bluuebunny/crossref_metadata_2025 huggingface dataset:
Dielectric properties of silicon oxynitride films
Authors: Niklasson G. A. , Eriksson T. S. , Brantervik K.
Published: July 2002

We have measured the frequency-dependent complex dielectric permittivity of silicon oxynitride films in the frequency range 10−4–107 Hz for temperatures of 290–365 K. The dielectric permittivity displays a conductivity relaxation at low frequencies and gradually goes over to an almost frequency-independent complex permittivity at high frequencies. The experimental data can be accounted for by assuming that the conductivity relaxation is superimposed on the frequency-independent contribution to the permittivity. On that premise, the conductivity relaxation and the onset of dc conductivity are in good agreement with calculations by the continuous time random walk model employing a distribution of transition rates pertinent to a fractal time process.
Observation of phonon-assisted laser operation of AlxGa1−xAs-GaAs quantum well heterostructures
Authors: Holonyak N. , Nam D. W. , Plano W. E. , Vesely E. J. , Hsieh K. C.
Published: July 2002

Data are presented showing that the key to observing the phonon-assisted photopumped laser operation of narrow rectangular samples of AlxGa1−xAs-GaAs quantum well heterostructures (QWHs) is the control of the edge-to-edge resonator Q across the sample. If the sample is heat sunk in metal, with metal reflectors folded upward along the edges, the resonator Q across the sample is high, and laser operation across the sample on confined-particle states (a reference) and along the sample a phonon lower in energy (ΔE≊ℏωLO) is observed. If the sample edges across the sample are left uncoated (weakly reflecting, low Q), laser operation is observed only along the sample (longitudinal modes) but shifted (ΔE≊ℏωLO) below the confined-particle states and absorption. A QWH rectangle, with proper heat sinking and control of its edge-to-edge resonator Q, can act as a hot-phonon ‘‘spectrometer’’ if it is fully photopumped across its width and is only partially pumped along its length.
Quantum calculations of ballistic transport
Authors: Lin J. , Chiu L. C.
Published: July 2002

Recent experimental studies of ballistic electron transport have pushed the transit time well into the subpicosecond dynamical regime. By applying the quantum dynamical theory to study ultrafast transient transport, we report results that are dramatically different from those predicted by the classical Boltzmann theory.
Nonrandom doping and elastic scattering of carriers in semiconductors
Authors: Levi A. F. J. , McCall S. L. , Platzman P. M.
Published: July 2002

High-density delta doping of semiconductors may result in partial ordering of dopant atoms. Under suitable circumstances, periodic delta doping leads to significant suppression of elastic scattering and a consequent enhancement in charge carrier mobility.
Growth of (111) CdTe on tilted (001) GaAs
Authors: Cibert J. , Gobil Y. , Saminadayar K. , Tatarenko S. , Chami A. , Feuillet G. , Dang Le Si , Ligeon E.
Published: July 2002

Twin-free growth of (111) CdTe on (001) GaAs is reported for substrates tilted around the [11̄0] axis, i.e., exposing Ga dangling bonds at the terrace edges. Layers grown on nominally (001) substrates and tilted substrates are characterized by double crystal x-ray diffraction, low-temperature reflectivity and photoluminescence, channeling, and high-resolution transmission electron microscopy.
Pressure-dependent optical delay time measurements in a coaxial electron beam pumped Ar:Xe laser
Authors: Peters P. J. M. , Mei Qi-Chu , Witteman W. J.
Published: July 2002

Optical delay times and pulse widths of five Ar:Xe laser lines have been measured as a function of the total gas pressure. Both the delay time and the pulse width appeared to be almost linearly dependent on the inverse gas pressure. For a total gas pressure of 14 bars the delay times were around 100 ns, at a total gas pressure of 1 bar the laser output typically appeared after 1–3 μs.
Growth temperature dependence of interfacial abruptness in Si/Ge heteroepitaxy studied by Raman spectroscopy and medium energy ion scattering
Authors: Iyer S. S. , Tsang J. C. , Copel M. W. , Pukite P. R. , Tromp R. M.
Published: July 2002

The influence of growth temperature on the interfacial abruptness of strained Ge layers, a few monolayers thick, embedded in Si has been studied using Raman spectroscopy to identify the presence of GeGe and GeSi bonds and medium energy ion scattering to characterize the spatial extent of the layers. Atomically sharp interfaces are observed for growth temperatures just above the crystalline to amorphous transition range, with pseudomorphic growth found for growth temperatures >∼250 °C. Asymmetric mixing of Ge into the Si capping layer occurs during growth at higher temperatures. Significantly less intermixing occurs on annealing after growth, pointing to the role of dynamical processes occurring at the growth front.
Improvements in the organometallic heteroepitaxy of indium phosphide directly on silicon
Authors: Wuu D. S. , Horng R. H. , Huang K. C. , Lee M. K.
Published: July 2002

Specular single-crystal InP epilayers have been grown directly on Si(100) substrates by low-pressure organometallic vapor phase epitaxy. The effects of the initial nucleation process on the structure properties of the films were investigated, and improvements in the growth technique leading to higher quality InP films are reported. The InP/Si epilayer grown under optimum conditions exhibits high optical quality compared with that of the InP homoepilayer. Post-growth thermal annealing at 780 °C was also confirmed to be effective in improving the overall quality of InP-on-Si. The results presented are superior to those reported previously for InP/Si heteroepitaxy.
Ambipolar diffusion length measurements in hydrogenated amorphous silicon
Authors: Balberg I. , Epstein K. A. , Ritter D.
Published: July 2002

Many studies have been devoted in recent years to the experimental determination of the diffusion length of the minority carriers in hydrogenated amorphous silicon. The most popular method for this purpose was the surface photovoltage technique while the most novel method is the photocarrier grating technique. In the present work we report the first experimental comparison of the two methods. It is found that the first method yields values which are typically twice as large as those of the second method. This disagreement can be explained by the recent theoretical studies of the two methods. On the other hand, the present results seem to indicate how some more information on the electronic structure of the above material can be derived by future comparisons between theoretical and experimental results.
Metallic contamination in silicon during plasma resist stripping: A deep level transient spectroscopy study
Authors: Joubert O. , Mathiot D. , Pelletier J.
Published: July 2002

Deep level transient spectroscopy is shown to be an easy way to investigate the defects induced in the silicon substrate during photoresist plasma etching. In this study it has been possible to discriminate between the contamination induced by the reactor environment and the contamination due to the resist itself. In particular, it is demonstrated that residual chromium and iron atoms present in the resist are responsible for a contamination of the Si substrate.
Infrared intersubband absorption in GaAs/AlAs multiple quantum wells
Authors: Covington B. C. , Lee C. C. , Hu B. H. , Taylor H. F. , Streit D. C.
Published: July 2002

Optical absorption spectra have been measured from 6 to 296 K for a GaAs/AlAs multiple quantum well sample which shows a strong peak at 11.1 μm at room temperature. These and previously published results are compared with predictions of an effective mass model which takes into account conduction-band nonparabolicity.
Optical and nonlinear optical properties of 4-(N,N-dimethylamino)-3-acetamidonitrobenzene single crystals
Authors: Kerkoc P. , Zgonik M. , Sutter K. , Bosshard Ch. , Günter P.
Published: July 2002

A method of growing high quality 4-(N,N-dimethylamino)-3-acetamidonitrobenzene (DAN) single crystals is presented. Crystal plates with dimensions of up to 10×5×2 mm3 were produced and optically characterized. The transparency region extends from 485 to 2270 nm. Large birefringence and strong dispersion of the refractive indices were measured allowing two branches of type I and two of type II phase-matched second-harmonic generation. From effective second-order nonlinear optical susceptibilities measured along the branches all nonlinear susceptibilities were evaluated, the highest being d23 =(50±15) pm/V.
Device quality Hg1−xCdxTe material by low-temperature precracking metalorganic chemical vapor deposition
Authors: Lu P.-Y. , Williams L. M. , Chu S. N. G. , Ross M. H.
Published: July 2002

We report properties of device quality Hg1−xCdxTe grown by a precracking metalorganic chemical vapor deposition technique. The refinement of the low-temperature growth process and a higher purity metalorganic mercury source enable us to obtain material which has a carrier concentration of 2×1015 cm−3 and mobility as high as 330 000 cm2/V s. Infrared transmission spectra and the photoluminescence measurements obtained from this material will be presented. With further development in the synthetic route of the metalorganic mercury source, further improvement in the purity of the Hg1−xCdxTe is possible.
Tribological properties of diamond films grown by plasma-enhanced chemical vapor deposition
Authors: Wong M. S. , Meilunas R. , Ong T. P. , Chang R. P. H.
Published: July 2002

Uniform and continuous diamond films have been deposited on Si, Mo, and many other substrates by plasma-enhanced chemical vapor deposition. We have developed processes to enhance the adhesion of diamond films to metal substrates for tribological applications. The tribological properties of the diamond films are found to be significantly different depending on their morphology, grain size, and roughness. However, under all cases tested using a ring-on-block tribotester, it is found that for diamond films with a small grain size of 1–3 μm, the coefficient of friction of the diamond films sliding against a steel ring under lubrication of a jet of mineral oil is about 0.04.
Absorption saturation and photodarkening in semiconductor-doped glasses
Authors: Kull M. , Coutaz J. L. , Manneberg G. , Grivickas V.
Published: July 2002

Transmission measurements show a large decrease of the absorption saturation in semiconductor-doped glasses which have been exposed to intense absorbing light. A simple saturation model including nonradiative and Auger recombination and an unsaturable part of the absorption, interpreted as free-carrier absorption, explains the observed changes.
Laser fabricated GaAs waveguiding structures
Authors: Willner A. E. , Ruberto M. N. , Blumenthal D. J. , Podlesnik D. V. , Osgood R. M.
Published: July 2002

We have applied the technique of laser-induced etching to fabricate rib waveguides on a GaAs/AlGaAs heterostructure system. Light confinement of these guides was controlled by varying the depth of the etched trenches. Additionally, we have demonstrated directional couplers and two-level waveguides using the in situ depth control of this single-step process.
Measurements of the atomic nitrogen population produced by a microwave electron cyclotron resonance plasma
Authors: Meikle Scott , Hatanaka Yoshinori
Published: July 2002

The atomic nitrogen population produced from a microwave electron cyclotron resonance plasma and a microwave plasma has been measured using the nitric oxide gas titration technique for pressures between 0.005 and 0.5 Torr. For 15 W microwave power the atomic nitrogen production efficiency is observed to reach a maximum of 12% at 0.006 Torr. The pressure dependence of atomic nitrogen production efficiency and concentration are found to fall by one order at the pressure where particle mean free path exceeds apparatus dimensions (0.015 Torr). The shift has been attributed to changing electron temperature.
Frequency chirped short pulse amplification in inhomogeneously broadened XeCl gain media
Authors: Kannari Fumihiko , Obara Minoru
Published: July 2002

The application of a frequency chirped pulse amplification sheme for XeCl excimer lasers is theoretically evaluated by solving the Maxwell–Bloch equations [A. Icsevgi and W. E. Lamb, Jr., Phys. Rev. 185, 517 (1969)]. The calculated effective saturation energies for subpicosecond nonchirped laser pulses are much higher than the values that have been obtained experimentally. If this evidence indicates that optical nonlinear effects at high laser intensities are reducing the extraction energy, frequency chirped amplification followed by pulse compression, as demonstrated with solid-state lasers, is also useful with XeCl lasers. This helps to reduce the peak laser intensity and increase the extraction energy.
Ion beam induced damage and superlattice formation in epitaxial YBa2Cu3O7−δ thin films
Authors: Chen C. H. , White A. E. , Short K. T. , Dynes R. C. , Poate J. M. , Jacobson D. C. , Mankiewich P. M. , Skocpol W. J. , Howard R. E.
Published: July 2002

We have studied the effect of ion beam irradiation on the microstructure of epitaxial YBa2Cu3O7−δ thin films. The ion beam induced defects are found to cluster in small (<100 Å) disordered areas. The size and density of the disordered areas are found to increase with the ion fluence. The presence of these small disordered areas can lead to the reduction of phase coherence of the electron pair wave function. Ion beam irradiation is also found to reduce the orthorhombicity of the lattice structure. A new incommensurate superlattice phase due to ion beam induced defect ordering has also been observed.
Study of the SiO2/Si interface endurance property during rapid thermal nitridation and reoxidation processing
Authors: Shih D. K. , Kwong D. L. , Lee S.
Published: July 2002

The effects of rapid thermal nitridation of oxides (RTN) and rapid thermal reoxidation of rapid thermal nitride oxides (RTO/RTN) on the SiO2/Si interface endurance property have been studied. It is found that in order to enhance the SixNyOz/Si interface ‘‘hardness’’ [i.e., less interface states (Dit) are generated during high electric field stress], an interfacial oxidation process during RTN or RTO/RTN must occur. This oxidation reaction not only removes the nitridation-induced damages but also grows an interfacial strainless oxide. The existence of small amounts of nitrogen at the interface is responsible for the strainless oxide growth, and hence the improvement of SixNyOz/Si interface strength. A physical model based on these observations is described, which considers the generation of silicon and oxygen dangling bonds at the SixNyOz/Si interface during rapid thermal processing.
Luminescence of the D
X center in AlGaAs
Authors: Alaya S. , Maaref H. , Bourgoin J. C.
Published: July 2002

Low-temperature photoluminescence of the DX center in the near band edge and in the near-infrared region is interpreted within the small lattice relaxation model. The 1.5 μm luminescence band is attributed to an internal transition between the excited DX state and its ground-state level.
Using a hydrogen ambient to eliminate interfacial boron spikes in reduced temperature silicon epitaxy
Authors: Robbins D. J. , Pidduck A. J. , Glasper J. L. , Young I. M.
Published: July 2002

We show that the concentration of boron at the interface between a silicon epitaxial layer and an n-type Si substrate can be reduced to 109–1010 atoms cm−2, near the detection limit of secondary-ion mass spectrometry, when passivating oxide is desorbed from the substrate surface in a hydrogen ambient. Interfacial boron contamination is found to be much higher when the substrate surface oxide is desorbed in ultrahigh vacuum prior to growth, consistent with previous studies of Si molecular beam epitaxy. The hydrogen ambient is effective in removing boron only during the decomposition of the surface oxide.
New deep acceptor in epitaxial cubic SiC
Authors: Freitas J. A. , Bishop S. G.
Published: July 2002

We have investigated the temperature and excitation intensity dependence of photoluminescence (PL) spectra in several undoped and lightly Al-doped thin films of cubic SiC grown by chemical vapor deposition on Si substrates. The low-power PL spectra in all samples studied exhibit a deep donor-acceptor pair PL band which involves a previously undetected deep acceptor (EA=470 meV). The pervasive character of this deep acceptor suggests the possibility that it is at least partially responsible for the high compensation observed in undoped films of cubic SiC.
Linear polarized luminescence from CdTe epilayers
Authors: Kuhn T. A. , Ossau W. , Bicknell-Tassius R. N. , Landwehr G.
Published: July 2002

We report for the first time the observation of strongly linearly polarized luminescence from CdTe epitaxial layers grown by photoassisted molecular beam epitaxy. Strong linear polarization was detected in the acceptor-bound exciton spectral region and in the pair band regions (1.54–1.56 eV and 1.46–1.48 eV). The linear polarization is believed to be due to the preferential alignment of complex centers along one of the [110] lattice directions. The cause of the preferential orientation of these complex centers is the inequivalence during the planar growth on the (100) surface of the [110] and [1̄10] directions in the zinc-blende lattice.
Ethyldimethylindium for the growth of InGaAs-GaAs strained-layer lasers by metalorganic chemical vapor deposition
Authors: York P. K. , Beernink K. J. , Kim J. , Coleman J. J. , Fernández G. E. , Wayman C. M.
Published: July 2002

The growth and characterization of strained In0.25Ga0.75As-GaAs-Al0.20Ga0.80As quantum well lasers grown by metalorganic chemical vapor deposition using ethyldimethylindium (EDMIn) are described. A vapor pressure of 0.56 Torr at 11 °C has been extracted from the growth rates of thin InGaAs layers by transmission electron microscopy. Data on reproducibility in quantum well size are presented which indicate long-term stability in the EDMIn vapor pressure. Laser performance in samples grown with EDMIn is equivalent to, and in some cases better than, those grown with trimethylindium.
Real-time, i
n s
i
t
u monitoring of GaAs and AlGaAs photoluminescence during plasma processing
Authors: Mitchell Annette , Gottscho Richard A. , Pearton Stephen J. , Scheller Geoffrey R.
Published: July 2002

Monitoring wafer changes in situ during plasma treatment provides real-time feedback for developing and controlling device processing. In this letter we report the use of photoluminescence spectroscopy to monitor epitaxial films of Al0.3Ga0.7As and semi-insulating GaAs substrates during BCl3 plasma etching and H2 plasma passivation. Photoluminescence monitoring is used for etching endpoint detection, surface damage quantification, and wafer temperature measurement.
Measurement of the valence-band offset in strained Si/Ge (100) heterojunctions by x-ray photoelectron spectroscopy
Authors: Yu E. T. , Croke E. T. , McGill T. C. , Miles R. H.
Published: July 2002

We have used x-ray photoelectron spectroscopy to measure the valence-band offset in situ for strained Si/Ge (100) heterojunctions grown by molecular beam epitaxy. Si 2p and Ge 3d core level to valence-band-edge binding energies and Si 2p to Ge 3d core level energy separations were measured as functions of strain, and strain configurations in all samples were determined using x-ray diffraction. Our measurements yield valence-band offset values of 0.83±0.11 eV and 0.22±0.13 eV for Ge on Si (100) and Si on Ge (100), respectively. If we assume that the offset between the weighted averages of the light hole, heavy hole, and spin-orbit valence bands in Si and Ge is independent of strain, we obtain a discontinuity in the average valence-band edge of 0.49±0.13 eV.
Low-threshold GaAs/AlGaAs graded-index separate confinement heterostructure lasers grown by molecular beam epitaxy on oxide-masked Si substrates
Authors: Burns Geoffrey F. , Blanck Hervé , Fonstad Clifton G.
Published: July 2002

Low-threshold GaAs/AlGaAs lasers have, for the first time, been grown selectively on 10 μm stripe openings patterned in oxide on Si substrates. Lateral current confinement provided by side facets reduces edge leakage, and results in threshold currents as low as 75 mA for a 10 μm by 210 μm device, a nearly two-fold improvement over comparable etched ridge waveguide lasers. Spectrum measurements show single longitudinal mode emission near 850 nm. This adaptation of selective heteroepitaxial growth for lateral current confinement of AlGaAs/GaAs lasers on Si substrates, adopted from similar work on GaAs substrates, offers potential for significant threshold current reductions of lasers integrable with Si.
Epitaxial growth of extended solubility CdxPb1−xTe alloys on BaF2 by rf magnetron sputtering
Authors: Cook J. G. , Das S. R. , Lockwood D. J. , McCaffrey J. P. , Timbrell P. Y.
Published: July 2002

Epitaxial (111)CdxPb1−xTe//(111)BaF2 films in the rocksalt structure have been made by codeposition from CdTe and PbTe magnetron targets in an rf discharge onto chemipolished substrates at 320 °C. Films were prepared with x values from 0 to 0.47, well past the range of bulk thermodynamic solubility. Raman spectroscopy, Auger spectroscopy, and transmission electron microscopy showed phase segregation had not occurred. The lattice spacing in the growth direction was observed to be insensitive to x.
Conductance statistics of small-area ohmic contacts on GaAs
Authors: Blanc N. , Guéret P. , Buchmann P. , Dätwyler K. , Vettiger P.
Published: July 2002

The conductance distributions of very small-area alloyed ohmic contacts on n+-GaAs have been studied as a function of lateral contact size d, with d ranging from 4 μm down to 0.3 μm. The data are fairly well represented by a Poisson distribution, which takes into account the granularity of the alloyed contacts, as previously reported. We deduce an average distance of dc ≂0.41 μm between conducting grains and a dead zone of ld ≂600 Å due to dry etching of the GaAs.
Two-wavelength optical switching in a GaAs multiple quantum well directional coupler
Authors: Cada M. , Keyworth B. P. , Glinski J. M. , Rolland C. , SpringThorpe A. J. , Miner C. J. , Hill K. O.
Published: July 2002

Preliminary experimental results are reported on two-wavelength switching in a GaAs-based multiple quantum well planar directional coupler. It is verified that a novel design of the multiple quantum well (MQW) coupling region leads to a wavelength multiplexing/demultiplexing/switching operation. It is shown that control of such a function can be exercised by either the wavelength of operation or by an applied electrical voltage through exciton resonance effects in the MQW layer. The layer structure exhibits two exciton-resonance peaks at which wavelength-selective switching can be achieved.
Epitaxial films of semiconducting FeSi2 on (001) silicon
Authors: Mahan John E. , Geib Kent M. , Robinson G. Y. , Long Robert G. , Xinghua Yan , Bai Gang , Nicolet Marc-A. , Nathan Menachem
Published: July 2002

Epitaxial thin films of the semiconducting transition metal silicide, beta-FeSi2, were grown on (001) silicon wafers. The observed matching face relationship is FeSi2(100)/Si(001), with the azimuthal orientation being FeSi2[010]‖‖Si〈110〉. This heteroepitaxial relationship has a common unit mesh of 59 Å2 area, with a mismatch of 2.1%. There is a strong tendency toward island formation within this heteroepitaxial system.
Thermal generation currents in hydrogenated amorphous silicon p-i-n structures
Authors: Street R. A.
Published: July 2002

Dark conductivity in amorphous silicon p-i-n devices arising from thermal generation through bulk defect states is explored. The current decays slowly after a voltage is applied, due to depletion of charge from the undoped layer, and is voltage dependent due to a field-enhanced generation rate. Creation of metastable bulk defects by light soaking reversibly increases the current. The steady-state generation current is dervied from the measured relaxation time and depletion charge.
Effect of base doping gradients on the electrical performance of AlGaAs/GaAs heterojunction bipolar transistors
Authors: Mohammad S. Noor , Chen J. , Chyi J-I. , Morkoç H.
Published: July 2002

Current-voltage characteristics of AlGaAs/GaAs heterojunction bipolar transistors (HBTs) grown by molecular beam epitaxy with nonuniform doping in the base region have been studied. Experimental measurements indicate that an optimization of the base doping leads to substantial improvement in the current gain and related properties. Unequal variations of the band-gap narrowing effect and Fermi–Dirac statistics effect seem to underlie this improvement. It is found that, in general, the higher the nonuniformity of the base doping, the lower is the offset voltage of the HBT.
Scanning electron acoustic microscopy of indentation-induced cracks and residual stresses in ceramics
Authors: Cantrell John H. , Qian Menglu , Ravichandran M. V. , Knowles K. M.
Published: July 2002

The ability of scanning electron acoustic microscopy (SEAM) to characterize ceramic materials is assessed. SEAM images of Vickers indentations in SiC whisker-reinforced alumina clearly reveal not only the radial cracks, the length of which can be used to estimate the fracture toughness of the material, but also reveal strong contrast, interpreted as arising from the combined effects of lateral cracks and the residual stress field left in the SiC whisker-reinforced alumina by the indenter. The strong contrast is removed after the material is heat treated at 1000 °C to relieve the residual stresses around the indentations. A comparison of these observations with SEAM and reflected polarized light observations of Vickers indentations in soda-lime glass both before and after heat treatment confirms our interpretation of the strong contrast.
Deep donors in GaSb grown by molecular beam epitaxy
Authors: Poole I. , Lee M. E. , Cleverley I. R. , Peaker A. R. , Singer K. E.
Published: July 2002

A deep state possessing similar properties to those reported for DX centers in the AlGaAs system has been observed at atmospheric pressure in GaSb moderately doped with sulfur. The first detailed deep level transient spectroscopy study of this material has revealed a large energy barrier to electron capture and a correspondingly small capture cross section for this deep level. The deep level activity of selenium- and tellurium-doped GaSb has also been investigated.
Epitaxial growth of ferroelectric bismuth titanate thin films by pulsed laser deposition
Authors: Ramesh R. , Luther K. , Wilkens B. , Hart D. L. , Wang E. , Tarascon J. M. , Inam A. , Wu X. D. , Venkatesan T.
Published: July 2002

Epitaxial thin films of ferroelectric bismuth titanate Bi4Ti3O12 have been grown by pulsed laser deposition on single-crystal [100] SrTiO3 substrates. Bismuth titanate has a high Curie temperature (675 °C) and saturation polarization values of 4 and 50 μC/cm2 along the c and b axis, respectively. Its a,b lattice parameters allow thin-film growth on substrates such as SrTiO3, LaAlO3, MgO, etc. These single crystalline films exhibit good quality as evidenced by x-ray diffraction, Rutherford backscattering, and transmission electron microscopy. Applications for these films include memory devices and optical displays.
Determination of the GaInP/AlGaInP band offset
Authors: Liedenbaum C. T. H. F. , Valster A. , Severens A. L. G. J. , Hooft G. W. ’t
Published: July 2002

Low-temperature photoluminescence excitation spectra of disordered Ga0.5In0.5P/Al0.3Ga0.2In0.5P quantum wells lattice matched to (311)B GaAs substrates have been measured for the first time. Transition energies calculated with a k̄⋅p̄ approach agree with experiment within 3 MeV, over the entire range of quantum well thicknesses (Lz=11–109 Å). A conduction-band discontinuity of 0.65±0.05 is derived.
Photointercalation effect of thin WO3 films
Authors: Nagasu Masahiro , Koshida Nobuyoshi
Published: July 2002

It is shown that thin amorphous films of WO3 exhibit a photoinduced reversible coloration in an electrochemical cell of the form quartz/semitransparent Au/ethanol/WO3/In2O3-coated glass. From measurements of the optical and electrical properties of the films, the coloration is attributed to the formation of HxWO3, presumably due to a photointercalation of protons into WO3 films. This effect is potentially useful for storage, learning, and modulation of two-dimensional optical information.
Novel metal ion surface modification technique
Authors: Brown I. G. , Godechot X. , Yu K. M.
Published: July 2002

We describe a method for applying metal ions to the near-surface region of solid materials. The added species can be energetically implanted below the surface or built up as a surface film with an atomically mixed interface with the substrate; the metal ion species can be the same as the substrate species or different from it, and more than one kind of metal species can be applied, either simultaneously or sequentially. Surface structures can be fabricated, including coatings and thin films of single metals, tailored alloys, or metallic multilayers, and they can be implanted or added onto the surface and ion beam mixed. We report two simple demonstrations of the method: implantation of yttrium into a silicon substrate at a mean energy of 70 keV and a dose of 1×1016 atoms/cm2, and the formation of a titanium-yttrium multilayer structure with ion beam mixing to the substrate.
Resonant tunneling in submicron double-barrier heterostructures
Authors: Su Bo , Goldman V. J. , Santos M. , Shayegan M.
Published: July 2002

We have fabricated submicron resonant tunneling devices from double-barrier AlGaAs/GaAs heterostructures using electron beam lithography and wet chemical etching. These devices exhibit step-like features in the current-voltage curves. We interpret these steps as arising from additional size quantization of the electronic states in the well due to in-plane lithographic confinement. Magnetotunneling experiments on these devices are reported for the first time. A simple model calculation describes well the experimental data.
Impurity trapping and gettering in amorphous silicon
Authors: Coffa S. , Poate J. M. , Jacobson D. C. , Polman A.
Published: July 2002

Palladium atoms have been gettered from the bulk of an amorphous Si (a-Si) layer to an ion-implanted surface region. The 2.2-μm-thick a-Si layers, formed by MeV Si implantation, were implanted with 500 keV Pd and then annealed at 500 °C. This produces a complete redistribution of Pd within the layer and relaxation or substantial defect annihilation in the a-Si. Subsequently, defects were introduced into the surface region (∼4000 Å) by 200 keV Si implantation at various doses. After low-temperature diffusion at 250 °C, Pd atoms are gettered in the Si-implanted region. At low Si fluences, Pd decorates the Gaussian depth distribution of the ion-induced damage, while at higher a saturation is reached in the gettering profile. The ion damage is calculated to saturate when 2% of the target Si atoms are displaced by atomic recoils. Below saturation, the displacement of two Si atoms is calculated to produce one Pd trapping site.
Molecular beam epitaxy of a low strain II-VI heterostructure: ZnTe/CdSe
Authors: Luo H. , Samarth N. , Zhang F. C. , Pareek A. , Dobrowolska M. , Furdyna J. K. , Mahalingam K. , Otsuka N. , Chou W. C. , Petrou A. , Qadri S. B.
Published: July 2002

We report the growth of a new closely lattice-matched II-VI heterostructure: ZnTe/CdSe (Δa/a∼0.3%). Epilayers of zinc blende CdSe grown on ZnTe buffer layers are shown to have much better quality than those grown earlier (with a 7% mismatch) on GaAs substrates. This permitted the first successful growth of high quality superlattices of ZnTe/CdSe. The superlattices were studied by x-ray diffraction, transmission electron microscopy, and optical techniques. Results of photoluminescence and optical transmission measurements show that ZnTe/CdSe superlattices have a very small valence-band offset.
Suppression of the magnetic-permeability relaxation in nanocrystalline Fe73.5Cu1Nb3Si13.5B9
Authors: Allia P. , Beatrice C. , Vinai F. , Knobel M. , Turtelli R. Sato
Published: July 2002

Room-temperature measurements of the reversible relaxation of the initial magnetic permeability have been performed in rapidly solidified Fe73.5Cu1Nb3Si13.5B9 ribbons at different stages of the transformation from the amorphous to the nanocrystalline phase. The intensity of the relaxation is observed to practically disappear in the nanocrystalline alloy. This result may modify the current views about the structural defects responsible for the magnetic-permeability relaxation in amorphous ferromagnets.
New designs for antenna-coupled superconducting bolometers
Authors: Mees J. , Nahum M. , Richards P. L.
Published: July 2002

We propose a novel antenna-coupled low Tc superconducting bolometer which makes use of the thermal boundary resistance and the trapping of quasiparticles at metal-superconducting interfaces. A thin strip of superconductor, whose temperature is regulated at the midpoint of its resistive transition, serves both as a resistive load to thermalize the infrared current from the antenna and as a thermometer to measure the resulting temperature rise. Calculations give a noise equivalent power (NEP)≊7×10−16 T5/2 WHz−1/2 and a time constant τ≊10−8 T−2 s for a 2×2 μm2 thermometer area at temperature T (K). Designs for efficient on-chip rf matching and filter networks with well-defined bandpasses are presented. These detectors can be used to make frequency-multiplexed array receivers for astronomical observations at near millimeter wavelengths.
Overgrowth of indium nitride thin films on aluminum nitride nucleated (00.1) sapphire by reactive magnetron sputtering
Authors: Kistenmacher Thomas J. , Bryden Wayne A.
Published: July 2002

The growth and properties of thin films of InN on (00.1) sapphire and (00.1) sapphire nucleated by a 400 Å layer of AlN have been found to be radically different. The unnucleated InN films exhibit a mixed morphology (largely textured with lesser amounts of epitaxial grains), a monofunctional thickness dependence on sputtering time, uniformly low mobility and carrier concentration, and high resistivity. In contrast, the AlN-nucleated overlayers show only heteroepitaxial grains, a bifunctional dependence for the film thickness and surface roughness on sputtering time, higher mobility and carrier concentration, and lower resistivity−even in the limit of an InN overlayer on the order of 20–40 Å.
Observation of anomalously large blue shift of the heavy-hole photocurrent peak and optical bistability in narrow asymmetric coupled quantum wells
Authors: Ding Y. J. , Guo C. L. , Li S. , Khurgin J. B. , Law K.-K. , Stellato J. , Law C. T. , Kaplan A. E. , Coldren L. A.
Published: July 2002

Blue shift of the heavy-hole peak of the photocurrent spectra has been observed, for the first time, in narrow GaAs/Al0.4Ga0.6As asymmetric coupled quantum wells near the heavy-hole resonance. With an external reverse bias of only −2.35 V, a maximum upward shift of the apparent peak position of ∼6.1 meV has been measured at 78 K. Sharp change of the inhomogeneous linewidth of the heavy-hole peak has also been observed. cw optical bistability has been observed with the external feedback.
Hot filament assisted deposition of silicon nitride thin films
Authors: Deshpande Sadanand V. , Dupuie Jeffrey L. , Gulari Erdogan
Published: July 2002

Hot filament assisted chemical vapor deposition (HFCVD) of silicon nitride thin films was studied with disilane (Si2H6) and ammonia (NH3) as the source gases. High optical density films were obtained at a low substrate temperature (375 °C) and high deposition rates (up to 1700 Å/min). The effects of disilane flow rate, filament temperature, and disilane carrier gas composition on film properties were investigated. Transmission infrared measurements showed low hydrogen content (<5%) in the films. Sputter depth profiling using x-ray photoelectron spectroscopy indicated high film purity with only surface oxygen contamination from air exposure after deposition.
Study of electron traps in semi-insulating gallium-arsenide buffer layers for the suppression of backgating by the zero-bias thermally stimulated current technique
Authors: Lau W. S. , Chong T. C. , Tan L. S. , Goo C. H. , Goh K. S. , Lee K. M.
Published: July 2002

Electron traps in undoped-GaAs epitaxial layers grown at low temperatures (<300 °C) by molecular beam epitaxy were studied by the zero-bias thermally stimulated current technique. Four traps T1-4 were detected in as-grown samples. It was also found that all the traps detected can be annealed out except the T1 trap. However, the buffer layer, with or without annealing, was found to be an effective remedy for backgating in high electron mobility transistors, indicating that the T1 trap may have a much more significant role than the three shallower traps in the suppression of backgating. The T1 trap is believed to be the EL3 electron trap which is related to oxygen contamination.
Growth of single crystalline γ-Al2O3 layers on silicon by metalorganic molecular beam epitaxy
Authors: Iizuka Hirohisa , Yokoo Kuniyoshi , Ono Shoichi
Published: July 2002

Single crystalline γ-Al2O3 layers have been successfully grown on silicon substrates by the metalorganic molecular beam epitaxy using aluminum alkoxide gas. Single crystalline γ-Al2O3 layers are grown only on crystalline silicon substrates, while polycrystalline Al2O3 layers are grown on amorphous oxidized silicon surface. By x-ray photoemission spectroscopy measurements, the stoichiometry of the single crystalline layers were confirmed to be identical to Al2O3 bulk crystals and carbon contamination was not detected within the sensitivity of the measurements.
Voltage gain in the single-electron transistor
Authors: Zimmerli G. , Kautz R. L. , Martinis John M.
Published: July 2002

We report the first observation of voltage gain in the capacitively coupled single-electron transistor (SET). Using parallel-plate and interdigital geometries for the gate capacitor (Cg=1.2 and 0.4 fF) and ultrasmall tunnel junctions with capacitances near 0.2 fF, we find maximum voltage gains of 2.8 and 1.5, respectively. The leakage resistance of the gate is of the order 1012 Ω for the parallel-plate capacitor and greater than 1018 Ω for the interdigital capacitor.
Estimation of carrier capture time of quantum-well lasers by spontaneous emission spectra
Authors: Hirayama Hideki , Yoshida Junji , Miyake Yasunari , Asada Masahiro
Published: July 2002

Carrier capture time was estimated for separate confinement heterostructure single quantum-well lasers by measuring the spontaneous emission from the optical confinement layers which increases with current even above the laser threshold due to finite carrier capture time of the well. By fitting theoretical analysis to the measurement, hole capture time was found to be the dominant factor for the spontaneous emission increase, and was estimated as 0.2–0.25 ps for GaInAs/GaInAsP/InP quantum well lasers. Additional transport time of 0.1–0.2 ps across the barrier was also obtained for multiquantum well lasers. It appears that the finiteness of carrier capture time affects not only the threshold current but also the differential quantum efficiency in high power operation through the absorption loss by the carriers in the optical confinement layers.
Ultraviolet stimulated emission and optical gain spectra in CdxZn1−xS-ZnS strained-layer superlattices
Authors: Yamada Yoichi , Masumoto Yasuaki , Mullins John T. , Taguchi Tsunemasa
Published: July 2002

Stimulated emission at 374.9 nm has been observed in an optically pumped Cd0.22Zn0.78S-ZnS strained-layer superlattice at room temperature. Using a pump-and-probe technique with nanosecond excitation pulses, optical gain has also been observed at the tail part of the n=1 heavy-hole exciton absorption spectrum in the presence of the clear absorption peak of the exciton. Our experimental results suggest that the stimulated emission originates from excitonic gain.
Improvement of the photorefractive efficiency of BaTiO3 by γ irradiation
Authors: Moore Thomas R. , Boyd Robert W.
Published: July 2002

We report that the photorefractive response of as-grown BaTiO3 crystals can be improved by γ irradiation from a Co60 source. An increase in photorefractive response was observed with irradiation doses exceeding 106 rad, with a maximum observed increase in two-beam coupling gain of ∼15%. We interpret our results within the context of a well-known model of photorefractivity in BaTiO3 and conclude that γ irradiation increases the effective trap density and possibly also increases the normalized conductivity in samples where both holes and electrons contribute to photorefractivity.
Low-temperature scanning tunneling spectroscopic observation of vortex in a NbCxN1−x thin film
Authors: Kashiwaya S. , Koyanagi M. , Shoji A.
Published: July 2002

Scanning tunneling spectroscopic studies were performed on superconducting NbCxN1−x thin films at 4.2 K. An image of a spatial variation of a gap obtained in a magnetic field of 0.3 T showed a clear vortex lattice. Two types of the spatial variations of the local density of states around the vortex cores were observed. Type I had a normal center in the core, and a gap variation around the core was consistent with a theory for dirty limit superconductors. Type II did not have a normal center and the origin of this core is not yet clear.
Rapid deposition of high temperature YBa2Cu3O 7−x superconducting thin films directly on silver substrates
Authors: Tao W. , Yuan M. P. , Huang H. T. , Liao X. Z. , Xie X. M. , Zhou H. L. , Wu Z. L.
Published: July 2002

The superconducting YBa2Cu3O7−x (YBCO) films have been deposited directly on silver (Ag) substrates by metalorganic chemical vapor deposition. Critical current density (Jc) as high as 1.4×104 A/cm2 (0 T, 77.3 K) was obtained. The high Jc was attributed to the small, compact grains of the YBCO films.
Degradation of superconducting tunnel junction characteristics with increasing barrier transparency
Authors: Kleinsasser A. W. , Rammo F. M. , Bhushan M.
Published: July 2002

Measurements are reported of the single-particle characteristics of Nb-Al oxide-Nb superconducting tunnel junctions. Subgap leakage, subharmonic gap structure, and excess current are observed to increase systematically with increasing Josephson critical current density above a few kA/cm2. These phenomena are attributed to multiple Andreev reflections in high transmittance regions of the barrier. Such effects may significantly impact the applications of high critical current density junctions in advanced circuits.
Enhancement of diffusion-induced grain boundary migration by ion irradiation
Authors: Alexander Dale E. , Rehn L. E. , Baldo P. M. , Gao Y.
Published: July 2002

Diffusion-induced grain boundary migration (DIGM) was observed in Au/Cu bilayers irradiated with 1.5 MeV Kr at T≥400 K. Rutherford backscattering spectrometry (RBS) showed nearly uniform distributions of Cu present throughout polycrystalline Au films after irradiation and after annealing treatments. Irradiation increased the amount of Cu relative to annealed-only areas. Cross-section transmission electron microscopy combined with x-ray energy dispersive spectroscopy (XEDS) identified alloyed zones (14–20 at. % Cu), confirming DIGM in the Au film of an ion bombarded bilayer. A description of DIGM is presented relating RBS measurements of the film-averaged Cu composition with treatment time, average grain size, and film thickness. Application of this model to the experimental results in combination with XEDS work indicates that irradiation enhances DIGM by increasing the grain boundary velocity.
Symmetric Si/Si1−xGex electron resonant tunneling diodes with an anomalous temperature behavior
Authors: Matutinović-Krstelj Ž. , Liu C. W. , Xiao X. , Sturm J. C.
Published: July 2002

We report the fabrication of symmetric, n-type resonant tunneling diodes grown by rapid thermal chemical vapor deposition in the Si/Si1−xGex material system. Up to four resonant features were observed for both positive and negative bias. This is the first time that such highly symmetric features are reported for electron resonant tunneling in the Si/SiGe material system. A peak-to-valley ratio of 2 was achieved at a temperature of 4 K and resonances were observed up to 240 K. An additional peak is observed at low voltages exhibiting an anomalous temperature behavior, disappearing at temperatures below 50 K. Models involving phonon absorption or emitter quantization are proposed to explain this behavior.
Deposition of amorphous fluoropolymers thin films by laser ablation
Authors: Blanchet Graciela B.
Published: July 2002

Thin films of the amorphous fluoropolymer, Teflon AF(r), were deposited by laser ablation using the 4th harmonic, at 266 nm, of a Nd-YAG laser. Infrared spectroscopy indicated that the composition of the ablated films were that of the starting materials and x-ray diffraction spectra corroborated the lack of crystallinity. The morphology of the films was controlled by the temperature of the substrate during film formation. We suggest pyrolitic decomposition and subsequent repolymerization as a possible mechanism to the formation of Teflon-AF(r) films by laser ablation.
Edge effects and a method of defect sizing for transient thermography
Authors: Almond D. P. , Lau S. K.
Published: July 2002

Thermal edge effects for a cracklike defect have been calculated using the Wiener–Hopf technique. These have been used in an analytical model to explain transient thermographic image formation. The analysis has led to a simple method for defect sizing which is demonstrated using experimental results.
Directional couplers with linear and nonlinear elements
Authors: Deering W. D. , Molina M. I. , Tsironis G. P.
Published: July 2002

The switching characteristics of simple mixed linear–nonlinear configurations of directional couplers for single-mode operation are investigated. For negative interaction coefficients, faster switching can be achieved at lower input power levels than in all-nonlinear coupler configurations.
Properties of epitaxial SrRuO3 thin films
Authors: Wu X. D. , Foltyn S. R. , Dye R. C. , Coulter Y. , Muenchausen R. E.
Published: July 2002

SrRuO3 thin films were deposited on (100) LaAlO3 using pulsed laser deposition. The films were (001) oriented normal to the substrate surface with a high degree of in-plane orientation with respect to the substrate’s major axes. An ion beam minimum yield of 2.5% was obtained for the films, indicating high crystallinity. The films exhibited metallic behavior with a room temperature resistivity of ∼200 mW cm. A kink in the resistivity, corresponding to a ferromagnetic phase transition, was observed at ∼160 K. It was found that SrRuO3 is structurally and chemically compatible with the YaB2Cu3O7−d (YBCO) superconductors. High quality YBCO films were obtained on SrRuO3 LaAlO3. Multilayers of YBCO/SrRuO3 were successfully fabricated.
Polyazomethine conjugated polymer film with second order nonlinear optical properties fabricated by electric-field-assisted chemical vapor deposition
Authors: Tatsuura Satoshi , Sotoyama Wataru , Motoyoshi Katsusada , Matsuura Azuma , Hayano Tomoaki , Yoshimura Tetsuzo
Published: July 2002

We fabricated polyazomethine head-to-tail conjugated polymer films with second order nonlinear optical (NLO) properties using a dry-processing technique, electric-field-assisted chemical vapor deposition (E-CVD). Molecular orbital calculations show that the polyazomethine conjugated polymer chain, to which methoxy groups are attached as donors, has second order NLO susceptibility, β, 3–5 times larger than that of paranitroaniline. During film deposition the monomers were ordered by an electric field applied between slit-type electrodes, and simultaneously polymerized. A channel waveguide for the TE mode of a He-Ne laser beam was formed in a polymer film between the electrode gap. An electro-optic (EO) effect in the polymer film was observed using a Mach–Zehnder interferometer. This indicates that head-to-tail conjugated polymers would be promising for second order NLO materials.