bluuebunny/crossref_metadata_2025 huggingface dataset:
Resonant cavity enhanced InP/InGaAs photodiode on Si using epitaxial liftoff
Authors: Salvador A. , Sverdlov B. , Lehner T. , Botchkarev A. , Huang F. , Morkoç H.
Published: July 2002

Epitaxial liftoff (ELO) is used in the fabrication of an InP/InGaAs resonant cavity photodetector on Si. External mirrors were employed with the bottom mirror consisting of an intermediate gold layer between the Si and ELO InP film. A dielectric stack of Si/SiO2 was used as the top mirror instead of a semitransparent metallic mirror to increase the quantum efficiency further. An external quantum efficiency of 0.57 in the spectral region of 1.55 μm was obtained for a 2500-Å-thick InGaAs absorbing layer. This is four times larger than the predicted value for a conventional pin photodiode with the same absorbing layer thickness. The spectral response showed wavelength selectivity. A full width at half-maximum of 150 Å is obtained with the top mirror reflectivity matched for optimum quantum efficiency. Further increase in the top mirror reflectivity improved spectral selectivity but at the expense of reduced quantum efficiency.
Optical transitions in strained In1−xGaxAsyP1−y quantum wells clad by lattice-matched barriers of InGaAsP
Authors: Jiang X. P. , Thiagarajan P. , Patrizi G. A. , Robinson G. Y. , Temkin H. , Forouhar S. , Vandenberg J. M. , Coblentz D. , Logan R. A.
Published: July 2002

We extend the deformation potential model developed previously for InGaAs/InP quantum wells to include strained quaternary wells, under compressive or tensile strain, and lattice-matched (or also strained) quaternary barriers. This requires interpolation of the needed quaternary materials parameters in a plane bound by the four binary parent compounds. The calculated energies of heavy and light hole transitions are compared to measured values obtained on a set of compressively strained multi-quantum-well quaternary structures grown on (100) InP with the lattice mismatch strain Δa/a as large as 0.75%. Our experimental results are in good agreement with the extended model.
Critical currents of YBa2Cu3Oy thick films prepared by liquid phase epitaxial growth
Authors: Yoshida Manabu , Nakamoto Takao , Kitamura Tasuku , Hyun Ok-Bae , Hirabayashi Izumi , Tanaka Shoji , Tsuzuki Akihiro , Sugawara Yoshihiro , Ikuhara Yuichi
Published: July 2002

We have succeeded in preparing c-axis oriented high-Jc YBa2Cu3Oy films on MgO(100) substrate by the liquid phase epitaxy (LPE) technique. The growth rate was typically about 2 μm/min, which was 10–102 times larger than that by ordinary vapor growth techniques. The film thickness ranged 10–50 μm by choosing the dipping time. The Tc of the best film exceeded 88 K after oxygen annealing, and the transport Jc was 1.1×105 A/cm2 at 77 K and 0 T. In-field Jc’s at 77 K and 1.5 T were 2.8×104 A/cm2 and 2.0×104 A/cm2 for the B⊥ab plane and B∥ab plane, respectively. In addition, the peak effect of Jc was observed at several tesla for B∥ab plane geometry. Based on the microstructure observed by high resolution transmission electron microscopy, the relevant peak effect is considered to be caused by stacking faults which act as a field induced pinning center.
Atomic layer control in Sr-Cu-O artificial lattice growth
Authors: Liu Ziyuan , Hanada Takashi , Sekine Rika , Kawai Maki , Koinuma Hideomi
Published: July 2002

Atomic layer growth control of the infinite-layer compound, SrCuO2, based artificial lattices is demonstrated on SrTiO3 (100). Two different patterns have been observed by reflection high-energy electron diffraction during the alternating supply of strontium and copper metal under the flow of NO2. The intensity of the incommensurate streak increases with an increasing supply of Cu and decreases to zero with an increasing supply of Sr. Precise control of atomic layer growth is successfully carried out by in situ intensity monitoring of the incommensurate streak.
Response function for gain and refractive index dynamics in active semiconductor waveguides
Authors: Mo/rk J. , Mecozzi A.
Published: July 2002

Based on semiclassical density matrix equations, we derive a simple analytical expression for the pump-probe response function of an active semiconductor optical waveguide. The results are in good agreement with published pump-probe measurements of gain and refractive index dynamics in laser amplifiers. In particular, an experimentally observed delay in carrier heating is explained, and spectral effects not previously considered are shown to be significant under typical experimental conditions.
High-efficiency laser oscillation of a microcavity laser excited by resonant optical pumping
Authors: Tezuka T. , Kushibe M.
Published: July 2002

High-efficiency laser oscillations by means of resonant optical pumping were observed in a planar microcavity laser with a single quantum well active layer. The threshold excitation power density was 19 W/cm2, and the differential energy conversion efficiency was 14%. This high efficiency is attributed to the absorption enhancement effect in the microcavity. Output power saturation was also observed in the input–output curve when the excitation wavelength was close to the band-edge wavelength. This saturation is considered to result from the resonance wavelength varying with the excitation intensity.
Increasing short minority carrier diffusion lengths in solar-grade polycrystalline silicon by ultrasound treatment
Authors: Ostapenko S. S. , Jastrzebski L. , Lagowski J. , Sopori B.
Published: July 2002

We have found that ultrasound treatment (UST) has a profound effect on the recombination rate in as-grown, B-doped cast polycrystalline silicon wafers for photovoltaic applications. As determined by surface photovoltage measurements of the minority carrier diffusion length L, the UST increases the corresponding lifetime by almost an order of magnitude. The maximum enhancement takes place in the wafer regions with the shortest L values. For L≳20 μm, both positive and negative changes of L after UST are revealed at different wafer regions. The UST effect is temperature dependent and exhibits maximum influence at about 60 °C. Enhanced dissociation of Fe-B pairs by UST is identified as a mechanism which leads to a negative change of large L values, and a complex post-treatment relaxation. A positive change of L is attributed to the influence of ultrasound vibrations on crystallographic defects.
Fast growth of hydrogenated amorphous silicon from dichlorosilane
Authors: Nakata Masami , Wagner Sigurd
Published: July 2002

We report the discovery of very high growth rates of hydrogenated amorphous silicon (a-Si:H) from a glow discharge in dichlorosilane (SiH2Cl2) with small additions of silane (SiH4). The growth rate reaches ∼50 Å s−1 at substrate temperatures between 200 and 300 °C. The rate depends on substrate temperature and is correlated with the concentrations of hydrogen and chlorine in the films in a way that suggests a SiH4-catalyzed mutual elimination of Cl and H from the growing surface. We observe no dust, and no growth on the cold walls of the chamber. The film properties suggest material close to device quality, with dark conductivities of ∼10−12 S cm−1 and photoconductivities of ∼10−7 S cm−1. We measured a midgap defect density of 3.3×1016 cm−3 in an as-grown film, and 4.5×1016 cm−3 after 73 h of light soaking at 1 W cm−2.
Short cavity distributed Bragg reflection lasers with a narrow band Bragg mirror: Dynamic characteristics
Authors: Tessler N. , Margalit M. , Eisenstein G. , Koren U. , Burrus C. A.
Published: July 2002

The dynamical characteristics of distributed Bragg reflection lasers with a Bragg reflection bandwidth narrower than the cavity mode spacing are reported. The operation of this Bragg reflector as an amplitude modulator (unlike the usual frequency modulator) is demonstrated in the small and large signal modulation regimes. In the conventional mode of gain modulation, this narrow Bragg reflector exhibits detuned loading effects. The laser is capable of efficient digital modulation as well as Q-switching, both with a very small drive current.
Interpretation of the silicon-hydrogen stretching doublet in a-Si:H hydrogenated amorphous silicon
Authors: Daey Ouwens J. , Schropp R. E. I. , van der Weg W. F.
Published: July 2002

We studied the correlation between the infrared integrated absorption strengths of the wagging, bending and stretching modes for four hydrogenated amorphous silicon (a-Si:H) series, deposited by rf glow discharge. The strength of these modes was varied by changing the deposition temperature while keeping other parameters fixed. For the first time it is shown that a straightforward correlation exists between these three modes. It is argued that the 2100-cm−1 mode is due to SiH2 bonds and that there is no contribution of SiH species on the inner surface of voids. The vibrational spectrum of a-Si:H can be well described by considering the vibrating dipole as a harmonic oscillator with an effective charge e*=0.44 electrons.
Vacuum ultraviolet and ultraviolet fluorescence and absorption studies of Er3+-doped LiLuF4 single crystals
Authors: Sarantopoulou E. , Kollia Z. , Cefalas A. C. , Dubinskii M. A. , Nicolaides C. A. , Abdulsabirov R. Yu. , Korableva S. L. , Naumov A. K. , Semashko V. V.
Published: July 2002

The laser induced fluorescence spectrum of LiLuF4:Er3+ single crystals, pumped by an F2 pulsed discharge molecular laser at 157 nm, was obtained in the vacuum ultraviolet (VUV) and ultraviolet (UV) regions of the spectrum at room temperature. A number of new fluorescence peaks were observed for the first time. They were assigned to the dielectric dipole allowed transitions 4f105d→4f11 of the Er3+ ion. In addition, the absorption spectrum of the same crystal samples was recorded. The positions of the bands within the 4f105d configuration were located at 65 098, 69 198, 71 422, 74 343, and 76 916 cm−1. The edge of the 4f105d bands was at 63 046 cm−1.
Amplitude squeezing of a multiple quantum-well distributed-feedback semiconductor laser operating at room temperature—Effect of reduction of spontaneous-emission noise by Interferometric method
Authors: Kikuchi Kazuro , Watanabe Kazuma , Katoh Kazuhiro
Published: July 2002

We demonstrate 3.4-dB amplitude squeezing of a multiple quantum-well distributed-feedback semiconductor laser operating at room temperature. The spontaneous-emission noise is eliminated by using a Michelson interferometer, where the intensity noise due to spontaneous emission is cancelled by the intensity noise converted from the frequency noise. The spectral density of the remaining noise is 3.4 dB below the shot-noise level, which is limited by the differential quantum efficiency of the laser.
Graphite thin-film formation by chemical-vapor deposition of o-methyl-diaryl ketones
Authors: Yudasaka M. , Kikuchi R. , Matsui T. , Ohki Y. , Yoshimura S. , Ota E.
Published: July 2002

Two kinds of o-methyl-diaryl ketones, 2,6-di(2′,6′-dimethyl-1′-naphthyl)-naphthalene, (O), and 2-methyl-1,2′-naphthyl ketone, (I), were used as starting materials for chemical-vapor deposition (CVD). Raman-scattering measurements and x-ray diffraction analyses for the obtained films made it apparent that well-crystallized graphite films could be grown on Ni substrate kept above 900 and 600 °C by using the materials (O) and (I), respectively. In order to obtain the crystalline graphite by CVD, the Ni substrate was necessary and the supply rate of the starting material must be in an optimum range. When the supply rate is too large, the obtained film contained the disordered graphite structure.
Novel wide-band time-resolved photoreflectance measurement technique
Authors: Pamplona Pires M. , Souza P. L. , von der Weid J. P.
Published: July 2002

We present a new versatile and simple pump-and-probe technique to measure the change in reflectivity (ΔR) and to time resolve the signal in a time scale faster than the responsivity of the detector used. Also, by slightly changing the experimental conditions, decay times ranging from 0.2 ns to 0.1 ms can be measured. This technique presents the advantage of eliminating in a natural way any undesirable photoluminescence or background signal. Important parameters for carrier dynamics studies are extracted from the time-resolved signal obtained. In addition, no contribution to the change in reflectivity due to band-filling effects was observed.
Band structure engineering and doping of wide gap II–VI superlattices
Authors: Faschinger W. , Ferreira S. , Sitter H.
Published: July 2002

It is shown that the free hole concentration for nitrogen doped ZnSe/ZnTe short period superlattices with a given average Te content of 15% can be increased from 1016 to 1019 cm−3 by just increasing the SL period from 2.5 to 4.5 nm. This behavior can be understood in terms of a model that assumes a pinning of the Fermi level at an energetic position that is fixed with respect to the vacuum level. The model can be applied to other II–VI superlattices, and alternative cladding layers for blue laser diodes are proposed that should exhibit significantly higher p-doping levels than the currently used ZnMgSSe claddings.
Real-time thickness control of resonant-tunneling diode growth based on reflection mass spectrometry
Authors: Celii F. G. , Harton T. B. , Kao Y.-C. , Moise T. S.
Published: July 2002

We used reflection mass spectrometry (REMS) to control the molecular beam epitaxial growth of resonant-tunneling diode (RTD) structures. The REMS-based thickness value controlled the effusion cell shutter actuation, and compensated in real time for flux transients and short-term flux drift. Use of REMS control during deposition of AlAs, InAs, and InGaAs layers resulted in improved symmetry and reproducibility of the RTD I-V characteristics, compared with time-based, dead-reckoning growth. REMS-based control for flux compensation during growth of GaAs/AlGaAs multi-quantum-well structures is also reported.
Oxide-nitride-oxide/Si(111) interfaces analyzed by optical second harmonic generation
Authors: Watanabe Kohji , Hirayama Hiroyuki , Kawata Masato
Published: July 2002

Optical second harmonic generation has been used to study oxide-nitride-oxide/Si(111) interfaces. The second harmonic (SH) intensity is measured as a function of an azimuthal rotation angle at a 45° incidence angle. The SH intensities change for wet oxidation, nitridation and reoxidation. The SH intensity from wet oxide/Si(111) interface decreases as the temperature during wet oxidation increases. With subsequent nitridation, this SH intensity of the oxidized interface then decreases. However, the SH intensity increases again with reoxidation.
Picosecond photoconductive sampling with nanosecond carrier lifetimes using an integrated inductive loop
Authors: Davidson Andrew C. , Wise Frank W. , Compton Richard C.
Published: July 2002

A noninvasive, photoconductive sampling technique, which does not require short-lifetime material to achieve picosecond temporal resolution, is demonstrated. The technique relies on electromagnetic coupling to generate the time derivative of the signal of interest in a separate sampling circuit. A slow photoconductive device in the sampling circuit integrates the coupled signal to produce the desired wave form. A 5-ps sampling response (limited only by circuit parasitics) was measured on GaAs with a lifetime of 1 ns by coupling to a small conducting loop.
Air stability of single crystal Rb1C60 from infrared reflectivity measurements
Authors: Winkler R. , Pichler T. , Kuzmany H.
Published: July 2002

Infrared reflectivity was measured in situ from single phase layers of Rb1C60 with a thickness of about 4 μm on a {111} face and of about 0.5 μm on a {100} face of C60 single crystals. The fcc→orthorhombic phase transition was traced by a splitting of the F1u (4) mode into three lines within a temperature range of 2° at 404/415 K for a cooling/heating cycle, respectively. The reflectivity spectra remained unchanged after exposing the orthorhombic Rb1C60 to air. Even the fcc phase appears to be vibrationally stable in air up to at least 450 K. The conductivity of the orthorhombic phase shows a weakly activated temperature dependence.
Ultrafast characterization of an in-plane gate transistor integrated with photoconductive switches
Authors: Ogawa K. , Allam J. , de B. Baynes N. , Cleaver J. R. A. , Mishima T. , Ohbu I.
Published: July 2002

An in-plane gate field-effect transistor is characterized by ultrafast electro-optic sampling. The transistor is monolithically integrated with photoconductive switches in coplanar waveguide and <0.5 ps measurement time resolution is achieved. The gate-drain capacitance of the transistor is obtained as 1.8 fF at zero drain voltage from displacement current transients. The gate-drain capacitance is dominated by parasitic capacitance and the intrinsic gate-drain capacitance is estimated as less than 0.2 fF.
Anomalous optical response of Nd1.85Ce0.15CuO4−y superconducting thin films
Authors: Bhattacharya S. , Mao S. N. , Jiang W. , Rajeswari M. , Li Qi , Xi X. X. , Venkatesan T.
Published: July 2002

A study of the normal state optical response of epitaxial thin films of electron doped superconductor Nd1.85Ce0.15CuO4−y is reported. The normal state optical response of these films were not proportional to the temperature derivative of the resistance of the films as expected by a bolometric model and as seen in p-type superconductors such as YBa2Cu3O7−δ. The normal state optical response of the films with different transition temperatures were also remarkably different from each other. The observation of anomalous optical response is attributed to the possible presence of photoconductivity in Nd1.85Ce0.15CuO4−y.
Nanoscale hardness and microfriction of titanium nitride films deposited from the reaction of tetrakis (dimethylamino) titanium with ammonia
Authors: Bae Y. W. , Lee W. Y. , Besmann T. M. , Blau P. J.
Published: July 2002

Nanocrystalline titanium nitride films with very low carbon and oxygen content were deposited on single-crystal silicon substrates from the reaction of tetrakis (dimethylamino) titanium, Ti[(CH3)2N]4, with ammonia at 633 K and a pressure of 665 Pa. The film consisted of ∼10 nm grains. The hardness of the film, measured by nanoindentation, was 12.7±0.6 GPa. The average kinetic friction coefficient, against type 440C stainless steel, was determined using a friction microprobe to be 0.43.
Very low level residual resistivity in silver-sheathed (Bi,Pb)2Sr2Ca2Cu3O10 tapes
Authors: Fukumoto Y. , Li Q. , Wang Y. L. , Suenaga M. , Haldar P.
Published: July 2002

Detailed measurements of voltage–current (E–J) characteristics have revealed a distinct low level resistive tail for silver-sheathed (Bi,Pb)2Sr2Ca2Cu3O10 superconducting tapes. The residual tail is observed at very low voltage (E≤10−8–10−7 V/cm) of the E–J curves and can be described by E∝(J−Jc′)n, where Jc′ is a field and temperature dependent critical current and n=1.0–1.2. The dynamic resistivity is, typically, in the range of 10−13 Ω cm, but could be as high as 10−11 Ω cm in some specimens. This residual resistance can be induced by a severe thermal cycling treatment, although it may also be intrinsic, i.e., as-grown, to some of the specimens.
Optical switching in a metal–semiconductor–metal waveguide structure
Authors: Bieber Amy E. , Prelewitz David F. , Brown Thomas G. , Tiberio Richard C.
Published: July 2002

We report the observation of all-optical switching in a metal–semiconductor–metal waveguide structure. A silicon-on-insulator waveguide with aluminum interdigitated fingers deposited on the surface and overcoated with amorphous silicon provided high-efficiency coupling and switching of Nd:YAG laser pulses. This structure is fully compatible with very large scale integrated manufacturing processes and represents a substantial leap forward in the quest for full-scale integration of silicon-based optoelectronic systems.
Experimental observation of efficient generation of femtosecond second harmonic pulses
Authors: Wang Gary Y. , Yang Y. , Garmire Elsa
Published: July 2002

Blues pulses 300 fs long have been generated from 150 fs infrared pulses by compressing second harmonic radiated in the Cerenkov geometry. Mode-locked Ti:sapphire pulses were prism coupled into a 1-cm long proton-exchanged MgO:LiNbO3 planar waveguide. The 2 ps Cerenkov output, chirped due to group velocity mismatch, was then compressed by a diffraction grating down to 300 fs. The use of mode-locked pulses results in a conversion efficiency of 1000%/W/cm, three orders of magnitude higher than by cw doubling in the same geometry. The Cerenkov geometry ensures that all wavelengths can be phase matched over long crystal length, so that even low power lasers can be efficiently doubled. The dispersion element ensures that the chirped output can be compressed into the femtosecond regime. This concept can be extended to femtosecond pulses in any two-photon process in any waveguide material and any mode-locked source.
Electron beam induced coalescence in plasma polymer silver composite films
Authors: Werner Jens , Heilmann Andreas , Mueller Falk
Published: July 2002

Plasma polymer thin films with embedded silver particles (5-50 nm) were irradiated by a small focussed electron beam of 10 kV. Before and after irradiation the films were investigated by transmission electron microscopy (TEM) to characterize the microstructure given by size and shape of the embedded silver particles. The changes of the microstructure after the electron beam irradiation were limited to small lines (<2 μm). Most changes were coalescence of the silver particles. Furthermore, after increased irradiation time and higher energy input areas nearly free of silver particles but without destruction of the plasma polymer matrix were found.
Piezoelectric interfacial waves in LiNbO3
Authors: Danicki E.
Published: July 2002

It is shown, by numerical analysis, that piezoelectric interfacial waves guided by a conducting plane embedded in a lithium niobate crystal exist in ∼6% of the volume of space of three Euler angles describing the plane orientation and the wave propagation direction with respect to crystallographic axes. Example wave solutions are presented.
Frequency modulation characteristics of gain-guided AlGaAs/GaAs vertical-cavity surface-emitting lasers
Authors: Kuksenkov D. V. , Temkin H. , Swirhun S.
Published: July 2002

We describe measurements of dynamic wavelength shift in single mode vertical cavity surface emitting lasers operating at 850 nm. Small signal modulation experiments yield a linewidth enhancement factor 3.7<α<4.5, depending on the modulation frequency. Under large signal modulation we measure Δν×Δτ∼3.6 for gain switched pulses. The dependence of dynamic chirp on the pulse width is accurately modeled by numerical solution of rate equations.
Continuous wave near-infrared atomic Xe laser excited by a radio frequency discharge in a slab geometry
Authors: Tskhai S. N. , Udalov Yu. B. , Peters P. J. M. , Witteman W. J. , Ochkin V. N.
Published: July 2002

Near-infrared atomic Xe laser lines have been generated from an Ar:He:Xe laser gas mixture excited by a radio frequency (rf) discharge in a slab geometry. A maximum continuous wave (cw) output power of 1.5 W (270 W/l) was obtained at an rf frequency of 125 MHz from a gas mixture containing Ar:He:Xe (50:49:1) at a total gas pressure of 90 Torr.
Growth and characterization of (Y3Fe5O12–Bi3Fe5O12) heterostructures by pulsed laser deposition
Authors: Simion B. M. , Thomas G. , Ramesh R. , Keramidas V. G. , Pfeffer R. L.
Published: July 2002

Superlattice heterostructures consisting of alternating single crystalline ferrimagnetic yttrium–iron–garnet (YIG) and bismuth–iron–garnet (BIG) thin film layers on gadolinium–gallium–garnet substrates show an increased saturation magnetization with respect to that of the monolayered structures grown under the same conditions. The observed effect is attributed to the distortions introduced in the YIG layers by the adjacent BIG layers. In this letter, we report our growth approach, by pulsed laser deposition, of these unusually performing thin film heterostructures.
Incorporation of oxygen and chlorine atoms into low-temperature (850 °C) silicon epitaxial films by chemical vapor deposition
Authors: Miyauchi Akihiro , Ueda Kazuhiro , Inoue Yousuke , Suzuki Takaya , Imai Yoshinori
Published: July 2002

A correlation between the partial pressure of dichlorosilane gas (SiH2Cl2) and the incorporation of oxygen (O) and chlorine (Cl) atoms into the low-temperature (850 °C) epitaxial films was found. The profiles of O and Cl concentrations in the epitaxial films were measured by secondary ion mass spectroscopy. Incorporation of O and Cl atoms into the growth films during the epitaxial growth was suppressed by increasing the partial pressure of SiH2Cl2. The growth rate linearly increased with the partial pressure of SiH2Cl2 and eventually saturated. Incorporation of O atoms was inhibited and fine removal of Cl atoms was achieved when the growth rates saturated. The epitaxial films with high O and Cl concentrations had a microroughened surface (root mean square of microroughness ≳0.4 nm). The microroughness was also improved by increasing the partial pressure of SiH2Cl2. The coverage of kinks and/or hollow bridge sites by hydrogen (H) and Cl atoms seems to restrict the reaction of O and water (H2O) with the growth front surface.
Spontaneous and stimulated emission by Eu-chelate in a planar microcavity
Authors: Ebina Kazuhito , Okada Yoshiko , Yamasaki Akira , Ujihara Kikuo
Published: July 2002

Characteristics of spontaneous and stimulated emission by Eu(BFA)4− chelate in a planar microcavity of 2.5λ length are studied experimentally. The spontaneous emission enhancement factor is close to unity. The observed spectral width and the angular divergence of spontaneous emission are consistent with theory. A distinct threshold for the transition from spontaneous to stimulated emission was observed with an associated decrease in the decay time of the emission. The spectral width decreased with increasing pumping power.
Critical thickness condition for growth of strained quantum wires in substrate V-grooves
Authors: Freund L. B. , Gosling T. J.
Published: July 2002

The physical system under study is a quantum wire of roughly triangular cross section grown epitaxially in a V-shaped groove on a patterned (100) surface of a cubic substrate. The walls of the groove are {111} planes of the substrate material, so that the wire extends along a 〈110〉 direction. For a given thickness, or depth, of the wire, an analysis is presented which leads to an estimate of the smallest elastic mismatch strain for which the wire remains stable against formation of misfit dislocations, in the spirit of the Matthews-Bladeslee condition, taking into account both the free surface effect and the mismatch strain effect. Comparison is made with the experimental observations of T. Arakawa, S. Tsukamoto, Y. Nagamune, M. Nishioka, J.-H. Lee, and Y. Arakawa [Jpn. J. Appl. Phys. 32, L1377 (1993)].
Study of photochemical reaction from C70 adsorbed on silver film by surface enhanced Raman scattering
Authors: Mo Yujun , Mattei Giorgio , Pagannone Mario , Xie Sishen
Published: July 2002

We have measured by micro-Raman spectroscopy the surface enhanced Raman scattering (SERS) spectra of about 2 monolayers of C70 on Ag surface. New Raman bands of the fullerene molecule have been found. The time evolution (from C70 to amorphous carbon) of the SERS spectra, under high laser power density illumination in air, provides evidence of photochemical reactions. New bands in the Raman spectra appearing with the time have been attributed to intermediate products of these photochemical reactions.
Optical second harmonic characterization of spontaneous symmetry-breaking at polymer/transparent conductor interfaces
Authors: Ghebremichael F. , Poga C. , Kuzyk M. G.
Published: July 2002

We report on the temperature dependence of optical second harmonic generation from a thin indium tin oxide (ITO)-coated glass substrate (commonly used as a transparent electrode), from a polymer layer on ITO, and from an antimony tin oxide (ATO) coating. We have found that when thin isotropic polymer films are deposited on the ITO-coated surface, the resulting second harmonic intensity is larger than the second harmonic intensity from ITO or polymer separately. We discuss how the ITO interface may act to induce polar order in the polymer and consider how interfacial second harmonic sources contribute to electric-field-induced second harmonic studies of dye-doped polymers in which ITO is used as a transparent electrode.
90° domains in Co/Cu giant magnetoresistance superlattices
Authors: Yang Z. J. , Scheinfein M. R.
Published: July 2002

The magnetic properties of Co/Cu superlattices grown in a dual-beam electron evaporation chamber have been investigated with the three-axis magneto-optical Kerr effect and magnetoresistance measurements. The magnetoresistance oscillates with a period of about 1 nm as a function of the Cu layer thickness. The magnitude of the component of the magnetization perpendicular to the field direction oscillates with the same period. The total magnetization, calculated from the two in-plane hysteresis loops, is used to determine that 90° domains are formed between ferromagnetic Co layers across the Cu spacer layers in the superlattice. The correlations between the 90° magnetization curves and magnetoresistance measurements suggest that the giant magnetoresistance in superlattices with imperfect interfaces results from the 90° orientation of domains within adjacent Co layers.
Monolithic optical transmitter circuit using the InGaP/GaAs material system
Authors: Nichols D. T. , Lopata J. , Hobson W. S. , Smith P. R. , Dutta N. K.
Published: July 2002

A strained InGaP/GaAs/InGaAs multiquantum well laser has been monolithically integrated with GaAs metal–semiconductor field effect transistors (MESFETs) in a differential pair configuration to form a transmitter circuit. The structure utilized a single epitaxial growth step in which the laser was grown on top of the MESFET. The circuits operated with bandwidths as high as 4 GHz.
Laser cavity mirror imperfections and reflectivity: A time-dependent numerical approach
Authors: Vurgaftman Igor , Singh Jasprit
Published: July 2002

While the cleaving process used for semiconductor Fabry–Pérot lasers produces atomically abrupt mirrors, there is considerable interest in mirrors defined by etching. Depending on the etching process employed, disorder of varying nature and degree results at the semiconductor–air interface. A theoretical approach capable of quantifying the impact of such disorder on the mirror reflectivity, to which laser performance is intimately connected, is presented. The theoretical technique is time-dependent to facilitate visualization of the scattering process and is based on a locally one-dimensional implicit-finite-difference approximation to the two-dimensional scalar wave equation with variable coefficients. Mirror disorder is described in terms of a feature depth parameter and an in-plane correlation length. The reflectivity falls off exponentially with disorder yet is found to remain close to its unperturbed value for the disorder scale attainable with the state-of-the-art etching technology.
Polymeric alkali fullerides are stable in air
Authors: Koller Daniel , Martin Michael C. , Stephens Peter W. , Mihaly Laszlo , Pekker Sandor , Janossy Andras , Chauvet Olivier , Forro Laszlo
Published: July 2002

Infrared transmission, electron spin resonance, and x-ray diffraction measurements show unambiguously that RbC60 and KC60 are stable in air, in contrast to Rb6C60 which decomposes rapidly upon exposure. The specimens studied transform to pure C60 and other by-products when heated above 100 °C, approximately the temperature of the orthorhombic-fcc phase transition. The stability of these compounds raises the possibility of applying them as protective layers for the superconducting fullerides.
Formation and decay dynamics of excitonic photoluminescence in a GaAs/AlGaAs superlattice under an electric field
Authors: Schneider H. , Kanamoto K. , Fujiwara K.
Published: July 2002

Photoluminescence (PL) dynamics of localized excitons in a strongly coupled 40 Å/40 Å GaAs/Al0.2Ga0.8/As superlattice under an electric field along the growth direction is reported. At zero field, a delayed PL formation due to the relaxation of dark excitons into radiative states is observed. With increasing field, both the PL decay time and the PL amplitude are strongly reduced. A rate equation analysis of the measured PL transients gives evidence that the field-induced dissociation of nonradiative excitons is important.
Infrared reflection spectra of CdIn2O4 films
Authors: Wang Wanlu , Liao Kejun
Published: July 2002

The infrared (IR) reflection spectra of CdIn2O4 films produced by rf reactive sputtering from a Cd-In alloy target in a reactive Ar+O2 atmosphere have been investigated. Experimental results show that IR reflection spectra from CdIn2O4 films changed with increasing oxygen concentration and heat treatment, and the results obtained are discussed briefly.
Electro-optic polymer films poled after cross linking
Authors: White K. M. , Kitipichai P. K. , Francis C. V.
Published: July 2002

The electro-optic response in a cross-linked nonlinear optical polymer has been determined as a function of the extent of curing that takes place after coating and drying a film of the material but prior to poling it. It was found that although the value of the electro-optic coefficient was reduced by partially curing the film before poling, the decrease was minimal even in a fully cured film. Furthermore, the thermal stability of the electro-optic response was unaffected by the extent of curing before poling.
Room-temperature deep-blue stimulated emission in ZnS/ZnSe and ZnSTe/ZnSe strained layer superlattices
Authors: Wang H. , Wong K. S. , Sou I. K. , Wong G. K. L.
Published: July 2002

The light emitting properties of ZnS/ZnSe and ZnSTe/ZnSe strained II–VI superlattices are investigated. Room-temperature stimulated emission by photopumping in the deep-blue spectral region is observed. An upper limit of threshold carrier density required to achieve lasing is estimated to be 3×1018/cm3.The peak of stimulated emission is several tens of meV red shifted from the spontaneous emission peak, suggesting that exciton-exciton scattering is involved in the stimulated emission process.
Study on the operation of a dual channel digital superconducting quantum interference device with direct-current-powered Josephson multiplexer readout
Authors: Takeda Eriko , Nishino Toshikazu , Takagi Kazumasa
Published: July 2002

Operation of a dual channel digital superconducting quantum interference device (SQUID) with a dc-powered Josephson multiplexer (MUX) readout has been observed successfully using a test circuit. In the circuit, output signals of two SQUIDs are digitized by Josephson comparators and read out by the MUX. The noise of the SQUIDs under the operation of the whole circuit is 0.54Φ0/√Hz at 1 kHz. Advantage of using a dc-powered circuit to realize a low noise SQUID measurement system is confirmed.
Reduction of the frequency chirp of two section distributed feedback laser by nonuniform current injection
Authors: Feng J. , Chen T. R. , Zhao B. , Yariv A.
Published: July 2002

The effect of nonuniform current injection on the frequency chirp of a two section distributed feedback (DFB) laser, which is under large signal modulation, is measured while the optical intensity and optical modulation depth are fixed. By adjusting the injection current distribution in the laser, the frequency chirp can be reduced since the effects of carrier density fluctuations in the two sections on the chirp partially compensate each other. The range of the injection current ratio of the two sections is found in which the chirp is at its minimum. The reduction of the frequency chirp is predicted by a computer simulation for two section DFB lasers which accounts for the longitudinal spatial hole burning.
Periodical nanostructure fabrication using electron interference fringes produced by scanning interference electron microscope
Authors: Fujita S. , Maruno S. , Watanabe H. , Kusumi Y. , Ichikawa M.
Published: July 2002

A scanning interference electron microscope (SIEM) has been developed for periodical nanostructure fabrication. This system can produce electron interference fringes with a period from 2 nm to several tens of micrometers. Fabrications of periodical nanostructures with 23 to 170 nm periods have been demonstrated by transferring the electron interference fringe onto the semiconductor surfaces.
Critical current limiting structural defects in melt-textured YBa2Cu3O7−δ
Authors: Hedderich R. , Schuster Th. , Kuhn H. , Geerk J. , Linker G. , Murakami M.
Published: July 2002

Structural analyses and investigations of flux penetration of typically melt-textured YBa2Cu3O7−δ samples were performed. This allows regions of suppressed critical current density to be directly related to microstructural defects. At small-angle grain boundaries the critical current density was found to be reduced by a factor of up to 20.
Response of electrons in coupled quantum wells to external perturbations: Enhancement due to interactions
Authors: Totsuji Hiroo
Published: July 2002

Theoretical analyses are given on the response of electrons in coupled symmetrical quantum wells to external perturbations which destroy the symmetry. It is shown that, when appropriate conditions are satisfied, small perturbations have an enhanced effect to polarize the distribution of electrons in this system. The result may be useful to control the status of electrons in such coupled wells.
Low temperature heteroepitaxy of InP on Si(111) substrates treated with buffered HF solution
Authors: Ababou Y. , Masut R. A. , Yelon A. , Poulin S.
Published: July 2002

Low temperature metalorganic vapor phase heteroepitaxy of InP on Si(111) using buffered HF solutions for preparation of the Si surface is reported. X-ray photoelectron spectroscopy analysis showed no presence of chemisorbed contaminants on the substrate surface after surface preparation. We used high-resolution x-ray diffraction to characterize the quality of the InP epilayers. Optimum InP layers were obtained when the surface was treated with a buffered HF solution with a pH of 6.2, which produces the minimum substrate surface roughness, as reported in the literature. The InP layers grown on normally oriented Si(111) show the presence of large antiphase domains.
Electronic structure of Si(111)-7×7 phase boundary studied by scanning tunneling microscopy
Authors: Miyake Koji , Shigekawa Hidemi , Yoshizaki Ryuzo
Published: July 2002

Remarkably low electron density of Si adatoms at the Si(111)-7×7 phase boundary was found by scanning tunneling microscopy. The observed charge transfer was apparent with sample bias voltages down to ∼−0.8 eV, close to the value of the dangling bond state of the rest atoms in the Si(111) 7×7 surface. In consideration of the DAS (dimer-adatom-stacking fault) model, the observed charge transfer could be related to the structural change in the dimer layer caused by phase mismatching at the boundary. In fact, such charge transfer was not observed at the less disordered boundaries formed by introducing 5×5 half unit cells. Similar large charge transfer was found to occur in the quenched disordered 1×1 structure. These results agree with the similar chemical reactivity observed in the two disordered structures.
Low-temperature vapor-phase etching of silicon carbide by dioxygen difluoride
Authors: Moalem M. , Olander D. R. , Balooch M.
Published: July 2002

Efficient room-temperature vapor-phase etching of SiC by the compound dioxygen difluoride (FOOF) has been demonstrated. FOOF was generated using a design based on thermal-atomization technique which produced gram quantities of the compound per hour. On both poly- and epitype silicon carbide at room temperature, about 6% of the FOOF molecules striking the surface reacted to form SiF4 and CO. Examination by atomic force microscopy (AFM) showed that the roughness and morphology of the etched surface were virtually indistinguishable from those of the original surface. No residues or anisotropies were present on the etched surface.
Photoluminescence characteristics of Se-doped GaInP/AlGaInP double heterostructures grown by metalorganic chemical vapor deposition
Authors: Toda A. , Nakano K. , Yamamoto T. , Ikeda M.
Published: July 2002

Photoluminescence (PL) characteristics of Se-doped Ga0.5In0.5P/(Al0.5Ga0.5)0.5In0.5P double heterostructure (DH) on GaAs substrates were investigated at room temperature. The PL intensity and the decay time both strongly depend on the cladding-layer carrier density. Up to a carrier density of 2.5×1017 cm−3, the PL intensity increases linearly with carrier density, while the decay time is almost constant. For carrier densities larger than 2.5×1017 cm−3, the PL intensity and the decay time decrease linearly and quadratically with carrier density, respectively. We also studied the PL characteristics of Se-doped Ga0.5In0.5P and (Al0.5Ga0.5)0.5In0.5P single layers on GaAs substrates. We found that the carrier density dependence of DH governed by the cladding layer is similar to that of (Al0.5Ga0.5)0.5In0.5P single layers. These results indicate that a nonradiative interfacial recombination process dictates the DH PL characteristics and that the quality of the cladding layer affects the PL radiative efficiency.
Excitation power dependence of photoluminescence enhancement from passivated GaAs
Authors: Liu Chang Sheng , Kauffman John F.
Published: July 2002

Photoluminescence (PL) efficiency plots versus laser excitation power are presented for bare and Na2S treated n-GaAs. The plots demonstrate an increase in PL quantum yield with increasing excitation power density for both samples. The PL enhancement observed in the Na2S treated sample is presented and is shown to depend strongly on excitation power density. Application of the deadlayer model to the analysis of low power PL efficiency from bare GaAs indicates that surface electron-hole recombination is significantly slower than surface minority carrier trapping.
Investigation of the distribution of silicon interstitials in silicon and silicon-on-insulator structures after thermal oxidation
Authors: Tsoukalas D. , Tsamis C.
Published: July 2002

In this work we investigate the diffusion of silicon interstitials in bulk silicon and silicon-on-insulator structures. The interstitials that are injected by an oxidation process are monitored by the growth of oxidation stacking faults. The silicon-on-insulator structures are obtained by the silicon wafer bonding technique that gives us the advantage of monitoring both the lateral and the vertical distribution of point defects by special pretreatment of the bonded wafers. We observe a decrease in the lateral diffusion of interstitials as the thickness of silicon decreases. Simulation of these results reveals fundamental properties of point defects.
High-field domain formation in GaAs/AlGaAs superlattices
Authors: Han Z. Y. , Yoon S. F. , Radhakrishnan K. , Zhang D. H.
Published: July 2002

The formation of high-field domains in a semiconductor superlattice is verified using a GaAs/AlGaAs superlattice structure with multiple-quantum wells of different well thicknesses but identical barrier width grown by molecular beam epitaxy. Low-temperature current–voltage (I–V) measurements under forward and reverse bias showed that the high-field domain is first formed at the region of wider well thickness instead of preferentially at the anode or the cathode. The electron tunneling process through a tight-binding superlattice with weak coupling between adjacent wells is discussed in terms of the formation and extension of the high-field domains through the superlattice region.
Compact design for photothermal deflection (mirage): Spectroscopy and imaging
Authors: Charbonnier F. , Fournier D.
Published: July 2002

We describe a new design for a mirage cell which is much more compact than the previously described setup and whose sensitivity has been improved by an order of magnitude. This cell has been successfully coupled to Fourier transform infrared spectrometers, visible spectrometers, and a thermal wave imaging setup.
Multiple specimen-exchange system for molecular beam epitaxy
Authors: Price G. L.
Published: July 2002

A relatively simple and inexpensive specimen-exchange system for molecular beam epitaxy or other similar UHV applications is described. It allows 12 samples to be simultaneously loaded and degassed in UHV.
Measurement of the recombination velocity at single crystalline/polycrystalline GaAs interfaces using time-resolved photoluminescence
Authors: Mochizuki Kazuhiro , Kasai Jun-ichi , Tanoue Tomonori
Published: July 2002

The recombination velocity at single crystalline/polycrystalline Be-doped GaAs interfaces is measured using time-resolved photoluminescence. Samples with AlGaAs/GaAs double heterostructures are grown by molecular beam epitaxy on GaAs substrates patterned with SiO2. For a Be doping level of 3×1016 cm−3, the interface recombination velocity at 77 K is in the range of (2 to 10)×6 cm/s, and it is independent of the polycrystal grain size. The latter is explained by assuming that the carrier capture cross section is constant on the polycrystal grain surface.
Characteristics of oxygen over-reduced Nd1.85Ce0.15CuO4−y films
Authors: Mao S. N. , Jiang Wu , Xi X. X. , Li Qi , Peng J. L. , Greene R. L. , Venkatesan T. , Beesabathina D. Prasad , Salamanca-Riba L. , Wu X. D.
Published: July 2002

We have studied the oxygen doping effect in thin Nd1.85Ce0.15CuO4−y (NCCO) films. Contrary to the common believe that the disappearance of superconductivity in the over-reduced NCCO samples is a consequence of phase decomposition, we found that there exists an over-reduced region in which the crystallographic structure of the film remains essentially the same as in the optimum-oxygen doped region, but the film becomes insulating. Rutherford backscattering spectroscopy channeling analysis reveals that the oxygen over-reduction increases atomic distortion in the lattice. This work provides strong support to previous transport studies by Jiang et al. [Phys. Rev. Lett. 73, 1291 (1994)], which suggested the existence of both electron and hole carriers in superconducting NCCO.
Phase response measurement technique for waveguide grating filters
Authors: Brooks Cameron J. , Vossler Gerald L. , Winick Kim A.
Published: July 2002

A simple interferometric technique is described which can be used to accurately measure the phase response of waveguide grating filters. A narrowband, tunable Ti:sapphire laser is used in a Michelson interferometer configuration, where light reflected from a waveguide grating filter is combined with a reference beam. The intensity of the combined beams is measured as the wavelength of the Ti:sapphire laser is tuned. The measured intensity exhibits a quasisinusoidal wavelength dependence, from which the phase response of the filter can be deduced. This method is successfully demonstrated using both an integrated optic waveguide grating filter and a bulk grating pair.
Across wafer etch rate uniformity in a high density plasma reactor: Experiment and modeling
Authors: Surendra M. , Guarnieri C. R. , Selwyn G. S. , Dalvie M.
Published: July 2002

A study of silicon oxide etch rate uniformity in a high density, rf inductively coupled system with an rf capacitively coupled substrate electrode is presented. By introducing spatial variation of rf coupling to the substrate, etch rate uniformity across the wafer can be altered from a profile that is ∼20% higher in the center to one that is ∼10% lower in the center. The effect of spatially varying rf coupling impedance to the substrate is dependent on substrate resistance. Predicted etch rate profiles are obtained with a two-dimensional analytic model of the plasma source that is coupled to an equivalent circuit discretization of the electrode assembly, substrate, and sheath. Model results compare favorably with experimental measurements.