bluuebunny/crossref_metadata_2025 huggingface dataset:
Negative differential resistance in InGaAs/AlAsSb/InGaAs single-barrier heterostructure
Authors: Chen W. K. , Cheng R. H. , Ou J.
Published: July 2002

We have observed negative differential resistance in InP lattice-matched InGaAs/AlAsSb/InGaAs single-barrier tunneling heterostructure. With a 10-nm-thick barrier, the diode exhibits a peak-to-valley current ratio of 4.2 (1.2) and peak current density of 54 (158) A/cm2 at 100 K (300 K).
Voltage responses to optical pulses of unbiased normal and superconducting samples
Authors: Van Vechten D. , Wood K. S. , Fritz G. G. , Horwitz J. S. , Daly G. M. , Thrasher J. B. , Photiadis D. M. , Ding J. , Pinto J. F. , Blamire M. G. , Burnell G. , Gyulamiryan A. L. , Vartanyan V. H. , Akopyan R. B. , Gulian A. M.
Published: July 2002

The direct transformation of the energy of an incident high-energy photon into a measurable potential difference within an absorbing metal is investigated. Experimental evidence is presented that the effect arises from the inherent energy dependence of the electronic density of states, rather than from a simple temperature excursion. The similarities between the results on Al and YBa2Cu3O7 samples indicate that the effect is universal in nature. We assert it may be used as the basis of a fast, energy resolving, individual photon detector for the ultraviolet radiation and x-rays.
Planar anisotropic oxidation of graded AlGaAs for high resolution vertical-wall current and light guiding in laser diodes
Authors: Evans P. W. , Holonyak N.
Published: July 2002

Data are presented on the planar (top–down) oxidation of graded AlxGa1−xAs upper confining layers of quantum well heterostructures in order to realize high resolution square-edge lasers (or waveguides). A model is developed to facilitate composition grading of AlxGa1−xAs for vertical-wall (square corner or edge) planar oxidation at convenient oxidation times and tolerances. A simple AlGaAs–GaAs quantum well laser structure is used to demonstrate the square-wall (square-corner) planar oxidation method.
Subpicosecond carrier lifetime in beryllium-doped InGaAsP grown by He-plasma-assisted molecular beam epitaxy
Authors: Qian Li , Benjamin S. D. , Smith P. W. E. , Robinson B. J. , Thompson D. A.
Published: July 2002

The carrier dynamics and absorption edges of InGaAsP samples grown by He-plasma-assisted molecular beam epitaxy and doped with various concentrations of beryllium are investigated via pump-probe experiments and Fourier transform infrared (FTIR) absorption spectroscopy. Carrier lifetimes from 10 to <1 ps are obtained for samples of increasing doping concentrations. The reduced in carrier lifetimes are attributed to Be compensation of the deep donor levels introduced by the He plasma. The carrier lifetime increases with photogenerated carrier density due to trap saturation. The FTIR results reveal sharp absorption edges in this material for doping concentrations up to 1×1018 cm−3. The fast carrier dynamics and the steep absorption edge make this material very attractive for ultrafast optical switching devices for use in high-speed time-division-multiplexing fiber communication systems.
Bi-directional switching based on semiconductor laser/amplifier with shallow-etched bending ridge waveguide
Authors: Lin Ching-Fuh , Lee Bor-Lin
Published: July 2002

A new type of optical switching device is developed. For a semiconductor laser amplifier with a shallow-etched bending ridge waveguide, the laser beam could propagate along the bending direction or the straight direction. Switching between the two directions is characterized. With the device fabricated on the substrate with two quantum wells of different widths, switching characteristics are found to significantly depend on the spectral separation of the two lasing modes.
A concept for nonvolatile memories
Authors: Shum Kai , Zhou Jianqin , Zhang Wei , Zeng Linfei , Tamargo Maria C.
Published: July 2002

A concept for nonvolatile memories is proposed in which a unique combination of a Schottky junction with tunable barrier height and an adjacent electron potential well is used. A proof-of-concept demonstration is given for such a class of memory devices using ZnCdMgSe/InP heterostructures.
Effect of surface polarity on gallium adsorption on 6H-SiC surfaces
Authors: Li L. , Tindall C. , Hasegawa Y. , Sakurai T.
Published: July 2002

We have performed the first scanning tunneling microscopy (STM) study of gallium adsorption on both the Si-terminated 6H-SiC(0001) (∛×∛) and C-terminated 6H-SiC(0001̄) (2∛×2∛) surfaces. The structure of the Ga terminated 6H-SiC surface showed strong polarity dependence. On the Si-terminated ∛×∛ surface, parallel rows of Ga atoms arranged in three different domains oriented at 120° with respect to each other at 1 ML coverage were observed. On the C-terminated 2∛×2∛ surface, sets of two concentric rings formed an overall 4∛×4∛ reconstruction at 1 ML coverage. We propose a structural model for the 4∛×4∛ structure which explains the STM image.
Photoinduced poling of lead titanate zirconate thin films
Authors: Kholkin A. L. , Setter N.
Published: July 2002

The influence of ultraviolet (UV) illumination on piezoelectric properties is investigated in lead zirconate titanate (PZT) thin films. It is found that the poling procedure is more effective when the film is exposed to a broadband UV light in the presence of a high electric field. Piezoelectric coefficients are increased and aging rates are decreased as compared to poling in dark conditions. Both an internal bias field and a polarization offset are observed in the piezoelectric hysteresis loops. The mechanism of the photoinduced poling effect in PZT films is probably due to electron trapping near the film-electrode interface.
Surface reaction of trisdimethylaminoarsenic on GaAs(001)-c(4×4) and (4×6)
Authors: Cui Jie , Ozeki Masashi , Ohashi Masafumi
Published: July 2002

The surface decomposition of trisdimethylaminoarsenic (TDMAAs) on GaAs (001) has been studied employing supersonic molecular beam scattering. It was found that TDMAAs molecules adsorbed dissociatively on GaAs (001) surfaces at room temperature through a Langmuir adsorption mechanism. The initial Ga-rich (4×6) surface changed into an As-rich c(4×4) surface after the injection of TDMAAs. The species such as dimethylamine and methylmethyleneimine desorbed at the surface temperatures of 150 and 230 °C, respectively, as measured by temperature-programmed desorption (TPD) spectra. The polar-angle dependence of desorption showed that the desorption of species has two maximal intensities, at the directions along surface normal and 60°, respectively.
Self-field ac losses in biaxially aligned Y–Ba–Cu–O tape conductors
Authors: Iijima Y. , Hosaka M. , Sadakata N. , Saitoh T. , Kohno O. , Takeda K.
Published: July 2002

Self-field ac losses were measured by the conventional ac four-probe method in biaxially aligned Y–Ba–Cu–O tapes using polycrystalline Hastelloy tapes with textured yttria-stabilized-zirconia buffer layers. The ac losses increased in proportion to the fourth power of transport current in the high Jc sample, and agreed well with Norris’ equation for thin strip conductors. However, the low Jc sample had rather higher losses than Norris’ prediction, suggesting excessive magnetic flux penetration caused by percolated current paths. The results confirmed Norris’ prediction of the low ac losses for thin strip conductors, and indicated the importance of removing percolated structures of current paths to avoid higher ac losses than the theoretical predictions based on uniform conductors.
Scanning tunneling microscopy of ordered coated cluster layers on graphite
Authors: Durston P. J. , Schmidt J. , Palmer R. E. , Wilcoxon J. P.
Published: July 2002

Surfactant stabilized gold clusters have been deposited on graphite and studied with scanning tunneling microscopy in vacuum. Cluster layers with a superlattice constant of ≈31 Å were found, extending over several micrometers. The clusters form a hexagonal lattice which is ordered over distances of about 100 Å. At low sample biases (<0.75 V) the clusters are not imaged, consistent with a Coulomb blockade effect.
Measuring hystereses of magnetic surfaces by ion scattering
Authors: Schleberger M. , Dirska M. , Manske J. , Närmann A.
Published: July 2002

Scattering of He ions off a magnetic surface results in the emission of circularly polarized light from a triplet transition. From the light polarization the spin polarization of the surface electrons can be deduced. We show that this electron capture spectroscopy (ECS) in the grazing incidence mode is an inherently surface sensitive method capable of measuring magnetic hystereses. The temperature dependence of the signal gives clear evidence that ECS is sensitive to the outermost atomic layer only. The signal follows a Bloch law with a surface prefactor of Asurf=3.33×10−5 K−3/2. The signal as a function of the applied magnetic field results in a hysteresis which is compared to a hysteresis obtained by means of the magneto-optical Kerr effect.
On stress evolution and interaction during electromigration in near bamboo structure lines
Authors: Liu Yongkun , Diefendorf R. J.
Published: July 2002

Electromigration-induced stress in near bamboo structure interconnects has been simulated by the finite element method. The maximum stress at the juncture of polygranular clusters and bamboo segments increases when the stress profile interacts with the line end. The maximum stress at final steady state depends on the relative location of the polygranular cluster in the line under the constant source boundary condition. Under the blocking boundary condition, the steady state stress profile (if it exists) is determined only by current density and total line length and is independent of the microstructure of the line. Finally, the ratio of effective diffusivity of the cluster to that of bamboo segments affects the magnitude of maximum stress at quasi-steady state.
Ultrafast optical probes of excited states in poly(1,4-phenylene vinylene) and poly(2-fluoro-1,4-phenylene vinylene)
Authors: Eom Hyo Soon , Jeoung Sae Chae , Kim Dungho , Lee J. I. , Shim H. K. , Kim C. M. , Yoon C. S. , Lim K. S.
Published: July 2002

We have investigated the photoexcitation dynamics of poly(1,4-phenylene vinylene) (PPV) and poly(2-fluoro-1,4-phenylene vinylene) (PFPV) by using the femtosecond transient absorption spectroscopic technique. It was demonstrated that photoinduced absorption originates from nonemissive indirect polaron pairs which are more efficiently produced in PFPV than in PPV. The decay processes of polaron pairs are mainly contributed by collisional annihilation and internal conversion by phonon emission in PFPV and PPV, respectively. The differences in photoexcitation dynamics between PPV and PFPV are believed to be caused by the strong electronegativity of substituted fluorine atom.
Mass spectrometric determination of the percent dissociation of a high-density chlorine plasma
Authors: Gaddy G. A. , Webb S. F. , Blumenthal Rik
Published: July 2002

Recent computer modeling of high-density chlorine plasmas has indicated that the gas is highly dissociated. This important prediction has only been recently confirmed by optical measurements, which require either external or internal calibration. Unfortunately, these optical techniques cannot readily be applied to the more chemically complex multicomponent plasmas commonly used in real processing. Using a new mass spectrometric method capable of detecting the local concentrations of both atomic and molecular atomic species within a plasma, a percent molecular dissociation of >85% has been measured in an electron cyclotron resonance chlorine plasma at low pressures.
Polarization of an organic monomeric glass
Authors: Karis T. E. , Twieg R. J. , Lundquist P. M. , Castro J. F.
Published: July 2002

A methylene dihydropyridine with a high ground-state dipole moment was investigated to explore the possibility of using it to form an organic monomeric glass “electret” film. Measurements were done in a specially designed test cell. An electric field was applied to a 100-μm-thick film of dihydropyridine while cooling from a melt. The cell potential was recorded as a function of time to study the homocharge and polarization relaxations. The homocharge relaxation time was ≈900 s. The polarization relaxation time was ≈2×105 s in the vicinity of the glass transition temperature. The polarization is linear over a wide range of electric field strength.
The analysis of one-dimensional conductance quantization in V|amorphous-V2O5|V thin film devices
Authors: Yun Eui-Jung , Kim Jwa-Yeon , Walser R. M.
Published: July 2002

We report experiments to determine whether the room temperature one-dimensional conductance quantization (1DCQ) is present at the V|amorphous-V2O5 interphase in as-deposited V|amorphous-V2O5|V devices, or nucleated by a critical event at the threshold voltage VT where ballistic transport was initiated. The fit of the material parameters (barrier width, barrier height, dielectric constant) to the I–V data, the oxide thickness independence of resistance, and variations in the device capacitance with junction area and oxide thickness, suggest that the 1DCQ is associated with the formation of a low dimensional conducting filament through a ∼20 Å-thick VOx interphase layer. The data show that VT is unusually low (∼8 kT/q where T=300 °K), nearly independent of device area and oxide thickness, and has only a small (∼kT/q) statistical variation from device to device. These data suggest that the interphase transition at the voltage VT is reversible, but, were inconclusive in determining whether the interphase transition occurs at a critical field or is induced by thermal effects. The threshold voltage VT also decreases as (T−Tc)n (n∼0.5) going to zero near Tc≈60 °C. An analysis of the data suggests that the interphase transition most likely occurs by a critical event associated with an inelastic transfer of energy ∼kTc/q at the V|a-V2O5 interphase.
Photoinduced hole-doping effect in (Y0.5Ca0.5)Ba2Cu3Oδ films
Authors: Lin C. L. , Lin Y. K. , Chi C. C. , Guan W. Y. , Wu M. K.
Published: July 2002

The persistent photoinduced changes in the critical temperature TC and the normal state conductivity of (Y0.5Ca0.5)Ba2Cu3Oδ thin films are studied. Previously such effects have been observed only in underdoped YBa2Cu3Oδ or YSrxBa2−xCu3Oδ, which always lead to the enhancement of both TC and conductivity. The current system can be doped from the underdoped regime to the overdoped regime by increasing its oxygen content. The photoinduced TC reduction in the overdoped films is observed. The simultaneous enhancement of conductivity is consistent with the interpretation that photoillumination always increases hole concentration in the “123” systems.
Effect of transmission through fiber gratings on semiconductor laser intensity noise
Authors: McAdams Matt , Provenzano Dan , Peral Eva , Marshall W. K. , Yariv Amnon
Published: July 2002

The effect of transmission through a fiber Bragg grating on the relative intensity noise of semiconductor laser light is investigated. We first present a model of the grating as a linear frequency discriminator that exchanges correlated power between frequency noise and intensity noise caused by spontaneous emission. This correctly explains observed increases in intensity noise of up to 30 dB at low frequencies, obeying an inverse-square frequency dependence. Next, we show that there exist conditions under which a grating can reduce intensity noise and that these are determined by the phase relationship between correlated intensity and frequency fluctuations. Finally, we demonstrate a 2 dB reduction of intensity noise at frequencies up to 15 GHz, and present a numerical calculation based on the complex transmittance of the grating that correctly describes the effect of grating dispersion.
Localized highly stable electrical passivation of the thermal oxide on nonplanar polycrystalline silicon
Authors: Mattausch Hans Jürgen , Kerber Martin , Allinger Robert , Braun Helga
Published: July 2002

A substantial reduction of leakage currents during voltage sweeps from 0 to +20 V is observed for overlap capacitors with polycrystalline silicon (polysilicon) capacitor plates and thermal SiO2 as an insulator. The responsible electrical passivation has a high thermal stability and is localized at the sharp corner, where the upper polysilicon wraps over (overlaps) the lower polysilicon. From baking and recycling electrical-sweep experiments, we conclude that: (1) stability of the localized electrical passivation comes from electrons trapped at deep neutral oxide traps, (2) more than one trap binding energy is involved, and (3) thermal activation energies for electron detrapping, with estimated magnitudes up to 1.3 eV, are about three times larger than previously reported.
Intergranular transport properties in c-axis oriented YBa2Cu3Oy polycrystalline films
Authors: Ishii H. , Shingo S. , Harada S. , Hirano S. , Iwata Y. , Hara T. , Yoshida N. , Fujino K. , Sato K.
Published: July 2002

The current–voltage (I–V) characteristics and the resistive transition under magnetic field were extensively investigated on c-axis oriented YBCO polycrystalline films with a different amount of an in-plane grain alignment. All the parameters deduced from the scaling analyses in the intergranular region along with the vortex-glass-to-liquid transition indicate that the intergranular current transport is not via weak links but is due to strongly coupled channels regardless of a degree of an in-plane grain alignment.
Effect of diamond film quality on tungsten related photoluminescence peaks
Authors: Lal S. , Liu S. , Gangopadhyay S. , Haque M. S. , Naseem H. A.
Published: July 2002

We have studied a series of polycrystalline diamond films of various qualities grown by arc jet chemical vapor deposition method. We have used continuous wave photoluminescence (PL) to study the intensity, width and emission energy of defects, and study the correlation of these parameters to the quality of the diamond films. Recently, it has been proposed that impurities are more easily incorporated into highly defective films, and thus the defect PL may be used to determine impurity concentration in the films. We find that the intensity of the PL from the 1.735 eV center is easily affected by the quality and may be quenched in poor quality samples, and thus it is not an appropriate marker for defect concentration. We find the center with an emission line at 1.805 eV to be a better candidate for being used as a marker for defect concentration. This center is observed in different quality samples, and its line width and emission energy are not affected by film quality.
Excitation of edge magnetoplasmons in a two-dimensional electron gas by inductive coupling
Authors: Deviatov E. V. , Dolgopolov V. T. , Williams F. I. B. , Jager B. , Lorke A. , Kotthaus J. P. , Gossard A. C.
Published: July 2002

We apply a novel inductive coupling technique to study edge magnetoplasmons (EMP) in two-dimensional electron gases in the time domain. This technique is mostly appropriated for measurements on gated samples in the low-magnetic-field limit. We obtain time delay, amplitude, and broadening of the EMP as a function of the magnetic field.
Boron implantation doping of diamond
Authors: Ittermann B. , Bharuth-Ram K. , Metzner H. , Füllgrabe M. , Heemeier M. , Kroll F. , Mai F. , Marbach K. , Meier P. , Peters D. , Thieß H. , Ackermann H. , Stöckmann H.-J. , Sellschop J. P. F.
Published: July 2002

Spin polarized B12 nuclei were produced in a B11(d,p)12B nuclear reaction and recoil implanted into a type Ib diamond sample at doses below 1011 cm−2. β-radiation detected nuclear magnetic resonance spectra were measured directly after implantation at sample temperatures ranging from 300 to 800 K. The polarization asymmetry at the Larmor resonance yielded fractions of boron ions at sites of full tetrahedral symmetry of 12(1)% at 300 K, increasing to 17(2)% at 800 K. It is argued that these boron atoms are incorporated substitutionally by direct replacement collisions during the implantation process. The resonance spectra also showed additional boron at low-symmetry sites.
AlGaN nanoparticle/polymer composite: Synthesis, optical, and structural characterization
Authors: Benaissa M. , Gonsalves K. E. , Rangarajan S. P.
Published: July 2002

The aluminum gallium nitride (AlGaN) alloy is uniquely suited for fabricating optoelectronic devices in the ultraviolet and visible bands of the spectrum. Its synthesis in a nanometer scale may potentially open the way for applications such as tunable optoelectronic devices. Presently, results concerning the synthesis and microstructural and optical characterization of nanometer-sized AlGaN imbedded in a poly-methylmethacrylate (PMMA) matrix are reported. Our optical measurement showed that the AlGaN/PMMA nanoparticle/polymer composite efficiently emits in the violet-blue region, while the microstructural characterization confirms the formation of defect-free zinc blende AlGaN nanoparticles.
Lasing and radiation-mode dynamics in a Van de Graaff accelerator–free-electron laser with an internal cavity
Authors: Abramovich A. , Arensburg A. , Chairman D. , Eichenbaum A. , Draznin M. , Gover A. , Kleinman H. , Merhasin I. , Pinhasi Y. , Sokolowski J. S. , Yakover Y. M. , Cohen M. , Levin L. A. , Shahal O. , Rosenberg A. , Schnitzer I. , Shiloh J.
Published: July 2002

The lasing of a Van de Graaff electrostatic accelerator–free-electron laser (EA–FEL) with an internal cavity is reported. An EA–FEL employing an internal cavity is a FEL configuration that has a potential to operate at high average power, high frequency, and possibly in a continuous wave (cw) mode. The initial lasing provided a pulsed radiation power of 1 kW at 100.5 GHz frequency. The FEL operated with a 1.4 A, 1.4 MeV electron beam in a recirculation (depressed collector) configuration. It utilizes a high quality (Q≈30 000) Talbot effect resonator and a Halbach-type wiggler placed internally in the center of the accelerator tank. Nonlinear features of the oscillation power buildup and decay near saturation and mode hopping were observed and are interpreted.
Identification of isolation-edge related random telegraph signals in submicron silicon metal–oxide–semiconductor field-effect transistors
Authors: Lukyanchikova N. , Petrichuk M. V. , Garbar N. , Simoen E. , Claeys C.
Published: July 2002

In this letter, evidence is given for a new class of random telegraph signals (RTSs) in submicron n-metal–oxide–semiconductor field-effect transistors (n-MOSFETs). These two-level fluctuations not only occur when the MOSFET is biased in linear operation but also when it is operated in the source or drain-substrate diode mode. A detailed investigation of the RTS parameters, i.e., the amplitude, the emission, and the capture time constants, reveal a close correlation with the current through the forward biased drain- (or source-) substrate diode. At the same time, from the substrate bias dependence of the trap characteristics, it is inferred that it behaves like a near-interface oxide trap. From this, it is concluded that the most likely position is along the channel width perimeter, at the isolation edges of the transistors and close to the source or drain junction.
Analysis of voltage noise in forward-biased silicon bipolar homojunctions: Low- and high-injection regimes
Authors: Martı́n M. J. , Pardo D. , Velázquez J. E.
Published: July 2002

An ensemble Monte Carlo (EMC) simulator has been used to study bipolar transport in silicon p+n and pn+ homojunctions under forward-bias conditions, both in low- and high-injection regimes. The study focuses on a microscopic analysis of voltage fluctuations in such devices. The method of voltage-noise operation mode provides spatial analysis of the spectral density of voltage fluctuations under constant-current conditions. In the low-frequency range, the presence of shot, thermal, and excess noise due to hot carriers was found when the bias conditions were modified. Also, the EMC method permits ready evaluation of the noise equivalent temperature in both structures from the observed voltage fluctuations.
Langmuir probe analysis of distributed electron cyclotron resonance silicon nitride deposition plasma
Authors: Delmotte F. , Hugon M. C. , Agius B. , Pointu A. M. , Teodoru S.
Published: July 2002

Single and double Langmuir probe analyses have been realized in the wafer region of an electron cyclotron resonance reactor in its distributed configuration. Results in nitrogen gas have shown unambiguously that two electron populations exist in this region: one with low temperature (about 1–2eV) and high density and the second with higher temperature (about 8 eV) and lower density. Measurements in silicon nitride deposition plasma (nitrogen and silane gases) have been successfully realized and have shown that these two populations are also present. Finally, we try to correlate the plasma parameters (electron temperatures and densities and ions’ energy) to the deposited film parameters (deposition rate and refractive index).
Two-peak electroluminescence of porous silicon in persulphate solution
Authors: Wang R. Q. , Li J. J. , Cai S. M. , Liu Z. F. , Zhang S. L.
Published: July 2002

A large blue shift of electroluminescence (EL) was achieved from oxidized n-type porous silicon (PS) in a persulphate solution under cathodic polarization. The two-peak phenomenon observed in the EL spectrum suggests that there are two types of luminescent centers located in the nanoscale silicon particles and at the surface of the oxidized PS layer, respectively. It is found that only the low-energy peak having luminescent centers in nanoscale silicon particles can be tuned by voltage, supporting the quantum confinement model.
The spin-polarized scanning electron microscope observation of 0.1 μm marks recorded by magnetic field modulation on a magneto-optical recording disk
Authors: Kohashi Teruo , Matsuyama Hideo , Koike Kazuyuki , Murakami Yoshiteru , Tanaka Yasuhito , Awano Hiroyuki
Published: July 2002

The magneto-optically recorded marks with magnetic field modulation method were studied using spin-polarized scanning electron microscopy. We confirmed that marks with as short a length as 0.1 μm could be written repeatedly even with laser spot sizes about 1.2 μm. This mark length is less than 16 that of present commercial products.
Superior two-dimensional electron gas on (511)A GaAs
Authors: Shtrikman Hadas , Soibel A. , Meirav U.
Published: July 2002

We present a comparative study of two-dimensional electron gas structures, which were grown on (511)A GaAs substrates and on conventional (100) GaAs substrates. The study included both normal interface and inverted interface structures. The (511)A presents consistently and substantially improved transport properties, whose origin can be traced to the growth dynamics of these surfaces. We conclude that (511)A GaAs promises to serve as an alternative and superior platform for realizing various n-type GaAs structures.
Critical thickness of Zn1−xCdxSe/ZnSe heterostructures grown on relaxed ZnSe buffer layers on bare GaAs substrates
Authors: Tournié E. , Ongaretto C. , Laügt M. , Faurie J.-P.
Published: July 2002

We study through high-resolution x-ray diffraction (HRXRD) and photoluminescence spectroscopy a series of Zn1−xCdxSe/ZnSe multi-quantum-well heterostructures grown by molecular-beam epitaxy on relaxed ZnSe buffer layers, themselves grown on bare GaAs substrates. We show that HRXRD experiments combined with simulations allow one to accurately assess the strain state of the heterostructures which appear to follow closely the Matthews and Blakeslee model [J. Cryst. Growth 27, 118 (1974)].
Coupled maximum entropy: Monte Carlo Estimation of microwave, millimeter-wave and submillimeter-wave spectrum of velocity fluctuations in GaAs
Authors: Pantoja Jose Miguel Miranda , Franco Jose Luis Sebastián , San Martin Sagrario Muñoz
Published: July 2002

The maximum entropy method is presented in this letter as a highly interesting procedure for the investigation of high frequency noise properties of bulk semiconductors and electron devices at microscopic level. A Monte Carlo simulation of the hot electron velocity fluctuations in bulk GaAs has been performed to illustrate the efficiency and usefulness of this procedure. Comparisons with the most popular techniques presently used in Monte Carlo simulations of noise have also been performed.
Alignment of misfit dislocations in the In0.52Al0.48As/InxGa1−xAs/In0.52Al0.48As/InP heterostructure
Authors: Wu J. , Li H. X. , Fan T. W. , Wang Z. G.
Published: July 2002

It was observed with transmission electron microscopy in the In0.52Al0.48As/InxGa1−xAs/In0.52Al0.48As system grown on the (001) InP substrate that misfit dislocation lines deviate 〈110〉 directions at an angle with its value depending on the gallium content. Such an abnormal alignment of misfit dislocations is explained in terms of an alloy effect on the formation of single jogs on misfit dislocations in the interface between the III–V ternary compounds.
Raman effect based modulator for high power fiber lasers
Authors: Torres I. , Starodumov A. N. , Barmenkov Yu. O. , Zenteno L. A. , Gavrilovic P.
Published: July 2002

We demonstrate experimentally an all-fiber nonlinear optical modulator which can find application for high power (greater than 20 W) single-mode fiber lasers. Stimulated Raman scattering is used to transfer the amplitude modulation from a low-power signal beam at the Stokes frequency onto a high-power beam. Efficient modulation of 1064 nm pump radiation by 100 ps Stokes pulses is demonstrated in a highly Ge-doped fiber.
Effect of column III vacancy on arsenic precipitation in low-temperature grown III–V arsenides
Authors: Chang M. N. , Pan J.-W. , Chyi J.-I. , Hsieh K. C. , Nee T.-E.
Published: July 2002

Separately grown p-type, intrinsic, and n-type GaAs at low temperatures as well as a combined p-i-n structure have been used to study the formation of As precipitates upon annealing at 800 °C. For the separate structures, least precipitates have been noticed in the n-type material. In contrast, the highest density of precipitates appears in the n region for the p-i-n structure. In addition, an obvious band depleted of precipitates, exists in the intrinsic region near the n-i interface. A general vacancy model, including Fermi level effect and crystal bonding strength (thermodynamic factor), has been developed to explain the current results as well as to predict As precipitation in various low temperature grown III–V heterostructures.
Magnetic expansion readout of 0.2 μm packed domains on a magneto-optical disk with an in-plane magnetized readout layer
Authors: Ying Xiao , Shimazaki Kastusuke , Awano Hiroyuki , Yoshihiro Masahumi , Watanabe Hitoshi , Ohta Norio , Rao K. V.
Published: July 2002

We have investigated an in-plane magnetized readout-layer-based magnetic domain expansion phenomenon in a magneto-optical (MO) medium. Very high-density 0.2 μm packed domains are expanded up to three times the readout signal level in comparison with the conventional approach of applying alternative external field in the readout process. This result suggests that more than 10 Gbits/in.Reference 2 MO recording density may be achieved by implementing the domain expansion technique, using even the currently available 680 nm laser and numerical aperture of 0.55.
Acoustic focusing associated with excimer laser ablation of the cornea
Authors: Siano S. , Pini R. , Rossi F. , Salimbeni R. , Gobbi P. G.
Published: July 2002

Focusing, as well as diffraction effects experienced by the stress wave produced by the argon–fluoride excimer laser ablation of corneal tissue have been studied in artificial and real eye samples. The evolution of the laser-induced acoustic front was imaged by means of fast shadowgraphy in an artificial eye model, while the absolute temporal profile of the pressure transient along the optical axis was directly measured in enucleated porcine eyes by a needle hydrophone inserted into the eyeball. Observations pointed out that the finite size of the acoustic source gave rise to diffraction effects during propagation, as the development of a negative tensile phase in the pulse shape, while the spherical shape of the acoustic source produced focusing of the wave front, causing pressure enhancements up to a factor of 3 in real eyes. The implications to surgical laser procedures as photorefractive keratectomy are discussed.
Bias independent heavy- and light-hole degeneracy in InGaAs/InGaAsP quantum wells
Authors: Shen H. , Pamulapati J. , Zhou W. , Dutta M. , Johnson F. G.
Published: July 2002

We present a type of strained semiconductor quantum-well structure that exhibits bias-independent heavy- and light-hole degeneracy. This effect is achieved by inserting thin layers of highly strained material in an unstrained quantum well. By adjusting the thickness and the position of the highly tensile strained layers, the quantum confined Stark effect for the heavy and light holes can be engineered separately to control the bias dependent polarization properties. Experimental results on such a structure agree well with the theory. These unique bias-dependent polarization properties have important applications in optoelectronic devices when specific polarization properties are required.
Enhancement of intersubband transition energies in GaAs quantum wells by Si delta doping of high concentration
Authors: Sasagawa R. , Sugawara H. , Ohno Y. , Nakajima H. , Tsujino S. , Akiyama H. , Sakaki H.
Published: July 2002

Intersubband light absorption measurements have been performed on a series of GaAs/AlAs quantum wells with heavy delta doping of Si atoms in the range 9.0×1011–6.5×1012 cm−2. The increase of intersubband transition energy by as much as 38 meV has been observed, and attributed to the deepening of the V-shaped potential by the Si layer and to the depolarization effects.
Collinear mirage effect measurement of the thermal diffusivity in Ferronematics
Authors: Shibli S. M. , Dantas A. L. L. , Walton D.
Published: July 2002

Thermal diffusivity results obtained for a lyotropic nematic liquid crystal sample doped with different amounts of ferrofluid (ferronematics) are reported. The collinear mirage technique was used for measurements along axes parallel and perpendicular to the director of this anisotropic material. The results show that as the ferrofluid concentration increases the thermal diffusivity decreases, leading to values even lower than those already reported for plain lyotropic nematic liquid crystals. The ratio of the two diffusivities increases as the ferrofluid concentration increases, reaching the exact value theoretically expected, though not achieved experimentally, for plain lyotropic nematic liquid crystals.
Transition from edge to vertical cavity operation of tunnel contact AlGaAs–GaAs–InGaAs quantum well heterostructure lasers
Authors: Wierer J. J. , Evans P. W. , Holonyak N.
Published: July 2002

Al x Ga 1−x As–GaAs–In y Ga 1−y As quantum well heterostructure lasers with thin sharply defined cavities that operate longitudinally or vertically are demonstrated. Longitudinally, the cavity is defined by cleaving (edge emission) while vertical definition is provided by a lower AlxOy/GaAs distributed Bragg reflector (DBR) and an upper SiO2/Si DBR that form a resonant structure. A reverse-biased tunnel contact junction provides lateral electron current to support hole injection through a native-oxide-defined aperture. This ultrathin cavity configuration produces low threshold high efficiency (η∼91%, L=140 μm) edge emission (longitudinal operation) in the case of long lasers (L≳90 μm), and vertical emission for shorter lasers (L≲65 μm). The transition from longitudinal to vertical laser operation as a function of cavity length, L, is demonstrated.
Accurate measurement of phase shift in electron holography
Authors: Duan X. F. , Gao M. , Peng L.-M.
Published: July 2002

A method is proposed for the accurate measurement of phase shift in electron holography. The method is based on the use of moiré fringes resulting from the subtraction of a null electron hologram by a real object hologram recorded under slightly different experimental conditions. This method does not require any optical or digital reconstruction of the electron hologram, and is shown to be highly sensitive to the phase shift of the electron wave passing through an object. Using experimental results obtained from a single particle of silicon, we demonstrate that the sensitivity of this method to phase shift may easily be amplified by more than 11 times compared with the conventional method using an ordinary electron hologram.
In situ determination of the surface roughness of diamond films using optical pyrometry
Authors: Akkerman Z. L. , Song Y. , Yin Z. , Smith F. W. , Gat Roy
Published: July 2002

The initial growth of diamond films in a microwave plasma reactor has been studied using in situ two-color infrared pyrometry. Analysis of the observed oscillations of the apparent temperature has yielded the substrate temperature and also the instantaneous film growth rate and rms surface roughness σ. Two distinct regimes of growth have been clearly identified: an initial period of rapidly increasing σ before the diamond nuclei coalesce, followed by a slower increase of σ with thickness as the continuous film grows further. The differing initial roughnesses and emissivities of Si and Mo substrates have been shown to have important effects on the growth of diamond.
Tayloring of the optical properties by symmetry modification of substituted quaterthiophene single crystals
Authors: Gigli G. , Rinaldi R. , Lomascolo M. , Cingolani R. , Barbarella G. , Zambianchi M.
Published: July 2002

We report an optical study of polymorphic single crystals of a polysubstituted α-conjugated quaterthiophene. The crystals exhibit two crystalline symmetries (monoclinic and triclinic) with different energy gaps and lifetimes of the elementary excitations. Their optical properties are correlated to the molecular structure, showing that the functionalization process determines an intrinsic tuning of the crystal properties.
Laser generation of ultrasound using a modulated continuous wave laser diode
Authors: Pierce S. G. , Culshaw B. , Shan Q.
Published: July 2002

A modulated continuous wave diode laser was used to generate ultrasonic Lamb waves in a thin steel plate. No surface damage was evident on the sample, a feature due to the low power density of the acoustic source in contrast to the high power pulsed laser systems usually employed for laser-ultrasound generation. The Lamb waves were monitored using a surface bonded optical fiber interferometer whose output was correlated with the pseudorandom binary sequence used to modulate the laser diode. In this fashion, it was possible to record a time domain history of the ultrasonic propagation in the sample.
X-ray characterization of GaN/AlGaN multiple quantum wells for ultraviolet laser diodes
Authors: Korakakis D. , Ludwig K. F. , Moustakas T. D.
Published: July 2002

GaN/Al 0.20 Ga 0.80 N (50 Å/50 Å) multiple quantum wells (MQW) with 15 periods were grown on (0001) sapphire substrates by molecular beam epitaxy and evaluated by x-ray diffraction. To simulate an ultraviolet laser diode structure, the substrate was coated first with n-GaN as the bottom contact layer and n-Al0.25Ga0.75N as the corresponding cladding layer. The crystal structure of this system was investigated by studying the reciprocal lattice map of off-axis diffraction peaks as well as the θ–2θ pattern around the (0002) reflection. The MQW was found to be coherent and has the a-lattice parameter of the underlying Al0.25Ga0.75N. The good agreement between experimental and theoretical data in the relative intensity of up to third-order satellite peaks supports that the interfaces of the MQW are abrupt, and thus, interdiffusion of Ga and Al atoms at the growth temperature was negligible.
Electron paramagnetic resonance and photoluminescence studies of chromium in SrS
Authors: Kreissl J. , Troppenz U. , Hüttl B. , Schrottke L. , Fouassier C.
Published: July 2002

Isotropic features with hyperfine structures in electron paramagnetic resonance spectra of SrS powder phosphors, which reflect the abundance of the natural Cr isotopes, are attributed to the isolated Cr impurity. The isotropy, which is typical for a A24 ground state of a 3d3 ion in an octahedral crystal field, and the g value of 1.9795 verify that Cr is observed in its charged donor state Cr3+. The observation of a broad photoluminescence band with a maximum at 900 nm, which can be attributed to an internal Cr3+ transition, supports the identification of the impurity as Cr3+.
Electrical properties of a W-B-N Schottky contact to GaAs
Authors: Kim Yong Tae , Woo Lee Chang , Joon Kim Dong
Published: July 2002

We have achieved the highest barrier height (0.90 eV) with a Schottky contact scheme of W-B-N/GaAs after rapid thermal annealing (RTA) at 700 °C, and even after the RTA at 900 °C, its barrier height (0.77 eV) is relatively higher than those of W (0.55 eV) and W-N/GaAs Schottky contacts (0.68 eV). Deep level transient spectroscopy and carrier density profile measurements show that the higher barrier height and lower leakage current of the W-B-N/GaAs diode are due to the W-B-N film that suppresses changes of the surface carrier and EL2 trap concentrations after the RTA.
Thermal equilibrium of Ge-related defects in a GeO2-SiO2 glass
Authors: Takahashi Masahide , Fujiwara Takumi , Kawachi Taiji , Ikushima Akira J.
Published: July 2002

In a 15.7 GeO2⋅84.3 SiO2 glass prepared by a vapor axial deposition method, optical absorptions at 4.92 and 5.08 eV were observed from 300 to 600 K. The results were then compared with electron spin resonance (ESR) measurement using the same samples. The absorption at 4.92 eV was found to increase with increasing temperature, while the optical absorption at 5.08 eV decreased with increasing temperature. These changes of optical absorption indicate that the concentration of neutral oxygen monovacancy is reduced at higher temperatures. The changes were quite reversible with the temperature. Concentration of Ge E′ center, estimated from ESR, increased with increasing temperature, which is in contrast with the decrease of neutral oxygen monovacancy. The present result strongly suggests the thermal equilibrium reaction between neutral oxygen monovacancy and Ge E′ center.
Experimental evidence for the transition of different indirect tunneling processes in p-HgCdTe
Authors: Huang He , Tong Feiming , Tang Dingyuan
Published: July 2002

We present an experimental observation of the transition of different indirect tunnelling processes in p-type HgCdTe. The results demonstrate that the indirect tunnel currents via Shockley–Read–Hall traps exhibit a transition from thermally assisted tunneling to two-step indirect tunneling over a temperature range of 25–200 K, which enables independent measurements to be made on the two processes. A 55 meV trap level which contributes strongly to the indirect tunneling mechanisms was estimated by measuring the activation energy.
Leakage current and dielectric breakdown behavior in annealed SiO2 aerogel films
Authors: Jo Moon-Ho , Park Hyung-Ho
Published: July 2002

Leakage current and dielectric breakdown behavior in annealed SiO2 aerogel films for intermetal dielectric applications was investigated in a metal–insulator–semiconductor structure. SiO2 aerogel films with porosities of 70% exhibited Poole–Frenkel conduction both before and after annealing. After annealing at 450 and 700 °C, the leakage current density improved over the current range of the applied field. This behavior was characterized by different chemical evolutions in each annealing step, beginning with the removal of residual organics up to 450 °C and then with the removal of residual surface hydroxyl, along with subsequent microstructural changes, up to 700 °C. Except in the few initial failure modes, intrinsic dielectric breakdown was not observed up to 1 MV/cm for as-deposited or 450 °C annealed films. However, in the case of the 700 °C annealed film, the dielectric breakdown strength was degraded. It was inferred that this early breakdown in 700 °C annealed film was caused by a randomly enhanced electric field at the irregular asperity of the rough interface. This was confirmed by investigation of the interface roughness between the electrode and the film.
Temperature dependence of a high-Tc single-flux-quantum logic gate up to 50 K
Authors: Saitoh Kazuo , Utagawa Tadashi , Enomoto Youichi
Published: July 2002

Basic characteristics of a simple single-flux-quantum (SFQ) logic gate using high-Tc material and Josephson junction (NdBa2Cu3O7−δ and focused ion beam junction) have been investigated. The logic gate consists of an rf-superconducting quantum interference device (rf-SQUID) and a dc-SQUID. In the logic gate, elementary SFQ logic operations, such as generating SFQ (dc/SFQ) and providing simultaneous readout (SFQ/dc), have been confirmed up to 50 K. The temperature dependencies of the output voltage level and the critical current-normal resistance (IcRn) product were compared, and the decreasing tendency of the output voltage level for increasing temperature was found to be more rapid than that of the IcRn product.
Submicron selective organometallic vapor phase epitaxy growth using tunable deep UV excitation
Authors: Wankerl A. , Emerson D. T. , Shealy J. R.
Published: July 2002

We report on selective area growth of AlGaAs from trimethylgallium, trimethylaluminum, and arsine by UV laser stimulated organometallic vapor phase epitaxy. Using a wavelength tunable pulsed laser system, we investigated the stimulation mechanism and wavelength dependence of the growth enhancement in the range from 235 to 255 nm. Adlayer photolysis constitutes the dominant stimulation mechanism at these wavelengths, since the observation of laser-induced, submicron periodic surface ripples restricts the growth enhancement to a surface process and laser enhanced pyrolysis can be excluded by temperature simulations. We observe an abrupt wavelength edge at 252 nm, below which the stimulation rate is constant and above which the growth enhancement ceases. The growth contrast under our experimental conditions is 3.2:1 and the selectively grown AlGaAs is of optical quality.
Theoretical study of a GaAs lateral p-i-n photodetector
Authors: Haralson J. N. , Parks J. W. , Brennan K. F.
Published: July 2002

We present a numerical study of a high speed GaAs lateral p-i-n (LPIN) photodiode. The LPIN is a planar structure composed of interdigitated p+ and n+ wells. A metal–semiconductor–metal (MSM) photodiode with identical finger spacing and geometry is simulated for comparison. When pulsed with an 827 nm optical source at 0.68 mW/cm2, the lateral p-i-n exhibited improved frequency performance and responsivity compared to the MSM. The dark current and capacitance are similar in magnitude between the two devices. Based on these results, it is concluded that a lateral p-i-n can be an attractive alternative to standard MSM photodetectors.
Localized excitonic transitions in a ZnSe-Zn0.75Cd0.25Se double-superlattice grown by molecular beam epitaxy
Authors: Guan Z. P. , Kuang G. K. , Griebl E. , Kastner M. , Gebhardt W.
Published: July 2002

A group of well-defined exciton transitions from the localized states were observed in ZnSe-Zn0.75Cd0.25Se double-superlattice structure. The photoluminescence and photoreflectance have been employed to study the subband transitions at low temperatures. At 1.4 K, except the two ground states and two higher subbands of n=1 light-hole and n=2 heavy-hole excitonic transitions, other four peaks (A, B, C, and D) also were observed in wider-well superlattice. Those peaks were attributed to the excitonic transitions from n=2 heavy-hole subband due to the fluctuation of well-barrier interface. Another localized excitonic transition from narrower-well superlattice appeared as increasing the modulated intensity in photoreflectance spectra.