bluuebunny/crossref_metadata_2025 huggingface dataset:
X–Γ indirect intersubband transitions in type II GaAs/AlAs superlattices
Authors: Fenigstein A. , Finkman E. , Bahir G. , Schacham S. E.
Published: July 2002

Intersubband transitions indirect in both real and momentum spaces were observed in GaAs/AlAs type II short period superlattices. Significant absorption of normal incident radiation, with ‘‘forbidden’’ polarization was measured, in addition to absorption in the ‘‘allowed’’ configuration. The transition energy shows a strong temperature dependence. This absorption is attributed to X–Γ transition. Both doped and undoped samples were investigated. Normal incidence absorption is stronger for the doped superlattices. Simulations using a two band model show good agreement to experimental data.
Study of dry oxidation of triangle-shaped silicon nanostructure
Authors: Liu J. L. , Shi Y. , Wang F. , Lu Y. , Gu S. L. , Zhang R. , Zheng Y. D.
Published: July 2002

Silicon nanostructures along [011] direction with upside down triangle cross sections on the top of the sawtooth structure with (111) facets are prepared by using the lithography technique, reactive ion etching, and anisotropic wet chemical etching. These triangle-shaped silicon nanostructures are thermally oxidized in dry oxygen over a range of temperature from 850 to 1000 °C, which is characterized by scanning electron microscopy. The self-limiting oxidation phenomenon observed in silicon nanostructures is discussed. Cross-sectional shape change of the silicon nanostructure under different oxidation temperatures is demonstrated. A silicon quantum wire is successfully fabricated by two-step thermal oxidation of the silicon nanostructures.
Resonant-cavity photodiode operating at 1.55 μm with Burstein-shifted In0.53Ga0.47As/InP reflectors
Authors: Murtaza S. S. , Chelakara R. V. , Dupuis R. D. , Campbell J. C. , Dentai A. G.
Published: July 2002

Traditionally, mirror design at the wavelengths important for fiber optic systems (1.3 and 1.55 μm) has suffered from the low refractive index step available between InP and its lattice-matched alloys; the InP/In0.53Ga0.47As combination provides the largest index step, but at λ=1.55 μm absorption in the In0.53Ga0.47As layers degrades reflectivity. We have used the Burstein shift in n+:In0.53Ga0.47As to reduce the band-to-band absorption. This has yielded InP/In0.53Ga0.47As Bragg reflectors with reflectivity greater than 97%. These mirrors have been incorporated into a high-efficiency resonant-cavity photodetector operating at 1.55 μm.
Carrier transport in asymmetrically confined 1.55 μm multiple quantum well laser structures
Authors: Zimmermann M. , Krämer S. , Hangleiter A. , Steinhagen F. , Hillmer H. , Burkhard H.
Published: July 2002

Asymmetrically confined multiple quantum well laser structures have recently been very successful in reaching high modulation bandwidths up to 26 GHz, reported in the InGaAs/InGaAlAs material system. We have measured the effective carrier transport time in structures of this kind by performing parasitic-free optical modulation experiments. The result is one specific transport time for each confinement layer width. We show that down to layer widths of about 100 nm this effective time for both types of carriers is given by a pure diffusion process for InGaAs/InGaAlAs. Finally, a diffusion constant for the barrier/confinement carriers results in InGaAlAs material which is in very good agreement with reported mobilities.
A single precursor photolitic chemical vapor deposition of silica film using a dielectric barier discharge xenon excimer lamp
Authors: Yokotani Atsushi , Takezoe Noritaka , Kurosawa Kou , Igarashi Tatsushi , Matsuno Hiromitu
Published: July 2002

Silica film has been produced at room temperature by a single precursor process of photolitic chemical vapor deposition using a newly developed Xe excimer lamp. Tetraethoxyorthosilicate (TEOS) has been used as a raw material. Transparent thin film of SiO2 was obtained on single crystalline Al2O3 substrates and its properties were evaluated by means of the reflection Fourier transformation-infrared spectroscopy, the scanning electron microscopy, and ultraviolet-visible spectrometry. Consequently, it was found that the main component of the film was SiO2 and very small amounts of residual organic materials were contained. It was also found that the film was very dense and the refractive indices were only 1.7% smaller than that of bulk silica glass.
Recombination dynamics of excitons and biexcitons in a hexagonal GaN epitaxial layer
Authors: Kawakami Yoichi , Peng Zhi Gang , Narukawa Yukio , Fujita Shizuo , Fujita Shigeo , Nakamura Shuji
Published: July 2002

Time-resolved photoluminescence (PL) spectroscopy has been performed at 18 K on excitonic-related emissions in an unintentionally doped hexagonal GaN epitaxial layer grown by two-flow metalorganic chemical vapor deposition (TF-MOCVD). Under low excitation condition, radiative recombination of A free exciton (EXA: 3.4921 eV) and neutral shallow-acceptor bound exciton [(A0s,X): 3.4805 eV] dominated the spectrum. Decay time of (A0s,X) emission is relatively long (585 ps) indicating a small number of non-radiative centers in the layer. At higher excitation densities, new PL peak appeared at 3.4864 eV and grew superlinearly with excitation densities. These features, combined with their transient behavior, suggest that this new emission band is due to the biexciton recombination.
Influence of the microstructure of a SrTiO3 buffer layer on the microwave properties of Y1Ba2Cu3O7−x films on MgO
Authors: Rao Muralidhar R.
Published: July 2002

YBa2Cu3O7−x (YBCO) films were grown on SrTiO3 buffered (100)-MgO substrates by pulsed laser deposition. The microstructure of the SrTiO3 layers was varied by changing the growth parameters and thickness. The surface morphology of the layers was characterized by atomic force microscopy. Stripline microwave resonators were fabricated from the films, and the resonator characteristics were measured. The microwave loss in the YBCO was found to correlate to SrTiO3 grain size.
Surface reconstruction of zinc-blende GaN
Authors: Bykhovski A. D. , Shur M. S.
Published: July 2002

We propose a model of the surface reconstruction for cubic GaN which accounts both for short- and long-range forces. Our analysis shows that short-range covalent contributions to the bond energies cannot by themselves explain the difference in stability of different surface configurations. Our analysis, which includes long-range ionic contributions, shows that at all typical molecular beam epitaxy (MBE) epitaxy temperatures the cubic GaN film with a free-carrier concentration larger than 1016 cm−3 should have a tendency to develop the surface reconstruction. The qualitative explanation of the reconstruction effects on Ga surface of (001) surface of cubic GaN can be linked to a large difference in atomic sizes of Ga and N.
Using neutral metastable argon atoms and contamination lithography to form nanostructures in silicon, silicon dioxide, and gold
Authors: Johnson K. S. , Berggren K. K. , Black A. , Black C. T. , Chu A. P. , Dekker N. H. , Ralph D. C. , Thywissen J. H. , Younkin R. , Tinkham M. , Prentiss M. , Whitesides G. M.
Published: July 2002

This letter describes the fabrication of ∼80 nm structures in silicon, silicon dioxide, and gold substrates by exposing the substrates to a beam of metastable argon atoms in the presence of dilute vapors of trimethylpentaphenyltrisiloxane, the dominant constituent of diffusion pump oil used in these experiments. The atoms release their internal energy upon contacting the siloxanes physisorbed on the surface of the substrate, and this release causes the formation of a carbon-based resist. The atomic beam was patterned by a silicon nitride membrane, and the pattern formed in the resist material was transferred to the substrates by chemical etching. Simultaneous exposure of large areas (44 cm2) was also demonstrated.
Real time observation of reconstruction transitions on GaAs (111)B surface by scanning electron microscopy
Authors: Ren Hong-Wen , Tanaka Masaaki , Nishinaga Tatau
Published: July 2002

Scanning electron microscopy (SEM) has been applied to directly observe the √19×√19 and (1×1)HT reconstructions and their transitions on the GaAs (111)B vicinal surfaces under As pressure. √19×√19 reconstruction and 1×1 high temperature reconstructions known as (1×1)HT reconstructions are observed in dark and bright contrast, respectively. During the transition, √19×√19 domains start to develop from the macrostep edges on to the lower (1×1)HT reconstructed terraces, while (1×1)HT domains start to develop from the macrostep edges on to the upper √19×√19 reconstructed terraces. The transition diagram in the surface coverage of domains shows hysteresis. Since Ga diffusion, As incorporation or reevaporation are enhanced during the transitions, heavy step bunching with rough macrostep edges is observed.
Comparison between optical nonlinearity relaxation times from coherent second-harmonic generation and from incoherent hyper-Rayleigh scattering
Authors: Matsuda Naoki , Olbrechts Geert , Put Erik J. H. , Clays Koen , Persoons André
Published: July 2002

Femtosecond hyper-Rayleigh scattering has recently been used to determine the spatial correlation length between nonlinear optical chromophores in polymer films [G. Olbrechts et al., Chem. Phys. Lett. 253, 135 (1996)]. This correlation length corresponds to the effective interaction length for frequency doubling in waveguide format, as derived from phase-matching curves. The temporal characteristics of this correlation length have now been studied and compared with thermal relaxation times, obtained with coherent second-harmonic generation. The correlation length decays much faster than the second-harmonic intensity, indicating that the efficiency of a second-order waveguide process could decay much faster than generally anticipated.
Hybridized approach to new polymers exhibiting large photorefractivity
Authors: Peng Zhonghua , Gharavi Ali Reza , Yu Luping
Published: July 2002

We report on a new photorefractive polymer that contains an ionic tri(bispyridyl) ruthenium complex as the charge generating species, a conjugated polymer backbone as the charge transporting channel, and a nonlinear optical chromophore. The ruthenium complex was introduced to utilize its efficient photoinduced metal-to-ligand charge transfer process. This polymer shows greatly enhanced photorefractive performance; a large net optical gain of about 200 cm−1 was obtained at a zero external electric field.
Determination of the composition of strained tetragonal epilayers
Authors: Fons P. , Bottomley D. J. , Tweet D. J. , Niki S. , Yamada A.
Published: July 2002

Elasticity theory is applied to calculate the total strain present in a tetragonal symmetry epilayer due to heteroepitaxial misfit. By relating pseudobinary alloy composition to the lattice constants of the epilayer, it is shown that the composition of a pseudobinary epilayer can be determined from measurement of the strained epilayer lattice constants. This is accomplished by expressing the misfit strain in terms of the composition and the individual lattice constants of the components of the epilayer and using Vegard’s rule. As a result, determination of the composition of two chalcopyrite symmetry epilayers from x-ray diffraction measurements is demonstrated. The approach presented here is general and can be applied to any substrate-epilayer combination in the elastic limit.
Effect of extended defects on the formation and dissociation kinetics of Zn–H complexes in heteroepitaxial p-type InP layers
Authors: Chatterjee B. , Ringel S. A.
Published: July 2002

Hydrogen passivation of Zn acceptors and Zn–H dissociation kinetics are compared for homoepitaxial and lattice-mismatched heteroepitaxial n+p InP structures. Doping profile measurements show a pronounced increase in the depth and degree of passivation in the p-type region of the heteroepitaxial samples indicating enhanced diffusion of hydrogen along dislocations, followed by additional Zn deactivation. Moreover, the strong affinity between hydrogen and extended defects is found to aid the subsequent dissociation of the Zn–H complexes as indicated by (i) reverse bias annealing (RBA) studies which show that the Zn–H dissociation energy decreases from 1.19 eV in homoepitaxial samples to 1.12 eV in heteroepitaxial samples, and (ii) enhanced passivation of extended defect-related traps by hydrogen that is liberated from Zn acceptors during the RBA process as determined by deep level transient spectroscopy.
Visible electroluminescence from nanocrystallites of silicon films prepared by plasma enhanced chemical vapor deposition
Authors: Tong Song , Liu Xiang-na , Wang Lu-chun , Yan Feng , Bao Xi-mao
Published: July 2002

We have observed visible electroluminescence (EL) from silicon nanocrystallites which are embedded in a-Si:H films prepared in a plasma enhanced chemical vapor deposition system. The EL spectra are in the range of 500–850 nm with two peaks located at about 630–680 and 730 nm, respectively. We found that the intensity of EL peaks is related closely to the conductivity of the deposited films. The carrier conduction path is discussed in terms of the material structural characteristics, and a tentative explanation of the light emission mechanism is proposed.
Heat to light energy conversion by emitters doped with rare-earth metal ions
Authors: Golovlev V. V. , Winston Chen C. H. , Garrett W. R.
Published: July 2002

A thermodynamical consideration of a selective wavelength emitter for thermophotovoltaic energy generation is presented to express emitter emission properties through spectroscopic parameters of dopant atoms. It is found the heat-light conversion can produce nonequilibrium conditions in the emitter material due to radiative cooling of the atomic excited states. A possible influence of inter- and intra-atomic energy transitions to emitter parameters is discussed.
Extreme ultraviolet line emission at 24.7 nm from Li-like nitrogen plasma produced by a short KrF excimer laser pulse
Authors: Kim N. S. , Djaoui A. , Key M. H. , Neely D. , Preston S. G. , Zepf M. , Smith C. G. , Wark J. S. , Zhang J. , Offenberger A. A.
Published: July 2002

Recently using KrF high power laser (248 nm; 350 fs; 5.0×1016 W/cm2) in the Rutherford Appleton Laboratory an experimental search for recombination extreme ultraviolet (XUV) laser action in Li-like nitrogen ions was performed. To understand the experimental results of line emission at 24.7 nm in the 3d5/2–2p3/2 transition of the Li-like nitrogen ion a simulation was undertaken using a one-dimensional Lagrangian hydrodynamic code. From the simulation results, we confirmed that there was nonlinear dependence of spectral line emission on the gas density which was well matched to the experimental results. Only a six times increase of the 24.7 nm emission intensity was obtained when the plasma length was increased 1000 times from 1 μm as an optically thin case to 1 mm. Also, the spatial profile of the electron density and temperature was obtained and the electron temperature was about 40–50 eV which was too high for the optical field ionization x-ray lasing. We could not find evidence of x-ray laser gain.
Excitonic optical properties in fractional-layer-superlattice wire structures
Authors: Ando Hiroaki , Saito Hisao , Chavez-Pirson Arturo , Gotoh Hideki , Kobayashi Naoki
Published: July 2002

We report on the evolution of the excitonic optical features from two dimensions (2D) to one dimension (1D) in GaAs/AlAs fractional-layer-superlattice (FLS) wire structures. We demonstrate for the first time how the excitonic optical properties continuously evolve from 2D to 1D by introducing the FLS lateral compositional modulation in an AlGaAs quantum well. We also present a theory numerically analyzing the optical absorption properties in the FLS wires. Present theory accurately reproduces the experimental results using the AlAs/GaAs FLS wires and clarifies the main optical features associated with excitons in the intermediate quantum-confinement regime between 1D and 2D.
Optical bistability in symmetrically strained (GaIn)As/Ga(PAs) superlattices
Authors: Bastian G. , von Plessen G. , Feldmann J. , Hader J. , Marschner T. , Stolz W. , Göbel E. O.
Published: July 2002

We have studied the electroabsorptive properties of symmetrically strained (GaIn)As/Ga(PAs) superlattices consisting of 100 periods. Photocurrent measurements at 4 K reveal a pronounced pseudo-blue shift and a Wannier–Stark splitting of the heavy-hole exciton transition. A self-electro-optic effect device has been realized which makes use of the pseudo-blue shift due to the Wannier–Stark localization and of the transparency of the GaAs substrate. The self-electro-optic effect devices show on–off contrast ratios of 2.1 at 77 K and of 1.3 at room temperature.
Evidence of diffusion characteristics of field emission electrons in nanostructuring process on graphite surface
Authors: Wang Chen , Bai Chunli , Li Xiaodong , Shang Guangyi , Lee Imshik , Wang Xinwen , Qiu Xiaohui , Tian Fang
Published: July 2002

The characteristics of the nanostructure on the surface of highly oriented pyrolytic graphite (HOPG) involving field emitted electrons is examined with scanning tunneling microscopy (STM). A simple model based on the continuum electron diffusion is proposed and is compared with the experimental results. It suggests that the process could be associated with the diffusion of electrons at the vicinity of the injection position. It also implies that the characteristics of the as-produced nanometer sized craters could be correlated to the anisotropy degree of the transport properties of HOPG.
Production of Eδ′ center induced by dry heat treatment of nonburied SiO2 films
Authors: Zvanut M. E. , Chen T. L.
Published: July 2002

Electron paramagnetic resonance data demonstrate that Eδ′, a radiation-induced defect consistently found in buried oxide films, can also be generated in nonburied oxides after heat treatment in a sufficiently dry ambient. The center appears in samples heated in either N2 or O2 with moisture content on the order of 1 part per million. The near equality of the number of Eδ′ centers in the N2 and O2 treated samples implies that the presence of O2 does not reduce the number of precursor defects. The results suggest that the center is related to a deficiency of hydrogen-related species in the ambient rather than an O 2 deficiency as has been previously suggested.
Laterally oxidized long wavelength cw vertical-cavity lasers
Authors: Margalit Near M. , Babic Dubravko I. , Streubel Klaus , Mirin Richard P. , Mars Dan E. , Bowers John E. , Hu Evelyn L.
Published: July 2002

We report a novel long wavelength(1.55 μm) vertical cavity laser using a current constricting AlAs oxidation layer. The devices exhibit record low room temperature continuous wave (cw) threshold current(1.3 mA) and highest cw operating temperature reported for long wavelength VCLs(39 °C). Wafer fusion is used to combined seven strain compensated InGaAsP wells between two Al(Ga)As/GaAs quarter wave mirrors.
Depletion-type thin-film transistors with a ferroelectric insulator
Authors: Prins M. W. J. , Zinnemers S. E. , Cillessen J. F. M. , Giesbers J. B.
Published: July 2002

We present a study of electrical characteristics of ferroelectric field-effect transistors made of PbZr0.2Ti0.8O3 and SnO2:Sb thin films. Due to properly chosen semiconductor parameters, the transistor channel can be totally depleted by the ferroelectric charge displacement. The observed remnant on/off ratio of the channel current amounts to 7×103. Pulse response measurements give information on data retention, device speed, and the occurrence of charge injection. The results lead to important design considerations for ferroelectric transistors.
Technique for measurement of the minority carrier mobility with a bipolar junction transistor
Authors: D’Souza S. L. , Melloch M. R. , Lundstrom M. S. , Harmon E. S.
Published: July 2002

A simple technique to measure the minority carrier mobility using a bipolar junction transistor is demonstrated. By fixing the base-emitter voltage, the carrier injection into the base is constant. The collector current is then monitored as a function of a magnetic field applied perpendicular to the current transport across the base. The magnetic field leads to an increase in base transit time and a corresponding decrease in collector current. From the resulting fractional change in collector current, the minority carrier mobility in the base can be determined. For narrow base transistors, quasiballistic transport across the base must be taken into account when determining the bulk minority carrier mobility.
Semiconducting polymer quantum wires
Authors: Chen X. Linda , Jenekhe Samson A.
Published: July 2002

Semiconducting polymer heterostructures with strong two-dimensional quantum confinement of excitons are prepared by self-assembly of two conjugated polymers in binary blends. Exciton confinement effects in the semiconducting polymer quantum wires were observed at room temperature by photoluminescence excitation and photoluminescence spectroscopies and by electric field-induced photoluminescence quenching. Observation of new exciton states, enhanced luminescence, and stability of luminescence at high electric fields (3×106 V/cm) confirmed the one-dimensionality of the excitons in the organic quantum wires.
Tunable negative differential resistance in anti-dot diffraction field effect transistor
Authors: Leburton J.-P. , Lyanda-Geller Yu. B.
Published: July 2002

Quantum diffraction of two-dimensional electrons by a periodic array of nanoscale quantum antidots is considered in the channel of a high mobility field effect transistor. A charge control model within a self-consistent analysis shows that the current characteristics of the new anti-dot diffraction field effect transistor exhibits tunable negative differential resistance and hysteresises which could persist above nitrogen temperature.
Severe gain suppression due to dynamic carrier heating in quantum well lasers
Authors: Grupen Matt , Hess Karl
Published: July 2002

Comparing the results of the quantum well laser diode simulator Minilase-II with modulation responses measured at the University of California, Santa Barbara, we show that electron and polar optical phonons are rapidly heated above equilibrium in conventional injection lasers. This heating essentially follows and counteracts the modulation of the carrier density, leading to degradation of the dynamic laser response even for relatively small changes in carrier temperature. With this in mind, we speculate about the use of tunneling injection to avoid the hot quantum carrier effects intrinsic to conventional injection lasers.
Surfactant effect of atomic H on Si incorporation in GaAs
Authors: Peng Zhongling , Horikoshi Yoshiji
Published: July 2002

The effect of atomic H on Si incorporation in GaAs was studied with different substrate orientations in molecular beam epitaxy process. It is found that with the irradiation of atomic H, the changeover As4/Ga flux ratios for the p- to n-type transition in (111)A and (311)A GaAs are shifted to higher values as if the effective surface As pressure is reduced. The Si-doped (100) GaAs grown at the same time shows n-type conductivity with the electrical activation of almost 100%. Photoluminescence measurements for (311)A samples show great influence by atomic H in the self-compensation region. The irradiation of atomic H helps to lessen the degree of self-compensation in the p-type side but seems to aggravate it in the n-type side of the self-compensation region.
Linearity of unshielded spin-valve sensors
Authors: Sugawara N. , Takiguchi M. , Yaoi T. , Negoro N. , Kagawa K. , Okabe A. , Hayashi K. , Kano H.
Published: July 2002

Linearity of the magnetoresistive (MR) transfer curve for an unshielded spin-valve (SV) sensor was studied. When the NiFe free layer thickness is greater than 5.0 nm, the anisotropic magnetoresistive (AMR) effect in it may overlap the giant magnetoresistive effect of the SV structure and deteriorate the linearity of the sensor response. By using a bilayer of NiFe/NiFeTa as the free layer for suppressing the AMR effect, superior linearity was obtained without a loss of the MR ratio. This new SV structure shows 5.0% as the MR ratio and −32.1 dB as second harmonic distortion, compared to −19.5 dB for a conventional one.
Electronic structure of delta-doped quantum well as a function of temperature
Authors: Gaggero-Sager L. M. , Pérez-Alvarez R.
Published: July 2002

We report on the electronic structure of a delta-doped quantum well of B in Si as a function of temperature from 0 K to room temperature. The calculation is carried out self-consistently in the framework of a Hartree approximation. The energy levels and the occupation number of the discrete states is reported. We conclude that the temperature is not an important factor below 60 K. If temperature is greater than 80 K the level positions are shifted but the changes in carrier concentration are not significant. We give a possible qualitative explanation of the widths of the intersubband absorption peaks.
On the inversion in GaAs metal-insulator-semiconductor heterostructures
Authors: Chen Zhi , Noor. Mohammad S. , Park Dae-Gyu , Morkoç Hadis , Chang Yia-Chung
Published: July 2002

We report the discovery that the [111] strained Si (∼10 Å) as an interlayer between Si3N4 and (111) GaAs may allow the Fermi level to fully scan the GaAs conduction band and induce inversion electrons in GaAs. The band structure calculations indicate that the strained Si on (111) GaAs or (111) AlGaAs has a much wider band gap (0.87 eV) than the strained Si on (001) GaAs (0.34 eV). The energy levels in the quantum well formed by Si3N4/Si/(111)GaAs are almost unconfined and those of Si3N4/Si/Al0.3Ga0.7As/(111)GaAs are confined, but the confined energy level in Si conduction band is ∼0.1 eV higher than the GaAs conduction band. Both structures may induce inversion electrons in GaAs potentially paving the way for the realization of GaAs based n-channel inversion mode metal-insulator-semiconductor transistors.
The tunnel thin film electroluminescent device
Authors: Summers C. J. , Wagner B. K. , Tong W.
Published: July 2002

A new electroluminescent device concept is proposed to achieve low voltage operation. The device is based on a lattice matched semiconductor/insulator/luminescent layer/insulator/semiconductor structure in which, under bias, electrons are injected from the semiconductor into the electroluminescent layer at high energy. This tunnel thin film electroluminescent device is integrable with silicon and suitable for use in very low voltage, high brightness electroluminescent displays. Preliminary results indicate operation as low as 15 V with a peak brightness of 22 fL at 24 V.
Microwave coupling of frequency-locked Josephson junction arrays
Authors: Song Insang , Eom Yongheum , Park Gwangseo , Lee E.-H. , Park S.-J.
Published: July 2002

A high temperature superconducting YBa2Cu3Oy array of five Josephson junctions designed with additional coupling lines has been developed to demonstrate the effects of frequency locking and impedance matching for applications such as oscillators, mixers, and detectors. The Josephson self-radiation power was directly detected by a superheterodyne receiver, and Shapiro steps were also measured. The Josephson self-radiation properties reveal good quality of phase locking and microwave coupling with external circuits. The maximum self-radiation power of our array is about 50 pW which is several ten times higher than that of a single Josephson junction, and its peak point exactly satisfies the Josephson current-voltage relation. The Shapiro-step measurements show that the behavior of current-voltage curve depends on the effective inductance of coupling lines which affects the total impedance of Josephson junction array and microwave coupling. The Josephson oscillation frequency was obtained up to about 880 GHz which is 73% of the maximum available frequency calculated from the characteristic voltage of the Josephson junctions. Experimental results show that this type of Josephson junction array can improve the Josephson self-radiation power and increase the maximum detectable frequency.
Nuclear magnetic resonance using a high temperature superconducting quantum interference device
Authors: Kumar S. , Matthews R. , Haupt S. G. , Lathrop D. K. , Takigawa M. , Rozen J. R. , Brown S. L. , Koch R. H.
Published: July 2002

In this letter, we present results of experiments in which nuclear magnetic resonance (NMR) signals were detected using an untuned pickup coil coupled to a high temperature superconductor (HTS) based superconducting quantum interference device (SQUID). We were able to operate the HTS SQUID in the presence of static fields of up to 500 Gauss and radio frequency fields of up to 6 Gauss. The ability of a HTS SQUID to detect NMR signals opens up the possibility of using a sensitive detector for practical applications involving NMR that require a broad detection bandwidth.
High-speed optical parametric oscillator pumped with an electronically tuned Ti:sapphire laser
Authors: Akagawa K. , Wada S. , Tashiro H.
Published: July 2002

High-speed and random-access tuning of output wavelengths was achieved in an optical parametric oscillator pumped with an electronically tuned Ti:sapphire laser, which was fully under computer control. The signal and idler wavelengths in 90° phase-matched KTiOPO4 were scanned without mechanical rotation of crystals or mirrors. Signal waves in the range from 1.06 to 1.31 μm and idler waves in the range from 2.27 to 2.97 μm accessed in random order by setting the pumping wavelengths between 713 and 923 nm.
Transmission electron microscopy observation of lateral order/disorder structures in (Al)GaInP
Authors: Burkard M. , Geng C. , Mühe A. , Scholz F. , Schweizer H. , Phillipp F.
Published: July 2002

Ion implantation damaging of ordered (Al)GaInP reduces the temperature threshold for thermal disordering from about 850 °C to temperatures below 800 °C, therefore, annealing at 800 °C leads to selective disordering of implanted regions. Dark-field transmission electron microscopy has been used to study the spatial resolution of implantation-induced disordering of CuPtB-ordered GaInP/AlGaInP heterostructures. Lateral order/disorder structures smaller than 200 nm have been realized using implantation masks defined by electron beam lithography. The lateral extension of disordering observed by transmission electron microscopy is in agreement with photoluminescence data and calculations of the lateral implantation straggling.
Dramatic effect of postoxidation annealing on (100) Si/SiO2 roughness
Authors: Chen Xidong , Gibson J. M.
Published: July 2002

We use a plan-view transmission electron microscope technique to unambiguously image the “physical” interface position between Si and furnace grown SiO2 layers. As-grown ∼6-nm-thick (100) oxides have a very high roughness (σ∼10–15 Å), which can be removed by short annealing in an inert gas at a growth temperature of 900 °C.
Large positive magnetoresistance in Cr/Ag/Cr trilayers
Authors: Verbanck G. , Temst K. , Mae K. , Schad R. , Van Bael M. J. , Moshchalkov V. V. , Bruynseraede Y.
Published: July 2002

Large positive magnetoresistance (LPMR) effects have been measured at temperatures T<100 K in epitaxial Cr/Ag/Cr trilayers grown by molecular beam epitaxy. Compared to single Ag films, the magnetoresistance at 4.2 K is enhanced by nearly two orders of magnitude reaching values up to 120% in a field of 8 Tesla. This behavior is related to a drastic modification of the electron scattering at the Ag interfaces due to the presence of the buffer and cap Cr layers. The LPMR curves measured at different temperatures demonstrate a scaling behavior typical for electron transport in two-dimensional systems. The magnitude of the LPMR is a function of temperature and residual resistance ratio and is influenced by the direction of the applied magnetic field.
Analog circuits simulation of communication with chaotic lasers
Authors: de Moraes Renato M. , Oliveira-Neto Luiz de B. , Rios Leite José R.
Published: July 2002

Masked signal communication between two chaotic lasers, described by rate equations, was implemented using analog circuits. Digital modulation of the gain parameter in the master circuit generated the messages. It is shown that there is a level of modulation for which the receiver circuit decodes the signal by on-off synchronization while the Poincaré sections, the first return maps and the time of return maps recovered directly from the master signal could not distinguish the bits. The circuits simulate the dynamics of two optically coupled CO2 lasers with intracavity saturable absorber. The signal appears to be unbreakable in such low dimensional systems because they operate at homoclinic chaos which corresponds to multibranched one-dimensional return maps.
Four-wave mixing in a distributed-feedback laser
Authors: Minch J. , Chang C. S. , Chuang S. L.
Published: July 2002

We present a detailed study of four-wave mixing in a long-wavelength distributed-feedback (DFB) laser for both nearly degenerate and nondegenerate pump-probe detunings. We characterize scaling laws of the power dependence of multiple conjugate waves on the pump and probe power levels for the nearly degenerate case. We also measure the output ratio of the probe and conjugate waves up to a detuning of 500 GHz and report the cavity enhancement of the DFB laser on this output ratio.
Synthesis of (111) oriented diamond thin films by electrophoretic deposition process
Authors: Lee Dong-Gu , Singh Rajiv K.
Published: July 2002

A method for (111) oriented diamond film synthesis has been developed using controlled seeding of micron-sized diamond particles by electrophoresis. Different sizes of diamond powders (0.25 and 5μm) were electrophoretically seeded on silicon substrates using diamond suspensions in organic solvents (acetone, methanol, and ethanol). The seeded samples were then consolidated by the hot filament chemical vapor deposition process. Diamond suspension in acetone was found to be the most suitable for obtaining uniform diamond seeding in electrophoresis. A preferred (111) orientation was obtained for a monolayer of 5 μm seeds. However, when smaller seeds (<1 μm) were used, randomly oriented films were obtained. The surface morphology, crystal orientation, and quality of diamond films were investigated using scanning electron microscopy, x-ray diffractometry, and Raman spectroscopy.
Nucleation barrier of voids and dislocation loops in silicon
Authors: Tan T. Y. , Plekhanov P. , Gösele U. M.
Published: July 2002

We have calculated the nucleation energy barrier of voids and vacancy (V) type dislocation loops in Si under V-supersaturation conditions. The barrier of V-type dislocation loops is higher than that of voids by more than one order of magnitude, with the former exceeding 35 eV at attainable V-supersaturation levels. Thus, voids can be nucleated, but not dislocation loops. This provides an explanation for the observations that, in Si crystals grown under V-supersaturation conditions, voids exist but V-type dislocation loops do not. Voids seriously degrade the Si device gate oxide integrity. It is highly probable that the D-type swirl defects in Si are nanoscopic voids. Our calculated results have also provided information for limiting the formation temperature range of the D-swirl defects to be lower than ∼1050 °C, and the Si V formation enthalpy to be above ∼3.0 eV.
Time-resolved photoluminescence investigations of cubic GaN layers and crystals up to room temperature
Authors: Klann R. , Brandt O. , Yang H. , Grahn H. T. , Ploog K. H.
Published: July 2002

We compare the recombination dynamics of GaN single crystals to that of epitaxial cubic GaN layers on GaAs(001) using picosecond photoluminescence (PL) spectroscopy. At low temperatures, the band-edge PL decay time of the layer is much shorter than that of the crystals, evidencing the importance of nonradiative processes in the case of the layer. However, at room temperature both the emission spectra and their decay times of layer and crystals are almost identical. At 300 K the decay times are short (10 ps) for low excitation density and increase to values of 100 ps at moderate excitation density reflecting the saturation of nonradiative recombination channels.
Selective surface modifications with a scanning tunneling microscope
Authors: Konsek S. L. , Coope R. J. N. , Pearsall T. P. , Tiedje T.
Published: July 2002

A combination scanning tunneling microscope (STM) and scanning electron microscope has been used to selectively pattern and image Si(111) and Si(001) surfaces in a SEM chamber. Both positive and negative STM tip polarities produce marks on the surface with linewidths as small as 20 nm. We have transferred these patterns to the silicon substrate via selective wet chemical etching. We demonstrate a well-defined voltage threshold for patterning at negative tip bias. The modifications are consistent with a model based on hydrogen depassivation and electric field mediated deposition. The physical mechanism for positive tip bias patterning is shown to be different than that for negative bias. At positive bias, the patterning is consistent with selective surface contamination.
InGaAs metal-semiconductor-metal photodetectors with a hybrid combination of transparent and opaque electrodes
Authors: Wohlmuth Walter , Arafa Mohamed , Fay Patrick , Adesida Ilesanmi
Published: July 2002

A metal-semiconductor-metal photodetector (MSMPD) with a hybrid combination of transparent cadmium-tin-oxide and opaque Ti:Au electrodes is proposed and demonstrated. A significant decrease in dark current is obtained by independently engineering the Schottky barrier heights at the anode and cathode. In addition, the use of transparent electrodes enables more light to be coupled into the front-side illuminated MSMPDs thereby increasing the responsivity. For an applied bias of 5 V, these devices exhibited an extremely low dark current density of 21.2 fA/μm2 and a high responsivity of 0.56 A/W to perpendicularly incident 1.31 μm wavelength light.
Direct current and high frequency performance of thin film InP-based tunneling hot electron transfer amplifiers
Authors: Evers N. , Laskar J. , Jokerst N. M. , Moise T. S. , Kao Y.-C.
Published: July 2002

We report the dc and high frequency performance of thin-film InP-based tunneling hot electron transfer amplifiers bonded to a variety of host substrates. The high-frequency device performance is slightly degraded since the InP substrate removal and bonding process for these devices have not yet been optimized. This demonstration represents an important step toward the development of high-frequency, thin-film InP-based electronic devices integrated with conventional Si-based circuit elements.
Application of near-field optics to critical dimension metrology
Authors: Bukofsky S. J. , Selberg S. A. , Grober R. D. , Trautman J. K.
Published: July 2002

Scanned-probe microscopes often have difficulty measuring absolute lengths due to nonlinearities in the piezo elements used to scan the tip. We have developed a method which allows for calibrated scanning of a near-field optical aperture. This method allows for point-by-point correction for piezo nonlinearities such as hysteresis and creep by imaging the light emanating from a near-field probe onto a position-sensitive detector. We have used this principle to fabricate a microscope with 20 nm accuracy in tip position. With further improvements, we believe single nanometer accuracy is possible.
Resonant-cavity InGaAs/InAlGaAs/InP photodetector arrays for wavelength demultiplexing applications
Authors: Hu S. Y. , Ko J. , Coldren L. A.
Published: July 2002

Resonant-cavity photodetector arrays are demonstrated in the InGaAs/InAlAs/InP material system grown by solid-source molecular beam epitaxy. To reduce crosstalk between channels, these devices are designed with a high-Q cavity to obtain narrow-band photoresponse. In addition, a novel double-absorber design has been proposed and implemented to avoid position sensitivity related to the cavity standing wave and eliminate the need for in situ cavity-mode adjustment. Both Schottky and P-i-N diode structures are studied and compared. Eight element arrays with linearly distributed resonant wavelengths spanning over 30 nm are fabricated by using a three-level anodic oxidation process. An experimental channel rejection ratio of 14.5 dB at 4 nm away from the resonant peak has been achieved.
Study of open-core dislocations in GaN films on (0001) sapphire
Authors: Vennéguès P. , Beaumont B. , Vaille M. , Gibart P.
Published: July 2002

This article deals with a plan view and cross section transmission electron microscopy study of columnar defects in GaN films epitaxially grown on sapphire (0001). They are identified as open-core (0001) Burgers vector dislocations. Their behavior along the film thickness is described: it alternates from open core sections (nanopipes) to closed core sections. This alternating behavior is observed in the first 0.5 μm close to the interface with sapphire.
Far-infrared propagation in metal wire microstructures
Authors: Huber T. E. , Luo Laura
Published: July 2002

Densely packed arrays (76% volume fraction) of 10 μm diameter parallel indium wires exhibit an enhanced transmission, of ∼103, relative to an indium foil of equal thickness for far-infrared (k<80 cm−1) propagating along the wire length. The absorption increases as k0.45±0.07 and is explained by the dynamic Maxwell–Garnett model, which includes eddy current dissipation. The effective surface conductivity is depressed fiftyfold with respect to the bulk. The implications for plasmons in metal wire microstructures and for developing simultaneously transmissive and conductive composites are discussed.
Influence of temperature on the optical properties of LiTaO3:Cr
Authors: Ryba-Romanowski W. , Gołab S. , Pisarski W. A. , Dominiak-Dzik G. , Palatnikov M. N. , Sidorov N. V. , Kalinnikov V. T.
Published: July 2002

Optical absorption, photoluminescence, and luminescence lifetimes of Cr3+ in LiTaO3 were studied. It was found that a relatively sharp absorption band assigned previously to the no-phonon A24–E2 transition shifted by 68 cm−1 when temperature decreased from 300 to 5 K. A sharp, four-component emission band recorded at low temperature was assigned on the basis of lifetime measurements to the no-phonon E2–A24 transitions of Cr3+ ions in Li+ and Ta5+ sites. Frequencies of these transitions are lower than that of the sharp absorption band at the same temperature implying that the latter band is not the no-phonon A24–E2 line but it may be associated with a phonon satellite of the T24 state. Strong thermal quenching of broad band luminescence of Cr3+ was observed.
Polarization switching control in vertical-cavity surface-emitting lasers
Authors: Russell Timothy H. , Milster Tom D.
Published: July 2002

Orthogonal polarizations within vertical-cavity surface-emitting lasers (VCSEL) lase at slightly different wavelengths. We describe the use of optical feedback to confine polarization variations to reproducible injection currents. An external cavity is used to select specific wavelengths that reflect back into the VCSEL, hence, changing the cavity Q for the different polarization states. With this control, we can change the polarization state of the laser output.
Analysis of a single-electron decimal adder
Authors: Fahmy Hossam , Ismail K.
Published: July 2002

In this letter, a decimal adder using single electron transistors as a building block is presented. The design is described and the equivalent circuit is extracted, from which the dc performance of the adder is derived. This simple analytical approach is found to be in good agreement with numerical simulation. A detailed sensitivity analysis is performed where the effects of temperature, capacitance, conductance, and background-charge variations are analyzed and the attendant change in device performance is described. This adder needs a number of wires four times less than binary adders and hence alleviates the interconnections problem present in high density circuits.
High quality crystalline ZnO buffer layers on sapphire (001) by pulsed laser deposition for III–V nitrides
Authors: Vispute R. D. , Talyansky V. , Trajanovic Z. , Choopun S. , Downes M. , Sharma R. P. , Venkatesan T. , Woods M. C. , Lareau R. T. , Jones K. A. , Iliadis A. A.
Published: July 2002

ZnO thin films with near perfect crystallinity have been grown epitaxially on sapphire (001) by pulsed laser deposition technique. The ω-rocking curve full width at half-maximum of the ZnO(002) peak for the films grown at 750 °C, oxygen pressure 10−5 Torr was 0.17°. The high degree of crystallinity was confirmed by ion channeling technique providing a minimum Rutherford backscattering yield of 2%–3% in the near-surface region (∼2000 Å). The atomic force microscopy revealed smooth hexagonal faceting of the ZnO films. It has been possible to deposit epitaxial AlN films of thickness 1000 Å on epi-ZnO/sapphire. Excellent crystalline properties of these epi-ZnO/sapphire heterostructures are, thus, promising for lattice-matched substrates for III–V nitride heteroepitaxy and optoelectronics devices.
External gettering by aluminum–silicon alloying observed from carrier recombination at dislocations in float zone silicon wafers
Authors: Martinuzzi S. , Perichaud I. , Simon J. J.
Published: July 2002

The influence of external gettering by a backside aluminum–silicon (Al–Si) alloy on the recombination strength of dislocation arrays in silicon was investigated. These arrays were made by scratching and bending float zone silicon wafers at 750 °C for 6 h. Light beam induced current maps showed that the recombination strength of these defects is drastically reduced at room temperature after the sample have been submitted to an external gettering treatment by means of Al–Si alloying at 900 °C. This can be explained by the removal of metallic impurities introduced by inadvertent contamination from dislocations and by their capture in the aluminum–silicon alloy by means of a segregation induced gettering mechanism.
Low threshold InGaAlAs monolithic vertical cavity bistable device at 1.5 μm wavelength
Authors: Debray J. P. , Lugagne-Delpon E. , Le Roux G. , Oudar J. L. , Quillec M.
Published: July 2002

A monolithic vertical cavity bistable device based on the InGaAlAs system has been grown by low pressure metalorganic vapor phase epitaxy in a single run. First observation of all-optical bistability is reported in this new monolithic structure, with a contrast of 15:1 and a threshold power of less than 300 μW. X-ray diffraction and reflectivity measurements confirmed the high crystallographic and optical qualities of the material. This result shows that the InGaAlAs system is well suited to the fabrication of vertical cavity devices in the optical communication wavelength range.
Infrared distributed Bragg reflectors based on amorphous SiC/SiO2 heterostructures
Authors: Convertino A. , Valentini A. , Giugno P. V. , Cingolani R.
Published: July 2002

Amorphous SiC/SiO2 distributed Bragg reflectors (DBR) deposited by ion beam sputtering at room temperature is reported on in this letter. The DBR consists of only 2.5 pairs and exhibits high peak reflectivity (84%) around ∼1.7 μm with a full width at half maximum of about 1000 nm. The measured reflectivity spectrum is well reproduced by the equivalent layer theory by using the measured refractive indices of SiC and SiO2 and including absorption losses.
Optimization of p-contacts on ZnSe diodes
Authors: Nürnberger J. , Faschinger W. , Schmitt R. , Korn M. , Ehinger M. , Landwehr G.
Published: July 2002

We show that a drastic improvement of the current voltage characteristics of a ZnSe diode can be achieved by lowering the growth temperature of a ZnSe/ZnTe multi-quantum well p contact. A similar trend is observed when the thickness of the ZnTe cap layer on top of the multi-quantum well is reduced. Both observations show that the suppression of interdiffusion plays a dominant role in the formation of Ohmic contacts to p-ZnSe. A comparison between a conventional diode and a diode where the p-ZnSe has been replaced by p-ZnSTe shows that the interdiffusion process affects the ZnSe underneath the contact, and not the multi-quantum well contact itself.