bluuebunny/crossref_metadata_2025 huggingface dataset:
Light emission from wavelength-tunable microcavities
Authors: Becker H. , Friend R. H. , Wilkinson T. D.
Published: July 2002

We report a novel microcavity design that allows the control in wavelength of the resonant modes of a microcavity operating in the visible spectrum. We have been able to shift the modes by up to 56 nm. The device is comprised of a thin film of a fluorescent semiconducting polymer combined with an electrically switchable liquid crystal layer, which are sandwiched between the two cavity mirrors. This structure serves as a tool for further experimental studies of the properties of microcavities and also has considerable technological potential, providing, for example, an efficient wavelength converter or tunable light source.
Magnetic properties of Fe films epitaxially grown on Cr/GaAs(100) by dc magnetron sputtering
Authors: Li Biao , Fermin J. R. , Azevedo Antonio , de Aguiar F. M. , Rezende S. M.
Published: July 2002

We report on the growth of single-crystal Fe films by magnetron sputtering onto GaAs substrates. In order to establish the epitaxial orientation with the substrate a 100 Å Cr buffer layer was rf sputtered. The crystalline and magnetic properties were studied by x-ray diffraction, ferromagnetic resonance, and Kerr effect magnetometry techniques. The θ-2θ x-ray measurements show that only the Fe (200) peak is present, and the rocking curve shows a full width half maximum of 2°. Ferromagnetic resonance lines exhibit a line width of about 30 Oe, and the in-plane resonance field as a function of the azimuth angle presents a fourfold symmetry with no induced anisotropy. The in-plane hard- and easy-axis magneto-optical hysteresis loop traces are consistent with the ferromagnetic resonance results.
Influence of oxygen plasma treatments on the structural properties of c-Si
Authors: Nickel N. H. , Sieber I.
Published: July 2002

The effects of hydrogen and oxygen plasma treatments on the structural properties of n-type c-Si were examined. Specimens were exposed to either an oxygen or a hydrogen electron-cyclotron-resonance plasma in a temperature range of 240–385 °C. Hydrogenations performed at low temperatures (<300 °C) introduced platelets. On the other hand, oxygen plasma treatments did not result in the formation of platelets. Analysis of O and H concentration depth profiles, measured by secondary-ion-mass spectrometry (SIMS), reveal that O and H migrate with a similar diffusion coefficient of Deff≈1012 cm2 s−1. Moreover, the O concentration exceeds the H concentration by roughly a factor of 2.5. This suggests that one H atom and 2–3 O atoms migrate as a cluster. Furthermore, evidence of deep traps for H and O was found from the SIMS depth profiles.
High-current-density ITOx/NiOx thin-film diodes
Authors: Lee W. Y. , Mauri D. , Hwang C.
Published: July 2002

Thin-film diodes 0.2–4×10−5 cm2 in size were fabricated on Al2O3–TiC ceramic substrates from junctions between p-type NiOx and n-type ITOx thin films sputter deposited at ambient temperature. These diodes show a room-temperature turn-on voltage of 0.3–0.6 V and a dc forward current density exceeding 104 A/cm2 at an applied voltage of ≃1.5 V. The current–voltage (I–V) and capacitance–voltage (C–V) characteristics of these diodes can be described by an exponential dependence of I on the applied V and by a linear I/C2 dependence on the reverse applied V, respectively, consistent with those predicted by the various models proposed for the mechanisms for charge-carrier transport in abrupt anisotype heterojunctions. The ideality factor at low-applied V (⩽0.3 V), the junction built-in potential, and the carrier concentration deduced from these I–V and C–V data are ≃1.5–2, 0.20–0.24 V, and 1.90–1.97×1018/cm3, respectively.
Proximity effect in bilayer films of YBa2Cu2.7Fe0.3Oy and YBa2Cu3O7−δ
Authors: Nesher O. , Koren G. , Polturak E. , Deutscher G.
Published: July 2002

We studied the proximity effect in a series of YBa2Cu2.7Fe0.3Oy/YBa2Cu3O7−δ bilayer film with varying YBa2Cu3O7−δ thickness. In a bilayer of isolated YBCO islands, a Tc of 72 K was observed, much higher than Tc of 32 K of the YBa2Cu2.7Fe0.3Oy film. Tc and Jc of thicker bilayers of continuous YBa2Cu3O7−δ films were found to decrease with decreasing YBCO thickness. This behavior of Tc and Jc can be explained by the Deutscher de Gennes theory for the proximity effect, provided one models the film as a series of grains whose lateral dimensions scale with the average film thickness.
Partial and total α parameters in semiconductor optical devices
Authors: Ning C. Z.
Published: July 2002

α parameters due to partial variation of carrier density (αN) or temperature (αT) are calculated for a two-dimensional semiconductor. We also introduce and investigate the total alpha parameter (αt) due to simultaneous variations of the carrier density and temperature. We find that, unlike the usual αN, the partial αT and total αt show quite different behavior with changes in underlying variables and could be positive, negative, or singular.
Electronic properties of arsenic-doped gallium nitride
Authors: Guido L. J. , Mitev P. , Gherasimova M. , Gaffey B.
Published: July 2002

Arsenic-doped GaN films were grown via metalorganic chemical vapor deposition using trimethylgallium, ammonia, and arsine precursors. The arsenic concentration increases from 3×1016 to 5×1017 cm−3 in response to a change in arsine mole fraction from 3.3×102 to 3.2×104 ppm. The electron mobility increases with arsenic content reaching a maximum value of 374 cm2/V s at 300 K. In addition, the integrated photoluminescence intensity exhibits a 35-fold increase in magnitude at 300 K. To explain these findings, a simple physical model is proposed in which arsenic “impurities” occupy otherwise vacant sites on both the gallium and nitrogen sublattices.
Observation of a Cole–Davidson type complex conductivity in the limit of very low carrier densities in doped silicon
Authors: Jeon Tae-In , Grischkowsky D.
Published: July 2002

Using THz time-domain spectroscopy to measure the complex conductivity of doped silicon from low frequencies to frequencies higher than the THz plasma frequency and the carrier damping rate, we were able to show in the limit of extremely low carrier densities N<1013/cm3, that the Cole–Davidson (C–D) type complex conductivity accurately describes the conductivity of doped silicon. In the low N limit the C–D parameter β converges to 0.83 for n-type and 0.70 for p-type silicon. In addition, we have observed a new absorption line at 1.9 THz from an unidentified defect in some of our Czochralski, single-crystal, low-N silicon samples.
Defect-enhanced second-harmonic generation in (SimGen)p superlattices
Authors: Zhang Chun , Xiao Xudong , Wang N. , Fung K. K. , Loy M. M. T. , Chen Zhenghao , Zhou Junming
Published: July 2002

Second-harmonic generation (SHG) has been applied to study the influence of defects in short-period (SimGen)p strained-layer superlattices. With a misfit stacking fault defect density of ∼1010 cm−2 shown by transmission electron microscopy, it is found that the SH intensity increases by about one order of magnitude from that of the defect-free samples. We propose that the inhomogeneous strain field around the fault planes in the superlattice layers is responsible for this abrupt increase of SHG. The expected symmetry and the magnitude of the nonlinear susceptibility from these stacking fault defects are shown to be in agreement with the experimental observations.
Demonstration of a six-dot quantum cellular automata system
Authors: Amlani Islamshah , Orlov Alexei O. , Snider Gregory L. , Lent Craig S. , Bernstein Gary H.
Published: July 2002

We report an experimental demonstration of a logic cell for quantum-dot cellular automata (QCA). This nanostructure-based computational paradigm allows logic function implementation without the use of transistors. The four-dot QCA cell is defined by a pair of series-connected double dots, and the coupling between the input and the output double dots is provided by lithographically defined capacitors. We demonstrate that, at low temperature, an electron switch in the input double dot induces an opposite electron switch in the output double dot, resulting in a polarization change of the QCA cell. Switching is verified from the electrometer signals, which are coupled to the output double dot. We perform theoretical simulations of the device characteristics and find excellent agreement with theory.
Lateral oxidation of InAlAs in InP-based heterostructures for long wavelength vertical cavity surface emitting laser applications
Authors: Gebretsadik H. , Kamath K. , Zhou W.-D. , Bhattacharya P. , Caneau C. , Bhat R.
Published: July 2002

We have studied the wet thermal oxidation of In0.52Al0.48As and its potential application in current and optical confinement in vertical cavity surface emitting lasers (VCSELs). Two types of InP-based heterostructures were used to study the effect of adjacent layer compositions on the lateral oxidation behavior of the InAlAs. It was found that the oxidation of In0.52Al0.48As with InP adjacent layers, compared with In0.53Ga0.47As adjacent layers, proceeded faster, more uniformly and with minimal degradation of the surrounding layers making it ideal for optoelectronic applications.
Long pulse operation of an x-ray preionized molecular fluorine laser excited by a prepulse–main pulse system with a magnetic switch
Authors: Bastiaens H. M. J. , Peeters S. J. M. , Renard X. , Peters P. J. M. , Witteman W. J.
Published: July 2002

The application of a prepulse–main pulse excitation scheme utilizing a saturable magnetic switch in combination with x-ray preionization has resulted in the generation of long optical pulses from a molecular fluorine laser. Optimum laser pulse durations of 70 ns (full width half maximum) have been obtained in a gas mixture of helium and 3 mbar fluorine at a total pressure of 2 bar. The laser pulse duration is limited by instabilities in the discharge. The laser pulse duration is found to decrease with increasing fluorine pressure and to saturate with increasing current density.
Amplified spontaneous emission spectroscopy on semiconductor optical amplifiers subject to active light injection
Authors: de Boer A. P. , Christianen P. C. M. , Maan J. C. , Rasing Th. , Tolstikhin V. I. , van de Roer T. G. , de Vrieze H. M.
Published: July 2002

It is shown that measurements of the effect of optical injection with an external laser on the spectral response of a semiconductor optical amplifier can probe intrinsic properties of a working device. The data demonstrate that under saturated gain conditions the carrier energy distribution within the active layer of a AlGaAs/GaAs amplifier neither shows spectral hole burning nor carrier heating, but only a decreased density.
Boltzmann machine neuron device using quantum-coupled single electrons
Authors: Wu Nan-Jian , Shibata Naoto , Amemiya Yoshihito
Published: July 2002

A quantum Boltzmann machine (QBM) neuron device is proposed. It consists of a two-dimensional (2D) arrangement of quantum dots that is occupied by quantum-coupled single electrons. The two possible polarizations, “down” and “up,” of the electron spin are used to encode the binary states 0 and 1. The QBM neuron device produces stochastic operations naturally because the electron spin takes the polarization down or up with a certain probability. Calculations for the operation of the QBM neuron device are presented and it is demonstrated that the device can perform the stochastic operations of the BM neuron.
Fabrication of multiperiod Si/SiO2/Ge layered structure through chemical bond manipulation
Authors: Prabhakaran K. , Matsumoto T. , Ogino T. , Masumoto Y.
Published: July 2002

In this letter, we report a method called chemical bond manipulation for fabrication of multiperiod nanometer sized Si/SiO2/Ge layered structure. Chemical bond manipulation is a self-organization process which involves selective breaking and making of surface chemical bonds and thereby enable formation of the desired species on a full wafer scale. We show that oxygen of germanium oxide layer formed on Si(111) are picked up by the Si atoms arriving at the surface during subsequent growth. This phenomenon involves breaking of Ge–O bonds and making of Si–O bonds and leads to the formation of ultrathin Si and Ge layers sandwiched between ultrathin silicon oxide layers, preserving the original wafer morphology. This material exhibits blue-green light emission at room temperature when excited by ultraviolet laser.
Contactless electroreflectance and piezoreflectance studies of temperature-dependent strain in ZnTe/GaAs heterostructures with ZnSe/ZnTe superlattice buffer layers
Authors: Tu R. C. , Su Y. K. , Chen H. J. , Huang Y. S. , Chou S. T.
Published: July 2002

The temperature-dependent optical properties of ZnTe epilayers grown on GaAs substrates by molecular beam epitaxy with and without ZnSe/ZnTe strained-layer superlattice (SLS) buffer layers have been studied using contactless electroreflectance (CER) and piezoreflectance (PzR). Our ZnTe epilayers of 1.5 μm in thickness grown on GaAs substrates are under a biaxial tensile strain according to the results shown in CER and PzR spectra. Furthermore, the strain induced energy splitting between heavy- and light-hole valence bands in the ZnTe epilayer can be reduced by using the ZnSe/ZnTe SLS buffer layers. We have also justified the temperature-dependent energy splitting between heavy- and light-hole valence bands for ZnTe through theoretical calculations. Discrepancy between experiments and calculations indicates that the residual mismatch-induced strain as well as the thermally induced strain during cooling must be taken into account at the same time.
Concurrent variation of giant magnetoresistance and saturation Kerr rotation in NiCo/Cu multilayers
Authors: Du J. , Tong L. N. , Lu M. , Xia K. , Pan M. H. , Wu J. , Feng D. , Zhai H. R. , Chen L. Y. , Jin X. F. , Xia H.
Published: July 2002

The dependences of magneto-optical effect, effective optical constants, and giant magnetoresistance (GMR) on the thickness of Cu layers were investigated in NiCo/Cu multilayers prepared by rf magnetron sputtering. A peak of saturation polar Kerr rotation θK, occurred simultaneously with that of GMR ratio when the Cu thickness is around 1.0 nm, where a clear drop of the effective optical constants n and k appeared. The peak of θK is mainly caused by the reduction of the effective optical constants, which dominate over the small drop of the effective off-diagonal elements of the dielectric tensor. The concurrent variation of GMR and θK is related to antiferromagnetic interlayer coupling, which may change the electron band structure and thus the optical and magneto-optical transitions of electrons.
Quantized conductance in quantum wires with gate-controlled width and electron density
Authors: Kane B. E. , Facer G. R. , Dzurak A. S. , Lumpkin N. E. , Clark R. G. , Pfeiffer L. N. , West K. W.
Published: July 2002

We describe quantum wires and point contacts fabricated in GaAs/AlxGa1−xAs heterostructures that are free of the disorder introduced by modulation doping and in which the electron density and the confining potential are separately adjustable by lithographically defined gates. We observe conductance plateaus quantized near even multiples of e2/h in 2 μm wires and up to 15 conductance steps in 5 μm wires at temperatures below 1 K. Near the conductance threshold the quantum point contact and the 2 μm wire both show additional structure below 2e2/h.
Effective area in slotted high Tc dc washer superconducting quantum interference devices
Authors: Jansman A. B. M. , Izquierdo M. , Eiguren A. , Flokstra J. , Rogalla H.
Published: July 2002

Slotted high Tc dc washer superconducting quantum interference devices (SQUIDs) exhibit increased effective areas with respect to their solid washer counterparts. To investigate this systematically, a series of SQUIDs with zero to eight slots is fabricated. A maximum gain in effective area of 24% was observed for four slots. A model, considering the slotted washer as a parallel circuit of pick-up inductances can account for the enhanced effective area. A good fit with the experiments is obtained if the London penetration depth at 0 K is taken to be 267 nm. Furthermore, the model provides the current distribution in the slotted SQUIDs.
Generation of 14 GHz radiation using a two frequency iodine laser
Authors: Nicholson J. W. , Rudolph W. , Hager G.
Published: July 2002

A mode-locked and gain-switched photolytic iodine laser Zeeman tuned to operate simultaneously on the two strongest hyperfine transitions is shown to emit 1.315 μm radiation modulated at 13.9 GHz. The interaction of this laser radiation with suitable targets leads to the generation of microwave pulses that consist of only a few cycles at 13.9 GHz, making the system attractive for ultra-wide-band, short pulse radar applications.
Continuous-wave, broadband tuning from 788 to 1640 nm by a doubly resonant, MgO:LiNbO3 optical parametric oscillator
Authors: Tsunekane Masaki , Kimura Shinji , Kimura Mikio , Taguchi Noboru , Inaba Humio
Published: July 2002

This letter reports exceptionally broadband tuning of a continuous-wave optical parametric oscillator (cw OPO) using a temperature tuned, nonlinear crystal of MgO:LiNbO3 pumped by a diode-pumped, intracavity doubled Nd:YAG laser. The tuning range from 788 to 1640 nm, is about four times broader than those ever reported in cw OPOs operating around 1 μm. This performance was accomplished by newly developed, extremely broadband, high-reflection mirrors for the doubly resonant oscillation, designed to have a reflectivity of 99% from 0.7 to 1.6 μm. Threshold pump power increased from 80 mW near degeneracy to 150 mW at the tuning band edge in a double pass pumping configuration.
1000 V/μm pulsed poling technique for photolime-gel electro-optic polymer with room-temperature repoling feature
Authors: Yue Zhou Z. , An Dechang , Chen Ray T. , Tang Suning
Published: July 2002

An electric pulsed-poling technique is developed for achieving high-performance electro-optic polymers. A high poling field of 1 kV/μm can be applied across a polymer thin film without experiencing breakdown. This poling technique has been applied to a guest-host nonlinear polymeric system of photolime gel and chlorophenol red with loading concentration of 30 wt %. An electro-optic coefficient up to 40 pm/V at the 632.8 nm wavelength is achieved, which is 35% higher than that obtained by using conventional poling approaches. After decay the electro-optic coefficient can be fully recovered using the same poling method at room temperature.
Effects of alloy ambient on PdGe contacts on n-type GaAs
Authors: Ahmari D. A. , Hattendorf M. L. , Lemmerhirt D. F. , Yang Q. , Hartmann Q. J. , Baker J. E. , Stillman G. E.
Published: July 2002

A high concentration of hydrogen in the alloy ambient slows the formation of PdGe contacts and increases the resistance of the PdGe to GaAs etchants. The effects of alloy ambient on alloy formation, specific contact resistance, and chemical reactivity of PdGe contacts on n-type GaAs have been studied. A very low specific contact resistance of <1×10−7 Ω cm2 has been achieved on GaAs with PdGe contacts alloyed at 300 °C for 15 min in a hydrogen ambient. These results indicate that PdGe may be a desirable contact for GaAs-based transistors.
Influence of partial dopant ionization on the capacitance–voltage profiles of delta-doped structures
Authors: Moon C. R. , Kwon S. D. , Lim H. , Choe Byung-Doo
Published: July 2002

The effects of partial dopant ionization on the capacitance–voltage (C–V) characteristics of δ-doped structures have been investigated using self-consistent simulations. The simulation results show that partially ionized δ-doped dopants should produce a much sharper C–V profile compared with the case of fully ionized dopants. The results reveal also that the main factor which determines the spatial resolution and the full width at half maximum of the C–V peak is the spatial extent of the dopant profile rather than the spatial extent of the ground-state wave function. From this, it is suggested that the δ-doped C–V data should be interpreted always with the effect of partial ionization of δ-doped dopants.
Void-free chemically vapor-deposited aluminum dual inlaid metallization schemes for ultra-large-scale-integrated via and interconnect applications
Authors: Ong T. P. , Fiordalice R. , Venkatraman R. , Garcia S. , Jain A. , Sparks T. , Farkas J. , Fernandes M. , Gall M. , Jawarani D. , Klein J. , Weitzman E. , Kawasaki H. , Wu Wei , Blumenthal R. , Pintchovski F. , Marsh R. , Zhang P. , Zhang H. , Guo T. , Mosely R.
Published: July 2002

This letter reports an investigation of two unique dual inlaid metallization approaches with low pressure chemical vapor deposition (LPCVD) of aluminum (Al) for sub-0.35 μm ultra-large-scale-integration interconnect technology: (1) warm Al/CVD Al/coherent (coh.) PVD Al/coh. PVD Ti and (2) warm PVD Al/CVD Al/coh. PVD Ti or Al/selective CVD Al. The integration of thin coh. PVD Al, deposited with a physical collimator or a variation of ionized metal plasma technique, was found to be the unique and simple solution in providing void-free via and interconnect structures, which have not been reported elsewhere. Excellent electrical and electromigration results have been obtained.
Nondestructive measurement of separated propagation loss for multimode waveguides
Authors: Lee Ching-Ting
Published: July 2002

We propose a method which applies a combination of the well-known phase modulator, butt-couple and prism coupler to the nondestructive measurement of each mode’s propagation loss in multimode waveguides. By tuning to the effective optical length of a channel waveguide with a phase modulator, the contrast in the transmitted intensity of Fabry–Perot resonance for each guided mode separated by a prism coupler can be measured. The associated propagation attenuation coefficient and the propagation loss for each guided mode are then determined from these experimental results.
Large (50 μm)2 metal–semiconductor–metal photodetectors with 18 GHz bandwidth at 3 V bias; Reduction of hole pileup
Authors: DeCorby R. G. , MacDonald R. I. , Noad J. , Gouin F.
Published: July 2002

Metal–semiconductor–metal photodetectors were fabricated on an AlGaAs/GaAs/AlGaAs double heterostructure with no graded layers. Devices with photolithographically defined finger spacing and width of 1 μm (“1×1”) exhibited a saturation bandwidth of greater than 20 GHz, for bias voltages between 3 and 4 V. We attribute this to minimal hole pileup, and propose a simple model for the energy of hot holes near the band offset at the cathode. Using this model, estimates of the bias required to reduce hole pileup in different material systems were derived. The model shows good agreement with results reported here and elsewhere.
Electric field controlled dynamic holograms on polarization gratings in a ferroelectric liquid crystal
Authors: Saad B. , Dinescu L. , Lemieux R. P. , Galstyan T. V.
Published: July 2002

The irradiation at 514.5 nm of a ferroelectric liquid crystal (FLC) film doped with a photochromic chiral thioindigo dye causes a change in the birefringence of the FLC film under a constant dc voltage. This birefringence photomodulation is used to create electric field controlled dynamic holograms. The diffraction efficiency of the hologram is found to depend resonantly on the applied dc voltage. The unwinding of the FLC helical structure into a planar alignment as a result of a photoinduced increase of the spontaneous polarization (Ps) and of the corresponding dielectric torque is thought to be at the origin of the observed birefringence photomodulation.
Effect of curvature and stress on reaction rates at solid interfaces
Authors: Tersoff J. , Tu Yuhai , Grinstein G.
Published: July 2002

We analyze the effect of interface curvature and stress on reaction rates at solid–solid or solid–fluid interfaces. Curvature affects the forward and reverse reactions differently, and cannot be related simply to an interface energy. To describe the effect of stress requires at least two parameters each for forward and reverse reactions. The distribution of local configurations may be ignored to linear order; but beyond the linear regime, this effect can cause large deviations from the expected exponential dependence.
The role of the solvent viscosity on the spatiotemporal instabilities of large aperture dye lasers
Authors: Calderón Oscar G. , Leyva I. , Guerra J. M.
Published: July 2002

Local intensity fluctuations in a large aperture dye laser have been measured for several solvent viscosities. A decrease on the relative fluctuations amplitude as the solvent viscosity increases is found. From a theoretical approach, we show that the intensity fluctuations follow the same behavior as the molecular polarization orientation driven by the laser field.
Enhancement of electrical and structural properties of GaN layers grown on vicinal-cut, a-plane sapphire substrates
Authors: Fatemi M. , Wickenden A. E. , Koleske D. D. , Twigg M. E. , Freitas J. A. , Henry R. L. , Gorman R. J.
Published: July 2002

We report the observation of significant enhancement in the electrical and crystalline properties of GaN layers grown on vicinally cut, a-plane sapphire substrates. Room-temperature Hall mobility and x-ray rocking curve data show a nearly twofold improvement, independent of the processing conditions, for layers grown on substrates having vicinal angles of 1.5° compared to on-axis substrates. Transmission electron microscopy shows reduced edge dislocation density and better alignment of the grains in layers grown on vicinally cut substrates. Preliminary photoluminescence measurements also indicate pronounced differences in the yellow band spectra between the on-axis and off-axis cut substrates. These findings contrast the relatively modest improvements observed in layers grown on c-plane substrates with vicinal angles as high as 10°.
Energy transfer from a naphthalimide functionalized side chain polymer towards DCM used as a dopant molecule
Authors: Bouché C.-M. , Le Barny P. , Facoetti H. , Robin P.
Published: July 2002

The influence of the introduction of a dopant molecule, namely DCM, in a matrix of a naphthalimide derived polymer (PNI) is studied by means of UV-visible absorption spectroscopy, photoluminescence emission and excitation spectrometry, and 2D photoluminescence spectrometry. We demonstrate that, contrary to previous observations on similar systems, energy transfer occurs between PNI and DCM. Moreover, photoluminescent (PL) and electroluminescent (EL) emissions are assigned to arise from the same excited state.
Influence of the number of deposited atoms per shuttering cycle on surface morphology of sequentially deposited Pb2Sr2EuCu3Oy films
Authors: Motoi Yuichi , Ikegawa Sumio
Published: July 2002

The relation between surface morphology and growth conditions on Pb2Sr2EuCu3Oy (Pb-3212) thin films has been studied. The Pb-3212 thin films were grown by the molecular beam epitaxy method with monolayer-by-monolayer deposition. It was found that the surface morphology depends on the amounts of atoms deposited per unit area during one cycle of deposition sequence to form the Pb-3212 unit cell. The Cu2O precipitates were observed when the amount for Cu is larger than the ideal value or that for Sr is less than the ideal value. The averaged roughness of the smoothest film grown under Sr-rich and Cu-deficient conditions is less than 0.30 nm.
Chemical vapor deposition of diamond growth using a chemical precursor
Authors: Leroy Eric , Küttel Olivier M. , Schlapbach Louis , Giraud Luc , Jenny Titus
Published: July 2002

A nucleation method to form diamond on chemically pretreated silicon (111) surfaces is reported. The nucleation consisted of binding covalently 2,2-divinyladamantane molecules on the silicon substrate. Subsequently, low pressure diamond growth was performed via microwave plasma chemical vapor deposition in a tubular deposition system. The resulting diamond layers presented a good crystallinity and the Raman spectra showed a very sharp peak at 1331 cm−1.
Reflective homeotropic mode in a twisted nematic liquid crystal
Authors: Suh Seong-Woo , Patel J. S. , Lee Sin-Doo
Published: July 2002

This letter reports on a novel liquid crystal (LC) display device capable of achromatic reflection in a twisted homeotropic configuration using a chiral nematic LC with negative dielectric anisotropy. Using the elastic continuum formalism, we arrived at simulated values for each parameter of interest, including external twist, cell gap, molecular chirality for the chiral pitch, and the surface anchoring energy. The experimental results correspond well with the calculated expectations, exhibiting EO properties that demonstrate excellent achromatic reflection, extinction, and a high contrast ratio.
Stress-related interdiffusion in dc sputtered TiN/B–C–N multilayers
Authors: Fayeulle S. , Nastasi M.
Published: July 2002

The diffusion in TiN/B–C–N multilayers during vacuum annealing at temperatures up to 1000 °C and/or 300 keV argon irradiation is studied. Changes in composition, stress field, bilayer repeat length, and interface quality are reported. The effect of stress on diffusion is proved by performing the same annealing or the same irradiation on a multilayer with and without compressive stress. During thermal annealing, demixing or phase separation is observed. On the contrary, during irradiation, mixing occurs. Both phenomena are enhanced in the presence of the stress field.
Frequency dependence of radar cross section for arbitrarily shaped scatterers
Authors: Liu Hongwei , Antar Yahia M. M. , Shi Zhendong , Wu Zhengde
Published: July 2002

This letter introduces a method to perform frequency dependence of radar cross section for either simple or complex scatters in terms of model measurement. To do so, the expressions of physical scale factor based on the electromagnetic similarity are suggested by means of dimensional analysis, geometric and physical optics approximation. Using the results of model measurement within a small range of frequency, the frequency dependence of an arbitrarily shaped scatterer can be obtained. For the purpose of verification and comparison, some measurements of simple and complex shapes have been carried out. The calculated results agree well with the experimental data on the prototype itself.
Microstructural evolution of GaSb self-assembled islands grown by metalorganic chemical vapor deposition
Authors: Kinder B. M. , Goldys E. M.
Published: July 2002

Studies of the growth of GaSb self-assembled islands on GaAs and their morphological evolution for varying GaSb coverage are presented. Islands had a mean height of 15 nm and planar dimensions of 60 by 130 nm. Evolution of the island height, width and length shows that the island height and width increases rapidly in the first 2 s and then stabilizes, while the island length increases linearly. This behavior is interpreted using the theory by Tersoff and Tromp [Phys. Rev. Lett. 70, 2782 (1993)]. The volume growth was found to be initially faster than bulk growth.
Solid phase epitaxial regrowth of ion beam-amorphized α-quartz
Authors: Roccaforte F. , Bolse W. , Lieb K. P.
Published: July 2002

Solid phase epitaxial growth of ion beam-amorphized α-quartz has been studied by means of Rutherford backscattering spectrometry in channeling geometry. α-quartz single crystals were irradiated with Cs+ and Xe+ ions and annealed in air or in vacuum at 500–900 °C. Complete epitaxial regrowth has been observed in the Cs-irradiated samples, after 875 °C annealing in air. On the other hand, vacuum annealing provided only incomplete regrowth of the amorphous layer, while Xe-irradiated α-quartz could not be regrown up to 900 °C. The behavior of Cs in the recrystallization process is discussed in terms of the SiO2-network topology.
Enhancement of the third-order nonlinear optical response of quantum wells in a semiconductor microcavity
Authors: Ishihara Hajime , Cho Kikuo
Published: July 2002

We discuss the enhancement effect of the third-order nonlinear response of excitons coupled with cavity modes, on the basis of a self-consistent calculation of response field and induced polarization. It is shown that a single framework is enough to describe the spectral features of nonlinear spectra in both strong and weak coupling regimes, where the splitting of coupled modes (cavity polaritons) in linear response is larger and smaller, respectively, than the widths. In the latter regime, the nonlinear signal is strongest at the bare excitonic resonance, and its enhancement due to the cavity effect is remarkable. In the former regime, on the other hand, the nonlinear signal appears at the energy positions of the coupled modes, whose spectral shape represents the reduction of normal-mode splitting due to the nonlinear effect.
Cathodoluminescence study of degradation in ZnSe-based semiconductor laser diodes
Authors: Toda A. , Nakano K. , Ishibashi A.
Published: July 2002

After continuous-wave operation of ZnSe-based semiconductor laser diodes, the degradation of these devices was investigated using cathodoluminescence imaging and spectroscopy. Inside the stripe region, i.e., the carrier injection area, there were several dots in which the peak wavelength of emission from a ZnCdSe strained quantum well (QW) shifted with time to a shorter wavelength (blueshift). We consider that the blueshift is due to Cd/Zn interdiffusion. This interdiffusion is enhanced by the electron–hole recombination process (recombination enhanced interdiffusion). Furthermore, there were dark line defects (DLDs) in the 〈100〉 direction, outside the stripe region and running away from the dots, having emission with a blueshift. The peak wavelength of emission from the QW in the DLDs shifted to a longer wavelength (redshift). We consider that the redshift is due to the relaxation of strain in the QW by existing defects, which may originate in the blueshift dots and move outside the stripe region.
High-frequency beam steering induced by switching of high-order transverse modes in vertical cavity surface emitting lasers
Authors: Valle A.
Published: July 2002

Selection over a wide current range of high-order transverse modes in vertical cavity surface emitting lasers is achieved by using appropriate current profiling. High-frequency beam steering in the azimuthal direction is then obtained by alternate current modulation of two orthogonal high-order transverse modes. Alternate modulation of these modes can double the pulse repetition frequency obtained by modulating just one high-order transverse mode, without increasing injected current density levels.
Self-defined AlAs-oxide–current-aperture buried heterostructure vertical cavity surface-emitting laser
Authors: Choi Won-Jin , Dapkus P. Daniel
Published: July 2002

We demonstrate a promising technique to fabricate self-defined AlAs-oxide–current-apertures for vertical cavity surface-emitting lasers (VCSELs). A self-defined AlAs-oxide–current-aperture buried heterostructure VCSEL was fabricated using a three-step growth sequence. The active region mesa size was 10 μm×10 μm. The lowest threshold current of the lasers was 0.7 mA under continuous-wave operation at room temperature. The differential quantum efficiency was 32%. The lasers operate at temperatures of up to 50 °C.
A normal incidence p-type strain layer quantum well infrared photodetector with 19.2 μm peak detection wavelength
Authors: Chu J. , Li Sheng S. , Singh A. , Ho P.
Published: July 2002

A normal incidence p-type compressively strained layer superlattice (SL) In0.27Ga0.73As/Al0.15Ga0.85As quantum well infrared photodetector with a spectral response peak at 19.2 μm and a cutoff wavelength λc>20 μm under moderate background illumination have been demonstrated in this work. A responsivity of 50 mA/W and a gain-quantum efficiency product (ηg) of 0.32% at Vb=20 mV and T=40 K were obtained for this device. The device layer structure consists of four InGaAs/AlGaAs SL-absorber layers sandwiched by wide GaAs barrier layers. Results of the responsivity, dark current, noise, background photocurrent measurements, and analysis of the device performance are discussed.
Red and infrared side by side semiconductor quantum well lasers integrated on a GaAs substrate
Authors: Sun D. , Treat D. W. , Beernink K. , Bringans R. D. , Kovacs G. J.
Published: July 2002

We report red and infrared quantum well (QW) semiconductor lasers integrated on a GaAs substrate by etching and regrowth. A separate confinement heterostructure infrared laser containing an In0.15Al0.15Ga0.7As/Al0.4Ga0.6As QW with AlInP cladding layers was grown on a GaAs substrate. The wafer was then patterned with stripes of etch masks and was etched back to the substrate. A Ga0.4In0.6P/(AlGa)0.5In0.5P QW separate confinement heterostructure laser was subsequently grown side by side with the infrared laser structure. Independently addressable dual-wavelength lasers of 50 μm spacing were fabricated by forming 4 μm wide buried ridge waveguides. The dual-wavelength lasers operated in threshold currents of 10 mA at a peak wavelength of 835 nm and 20 mA at a peak wavelength of 670 nm.
Back-side reflectance of high Tc superconducting thin films in the far infrared
Authors: Zhang Z. M. , Kumar A. R. , Boychev V. A. , Tanner D. B. , Vale L. R. , Rudman D. A.
Published: July 2002

We have measured the far-infrared reflectance of YBa2Cu3O7−δ high Tc superconducting (HTS) films, for radiation incident on the substrate side (back-side illumination), in the spectral region from 15 to 650 cm−1 and at temperatures between 10 and 300 K. The HTS films were deposited on Si substrates (with YSZ/CeO2 buffer layers) by pulsed laser ablation. The extremely large temperature dependence of the reflectance experimentally demonstrates the feasibility of using HTS films to construct far-infrared intensity modulators. In this letter, we present the measured results, as well as an analysis based on thin-film optics and a simple two-fluid model.
Photochemical color switching behavior of induced cholesteric liquid crystals for polarizer free liquid crystalline devices
Authors: Kurihara Seiji , Kanda Tomoko , Nagase Takashi , Nonaka Takamasa
Published: July 2002

Photoresponsive cholesteric (Ch) liquid crystals (LCs) showing reflection of visible light were prepared by the addition of chiral molecules and azobenzene molecules in a host nematic LC. The Ch–isotropic phase transition temperature and wavelength of reflected light were controlled by varying the enantiomer excess. Switching between reflection and transparent states was achieved by ultraviolet irradiation. In addition, the switching time was also explored by means of time-resolved measurements.
Preliminary investigation of the kinetics of postoxidation rapid thermal anneal induced hole-trap-precursor formation in microelectronic SiO2 films
Authors: Conley J. F. , Lenahan P. M. , McArthur W. F.
Published: July 2002

Measurements of the growth of E′ center precursor and hole trap precursor densities versus postoxidation anneal time show that both approach saturation values and that the approach to these values is more rapid at higher temperatures. Our results, at least qualitatively, show that a kinetic component can be added to a predictive thermodynamics-based model of oxide hole trapping. The results also indicate quite strongly that a thermodynamics approach to oxide hole trap precursor modeling is appropriate, i.e., the relevant defect densities approach thermodynamic equilibrium or quasiequilibrium in reasonable times.
All-optical liquid device derived from negative nonlinear absorption effect in an erbium chloride solution
Authors: Maeda Yoshinobu , Akidzuki Yoshiki , Yamada Toshikazu
Published: July 2002

The dependence of the negative nonlinear absorption effect on the modulation degree and frequency was investigated in an erbium chloride solution using a 807.6 nm laser diode. The reverse-phased wave forms were obtained in the transmitted wave form for sample lengths greater than 6 cm. Though the reverse-phased wave form was observed symmetrically at modulation frequency of 0.1 MHz, they were asymmetrical at higher than 0.25 MHz. The effect has a characteristic which is almost independent of the state of erbium ions because it is formed by optical transitions of the inner shell of the erbium atom.
Photoluminescence decay dynamics of ion-irradiated porous silicon: Evidence for the absence of carrier migration
Authors: Tanaka Satoshi , Koyama Hideki , Koshida Nobuyoshi
Published: July 2002

We have measured the photoluminescence (PL) decay properties of porous silicon (PS) samples subjected to ion irradiation up to a dose of 1015 cm−2 at 30 kV. It is found that while the PL intensity decreases down to 1/100 of the initial value due to induced nonradiative recombination centers, its decay constant is unchanged. This observation is inconsistent with the hypothesis that photoexcited carriers migrate among the Si nanocrystallites in PS. The results are compared with those of PS samples subjected to thermal annealing instead of ion irradiation, where the PL quenching in this case is accompanied by a large reduction in the decay constant. Infrared absorption spectra of ion-irradiated samples show essentially no chemical bonding change. In contrast, those of the annealed samples show loss of hydrogen bonding and increase of surface oxidation.
Demonstration of a current-controlled three-terminal Nb–InxGa1−xAs/InP Josephson contact
Authors: Schäpers Th. , Malindretos J. , Neurohr K. , Lachenmann S. , van der Hart A. , Crecelius G. , Hardtdegen H. , Lüth H. , Golubov A. A.
Published: July 2002

The supercurrent in a Nb–In0.53Ga0.47As/In0.77Ga0.23As/InP weak link structure is controlled by means of a current injected into the two-dimensional electron gas. For small injection currents the critical current to control current ratio is as large as 20. The measured features can be qualitively explained in terms of a modification of the Andreev level occupation by the injected carriers.
Competition of shot noise and hot-electron noise in GaAs planar-doped barrier diode
Authors: Gružinskis V. , Liberis J. , Matulionis A. , Sakalas P. , Starikov E. , Shiktorov P. , Szentpáli B. , Van Tuyen V. , Hartnagel H. L.
Published: July 2002

Microwave noise in GaAs planar-doped barrier diodes is investigated over a wide range of bias. Suppression of shot noise at intermediate densities of current and an onset of hot-electron noise at high densities are evidenced by experimental data and Monte Carlo simulation.
Conduction properties of metal/organic monolayer/semiconductor heterostructures
Authors: Li DeQuan , Bishop A. , Gim Y. , Shi X. B. , Fitzsimmons M. R. , Jia Q. X.
Published: July 2002

We have fabricated and characterized rectifying devices made of metal/organic monolayer/semiconductor heterostructures. The devices consist of an organic barrier layer sandwiched between an aluminum (Al) metal contact and a p-type Si semiconductor. The barrier materials were chosen from three types of self-assembled monolayers (SAMs) with different electronic properties: (1) wide-band gap poly(diallydimethyl ammonium) chloride (PDDA), (2) narrow-band gap PDDA/NiPc (nickel phthalocyanine tetrasulfonate), and (3) donor type PDDA/PPP (poly p-quaterphenylene-disulfonic-dicarboxylic acid). From current–voltage (I–V) measurements at room temperature, we have found the turn-on voltage of the devices can be tuned by varying the structure, hence electronic properties, of the organic monolayers, and that there exists a power-law dependence of I on V, I∝Vα, with the exponent α=2.2 for PDDA, 2.7 for PDDA/NiPc, and 1.44 for PDDA/PPP as the barrier layer, respectively. Our results imply that the transport properties are controlled by both the electronic properties of the SAMs and those of the metal and semiconductor, as indicated by the power-law dependence of the I–V characteristics.
Recombination dynamics in InAsSb quantum-well diode lasers measured using photoluminescence upconversion
Authors: Cooley W. T. , Hengehold R. L. , Yeo Y. K. , Turner G. W. , Loehr J. P.
Published: July 2002

We report Shockley–Read–Hall (SRH), radiative, and Auger recombination rates in midinfrared laser structures from time-resolved photoluminescence using frequency upconversion. The devices studied were actual InAsSb/InAlAsSb multiple-quantum-well (MQW) diode lasers emitting near 3.3 μm, which have been previously characterized for laser performance. We extend the initial studies and report on the carrier recombination dynamics. The importance of carrier density motivates a careful examination of carrier density and quantum-well effects. SRH, radiative, and Auger recombination rates (ASRH, Brad, and CAuger, respectively) were measured at 77 K and found to be ASRH−1≈10 ns, Brad≈2×10−10 cm3 s−1, and CAuger⩽1.0×10−29 cm6 s−1, respectively. At 150 K the nonradiative recombination coefficients increased to ASRH−1≈1.7 ns, Brad≈0.78×10−10 cm3 s−1 and CAuger≈7.0×10−28 cm6 s−1, respectively. This study suggests InAsSb/InAlAsSb MQW diode laser performance may be limited by SRH nonradiative recombination mechanisms rather than Auger recombination.
Observation of ultrahigh-quality crystalline YBa2Cu3Ox in submicron thick films
Authors: Lin Wen-Jih , Hatton Peter D. , Baudenbacher F. , Santiso J.
Published: July 2002

By examining low-angle Bragg reflections of submicron thick YBa2Cu3O7 grown on SrTiO3 substrates with synchrotron radiation, we have found evidence that some high-Tc oxide thin films are composed of extremely high-quality single-crystal material. Our results evidence material ordered over a distance ten times that previously measured, displaying a micron-sized lateral correlation length and completely correlated vertically. The partially correlated roughness of the lattice planes causes the intensity of the Bragg reflections from this ultrahigh-quality crystal to quickly diminish, such that conventional high-angle x-ray measurements cannot observe it. These observations may thus account for the enhanced transport properties of thin films compared to their bulk counterparts.
Direct time-domain observation of transition from strong to weak coupling in a semiconductor microcavity
Authors: Jiang Shudong , Machida Susumu , Takiguchi Yoshihiro , Yamamoto Yoshihisa , Cao Hui
Published: July 2002

We measured temporal evolution of the coherent emission from a semiconductor microcavity by a very sensitive ac balanced homodyne detection system. The experimental results can be well explained by the coupled exciton–photon model with varying exciton linewidth.
Artificial ferroelectricity in coupled strained quantum dots
Authors: Khurgin Jacob B. , Jin Feng
Published: July 2002

A multiple quantum dot structure consisting of alternating strained and unstrained quantum dots and having nonzero net dipole moment, i.e., possessing ferroelectric properties, is proposed. Curie temperature and spontaneous polarization are estimated to be of the order of 20 K and 10−5 C/m2, respectively, for the case of InGaAs quantum dots grown on InP substrate and are shown to be insensitive to the lateral arrangement of the dots. Practical applications in information processing and storage are considered.
Observation of vibrational modes of irregular drums
Authors: Haeberlé Olivier , Sapoval Bernard , Menou Kristen , Vach Holger
Published: July 2002

Vibrational modes of irregular or prefractal drums have been calculated using a correspondence between the wave propagation and the diffusion equations. The resonance frequencies and the vibrational-mode structures measured on low thickness plastic film membranes using a holographic setup are found to be in good agreement with theoretical predictions.
Evaluation of electrical stress effects on SiO2–Si structures using scanning electron microscope cathodoluminescence
Authors: Liu X. , Chan D. S. H. , Chim W. K. , Phang J. C. H.
Published: July 2002

In this letter, we describe the hot-electron-injection-induced 2.7 eV luminescence centers and the interfacial stress dependence of the 2.7 eV cathodoluminescence peak buildup in SiO2–Si structures. The results suggest that electrical stress may relax the interface strain and modulate the radiation sensitivity. This phenomenon may be extended to provide a nonelectrical and physical evaluation of the electrical stress degradation of SiO2–Si structures. Possible mechanisms are proposed to explain the observations.