic structure with relevant length scales on the order of tens of nanometers, SEMPA and MO Kerr microscopy yield equivalent quantitative micromagnetic information within the transverse spatial resolution limits of each technique. Near-surface effects such as enhanced surface moments, weakened surface exchange, and surface anisotropy are not important in determining the surface domain wall profiles that we observe.
Defect formation caused by a transient decrease in the ambient oxygen concentration during growth of YBa2Cu3O7−δ films
Authors: Gupta A. , Hussey B. W. , Kussmaul A. , Segmüller A.
Published: July 2002

Thin films of YBa2Cu3O7−δ have been grown in an oxygen atmosphere by pulsed laser deposition using two synchronized lasers, separated by a variable delay (1 μs–10 ms). The ablated fragments from the first laser lead to formation of a blast wave in O2, leaving behind a rarefied ambient. If the second laser is triggered before the O2 pressure returns to equilibrium, the resulting films show a decrease in transition temperature with an expanded c-lattice parameter caused by defects in the nonchain sites of YBa2Cu3O7−δ. This demonstrates the necessity of maintaining a sufficiently high concentration of oxygen within the time period that the fragments travel and deposit on the substrate.
Influence of temperature on defect creation during plasma exposure of SiO2 films
Authors: Devine R. A. B.
Published: July 2002

Chemical vapor deposited silicon dioxide films have been exposed to ultraviolet radiation from a microwave excited Kr/F plasma. Sample temperatures during exposure were in the range 82–300 K. The creation of oxygen-vacancy like defects was measured as a function of exposure time and temperature. Two possible defect creation mechanisms are suggested which would account for reduced creation efficiency at low temperatures, one involving hole injection from the substrate and the other, interaction of H with Si—H bonds. Both processes are diffusion limited.
Interface engineering with pseudormorphic interlayers: Ge metal-insulator-semiconductor structures
Authors: Hattangady S. V. , Fountain G. G. , Rudder R. A. , Mantini M. J. , Vitkavage D. J. , Markunas R. J.
Published: July 2002

Significant improvements in gating of Ge surfaces are achieved with the use of thin, pseudomorphic Si interlayers. Metal-insulator-semiconductor structures with mid-gap interface state densities of 5×1010 cm−2 eV−1 and showing no hysteresis have been realized on both n- and p-type Ge. The key elements of this technology are: surface cleaning, deposition of a thin Si interlayer, and the deposition of the gate dielectric, SiO2, all of which are performed in situ and sequentially at 300 °C in a single chamber with the remote plasma technique. Ion scattering spectroscopy shows complete coverage of the Ge surface by the Si layer. X-ray photoelectron spectroscopy shows the Si interlayer is about 18 Å thick. The Si interlayer prevents the interfacial oxidation of the underlying Ge.
Magnetic relaxation in the 110 K superconducting phase in Bi-Sr-Ca-Cu-O thin films
Authors: Tanaka Atsushi , Crain Jason , Niwa Koichi
Published: July 2002

The relaxation of the remanent moment induced in a nearly single-phase high Tc thin film of Pb-doped Bi-Sr-Ca-Cu-O has been investigated. Measurements reveal that the relaxation obeys a logarithmic time dependence for observation intervals up to 2000 s. The temperature dependence of the initial magnetization and its decay rate are obtained. The decay rate normalized by initial magnetization exhibits a peak around 14 K. The peak shifts to lower temperature for stronger magnetic field. These data are compared with existing data on other high Tc superconducting materials.
Novel mechanism of a real-space transfer oscillator
Authors: Schöll E. , Aoki K.
Published: July 2002

A new mechanism for self-generated current oscillations in modulation-doped semiconductor heterostructures under parallel conduction is proposed. It is based upon the nonlinear dynamics of real-space electron transfer and delayed dielectric relaxation of the interface potential barrier resulting from the space charge in the doped AlGaAs layer. From our simulations we predict current oscillations in the 20–80 GHz range under dc bias.
Intense broadband vacuum-ultraviolet emission from a dual-segment cylindrical surface discharge
Authors: Beverly III R. E.
Published: July 2002

A cylindrical surface-discharge device was developed to study photolytically pumped gas laser schemes. The discharge plasma produces intense ultraviolet/vacuum-ultraviolet broadband irradiation of a 3 ℓ active volume. Homogeneous, large-area (≳103 cm2) plasma shells are formed adjacent to the interior surfaces of dielectric cylinders by an electric discharge. Operation at a peak current of 94 kA produced approximately 45 J of radiated energy within the VUV spectral band from 170 to 210 nm in a 1.7 μs (full width half maximum) pulse, which represents a conversion efficiency for stored electrical energy into radiation of 2.7% and an equivalent brightness temperature of 13 500 K.
Pseudomorphic InyGa1−yAs/GaAs/AlxGa1−xAs single quantum well surface-emitting lasers with integrated 45° beam deflectors
Authors: Kim Jae-Hoon , Larsson Anders , Lee Luke P.
Published: July 2002

We report on the first demonstration of pseudomorphic InGaAs single quantum well surface-emitting lasers (SELs), with etched vertical mirrors and integrated 45° beam deflectors fabricated by ion beam etching. 100-μm-wide broad-area SELs exhibited a threshold current of 320 mA, a total power of 126 mW, and a total external differential quantum efficiency of 0.09 W/A for a 500-μm-long cavity. The perpendicular far-field pattern of broad-area SELs showed a full width at half maximum of ∼20°. The lasers with various types of cavities fabricated from the same wafer were compared. Broad-area edge-emitting lasers had a threshold current of 200 mA, a total power of 700 mW, and a total external differential quantum efficiency of 0.52 W/A.
Annealing stability in superconducting Nb wiring with nitrogen plasma treatment
Authors: Shiota Tetsuyoshi , Imamura Takeshi , Hasuo Shinya
Published: July 2002

We improved the annealing stability in superconducting Nb wiring used in Josephson circuits. Nb film was exposed to nitrogen plasma just after sputtering. We measured the critical current of the Nb wiring before and after annealing. Even before annealing, the critical current with nitrogen plasma treatment is 50% higher than that without treatment. The decrease in critical current after annealing is markedly suppressed. We confirmed using secondary-ion mass spectroscopy profiles that very little oxygen diffuses into Nb films treated using the nitrogen plasma.
Continuous fabrication of high-temperature superconductor coated metal fiber and multifilamentary wire
Authors: Woolf L. D. , Raggio W. A. , Elsner F. E. , Fisher M. V. , Stephens R. B. , Figueroa T. L. , Shearer C. H. , Rose J. D. , Schaubel K. M. , Olstad R. A. , Ohkawa T. , Duggan D. M. , DiMartino M. , Fagaly R. L.
Published: July 2002

Long superconductor fibers have been continuously produced by electrophoretically depositing REBa2Cu3O7−x (where RE=Y or a selected rare-earth element) powder onto a metal substrate fiber and sintering, then electrophoretically depositing silver and sintering. After collecting the coated fiber on a take-up spool, the entire spool is batch-oxygenated to form the 90 K superconducting phase. Multiple fibers are then continuously unspooled and soldered into a copper channel to form the final multifilamentary high-temperature superconductor wire. Superconducting fibers over 1000 m long and multifilamentary wire 70 m long have been produced.
Tunable near-infrared radiation by difference frequency mixing in beta barium borate crystal
Authors: Bhar G. C. , Chatterjee U. , Das S.
Published: July 2002

Noncollinear difference frequency mixing is reported for the first time in a barium borate crystal that generates near-infrared radiation tunable from 2.04 to 3.42 μm. The technique apart from verifying a very simple relation correlating the phase-matching angle with the noncollinear angle of the interacting beams provides a simple alternative scheme for generating coherent radiation in this important spectral range.
Luminescence intensity and lifetime dependences on temperature for Nd-doped GaP and GaAs
Authors: Taniguchi Moriyuki , Nakagome Hiroshi , Takahei Kenichiro
Published: July 2002

We report the studies of luminescence intensity and lifetime dependences on temperature for Nd-doped GaP and GaAs samples grown by metalorganic chemical vapor deposition. It is found that, with above band-gap excitation, the temperature dependence of GaP:Nd reveals a two-step decreasing behavior as the sample temperature increases. This phenomenon is due to the fact that there exist two kinds of Nd centers (type I and type II) in GaP. Although type I Nd centers produce strong luminescence at low temperatures, their intensities drop rapidly above 40 K. On the other hand, type II Nd centers show a near constant intensity up to 150 K and can still be observed up to room temperature. We also found, for a given Nd center, that the luminescence lifetime dependence on temperature is identical to the temperature quenching behavior of luminescence intensity. From the similarity between the quenching behaviors of Nd-related luminescence intensities and lifetimes, we conclude that the temperature quenching of luminescence intensity of these Nd-doped GaP and GaAs samples is mainly due to deexcitation rather than the reduction of excitation efficiency.
p-i-n HgCdTe photodiodes grown by molecular beam epitaxy
Authors: Arias J. M. , Zandian M. , Zucca R. , DeWames R. E.
Published: July 2002

We report the successful molecular beam epitaxy (MBE) growth of in situ arsenic- and indium-doped p-i-n HgCdTe double heterostructures. High-performance, short-wavelength, infrared (2.09 μm) photodiodes operating at 300 K have been fabricated with these double heterostructures. The observed current-voltage characteristics and quantum efficiency of these diodes can be explained by assuming that the current components are dominated by generation-recombination currents. These photodetectors exhibit quantum efficiencies of 78%. Growth of this kind of in situ doped structures indicates that the HgCdTe MBE technology has matured to the point where doped HgCdTe multilayer heterostructures can be grown and used to fabricate advanced infrared electronic devices.
Bistability in an AlAs-GaAs-InGaAs vertical-cavity surface-emitting laser
Authors: Deppe D. G. , Lei C. , Rogers T. J. , Streetman B. G.
Published: July 2002

Data are presented demonstrating bistability in the current versus voltage and light versus current characteristics of a quantum well vertical-cavity surface-emitting laser. The laser structures are grown using molecular beam epitaxy, and use an AlAs/GaAs Bragg reflector for the n-side mirror, and a combination of AlAs/GaAs and either ZnSe/CaF2 or Si/SiO2 quarter-wave dielectric layers for the p-side mirror. Regrowth of molecular beam epitaxial layers is used for current funneling into the device active region. Light emission is measured from the epitaxial side of the device, and threshold currents range from 2 to 4 mA. The bistability stems from switching in a parasitic pnpn structure triggered by lasing in the vertical-cavity laser, with the observed hysteresis width influenced by leakage current around the device active region.
Occupancy of the DX center in n-Al0.32Ga0.68As under uniaxial stress
Authors: Wang Zhiguo , Chung Ki-woong , Miller T. , Williamson F. , Nathan M. I.
Published: July 2002

We have used the deep level transient spectroscopy signal height as a function of applied stress data and the statistics of the occupancy of the DX center to obtain the stress dependence of the thermal binding energy of the neutral DX center, EDX. We find that EDX decreases with about the same rate for uniaxial stresses along 〈100〉 and 〈111〉 directions. Our results confirm that the DX center is a highly localized center as proposed by Chadi and Chang and disagree with the model assuming the DX center being an effective mass state of the doping impurity associated with the L band.
Optically controlled surface-emitting lasers
Authors: Chan W. K. , Harbison J. P. , von Lehmen A. C. , Florez L. T. , Nguyen C. K. , Schwarz S. A.
Published: July 2002

Vertical cavity surface-emitting lasers are integrated with GaAs/AlGaAs heterojunction phototransistors to yield optically controlled lasers. The two-terminal device operates in several modes: As an amplifier with a large signal, external optical gain of 5, as in optical logic gate, and as an optically or electrically triggerable latch. The optical AND gate has an output on-to-off ratio of 10:1. Although the device has no optical feedback, latching is achieved with appropriate biasing through impact ionization. The device structure is advantageous for forming large two-dimensional arrays for optical signal processing.
Microstructure of the high T
c phase (T
c∼111 K) in the Sb-Pb-Bi-Sr-Ca-Cu-O system
Authors: Kijima Naoto , Gronsky Ronald , Endo Hozumi , Oguri Yasuo , McKernan Steffen K. , Zettl Alex
Published: July 2002

The microstructure of the high Tc phase (Tc∼111 K) in the Sb-Pb-Bi-Sr-Ca-Cu-O system has been determined using transmission electron microscopy. Its crystal structure belongs to the superspace group NBbmb11̄1, NBb2b111, PBbmb11̄1 or PBb2b111 with subcell lattice parameters a=5.411(1) Å, b=5.411(1) Å, and c=37.22(6) Å. The high Tc phase has a modulated structure with b-axis wavelengths 26.9 and 36.1 Å. Stacking faults along the c axis in the high Tc phase are much less numerous than in the Bi-Sr-Ca-Cu-O system, but comparable to the Pb-Bi-Sr-Ca-Cu-O system. Sb substitution for Ca may affect the internal strain of the crystal.
High quality Fe-doped semi-insulating InP epitaxial layers grown by low-pressure organometallic vapor phase epitaxy using tertiarybutylphosphine
Authors: Huang Rong-Ting , Appelbaum Ami , Renner Daniel , Zehr Stanley W.
Published: July 2002

High quality Fe-doped semi-insulating InP epitaxial layers were grown by low-pressure organometallic vapor phase epitaxy using tertiarybutylphosphine (TBP) and triethylindium (TEI) as the reactant sources. Semi-insulating InP epitaxial layers with specular surface morphology and low defect density were obtained at TBP partial pressure higher than 0.38 Torr. Electrical measurements on these layers showed the resistivity of TBP-grown materials to be comparable to that of PH3-grown materials over a measurement temperature range of 25 to 110 °C. A premature reaction between TEI and TBP was observed upstream from the substrate in which things such as TEI:TBP adducts and/or polymers could have been formed. This reaction occurred under low pressure, high gas flow conditions which effectively suppressed analogous reactions for TEI:PH3. As a result, the growth rate of Fe-doped semi-insulating InP layers grown at low pressure with TBP in our reactor decreased by 35% as the V/III ratio was increased from 15 to 46.
Strain tolerant microfilamentary conductors of Bi2Sr2Ca1Cu2O8−δ
Authors: Miller T. A. , Ostenson J. E. , Li Q. , Schwartzkopf L. A. , Finnemore D. K. , Righi J. , Gleixner R. A. , Zeigler D.
Published: July 2002

A highly strain tolerant family of conductors has been developed for the high-temperature superconductor Bi2Sr2Ca1Cu2O8−δ by fabricating a microfilamentary composite in which discontinuous filaments of the superconductors are separated from one another by very thin layers of Ag. The Ag provides a region of plastic flow and the strain tolerance. The Ag also provides barriers to supercurrent flow and to overcome these barriers, long slender filaments of Bi(2212) are arranged to have enormous overlap areas perpendicular to the direction of average current flow. This requires filament length to diameter ratios of about 10 000 to 1 and Ag barrier thicknesses on the order of 20 nm. This permits high Jc values even though the sample has a dense array of barriers. At 4.2 K and 0.3 T, critical current densities typically fall smoothly from 1000 to 800 A/cm2 as the strain increases from 0 to 1.6%.
In situ preparation of superconducting Y1Ba2Cu3O7−δ thin films by on-axis rf magnetron sputtering from a stoichiometric target
Authors: Blue C. , Boolchand P.
Published: July 2002

Superconducting Y1Ba2Cu3O7−δ thin films have been fabricated in situ by on-axis rf reactive magnetron sputtering from a single stoichiometric 1-2-3 target. By using high total sputtering pressures (≳400 mTorr) and low oxygen pressures (≤10 mTorr), negative ion resputtering is almost eliminated and high quality oriented films on (100)MgO are realized with excellent reproducibility. Such films display zero resistance Tc’s as high as 88 K with transition widths ΔTc (90%–10%) of about 2 K, residual resistivity ratios R(300 K)/R(100 K) of 2.5, and critical current densities greater than 106 A/cm2 at 14 K.