bluuebunny/crossref_metadata_2025 huggingface dataset:
D (donor) X center behavior for holes implied from observation of metastable acceptor states
Authors: Han J. , Ringle M. D. , Fan Y. , Gunshor R. L. , Nurmikko A. V.
Published: July 2002

The observation of persistent photoconductivity in nitrogen-doped p-ZnMgSSe at low temperature is reported. The increase of conductivity after illumination appears due to a metastable population of holes which are in thermodynamic equilibrium with hydrogenic acceptors having reduced activation energy. The experimental evidence suggests the presence of a DX-like [D (donor) X center] behavior for holes.
Novel low-resistance ohmic contact to n-type GaAs using Cu3Ge
Authors: Aboelfotoh M. O. , Lin C. L. , Woodall J. M.
Published: July 2002

We show that ε1-Cu3Ge forms a low-resistance ohmic contact to n-type GaAs. The ε1-Cu3Ge contact exhibits a planar and abrupt interface and contact resistivity of 6.5×10−7 Ω cm2 which is considerably lower than that reported for Ge/Pd and AuGeNi contacts on n-type GaAs with similar doping concentrations (∼1×1017 cm−3). The contact is electrically stable during annealing at temperatures up to 450 °C. We also show that in the Ge/Cu/n-type GaAs system, the contact remains ohmic over a wide range of Ge concentration that extends from 15 to 40 at. %. n-channel GaAs metal–semiconductor field-effect transistors using the ε1-Cu3Ge ohmic contacts demonstrate a higher transconductance compared to devices with Ge/Pd and AuGeNi contacts.
Surface scattering of x rays from InP (001) wafers
Authors: Li J. H. , Cui S. F. , Li M. , Li C. R. , Mai Z. H. , Wang Y. T. , Zhuang Y.
Published: July 2002

We have studied the surface scattering of x rays from mechanical-chemical polished InP (001) wafers with sulfur and/or iron doping. The scattering intensities in the scans transverse to the specular reflection rod were found to contain two components. A simple surface model was proposed to explain the experimental data. The results were also compared with those obtained from crystal truncation rod measurements.
Strontium and SrO epitaxy on hydrogen-terminated Si(111)
Authors: Hirata Akihiko , Saiki Koichiro , Koma Atsushi
Published: July 2002

Epitaxy of Sr and SrO films onto hydrogen-terminated Si (111) has been demonstrated. The use of hydrogen-terminated Si (111) has enabled the epitaxy of metallic Sr films, whereas direct epitaxy on a clean 7×7 Si (111) surface has not been successful. The alternate supply of Sr and O during growth has made it possible to grow good epitaxial SrO films. It has been revealed by electron energy loss spectroscopy that stoichiometric SrO films are obtained by this method.
Ho:YLiF4 saturable absorber Q-switch for the 2-μm Tm,Cr:Y3Al5O12 laser
Authors: Kuo Yen-Kuang , Birnbaum Milton , Chen Wei
Published: July 2002

Passive Q-switching of the flashlamp pumped Tm,Cr:Y3Al5O12 2-μm laser with a Ho:YLiF4 saturable absorber has been demonstrated at room temperature. A single Q-switched laser pulse of 11 mJ in energy and ∼45 ns in duration at 80 J flashlamp input energy was obtained. The wavelength of the Q-switched laser output pulse and the Tm,Cr:Y3Al5O12 free-running output was 2.017 μm.
Superconducting Bi-cuprate thick film T
c(0)=110 K on DyBa2SnO5.5: A newly developed perovskite substrate
Authors: Koshy J. , Kumar K. S. , Kurian J. , Yadava Y. P. , Damodaran A. D.
Published: July 2002

A new ceramic perovskite DyBa2SnO5.5 has been synthesized and developed for its use as a substrate for Bi(Pb)–Sr–Ca–CuO superconductors. The dielectric constant and loss factor of this material are in a range suitable for its use as a substrate for microwave applications. DyBa2SnO5.5 is found to be chemically compatible with Bi(Pb)–Sr–Ca–CuO superconductors. Bi(2223) superconducting thick film fabricated on DyBa2SnO5.5 substrate gave a Tc(0)=110 K with a transition width of 2 K.
SrCuO2/(Sr,Ca)CuO2 superlattice growth by pulsed-laser deposition
Authors: Norton D. P. , Budai J. D. , Lowndes D. H. , Chakoumakos B. C.
Published: July 2002

Superlattice structures, consisting of SrCuO2 and (Sr,Ca)CuO2 layers in the tetragonal, ‘‘infinite layer’’ crystal structure, have been grown by pulsed-laser deposition. Superlattice chemical modulation is observed for structures with SrCuO2 and (Sr,Ca)CuO2 layers as thin as a single unit cell (∼3.4 Å). X-ray diffraction intensity oscillations, due to the finite thickness of the film, indicate that these films are extremely flat with a thickness variation of only ∼20 Å over a length scale of several thousand angstroms. These results show that unit-cell control of (Sr,Ca)CuO2 growth is possible in an oxygen pressure regime in which in situ surface analysis is not possible.
Wavelength switching in pump-diode-modulated mode-locked and Q-switched Er-fiber laser
Authors: Okhotnikov O. G. , Araújo F. M. , Salcedo J. R.
Published: July 2002

An Er-doped fiber laser configuration is described which utilizes a coupled cavity terminated with Bragg reflectors with intracavity 1.48 μm laser diode used as pump source and modulator. This approach represents a minimal configuration for a mode-locked and Q-switched fully integrated fiber laser. Individual addressing of reflectors and fast wavelength switching can be obtained by current modulation of the laser diode in a dispersive compound resonator.
CuInSSe-doped glass saturable absorbers for the passive mode-locking of neodymium lasers
Authors: Yumashev K. V. , Mikhailov V. P. , Prokoshin P. V. , Jmako S. P. , Bodnar I. V.
Published: July 2002

By using a CuInS2xSe2(1−x)-doped glass as an intracavity saturable absorber, passive mode-locking of Nd:YAG and Nd:YAlO3 lasers is obtained. Ultrashort laser pulses are achieved with duration of 16 ps (for Nd:YAlO3 at 1.08 μm) and 36 ps (for Nd:YAG at 1.064 μm), respectively. The intensity dependent transmittance and transient absorption change measurements are performed on CuInS2xSe2(1−x)-doped glasses at 1.08 μm with the use of laser pulses of 15 ps width. The bleaching relaxation time is found to be ∼11 ps.
Preparation and analysis of the negative resistance characteristic in an amorphous silicon and silicon–carbide single-barrier device
Authors: Chen K. H. , Fang Y. K. , Shieh K. H. , Liou W. R.
Published: July 2002

The characteristics of negative differential resistance in an amorphous silicon and silicon–carbide single-barrier device have been experimentally observed at room temperature. Based on the calculated and measured results, the barrier thickness is the important factor in determining the current–voltage characteristics of this device. In addition, the effective mass and the series resistance of amorphous materials are larger than that of crystalline materials. Thus the behavior of negative differential resistance of an amorphous silicon single-barrier device would be different from that of single-crystalline devices.
Optically multistable operation of a waveguide device based on the Wannier–Stark effect in an InGaAs/InP superlattice
Authors: Neitzert H. C. , Campi D. , Cacciatore C. , Rigo C. , Stano A. , Coriasso C.
Published: July 2002

An optically multistable device in waveguide configuration has been fabricated, which is based on the Wannier–Stark effect in an InGaAs/InP superlattice. It implements a waveguided version of the self-electro-optic effect device and it operates at room temperature at a wavelength of 1.55 μm.
Lead loss, preferred orientation, and the dielectric properties of sol-gel prepared lead titanate thin films
Authors: Sato Eiichi , Huang Yuhong , Kosec Marija , Bell Andrew , Setter Nava
Published: July 2002

The PbO loss during rapid thermal annealing of PbTiO3 thin films prepared by the sol-gel method has been investigated using electron probe microanalysis. The results have been correlated with the x-ray diffraction analyses and the dielectric properties of the films. The films start to loose PbO significantly during annealing at 600 °C for 60 s. After annealing at 700 °C the Pb/Ti ratios decrease down to 1.0 independent of the amount of excess PbO of the solutions. No PbO crystalline phases are observed in the x-ray diffraction patterns, therefore the excess PbO is assumed to remain in the films as an amorphous phase.
Radiative isoelectronic complexes introduced during the growth of Si and Si1−xGex/Si superlattices by molecular beam epitaxy
Authors: Moore Karen L. , King Oliver , Hall Dennis G. , Bevk Joze , Furtsch Matthias
Published: July 2002

Radiative isoelectronic impurity complexes consisting of pairs of Be atoms that bind excitons can be formed in both Si and SiGe/Si superlattices during growth by molecular beam epitaxy. We describe in this letter the conditions under which these radiative complexes can be formed, show that they can be localized in the alloy layers of a superlattice, and demonstrate that the blueshift of the bound-exciton’s no-phonon line that occurs for Be-implanted superlattices is absent for grown-in Be complexes. Be densities in excess of 5×1017 cm−3 can be achieved.
Novel technique for growth-etch cycling of flame-deposited diamond films
Authors: Thorpe T. P. , Weimer R. A. , Freitas J. A.
Published: July 2002

We have developed a novel technique for growth-etch cycling of diamond films deposited with an oxygen-acetylene torch, whereby a spinning wheel with removable teeth periodically disrupts the depositing flame in open atmosphere to allow air etching of a heated substrate. Cycling times as short as 0.02 s, with a growth/etch time ratio of approximately 19, have produced films with macro-Raman peak widths (full width at half-maximum) of approximately 3 cm−1. A predominance of large 100 crystal faces, with dimensions up to 300 μm, is evident in optimized films.
Generation of 290 fs pulses at 1.3 μm by hybrid mode-locking of a semiconductor laser and optimization of the time-bandwidth product
Authors: Yu J. , Schell M. , Schulze M. , Bimberg D.
Published: July 2002

With hybrid mode-locking of an ion-implanted semiconductor laser in an external cavity and subsequent chirp compensation, 290 fs pulses at 1.3 μm are generated. Due to the nonlinear chirp component, the time-bandwidth product is a factor of 2.3 above the Fourier limit. Using a folded grating-mirror cavity, the nonlinear chirp is effectively suppressed, leading to 1.6 ps pulses with a time-bandwidth product only 12% above the theoretical limit. The influence of the cavity geometry upon the chirp is investigated in detail.
Structural and electrical properties of (Ti0.9Zr0.1)Si2 thin films on Si(111)
Authors: Dao Y. , Edwards A. M. , Ying H. , Chen Y. L. , Sayers D. E. , Nemanich R. J.
Published: July 2002

Alloy films of Ti and up to 20% Zr were prepared by codeposition onto Si(111) surfaces in ultrahigh vacuum. After in situ thermal annealing at temperatures of ∼600 °C, the films form the C49 phase and are stable in this phase up to at least 910 °C. In contrast, Ti films on Si(111) initially react to form the C49 phase and transform to the C54 phase at ∼700 °C. The surfaces of the (Ti0.9Zr0.1)Si2 alloy films are studied by atomic force microscopy and are shown to be smoother than the surfaces of TiSi2 films on Si substrates. In addition the tendency to island formation is also not observed for annealing temperatures less than 910 °C. The sheet resistivity of the (Ti0.9Zr0.1)Si2 alloy films is found to be ∼46 μΩ cm for annealing temperatures from 600 to 910 °C.
Thick c-axis textured (Tl,Pb)(Ba,Sr)2Ca2Cu3O9/Ag0.37 superconducting tapes by an ink spray pyrolysis method using a Tl-free precursor
Authors: Schulz Douglas L. , Parilla Philip A. , Ginley David S. , Voigt James A. , Roth E. Peter
Published: July 2002

In this letter we demonstrate a synthetic route to thick (5–20 μm) highly c-axis textured, nearly phase-pure superconducting (Tl,Pb)(Ba,Sr)2Ca2Cu3O9/Ag0.37 tapes. First, a Tl-free ink consisting of Pb0.5Ba0.4Sr1.6Ca2.0Cu3.0O9/Ag0.37 precursor powder in an ethanolic ethyl cellulose binder is sprayed onto a heated LaAlO3 substrate. After an intermediate oxygen anneal to remove the carbonaceous binder, a static 2-zone thallination anneal is performed to promote superconducting phase formation. Films exhibit excellent c-axis texturing as evidenced by x-ray diffraction θ/2θ and rocking curve characterization with morphological evidence for partial melting by scanning electron microscopy. Electrical characterization of these films give Tc onset values of 106–115 K with Tc zero reached by 99–101 K and transport Jc(77 K) up to 2.9×104 A/cm2. A mixed strong/weak-linked magnetic field dependence is observed for these films at 77 K and 0.4 T.
Experimental study of forward current transients in amorphous silicon p-i-n structures
Authors: Yan B. , Eliat A. , Adriaenssens G. J.
Published: July 2002

The delay time of forward current onset from initial electron space-charge-limited current to recombination-limited current in a-Si:H p-i-n devices was studied as a function of bias voltage, temperature and illumination intensity. The results show that the delay time and the initial electron current are related by a power law, td∝I−γSCLC, where γ is a temperature-independent constant. The value of γ is sensitive to the device properties such as the thickness of the intrinsic layer and the density of states. For a good quality device with 3.74 μm intrinsic layer, γ=0.70±0.05, while for a thin one deposited in the same conditions, γ changes to 0.99±0.05. A physical interpretation is presented.
Highly monochromatic electron point-source beams
Authors: Morin Roger , Fink Hans-Werner
Published: July 2002

We have evaporated Cs atoms onto ultrasharp W field emitter tips that act as point sources for electrons. Significant current increases associated with individual atomic adsorption events have been observed while using these tips in the field emission mode. This indicates that only a small number of atoms is involved in the emission process. The decoration of the tip apex with several tens of Cs atoms leads to an emission voltage of only one-fourth of that required for the pure W emitter. The spread of the energy distribution of the emitted electrons is reduced by a factor of 3 compared to the pure W point-source tip. Thus we have devised a fairly monochromatic electron source with a full width at half-maximum energy spread of 100 meV.
Low temperature mobility limiting defects in CdTe/CdMnTe multi-quantum-well structures
Authors: Godlewski M. , Harris C. I. , Bergman J. P. , Monemar B. , Waag A.
Published: July 2002

The results of optically detected cyclotron resonance and photoluminescence kinetics of CdTe/CdMnTe multi-quantum-well structures are presented. These experiments indicate that for nominally undoped wide quantum wells ionized shallow donor impurities limit carrier mobilities at low temperature.
Negative differential conductance frequency resonances in X valley superlattice minibands
Authors: Sibille A. , Palmier J. F. , Wang H. , Planel R.
Published: July 2002

Electron transport along the growth axis of a series of slightly indirect GaAs/AlAs superlattices (SL) is experimentally investigated. Our results, based on current-voltage and frequency resonance measurements in agreement with calculated characteristics, reveal unambiguously the existence of negative differential velocity at 80 K. Miniband transport in the lower Xxy miniband appears to explain this effect, owing to the low effective mass of Xxy states along the quantization axis.
Growth and characterization of thallium- and gold-doped PbSe0.78Te0.22 layers lattice matched with BaF2 substrates
Authors: McCann Patrick J. , Aanegola Srinath K. , Furneaux John E.
Published: July 2002

We report on liquid phase epitaxial growth and Hall effect characterization of thallium- and gold-doped PbSe0.78Te0.22 layers lattice matched with BaF2 substrates. Thallium behaved as an acceptor allowing growth of compensated p-type PbSe0.78Te0.22 layers with hole concentrations as high as 2.2×1018 cm−3. (Undoped PbSe0.78Te0.22 epitaxial layers were n-type with electron concentrations of 4.3×1018 cm−3.) The transition from n-type to p-type occurs at approximately 1.2 at. % thallium in the growth solution. Gold also exhibited acceptor behavior for low doping concentrations but behaved as a donor for doping concentrations greater than 1 at. % such that p-type layers could not be obtained. Electron mobilities as high as 7846 cm2/V s at 77 K were measured in this ternary alloy.
Measurement of nonuniform distribution of strain in InGaAs/GaAs quantum wires
Authors: Chen Yu-Pei , Reed Jason D. , Schaff William J. , Eastman Lester F.
Published: July 2002

Nonuniform strain distribution in In0.2Ga0.8As/GaAs strained wires has been observed by measuring the lattice spacing from the lattice image of the cross section of a single 10 nm×400 nm wire. It was found that in the wire, the region near the wire sidewall was under a larger compressive strain in the growth direction (vertical strain) than the center of the wire. In the barrier, near the wire sidewall, GaAs was under a vertical tensile strain by the In0.2Ga0.8As wire. This observation explains experimental observation of quantum confinement in strained InGaAs/GaAs quantum wires where the possibility of nonconfining band offsets was previously hypothesized. The assumptions underlying theory which predicts the absence of quantum confinement can now be modified to include actual strain variations. The nonuniform strain distribution observed also has ramifications for stability of strained quantum wire, or buried quantum well lasers.
Photoexcited carrier transport in InGaAsP/InP quantum well laser structure
Authors: Marcinkevičius S. , Olin U. , Wallin J. , Streubel K. , Landgren G.
Published: July 2002

Measurements of photoexcited carrier transport in InGaAsP/InP graded-gap separate-confinement quantum well laser structures with a step-like profile of the graded layers are performed by time-resolved photoluminescence using upconversion. In all the investigated structures ambipolar carrier motion can be characterized by a constant velocity of (1.5±0.2)×106 cm/s. The experimental results are discussed in terms of step-driven and ordinary diffusion.
Comparison of Be and C diffusion in heavily doped polycrystalline GaAs
Authors: Mochizuki Kazuhiro , Nakamura Tohru
Published: July 2002

The diffusion of Be and C in heavily doped polycrystalline GaAs grown by molecular beam epitaxy and metalorganic chemical vapor deposition has been studied by secondary-ion mass spectrometry and Hall measurement. It is found that Be rapidly diffuses into the undoped buffer layer at a growth temperature of 450 °C. Concentration-depth profiles of Be in AlGaAs/GaAs heterojunction bipolar transistor layers indicate that Be diffuses mainly along polycrystal grain boundaries. On the other hand, C diffusion is negligible even for post-growth annealing at 800 °C. However, annealing increases the resistivity of C-doped GaAs, which is probably due to a change in the occupation site preference of C atoms from As sites.
Experimental evidence of photoeffects in silicon rapid isothermal diffusion
Authors: Mavoori J. , Singh R. , Narayanan S. , Chaudhuri J.
Published: July 2002

Rapid isothermal processing (RIP) based on incoherent radiation as a source of optical and thermal energy is emerging as a key low thermal budget technique for the processing of semiconductor devices and circuits. The continuing development of RIP technique for the fabrication of electronic and optical devices requires a microscopic understanding of various phenomena associated with RIP. Junction formation by diffusion process is an integral part of all semiconductor devices. In this letter, we have shown that for identical thermal budget, different values of sheet resistivity are observed when the samples are irradiated from front or back. These results cannot be explained by the various process models and computer aided design tools available in the literature. We have offered a qualitative explanation of the observed results based on the role of photoeffects in RIP. The availability of high-energy photons in the front irradiation configuration and consequent electronic excitation can lead to higher diffusion coefficients as well as higher activation of dopants, compared to the back irradiated case.
‘‘Plastic’’ infrared polarizers from uniaxially oriented polyaniline blends
Authors: Cao Y. , Colaneri N. , Heeger A. J. , Smith Paul
Published: July 2002

We describe the preparation, characterization, and use of ‘‘plastic’’ infrared polarizers that consist of electrically conductive polyaniline blends with common bulk polymers such as poly(acrylonitrile), polyethylene, and poly(vinylalcohol). It is shown that uniaxially oriented blends of protonated polyaniline in, for example, poly(acrylonitrile) display a polarizing efficiency over the range from 400 to 4000 cm−1 that matches or surpasses that of commercial wire grid polarizers.
Effect of sublevel coupling on the line shape of the intersubband transitions in double quantum wells
Authors: Zal/użny M.
Published: July 2002

Intersubband resonance line shapes near sublevel crossing in asymmetric coupled double quantum wells are analyzed including the depolarization effect. Obtained results show that in the weakly tunneling system the sublevels-anticrossing effects occur at the depolarization-shifted intersubband energy.
Characterization of the near-interface region of chemical vapor deposited diamond films on silicon by backscatter Kikuchi diffraction
Authors: Geier S. , Schreck M. , Hessmer R. , Rauschenbach B. , Stritzker B. , Kunze K. , Adams B. L.
Published: July 2002

The lattice orientations near the interface of chemical vapor deposited diamond films on Si(001) have been studied by orientation imaging microscopy. This technique is based on the automated analysis of electron backscatter Kikuchi diffraction patterns. The electron beam has been scanned in discrete steps over the reverse side of the diamond film after having removed the substrate. The obtained data have allowed us to determine the texture and to visualize quantitatively the orientational arrangement of and among individual diamond crystallites in the near-interface region. A comparison with the orientation of the substrate has proved the existence of epitaxially nucleated grains. A high amount of twinned diamond has been deduced from the pole figures and verified by analysis of orientation correlations between neighboring crystallites. Moreover, the grain boundary maps have allowed us to monitor and quantify directly the occurring twin boundaries.
Discussion of domain inversion in LiNbO3
Authors: Huang Lisheng , Jaeger Nicolos A. F.
Published: July 2002

A simple model is proposed to explain the ferroelectric domain inversion which occurs in LiNbO3 during high-temperature processes. This domain inversion is believed to be due to a space-charge electric field resulting from a Nb....Li defect gradient and the associated free electrons, which are produced by the Li outdiffusion associated with such high-temperature processes.
Determination of complex tensor components of electro-optic constants of dye-doped polymer films with a Mach–Zehnder interferometer
Authors: Qiu Fusheng , Misawa Kazuhiko , Cheng Xiaoman , Ueki Akikatsu , Kobayashi Takayoshi
Published: July 2002

The complex electro-optic constants of disperse red 1 (DR1) dye molecules doped in polymethylmethacrylate film were measured by a scanning Mach–Zehnder interferometric technique. Despite a very small absorbance at 632.8 nm, DR1 molecules still have a measurable imaginary part of the EO constants. Two independent complex components, r̃13 and r̃33 were determined by incident angle dependence. The ratios Re[r̃33]/Re[r̃13] and Im[r̃33]/Im[r̃13] are 3.5±0.5 and 3.2±0.9, respectively. These results show that EO response is dominated by the electronic mechanism. The influence of multiple reflection in polymer film on the experimental results are briefly discussed.
Double-etch geometry for millimeter-wave photonic band-gap crystals
Authors: Özbay E. , Michel E. , Tuttle G. , Biswas R. , Ho K. M. , Bostak J. , Bloom D. M.
Published: July 2002

We have designed and developed a new double-etch technique for fabricating three-dimensional millimeter-wave photonic band-gap crystals. This technique doubles the band-gap frequency obtainable from silicon wafers. By introducing overetching, the double-etch geometry allows one-way tuning of the midgap frequency. We have experimentally demonstrated this property by fabricating and testing structures with different overetch ratios. Terahertz spectroscopy techniques were used to measure photonic band-gap crystals with midgap frequencies ranging from 340 to 375 GHz.
Design of high-performance quantum well electron transfer modulators via self-consistent modeling
Authors: Wang Jin , Zucker J. E. , Leburton J. P. , Chang T. Y. , Sauer N. J.
Published: July 2002

We successfully use a self-consistent physical model to predict device performance in a chopped quantum well electron transfer modulator. Large built-in electric fields for this structure cause delocalization of the electron wave function, requiring a careful evaluation of excitonic effects. Our calculations of both the electrical and electro-optic properties are in remarkably good agreement with the experimental data once Coulomb interactions are properly taken into account.
Spin-flip Raman scattering from shallow and deep donor centers in nitrogen-doped p-type zinc selenide
Authors: Boyce P. J. , Davies J. J. , Wolverson D. , Ohkawa K. , Mitsuyu T.
Published: July 2002

The net acceptor concentration in p-type ZnSe doped with increasing amounts of nitrogen is believed to be limited by the formation of a compensating donor species at a depth of about 45–55 meV beneath the conduction band. We report spin-flip Raman scattering from these and other donor-like centers in specimens produced by nitrogen radical doping during molecular beam epitaxial growth. The experiments show that the main compensating donor center introduced by nitrogen doping has a g value of 1.36±0.07, in agreement with the interpretation of previous optically detected magnetic resonance spectra from nitrogen-doped layers.
Just-on-surface magnetic force microscopy
Authors: Hosaka Sumio , Kikukawa Atsushi , Honda Yukio , Hasegawa Tsuyoshi
Published: July 2002

We propose a just-on-surface magnetic force microscope (JS-MFM) for advanced spatial resolution of magnetic stray field image. In this letter, we describe that the JS-MFM provides better resolution of the stray field image than that in conventional magnetic force microscope, theoretically and experimentally. In the rough estimations, magnetic stray field image just on the surface provides higher resolution of less than 10 nm. In the experiments, initial results demonstrate that JS-MFM can observe a localized surface magnetic stray field caused by small magnetizations in the perpendicularly recorded magnetic domains with a high resolution of around 10 nm.
Conductance resonance of metal-insulator-metal junction with embedded metal cluster
Authors: Chen Xiaoshuang , Zhao Jijun , Wang Guanghou
Published: July 2002

Conductance resonance of a metal-insulator-metal junction with an embedded metal cluster, which has different size and structure, is studied by the generalized Breit–Wigner formula in a tight-binding approximation. We find that a certain metal cluster possesses a specific peak pattern in the conductance data, that is, the conductance resonance peaks depend on the size and structure of metal clusters and the resonant broadening Γ is related to the tunnel barrier parameters. This arrangement can induce a high-quality tunneling structure with very narrow resonance peaks. Therefore, both the size effect and structure effect of the metal clusters can be predicted by observing conductance resonance of tunneling structure of embedding metal clusters in metal-insulator-metal junction. It is also possible to develop some new microelectronic devices with this structure.
Multiple colliding pulse mode-locked operation of a semiconductor laser
Authors: Martins-Filho J. F. , Ironside C. N.
Published: July 2002

Multiple colliding pulse mode-locked operation where 3 or 4 ultrashort pulses are present simultaneously within a semiconductor laser is described. Frequency and time domain measurements show that a multisectioned laser can be switched between two, three, and four pulse operation. In four pulse operation, pulse widths of approximately 1.3 ps at repetition rates of 240 GHz have been observed from a 600-μm-long laser.
Gain switching in high-speed semiconductor lasers: Intermediate-signal analysis
Authors: Schneider H. , Ralston J. D. , O’Reilly E. P. , Weisser S. , Larkins E. C.
Published: July 2002

We present a simple analytical treatment of gain switching in semiconductor lasers at intermediate intensities, based on a second-order perturbative treatment of the rate equations. The analytical solution is compared with experimental nonlinear transient relaxation oscillations measured using high-speed, p-doped In0.35Ga0.65As/GaAs multiple quantum well lasers, under perturbation of the dc electrical bias by pulsed optical excitation. The experimental results show excellent agreement with the analytical solution, even at excitation densities beyond the small-signal regime.
Panchromatic cathodoluminescence investigation of defects in CdTe bulk crystals and homoepitaxial layers
Authors: Salviati G. , Franzosi P. , Scaffardi M. , Bernardi S.
Published: July 2002

Scanning electron microscopy panchromatic cathodoluminescence has been used to investigate extended crystal defects in (111) CdTe bulk crystals and homoepitaxial layers grown by liquid phase epitaxy. Good defect images have been obtained by a very simple experimental setup using a Si photodiode at room temperature. The bulk crystals have been found to be affected by dislocations arranged in cellular structures, lineages roughly parallel to the [110] directions, [110] slip bands, and precipitates. The homoepitaxial layers exhibited dislocations, precipitates, and inclusions of growth solution. The wavy morphology typical of the layers grown by liquid phase epitaxy did not give rise to cathodoluminescence contrast.
High quality YBa2Cu3Ox films prepared in air using pulsed laser deposition
Authors: Jiang H. , Drehman A. J. , Andrews R. J. , Horrigan J. A. , Vittoria C.
Published: July 2002

High quality YBa2Cu3Ox superconducting films have been deposited by laser deposition on yttrium stabilized cubic zirconia (YSZ) substrates using a partial pressure of air instead of oxygen. The Tc of these films was over 2° higher than films made in the same deposition system using oxygen. X-ray diffraction indicated that the films were oriented with the c axis normal to the substrate surface. The critical current densities of the films were on the order of 106 A/cm2 at 77 K and self-magnetic field, and the room-temperature resistivities were about 245 μΩ cm. A unique aspect of these films was that the normal state resistivities showed nonlinear behavior with respect to temperatures. No secondary phase was detected by x-ray diffraction and SQUID magnetometry.
Differential optical PnpN switch operating at 16 MHz with 250-fJ optical input energy
Authors: Heremans P. , Kuijk M. , Vounckx R. , Borghs G.
Published: July 2002

We present an optoelectronic switch with exceptional optical sensitivity (250 fJ) operating at high speed (16 MHz). The switch consists of a differential pair of optical PnpN devices. Its excellent optical sensitivity directly ensues from the differential switching principle. The operation speed results from the use of a specially conceived PnpN layer structure, called the depleted optical thyristor, in combination with a particular operation cycle. The performance of our switch corresponds to an improvement of about five orders of magnitude in speed for comparable sensitivity, and of two orders of magnitude in optical sensitivity for the given speed as compared to that of conventional PnpN switches.
Impact ionization coefficients in Si1−xGex
Authors: Lee J. , Gutierrez-Aitken A. L. , Li S. H. , Bhattacharya P. K.
Published: July 2002

We have measured the electron and hole impact ionization coefficients in Si1−xGex alloys. Carrier multiplication measurements were made on relaxed Si1−xGex/Si diodes grown by gas source molecular beam epitaxy. The hole to electron impact ionization coefficient ratio, β/α, varies from 0.3 to 4 in the composition range of x=0.08–1.0.
InAlAs/InGaAs high electron mobility transistors on low temperature InAlAs buffer layers by metalorganic chemical vapor deposition
Authors: Pan N. , Elliott J. , Hendriks H. , Aucoin L. , Fay P. , Adesida I.
Published: July 2002

InAlAs/InGaAs high electron mobility transistors (HEMT) with excellent high frequency performance were demonstrated. Device sizes of 0.25×50 μm and 0.10×50 μm showed current gain cutoff frequencies of 143 and 205 GHz, respectively. The HEMT structures were grown on a low temperature InAlAs buffer layers designed to eliminate conductive impurity spikes situated at the epitaxial/substrate interface. The highly resistive buffer layer (2×105 Ω cm) was obtained at a growth temperature of 475 °C using a combination of trimethylarsenic and arsine as the arsenic sources.
Characteristics of graded-like multiple-delta-doped GaAs field effect transistors
Authors: Kao M. J. , Hsu W. C. , Hsu R. T. , Wu Y. H. , Lin T. Y. , Chang C. Y.
Published: July 2002

Multiple-δ-doped GaAs field effect transistors using graded-like δ-doping profile are demonstrated and investigated. An extremely high carrier density of 1.2×1013 (7.9×1012) cm−2 along with an enhanced Hall mobility of 1700 (3300) cm2/v s at 300 (77) K for a triple-δ-doped GaAs structure are achieved. The dc characteristic reveals an extrinsic transconductance as high as 110 mS/mm at room temperature with a gate length of 2 μm. Three separated peaks in the transconductance versus gate bias curve are observed. Meanwhile, a broad and flat transconductance region is obtained.
Current induced intersubband absorption in GaAs/GaAlAs quantum wells
Authors: Fenigstein A. , Fraenkel A. , Finkman E. , Bahir G. , Schacham S. E.
Published: July 2002

The observation of intersubband (e1–e2) absorption induced by current injection in GaAs/GaAlAs multiquantum wells is reported. The new technique enables sensitive measurement of intersubband transitions in undoped quantum wells. The carrier concentration in the wells is easily controlled by varying the current density. The technique is demonstrated on undoped multiquantum well layers sandwiched in a p-i-n laser-diodelike structure. The lowest confined level was populated by biasing the junction and hence injecting carriers into the quantum wells. The spectra were taken by a Fourier transform infrared (FTIR) spectrometer, modulating the current and using the double modulation method. The dependence of the absorption on current intensity was examined and excess carrier concentration and lifetime were calculated. The induced absorption saturates at current densities higher than 100 mA/cm2.
Superconductivity in Srn+1CunO2n+1+δ ‘‘infinite layer’’ films induced by postgrowth annealing
Authors: Feenstra R. , Budai J. D. , Christen D. K. , Kawai T.
Published: July 2002

Superconductivity with Tc≂25–45 K has been induced in films based on the ‘‘infinite layer’’ structure though high temperature annealing in an oxygen ambient. The films had compositions Srn+1CunO2n+1+δ (n=3–9) and were previously grown by laser molecular beam epitaxy by periodic insertion of SrO defect layers into the SrCuO2 infinite layer matrix. A marked dependence on the cooling rate at the end of the postgrowth anneals indicates that preservation of a high temperature oxygen sublattice forms the key to enhancing the carrier density in these films, opposite to the situation with YBa2Cu3O7−δ .
Indirect–direct band gap transition and enhanced optical absorption of GaP/AlP random superlattice
Authors: Wang E. G. , Ting C. S.
Published: July 2002

By the application of disorder, an indirect–direct band gap transition can be achieved in a random superlattice composed of GaP and AlP monolayers. In all random models studied here, optical absorption intensities are found to be larger than that of the ordered ultrathin-layer GaP/AlP superlattice. With increasing disorder, a considerable optical enhancement, which is about 44 times stronger than that of the ordered structure with equal composition, is obtained in a proposed random system. These properties suggest that the disordered superlattice offers great potential for application to optical devices.
Photoluminescence study of excess carrier spillover in 1.3 μm wavelength strained multi-quantum-well InGaAsP/InP laser structures
Authors: Garbuzov D. , Shiau G.-J. , Bulovic V. , Boroditsky M. , Chao C.-P. , Forrest S. R.
Published: July 2002

Photoluminescence of 1.3 μm wavelength strained multiple quantum well InGaAsP/InP laser structures has been used to understand the excess carrier redistribution between the quantum well and waveguide regions at a high level of excitation. A model is developed to describe the experimental results. The model suggests that space charge barriers play a significant role in the electron confinement in quantum wells at the high excitation range typical of laser diode operation.
Dislocation filtering in SiGe and InGaAs buffer layers grown by selective lateral overgrowth method
Authors: Bryskiewicz T.
Published: July 2002

A quantitative analysis based on the Luryi and Suhir model [Appl. Phys. Lett. 49, 140 (1986)] has shown that the growth of strain relaxed and low dislocation density SixGe1−x and InxGa1−xAs buffer layers on Si and GaAs substrates, respectively, is feasible despite the layer/substrate lattice mismatch. A successful growth of such layers is possible on partially masked substrates by selective lateral overgrowth method. In this case, the buffer layer/substrate misfit stress is of limited lateral extent, in accordance with Saint-Venant’s principle, and its effective length does not exceed 15% of the seeding window width even for very thick buffer layers. High threading dislocation density in the buffer layer can be avoided by reducing the window width such that the effective stress zone length is comparable with the critical layer thickness for misfit dislocation formation. However, a thin alloy layer deposited by molecular beam epitaxy or metalorganic chemical vapor deposition on both the Si and GaAs substrates, prior to coating with SiO2 mask and patterning with oxide-free seeding windows, is required for a quite broad range of alloy compositions
Photochemical hole burning of organic dye doped in inorganic semiconductor
Authors: Machida Shinjiro , Horie Kazuyuki , Yamashita Takashi
Published: July 2002

We report a new type photochemical hole burning material; organic dye, zinc porphyrin, doped in inorganic semiconductor, titanium dioxide. The hole burning mechanism of this system is concluded to be photoionization via single-photon process. The small temperature dependence of Debye–Waller factor was indicated by cyclic annealing experiment. A hole could be burned and observed at 140 K.
Characterization of benzoic acid ion exchange waveguides in lithium tantalate
Authors: Anastassopoulou Nikoletta , Davis Gillian M.
Published: July 2002

We report the fabrication and characterization of benzoic acid ion exchanged planar waveguides in lithium tantalate in order to investigate the conditions suitable for achieving quasiphase matching. Samples from a z-cut lithium tantalate wafer were ion exchanged at 205 °C for 3 or 6 h and annealed for between 16 and 120 s at temperatures of between 465 and 594 °C. The anneal diffusion coefficient at a temperature of 525 °C was measured to be 264 μm2/h. Domain inversion was observed for anneals at 594 °C/30 s and at 594 °C/60 s.
Effects of additives on the preferred orientation of Mn–Zn ferrite thin films deposited by ion beam sputtering
Authors: Cho Hae Seok , Kim Hyeong Joon
Published: July 2002

We investigated the effects of additives on the preferred orientation of the Mn–Zn ferrite thin films deposited on SiO2(1000 Å)/Si(100) at 350 °C by ion beam sputtering. A mosaic target, consisting of a single crystal (100) Mn–Zn ferrite with a metal strip on it, was employed as the target. The preferred orientation of the ferrite films was (hhh) for the target with or without Fe and Zn additives, and (h00) for Ti addition. In the case of Cu addition, a weak (311) orientation appeared with a strong (hhh) preferred orientation. The origin of the changes in the preferred orientation with different additives was discussed. The easy axis of magnetization, however, lay in the direction parallel to the film plane due to large shape anisotropy, irrespective of the preferred orientation.
On temperature dependence of the optically active behavior of an infrared active defect in silicon
Authors: Shi Yi , Wu Fengmei , Zheng Youdou , Suezawa Masashi , Imai Masato , Sumino Koji
Published: July 2002

Optically active behaviors of the infrared active defect, so-called higher order bands, have been investigated at different temperatures in fast neutron irradiated silicon. It is found that the optically active decay follows logarithmic time dependence with a decay time of about 105 s, which is nearly temperature independent below 80 K. The residual absorption remains up to heating temperatures of 180 K. The experimental findings are discussed in terms of the relaxation characteristic of photoexcited carriers governed by neutron irradiation induced defect clusters.
Enhancement of the Schottky barrier height of Au/ZnSSe diodes
Authors: Wang A. Z. , Anderson W. A.
Published: July 2002

We report a significant enhancement of the Schottky barrier height of Au/N–ZnS0.07Se0.93 diodes formed by the cryogenic process. The improvement is around 25%. This technique had previously been successfully applied to some narrow band gap semiconductors, such as InP and InGaAs. We explain this improvement by the metal–insulator–semiconductor model and the uniformity of the metal film so-obtained. This technique is proven to be of importance for making low dark/leakage current visible light sensitive optoelectronic devices.
Solid state ionic polishing of diamond
Authors: Yehoda J. E. , Cuomo J. J.
Published: July 2002

A new process for polishing diamond is presented. The reaction and polishing take place at the interface of an oxygen superionic conductor (yittria-stabilized zirconia) and the diamond. Oxygen anions are transported to the interface under the influence of an electric field and react with the diamond. It is believed that a volatile product of CO and/or CO2 is formed during the polishing. The process takes place at moderately low temperatures, without mechanical motion, and can be accomplished in ambient air, making it an attractive and useful method. In addition, the process is damage-free with no polishing residue, as has been determined by energy dispersive x-ray analysis.
Study of surface alignment of nematic liquid crystals on polyimide Langmuir–Blodgett films
Authors: Sun Ruipeng , Guo Jianxin , Huang Ximin , Ma Kai
Published: July 2002

The orientation effect of liquid crystal and polyimide molecules on the Langmuir–Blodgett (LB) films was studied. The orientation degree of polyimide chain in the LB films is less than that in the strong rubbing films. This result may be due to bad linear structure of polyimide. The 9 or 11 LB film layers may well align liquid crystals, but the orientation effect of liquid crystals on the polyimide LB films is worse than that on the strong rubbing films. The surface azimuthal anchoring energy of liquid crystals on the polyimide LB films was measured by a torque balance method proposed by our group. The intermolecular interaction between liquid crystal and polymer molecules is considered to be very important for aligning liquid crystals on the polymer surface.
Evidence for ballistic transport of two-dimensional electron gas at liquid-nitrogen temperatures in a silicon metal–oxide semiconductor field effect transistor with a neck in the middle
Authors: Takeuchi Kan , Hisamoto Dai , Yamashita Hisaomi
Published: July 2002

The transconductance of a silicon metal–oxide semiconductor field effect transistor with a neck in the middle was measured at liquid-nitrogen temperatures. The narrowest part of the gate with p+ isolations is 0.24 μm wide and about 0.2 μm long. The transconductance shows a peaked structure near the threshold voltage. The calculated transconductance based on the ballistic transport model of two-dimensional electron gas explains well the peaked structure.
Phonon replicas in the photoluminescence emission of AlxGa1−xAs alloys
Authors: Reynolds D. C. , Look D. C. , Kaspi R. , Talwar D. N.
Published: July 2002

Phonon replicas in the photoluminescence spectra of a direct gap AlxGa1−xAs alloy have been observed. The GaAs-like transverse optical and longitudinal optical as well as AlAs-like longitudinal optical modes were observed at the Γ-point. We also observe what we believe to be the longitudinal acoustical phonons at the L-point in the Brillouin zone.
Anisotropic relaxation during the first stages of the growth of ZnTe/(001) CdTe strained layers studied by reflection high energy electron diffraction
Authors: Eymery J. , Daudin B. , Brun-Le Cunff D. , Boudet N. , Tatarenko S.
Published: July 2002

The first stages of the growth of highly strained ZnTe on (001)CdTe are studied by reflection high energy electron diffraction (RHEED) with real-time monitoring of the surface in-plane lattice spacing and of the width of the streaks along the [100], [110], and [11̄0] azimuths. A large, oscillating, elastic relaxation is measured below the critical thickness (≊5 ZnTe monolayers) in the [11̄0] azimuth while a small excess of tensile stress with regard to the CdTe substrate is observed in the [110] azimuth. These effects are attributed to an anisotropic nontetragonal elastic distortion at the free edges of elongated 2D ZnTe-monolayer islands. For large deposition times (i.e., after the critical thickness), the RHEED observation gives very good information about the nature of the dislocations occurring in the multiplication process.
Reliability of aluminum-free 808 nm high-power laser diodes with uncoated mirrors
Authors: Eliashevich I. , Diaz J. , Yi H. , Wang L. , Razeghi M.
Published: July 2002

The reliability of uncoated InGaAsP/GaAs high-power diode lasers emitting at 808 nm wavelength has been studied. 47 W of quasicontinuous wave output power (pulse width 200 μs, frequency 20 Hz) have been obtained from a 1-cm-wide laser bar. A single-stripe diode without mirror coating has been life tested at 40 °C for emitting power of 800 mW continuous wave (cw) and showed no noticeable degradation and no change of the lasing wavelength after 6000 h of operation.
Preannealing effects on carrier concentration profile after Au diffusion in Si
Authors: Monson T. K. , Van Vechten J. A. , Zhang Q. S.
Published: July 2002

After Au diffusion, carrier concentration profiles in low O (float zoned), lightly doped, p-type Si were found to be a function of heat treatment received by the Si crystal prior to Au deposition. We interpret anomolous carrier concentration profiles in terms of vacancy diffusion and clusters of excess vacancies retained from the crystal growth processing.
Tellurium-doped Al0.43Ga0.57As/(In0.2)GaAs modulation doped heterostructures by molecular-beam-epitaxy
Authors: Jiang W.-N. , Nguyen N. X. , Underwood R. D. , Mishra U. K. , Wilson R. G.
Published: July 2002

Te has previously been demonstrated to have a shallower deep donor (DX-center) level than Si in AlGaAs. In this work, Te-doped Al0.43Ga0.57As/GaAs and pseudomorphic Al0.43Ga0.57As/ In0.2Ga0.8As modulation-doped heterostructures (MDHs) grown by MBE have been studied. The conduction band offset ΔEc in the pseudomorphic AlGaAs/InGaAs material system has a maximum at 43% Al mole fraction. This allows maximum carrier confinement in the quantum well. Two-dimensional electron densities and mobilities 2.36×1012 cm−2 and 7794 cm2/V s at 300 K and 2.17×1012 cm−2 and 24 379 cm2/V s at 77 K (in the dark) have been obtained in Te-doped pseudomorphic MDHs.