bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanometer-scale absorption spectroscopy by near-field photodetection optical microscopy
Authors: Davis R. C. , Williams C. C.
Published: July 2002

Near-field photodetection optical microscopy (NPOM) is a fundamentally new approach to near-field optical microscopy. This scanning probe technique uses a nanometer-scale photodiode detector which absorbs optical power directly as it is scanned in the near field of an illuminated sample surface. We have applied NPOM to measure the visible absorption spectrum of dye molecules embedded in a single 300 nm polystyrene sphere. The near-field absorption spectrum is obtained by measuring the NPOM probe photocurrent while the wavelength of the illumination pump beam is scanned from 450 to 800 nm. Peaks are identified at 567, 608, and 657 nm in the near-field spectrum of the single-dyed polystyrene sphere. These peak positions are in good agreement with far-field absorption measurements performed on many dyed polystyrene spheres.
The effects of oxygen content on the magnetoresistive behavior in La–Ca–Mn–O films grown on Si
Authors: Zhang Wei , Boyd W. , Elliot Martin , Herrenden-Harkerand William
Published: July 2002

Giant magnetoresistance La–Ca–Mn–O films, with 32% at 5.7 K and 20% near room temperature change in resistivity ( Δρ/ρ0) at a magnetic field of 4.7 T, have been deposited on Si (100) substrates using pulsed laser deposition. The effects of preparation conditions on the properties of the films are described. Deposition at a high temperature shifts the resistivity peak to lower temperatures and simultaneously increases the maximum resistivity value. Annealing at a high temperature, however, produces the opposite effect on the resistivity behavior. Our results suggest that the oxygen stoichiometry in the films is a crucial factor in causing the ferromagnetic transition and the noted peak of the resistivity characteristics to shift to higher temperatures. Some possible mechanisms are suggested.
Color-tunable organic light-emitting devices
Authors: Burrows P. E. , Forrest S. R. , Sibley S. P. , Thompson M. E.
Published: July 2002

We demonstrate an integrated, two-color organic light-emitting device for flat-panel display applications. The device utilizes a unique stacked pixel architecture which allows for independent tuning of color and intensity. Each of the two addressable colors is sufficiently bright for video display applications, so that the compact stacked pixel, which maximizes display resolution, may form the basis of a new type of full-color display.
Reduction of 1/f noise in high-T
c dc superconducting quantum interference devices cooled in an ambient magnetic field
Authors: Dantsker E. , Tanaka S. , Nilsson P.-Å. , Kleiner R. , Clarke John
Published: July 2002

The spectral density SΦ(f ) of the low-frequency 1/f noise of high transition temperature dc superconducting quantum interference devices (SQUIDs) with narrow linewidths was independent of B0, the magnetic field in which they were cooled, up to a threshold value, about 33 μT in the best case. Above this threshold, which is associated with the entry of flux vortices into the film, the noise increased rapidly. By contrast, for large square washer SQUIDs, SΦ(f ) scaled linearly with B0. Estimates indicate that the 1/f flux noise produced by the pickup loop of a directly coupled magnetometer is negligible.
Electron emission from a hydrogenated diamond surface
Authors: Liu J. , Zhirnov V. V. , Choi W. B. , Wojak G. J. , Myers A. F. , Cuomo J. J. , Hren J. J.
Published: July 2002

Electron emission from a polycrystalline diamond coated silicon field emitter surface was studied using in situ exposure to various gas species during its operation. Significant enhancement of the electron emission was found after the emitting surface was exposed to hydrogen at pressures in the range 5×10−4 to 10−3 Torr. Introducing other gases such as Ne and He only suppressed the emission current. A continuous emission current was measured from such a hydrogen-exposed surface even after the electric field was reduced to below the initial threshold for electron emission. No similar result was found for pure silicon surface when identical conditions applied. This phenomenon was interpreted as the formation of a dynamically vacuum-stable layer by polarized hydrogen and the diamond surface. Such a surface layer may significantly lower the surface barrier and exhibit the negative electron affinity property.
Response mechanism of nematic liquid crystals using the in-plane switching mode
Authors: Oh-e Masahito , Kondo Katsumi
Published: July 2002

A response mechanism of nematic liquid crystals following the switching-on and off of an in-plane electric field when using the in-plane switching (IPS) mode was investigated. Simplified theoretical expressions, which were derived with an assumption that an in-plane electric field was applied to the liquid crystals, were used to explain the dynamical switching process in the IPS mode. In particular, the relaxation time of the liquid crystals when removing the electric field was described as a proportional relationship to the square of the cell gap. A thinner cell gap also proved to be effective in obtaining a fast response time in the IPS mode. By contrast, the switching-on time when applying the in-plane electric field proved to be inversely proportional to the difference between the square of the electric field strength and the square of the critical electric field strength at which the liquid crystals begin to deform.
Metal-insulator-semiconductor structures on p-type GaAs with low interface state density
Authors: Chen Zhi , Park Dae-Gyu , Stengal Francke , Mohammad S. Noor , Morkoç Hadis
Published: July 2002

Interfacial properties of in situ deposited Si3N4/Si/p-GaAs metal-insulator-semiconductor structures have been investigated. Conductance loss measurements show that a minimum interface trap density as low as 5.5×1010 cm−1 eV−1 has been achieved on p-type GaAs by using a high quality strained Si interlayer. The quasistatic and high-frequency capacitance-voltage measurements as well as the theoretical high-frequency capacitance-voltage calculation clearly demonstrate the accumulation, depletion, and inversion regions. The interface trap density as a function of the band-gap energy near the midgap has been determined with the conductance method. The reduced band bending (0.84 V) may be mainly caused by the narrower band gap of the strained Si interlayer.
Parameterization of the optical functions of amorphous materials in the interband region
Authors: Jellison G. E. , Modine F. A.
Published: July 2002

A parameterization of the optical functions of amorphous semiconductors and insulators is presented in which the imaginary part of the dielectric function ε2 is determined by multiplying the Tauc joint density of states by the ε2 obtained from the Lorentz oscillator model. The real part of the dielectric function ε1 is calculated from ε2 using Kramers–Kronig integration. The parameters of this model are fit to n and k data for amorphous Si (2 data sets), SiO, As2S3, and Si3N4. Comparative fits are made with a similar parameterization presented earlier by Forouhi and Bloomer [Phys. Rev. B 34, 7018 (1986)]. In all cases, the new parameterization fits the data better.
Laser-plasma interaction during visible-laser ablation of methods
Authors: Chang Jim J. , Warner Bruce E.
Published: July 2002

We have investigated the dynamics of high-radiance visible-laser interaction with a metal vapor plasma during laser ablation of aluminum and carbon steel. The experiment with a copper vapor laser reveals strong plasma-absorption induced ignition at laser intensities above 1–2 GW/cm2. Approximation based on hydrodynamic relations indicates that the vapor density at the end of the 40-ns laser pulse is 3×1020–1×1021 cm −3 with a pressure of a few thousand atmosphere at the target surface. This high-density vapor with a temperature exceeding 10 000 K leads to pronounced plasma absorption via photoionization. Plasma absorption via inverse bremsstrahlung is determined to be negligible because of a relatively low electron density, measured to be peaked at ∼5×1018 cm−3.
Blue light emission from an organic nonlinear optical crystal of 4-aminobenzophenone pumped by a laser diode
Authors: Li Zhengdong , Wu Baichang , Su Genbo , Huang Gongfan
Published: July 2002

The bulk crystals of 4-aminobenzophenone were grown from organic solution. The refractive indices and nonlinear-optical coefficients deff were measured and were reported. Blue second harmonic emission with wavelength of 433 and 460 nm was observed as pumped by a laser diode, second-harmonic generation and a conversion efficiency of 2.5×10−5 was obtained at 866 nm.
Hole-filling of persistent spectral holes in the excitonic absorption band of CuBr quantum dots
Authors: Valenta J. , Moniatte J. , Gilliot P. , Levy R. , Hönerlage B. , Ekimov A. I.
Published: July 2002

Persistent spectral-holes (p-SH) are burned in the Z1,2 excitonic band of CuBr nanocrystals by a pulsed laser excitation. The annealing of p-SH is studied by three types of hole-filling (HF) experiments: (i) the spontaneous HF, (ii) thermally-induced HF, and (iii) the laser-induced HF. Results are compared to the well developed theory of the persistent spectral hole-burning (p-SHB) in the system of molecules in amorphous matrices. Both p-SHB and HF phenomena can be explained within the framework of a photochemical reaction like the photoionization of nanocrystals. The potential application of p-SHB to the frequency-domain optical data storage is discussed.
Long-range surface plasmon resonances in grating-waveguide structures
Authors: Glasberg S. , Sharon A. , Rosenblatt D. , Friesem A. A.
Published: July 2002

Resonant grating-waveguide structures were used for the excitation of long-range surface plasmons. Resonance spectral bandwidths of 1.9 nm were experimentally measured in both the reflected and transmitted intensities from these structures. Numerical calculations indicate that interference rather than the usual surface plasmon absorption mechanism plays the dominant role in the resonance response when the thickness of the guiding metal layer in the structures is reduced below 10 nm.
Thermal stability of Si3N4/Si/GaAs interfaces
Authors: Park D.-G. , Chen Z. , Diatezua D. M. , Wang Z. , Rockett A. , Morkoç H. , Alterovitz S. A.
Published: July 2002

An investigation on the thermally induced interface degradation of Si3N4/Si/p-GaAs metal– insulator–semiconductor (MIS) structures is presented. We characterize the mutation of chemical identities by in situ angle-resolved x-ray photoelectron spectroscopy and the nature of an insulator and interface by a variable angle spectroscopic ellipsometry after high temperature annealing. The minimum interface state density of the Si3N4/Si/p-GaAs MIS capacitor as determined by capacitance–voltage and conductance loss measurements was about 8×1010 eV−1 cm−2 near GaAs midgap after rapid thermal annealing at 550 °C in N2. However, this density increased to 5×1011 eV−1 cm−2 after annealing at 750 °C in N2. The underlying mechanisms responsible for this degradation are described.
Frequency doubling in two-component self-assembled chromophoric waveguide structures
Authors: Lundquist P. M. , Lin W. , Zhou H. , Hahn D. N. , Yitzchaik S. , Marks T. J. , Wong G. K.
Published: July 2002

Self-assembled chromophoric multilayers having large second-order optical nonlinearities can be combined with linear guiding materials such as polymethylmethacrylate to produce two-component frequency doubling waveguides. This approach introduces considerable flexibility in optimizing the trade-off between the overlap of waveguide mode profiles and linear absorption. Extremely low waveguide propagation losses can be achieved because electric field poling and the accompanying poling-induced optical scattering are obviated.
Distributed feedback quantum cascade lasers
Authors: Faist Jérome , Gmachl Claire , Capasso Federico , Sirtori Carlo , Sivco Deborah L. , Baillargeon James N. , Cho Alfred Y.
Published: July 2002

Pulsed single mode operation of distributed feedback quantum cascade lasers is reported above room temperature at both 5.4 and 8 μm wavelengths. Peak optical powers up to 60 mW at 300 K are obtained with a tuning range of ∼60 nm from 100 to ∼320 K. The linewidth is limited by thermal drift during the pulse with a typical value of 0.3 cm−1 for a 10 ns long pulse at 300 K.
Room temperature intrinsic optical transition in GaN epilayers: The band-to-band versus excitonic transitions
Authors: Smith M. , Lin J. Y. , Jiang H. X. , Asif Khan M.
Published: July 2002

The mechanism of room-temperature (RT) intrinsic optical transition in high quality and purity GaN epilayer grown by metalorganic chemical vapor deposition (MOCVD) has been investigated. Our results show that the band-to-band instead of excitonic transition is the dominant transition in MOCVD grown GaN epilayer at RT. This conclusion is supported by the observation of the excitation intensity dependence of the photoluminescence emission peak position and by a model calculation. The band-to-band transition energy at RT at the limit of low carrier concentration has been determined to be 3.429 eV. Since the band-to-band transition is the dominant optical transition at RT, it thus suggests that the electron-hole plasma is most likely responsible for gain in GaN blue lasers similar to the case in other III–V semiconductor lasers.
Theory of magnetic dissipation imaging
Authors: Liu Y. , Ellman B. , Grütter P.
Published: July 2002

A model is presented for magnetic dissipation imaging and magnetic force gradient imaging obtained with a vibrating ferromagnetic tip and a ferromagnetic thin film sample. Results of calculations are compared to recent experiments and show good agreement using known bulk values for the magnetic parameters of tip and sample. We suggest that oscillations of domain wall width result in magnetoelastic emission of phonons. These phonons carry energy from the tip, leading to image contrast at domain walls. We also discuss the energy dissipation resulting from eddy current losses in the tip and sample.
In-plane aligned Pr6O11 buffer layers by ion-beam assisted pulsed laser deposition on metal substrates
Authors: Betz V. , Holzapfel B. , Raouser D. , Schultz L.
Published: July 2002

Biaxially aligned praseodymium oxide (Pr6O11) thin films were prepared by ion-beam assisted laser deposition on mechanically polished metal alloy substrates. A low divergence rf plasma source was used as an assisting source. Deposited films showed (001) oriented film growth with a strong biaxial alignment in the film plane. The degree of in-plane orientation dependent on ion-to-atom ratio and ion bombardment angle was studied. Planar ion channeling along the {110} planes is used to explain the observed alignment features. At an ion-to-atom ratio of 0.17 and an ion incident angle of 60°, in-plane orientations of 16° full width at half-maximum were obtained. Due to the low lattice mismatch (0.3%) to YBa2Cu3Ox films, the material could be an alternative to the YSZ/CeO2 buffer layer system currently used for high critical current carrying superconducting tapes.
InGaN/GaN/AlGaN-based laser diodes with modulation-doped strained-layer superlattices grown on an epitaxially laterally overgrown GaN substrate
Authors: Nakamura Shuji , Senoh Masayuki , Nagahama Shin-ichi , Iwasa Naruhito , Yamada Takao , Matsushita Toshio , Kiyoku Hiroyuki , Sugimoto Yasunobu , Kozaki Tokuya , Umemoto Hitoshi , Sano Masahiko , Chocho Kazuyuki
Published: July 2002

InGaN multi-quantum-well-structure laser diodes with Al0.14Ga0.86N/GaN modulation doped strained-layer superlattice cladding layers grown on an epitaxially laterally overgrown GaN (ELOG) substrate was demonstrated to have a lifetime of more than 1150 h under room-temperature continuous-wave operation. After 4 μm etching of the ELOG substrate, the etch pit density was about 2×108 cm2 in the region of the 4-μm-wide stripe window, but almost zero in the region of the 7-μm-wide SiO2 stripe.
Anisotropic transport properties of single-crystal (La,Ca)MnOδ thin films
Authors: Zeng X. T. , Wong H. K.
Published: July 2002

We report on the observation of anisotropic transport properties in La2/3Ca1/3MnOδ that has a nearly cubic perovskite structure. We prepared single-crystal La2/3Ca1/3MnOδ thin films with a-axis orientation. It is found that the resistivity and magnetoresistance of the samples annealed in oxygen at 920 °C for 1 h are higher along the c-axis direction than along the a-axis direction by about 34%–37% near the metal–semiconductor transition temperature. Further post-annealing in oxygen at 950 °C for 6 h increased the anisotropy ratio of magnetoresistance to 1.9. This indicates that the anisotropic transport properties result from additional magnetic scattering along the c-axis direction of the films.
Improvement of dielectric properties of (Ba,Sr)TiO3 thin films deposited by pulse injection chemical vapor deposition
Authors: Cho Ho Jin , Kim Hyeong Joon
Published: July 2002

( Ba,Sr)TiO 3 (BST) thin films were prepared on Pt/SiO2/Si substrates by the pulse injection chemical vapor deposition (CVD) process, in which the vapor of precursors was allowed to flow periodically into the reaction chamber. The dielectric constants of BST thin films, which were deposited by pulse injection CVD, were slightly higher than those of continuous BST thin films. In addition, the leakage currents were lowered by an order of magnitude. 35 nm thick BST thin films, deposited by pulse injection CVD and postannealed at 600 °C under O2 atmosphere for 30 min, showed a SiO2 equivalent thickness of 0.64 nm, a dielectric dissipation factor less than 0.5%, and a leakage current density of 1×10−7 A/cm2 at +1.5 V bias. The improvement in the electrical properties of pulse BST thin films seems to originate from better crystallinity and less carbon contamination during the pulse deposition process.
Investigation of electroluminescence from Au/poly-4-dicyanomethylene-4H-cyclopenta[2,1-b:3,4-b′]dithiophene/porous Si/Si/Al light emitting diodes
Authors: Dong Y. , Bayliss S. C. , Parkinson M.
Published: July 2002

We report simple porous silicon-based devices producing stable electroluminescence (EL) by the deposition of a poly-4-dicyanomethylene-4H-cyclopenta[2,1-b:3,4-b′]dithiophene monolayer (PCDM) into the nanostructure. The structure of these devices is Au/PCDM/porous silicon/Si/Al. The EL emission is bright, visible by the naked eye under normal daylight, and broad in wavelength, covering the whole visible range with a peak at 650 nm. The emission area of the devices is 1 cm2. The EL starting voltage is in the range of 14–30 V and the current is around 300 mA. The time stability was good for all the devices tested. After exposure to the air for more than three months, the devices show nearly the same emission intensity without increase of external power supplied.
Molecular-beam epitaxy of BeTe layers on GaAs substrates studied via reflection high-energy electron diffraction
Authors: Tournié E. , Bousquet V. , Faurie J.-P.
Published: July 2002

We study through reflection high-energy electron diffraction (RHEED) the growth by molecular-beam epitaxy of the II-VI compound-semiconductor BeTe on GaAs substrates. Long lasting RHEED oscillations reveal that BeTe nucleates on GaAs buffer layers in a two-dimensional mode when the GaAs surface is not Te reacted. The growth temperatures of BeTe and ZnSe are only marginally compatible. We show that the Te- and Be- terminated BeTe surfaces are (2×1) and (3×1) reconstructed, respectively. The transition from (2×1) to (3×1) surface occurs via the formation of a faint (4×1) reconstruction. We determine the surface phase diagram under static as well as growing conditions.
Backscattering from a tethered bead as a probe of DNA flexibility
Authors: Shivashankar G. V. , Stolovitzky G. , Libchaber A.
Published: July 2002

Using an optical tweezer, we trap a DNA polymer tethered bead. Collinear with the tweezer, a red laser light beam probes the bead fluctuations through backscattered radiation measurement. Those fluctuations give information on the flexibility of DNA and can be used to probe the interaction of proteins with DNA. We use this approach to directly monitor the extension of a single DNA polymer beyond its contour length induced by the polymerization of Rec A protein on DNA.
Mott transition field effect transistor
Authors: Newns D. M. , Misewich J. A. , Tsuei C. C. , Gupta A , Scott B. A. , Schrott A.
Published: July 2002

A field effect transistor fabricated with an oxide channel has been shown to demonstrate switching characteristics similar to conventional silicon metal oxide field effect transistors. This device is believed to operate via a Mott metal-insulator transition induced by the gate field, and offers a potential technology alternative for the regime beyond silicon scaling limitations.
Electronic structure of self-assembled InAs quantum dots in GaAs matrix
Authors: Brounkov P. N. , Polimeni A. , Stoddart S. T. , Henini M. , Eaves L. , Main P. C. , Kovsh A. R. , Musikhin Yu. G. , Konnikov S. G.
Published: July 2002

Capacitance–voltage characteristics have been measured at various frequencies and temperatures for structures containing a sheet of self-assembled InAs quantum dots in both n-GaAs and p-GaAs matrices. Analysis of the capacitance–voltage characteristics shows that the deposition of 1.7 ML of InAs forms quantum dots with electron levels 80 meV below the bottom of the GaAs conduction band and two heavy-hole levels at 100 and 170 meV above the top of the GaAs valence band. The carrier energy levels agree very well with the recombination energies obtained from photoluminescence spectra.
Quantum interference in SiO2: A conduction-band mass reappraisal
Authors: Ludeke R. , Wen H. J. , Schenk Andreas
Published: July 2002

Quantum oscillations arising from interference in over-the-barrier injected electrons crossing a metal–oxide–semiconductor structure were observed for a 2.8 nm SiO2 layer. Model calculations that include image force effects are fitted to the data to obtain a conduction-band mass of mox=(0.63±0.09)m0. The field dependence of the oscillations was used to deduce the polarity and magnitudes of oxide charge induced by the high fluence of electrons injected with the scanning tunneling microscope during spectral acquisitions.
Theoretical background of the optical charging spectroscopy method used for investigation of trapping levels
Authors: Pintilie I. , Pintilie L. , Petre D. , Tivarus C. , Botila T.
Published: July 2002

An analytical formula for the optical charging spectroscopy (OCS) discharging current in the case of homogeneous semiconductors is deduced. The computation shows that the OCS current is proportional with the square of the initially trapped carrier concentrations. This result leads to a higher sensitivity in case of the OCS method compared with the thermally stimulated current method. The OCS current formula obtained for one trapping level is generalized in the case of many trapping levels. From the generalized formula it can be seen that the OCS current can change the sign if both electron and hole traps exist in the sample.
Enhanced GaN decomposition in H2 near atmospheric pressures
Authors: Koleske D. D. , Wickenden A. E. , Henry R. L. , Twigg M. E. , Culbertson J. C. , Gorman R. J.
Published: July 2002

GaN decomposition is studied at metallorganic vapor phase epitaxy pressures (i.e., 10–700 Torr) in flowing H2. For temperatures ranging from 850 to 1050 °C, the GaN decomposition rate is accelerated when the H2 pressure is increased above 100 Torr. The Ga desorption rate is found to be independent of pressure, and therefore, does not account for the enhanced GaN decomposition rate. Instead, the excess Ga from the decomposed GaN forms droplets on the surface which, for identical annealing conditions, increase in size as the pressure is increased. Possible connections between the enhanced GaN decomposition rate, the coarsening of the nucleation layer during the ramp to high temperature, and increased GaN grain size at high temperature are discussed.
Optical limiting performances of asymmetric pentaazadentate porphyrin-like cadmium complexes
Authors: Sun Wenfang , Byeon Clare C. , McKerns Michael M. , Lawson Chris M. , Gray Gary M. , Wang Duoyuan
Published: July 2002

The optical limiting performances of seven asymmetric pentaazadentate porphyrin-like cadmium complexes have been measured at 532 nm with nanosecond pulses. In a f/38 geometry, with sample transmission of 0.51–0.80 in a 2 mm cell, the limiting thresholds for these complexes were 1.4–3.0 mJ/cm2.The throughputs of these complexes were limited to 0.31–1.13 J/cm2 for incident fluences as high as 3.5 J/cm2. The limiting throughput was strongly influenced by the nature of the ligand. Lower bounds for the ratio of triplet excited-state to ground-state absorption cross sections have been estimated at 3.4–5.7. The lower limiting thresholds, lower limiting throughputs, as well as the ease of modification of the ligands, make these complexes promising candidates for optical power limiters.
Antireflection coatings for PbSe diode lasers
Authors: Beyer T. , Tacke M.
Published: July 2002

The antireflection coating of PbSe laser diodes is crucial for external resonator lasers. In situ determination of the threshold current in cryogenic temperature operation is used in order to optimize the thickness of evaporated layers for minimum reflection.
Cold-field-emission test of the fatigued state of Pb(ZrxTi1−x)O3films
Authors: Stolichnov I. , Tagantsev A. K. , Colla E. L. , Setter N.
Published: July 2002

Fatigue phenomena occurring in Pb(ZrxTi1−x)O3 ferroelectric thin-film capacitors (FECAP) with Pt electrodes are studied by means of conduction measurements in the cold-field-emission (tunneling) regime. We have determined that conduction in virgin FECAPs is controlled by tunneling at temperatures 100–140 K and electric fields (2.3–3.0 MV/cm). The Fowler–Nordheim equation successfully describes observed current–voltage relations for reasonable values of the semiconductor parameters of the system. Fatigue of the switching polarization induced by bipolar voltage cycling provokes a substantial increase in tunneling conduction, shifting the I–V curve to lower fields by some 0.5 MV/cm. The partial restoration of the switching polarization produced by heating of the sample up to 490 K results in a complete restoration of the initial current–voltage characteristic. It is shown that the fatigue-induced increase in conduction can be modeled by the charging of an interfacial layer of a thickness comparable with the tunneling length. This interpretation is consistent with a fatigue scenario related to the space-charge-assisted blocking of near-by-electrode centers of domain nucleation.
Microstructure of the GaSb-on-InAs heterojunction examined with cross-sectional scanning tunneling microscopy
Authors: Harper J. , Weimer M. , Zhang D. , Lin C.-H. , Pei S. S.
Published: July 2002

We have investigated the atomic-scale morphology and composition of the GaSb-on-InAs heterojunction with cross-sectional scanning tunneling microscopy, and find a new “white-noise” component in the wave-vector-dependent roughness spectrum under epitaxial growth conditions routinely employed for type-II quantum well and interband cascade lasers. This phenomenon is associated with random substitutional defects at the interface whose concentration exceeds that due to bulk cross incorporation. We propose these defects originate from the thermodynamically favored but incomplete replacement of As by Sb at the InAs surface during anion exchange.
Morphology and microstructural evolution in the early stages of hydride vapor phase epitaxy of GaN on sapphire
Authors: Golan Y. , Wu X. H. , Speck J. S. , Vaudo R. P. , Phanse V. M.
Published: July 2002

The early stages of hydride vapor phase epitaxy (HVPE) of GaN on sapphire were studied using atomic force microscopy, field-emission scanning electron microscopy, cross-sectional transmission electron microscopy, and x-ray diffraction rocking curves. At the high growth rate used (∼33 nm/s), the films appear to be fully coalesced for growth periods as short as 1 s. A distinct surface and subsequent bulk transformation were observed, resulting in significantly smoother film surfaces and improved bulk morphology. The growth of thick (i.e., 300 μm) GaN films using HVPE offers a promising technique for the deposition of high-quality substrates for GaN homoepitaxy.
Ohmic contacts to p-6H–SiC using focused ion-beam surface-modification and pulsed laser epitaxial TiN deposition
Authors: Iliadis A. A. , Andronescu S. N. , Edinger K. , Orloff J. H. , Vispute R. D. , Talyansky V. , Sharma R. P. , Venkatesan T. , Wood M. C. , Jones K. A.
Published: July 2002

The development of low-resistance Ohmic metallizations to p-type 6H–SiC, using a focused ion-beam (FIB)-Ga surface-modification and ex situ pulsed laser (PLD) epitaxial TiN deposition without further annealing, is reported. The FIB-Ga surface-modification and PLD epitaxial TiN metallizations showed a minimum value of contact resistance of 4.4×10−5 Ω cm2 at an ion dose and energy of 5.0×1016 ions/cm2 and 20 keV, respectively. Auger analysis data indicated well-defined interfaces between the metal and the semiconductor, and a significant subsurface Ga concentration.
Light-emissive nonvolatile memory effects in porous silicon diodes
Authors: Ueno Koki , Koshida Nobuyoshi
Published: July 2002

It is demonstrated that there are distinct off and on states in the current–voltage characteristics of porous silicon (PS) diodes, and that the visible electroluminescence (EL) is observed in the on state. The PS diodes are composed of semitransparent thin Au films, rapid thermal oxidization (RTO)-treated PS layers (∼0.5 μm thick), p-type Si substrates, and ohmic back contacts. After the PS layers were prepared by anodizing Si wafers in an ethanoic HF solution, the samples were treated by RTO process. The bistable states of this PS diode can be simply and reversibly controlled by the external bias voltage. Based on the behavior of the EL and capacitance–voltage characteristics, the model of memory effect is presented, in which field-induced carrier injection and ejection into and from silicon nanocrystallites strongly affects the carrier transport.
Substitutional carbon incorporation in epitaxial Si1−yCy alloys on Si(001) grown by molecular beam epitaxy
Authors: Osten H. J. , Griesche J. , Scalese S.
Published: July 2002

We show that C incorporation kinetics depend significantly on the carbon concentration. The carbon substitutionality (fraction of substitutional incorporated carbon atoms) is strongly influenced by the growth conditions, such as growth temperature and Si growth rate. In addition, reduction in the growth temperature and increase of the growth rate can both increase the substitutional carbon fraction. This behavior is well described by a kinetic model, with the energy barrier and preexponential frequency factor decreasing with increasing carbon concentration. Very low carbon concentrations (in the dopant range) can be predominantly incorporated substitutionally, independent of the growth temperature. At higher C concentrations (in the percentage range), the substitutional carbon fraction is shifted to lower values. We predict the existence of an upper limit for substitutional C incorporation, with its value depending on the specific growth conditions.
Photoconductive detectors based on partially ordered AlxGa1−xN alloys grown by molecular beam epitaxy
Authors: Misra M. , Korakakis D. , Ng H. M. , Moustakas T. D.
Published: July 2002

Photoconductive detectors based on partially ordered AlxGa1−xN alloys with AlN mole fractions up to 45% were fabricated and evaluated. The degree of ordering in these alloys was found to increase with the AlN mole fraction and it has a maximum value at about 50%. The resistivity of the AlxGa1−xN films was found to increase from 10 to 108 Ω cm by increasing the Al content in the films. Correspondingly, the mobility-lifetime (μτ) product, which was determined by measuring the photoconductive gain, was found to decrease from 10−2 to 10−5 cm2/V. These high values of the μτ product at the high AlN mole fraction are attributed to spatial separation and indirect recombination of the photogenerated electron hole pairs, due to band-gap misalignment of the ordered and disordered domains in these films.
Deposition of a thin polystyrene film by anthracene-photosensitized laser ablation at 351 nm
Authors: Tsuboi Yasuyuki , Itaya Akira
Published: July 2002

Pulsed laser deposition of polystyrene (PSt) was investigated using infrared and UV absorption spectroscopy. The essential of the present study is to use a PSt target doped with anthracene which plays an important role as a photosensitizer to induce ablation. Four types of deposition were examined by changing laser wavelength (248 and 351 nm) and ablation target (neat and doped PSt). For both of the targets, 248 nm ablation deposited no film, while 351 nm deposition gave thin films. In the latter, only when 351 nm laser light and the doped target were employed, a thin PSt film was deposited.
An efficient way to improve compositional abruptness at the GaAs on GaInAs interface
Authors: Chirlias E. , Massies J. , Guyaux J. L. , Moisan H. , Garcia J. Ch.
Published: July 2002

Indium surface segregation during the growth of Ga1−xInxAs by chemical beam epitaxy is evidenced in real time by reflection high-energy electron diffraction. An efficient way to suppress the compositional broadening of GaAs on the GaInAs interface resulting from the In segregation effect is proposed. It consists in using the chemical reaction of AsCl3 molecules at the surface, which is shown to etch layer by layer the Ga1−xInxAs alloy. Monolayer etching precision is thus obtained and used to eliminate the In accumulation at the GaInAs surface and the related interface broadening.
Origin of the time dependence of wet oxidation of AlGaAs
Authors: Ashby Carol I. H. , Bridges Monica M. , Allerman Andrew A. , Hammons B. E. , Hou Hong Q.
Published: July 2002

The time dependence of the wet oxidation of high-Al-content AlGaAs can be either linear, indicating reaction-rate limitation, or parabolic, indicating diffusion-limited rates. The transition from linear to parabolic time dependence can be explained by the increased rate of the formation of intermediate As2O3 versus its reduction to elemental As. A steadily increasing thickness of the As2O3-containing region at the oxidation front will shift the process from the linear to the parabolic regime. This shift from reaction-rate limited (linear) to diffusion-limited (parabolic) time dependence is favored by increasing temperature or increasing Al mole fraction.
Integrated nanotube circuits: Controlled growth and ohmic contacting of single-walled carbon nanotubes
Authors: Soh Hyongsok T. , Quate Calvin F. , Morpurgo Alberto F. , Marcus Charles M. , Kong Jing , Dai Hongjie
Published: July 2002

Single-walled carbon nanotubes are synthesized by chemical vapor deposition of methane at controlled locations on a substrate using patterned catalytic islands. The combined synthesis and microfabrication technique presented here allows a large number of ohmically contacted nanotube devices with controllable length to be placed on a single substrate. Transport studies demonstrate ohmic contacting, giving two-terminal resistances as low as 20 kΩ at low temperatures.
Facet temperature distribution in broad stripe high power laser diodes
Authors: Hayakawa Toshiro
Published: July 2002

Facet temperature distribution has been measured for broad stripe high power lasers using reflectance modulation. Temporal evolution of the two-dimensional facet temperature distribution is directly measured. Measurements have been made for devices with various stripe widths. Devices with wider stripes show higher temperature and broader region of high temperature because the lateral heat dissipation becomes more ineffective.
Colloidal CdTe/HgTe quantum dots with high photoluminescence quantum efficiency at room temperature
Authors: Kershaw Stephen V. , Burt Mike , Harrison Mike , Rogach Andrey , Weller Horst , Eychmüller Alex
Published: July 2002

We have used an aqueous colloidal growth technique to form hybrid CdTe/HgTe quantum dots with a broad, strong fluorescence in the infrared (800–1200 nm). The quantum efficiency is high, around 44%, when pumped in the visible (488 nm), and the excited state lifetime is around 130 ns, making the material interesting as an optical amplifier medium. Using a pump-probe experiment, we have demonstrated weak optical amplification in a dilute aqueous suspension of CdTe/HgTe dots in the short wavelength wing of the emission spectrum at 808 nm.
Standing wave detection and interferometer application using a photodiode thinner than optical wavelength
Authors: Sasaki Minoru , Mi Xiaoyu , Hane Kazuhiro
Published: July 2002

A thin film photodiode whose active layer is thinner than the wavelength of the incident light is described. A part of the incident photon is detected and the rest transmits through the thin film photodiode without absorption. Being inserted in the optical field, this sensor is applied to construct the new interferometer detecting the intensity profile of the standing wave of the thinnest interference fringe.
Localization of the Si–H stretch vibration in amorphous silicon
Authors: Rella C. W. , van der Voort M. , Akimov A. V. , van der Meer A. F. G. , Dijkhuis J. I.
Published: July 2002

Vibrational transient grating measurements have been performed on the Si–H stretch vibration of amorphous silicon using intense picosecond infrared pulses from a free electron laser. From these data, the vibrational lifetime can be obtained directly, providing a valuable probe of the microscopic structure and dynamics in the vicinity of the Si–H bond. The stretch mode lifetime has been studied as a function of temperature and across the absorption band. Unexpectedly, the Si–H stretch vibration is demonstrated to be highly localized, and the bulk of the vibrational energy is shown to flow directly to bend vibrations, rather than to other stretch states or to host phonons.
The use of the in-field critical current density, Jc(0.1 T), as a better descriptor of (Bi, Pb)2Sr2Ca2Cu3Ox/Ag tape performance
Authors: Schwartzkopf L. A. , Jiang J. , Cai X. Y. , Apodaca D. , Larbalestier D. C.
Published: July 2002

Extended voltage–current characteristics of 13 optimized (Bi, Pb)2Sr2Ca2Cu3Ox/Ag multifilamentary tapes from four different manufacturers were extensively evaluated so as to extract the field-dependent Jc(H), the characteristic field Hp obtained from the relation Jc∼exp(−H/Hp), and the irreversibility field H*. Values of the self-field critical current density Jc(0 T, 77 K) ranged from 12 to 63 kA/cm2, Ic(0 T,77 K) from 11 to 139 A, Hp from 128 to 204 mT, and H* from 163 to 369 mT, this range thus being representative of present optimized composites. Self-field can strongly dominate Jc(H) in fields below 20 mT; thus, Jc(0 T,77 K) is a flawed parameter for characterizing tapes because of its very heavy dependence on self-field. We propose that a much better descriptor of tape performance is Jc(0.1 T,77 K), because it lies outside the self-field and weak-link-destruction regimes and clearly within the flux-pinning-controlled domain where the connectivity-determined active cross-section carrying current is constant.
Optical switching of nematic liquid crystal by means of photoresponsive polyimides as an alignment layer
Authors: Kim Gi Heon , Enomoto Shintaro , Kanazawa Akihiko , Shiono Takeshi , Ikeda Tomiki , Park Lee-Soon
Published: July 2002

Photosensitive polyimides (PIs) as an alignment layer induced optical switching of nematic liquid crystal (NLC) on photoirradiation at 366 nm. The orientation of NLC molecule was changed from homogeneous to homeotropic alignment on photoirradiation with a dc electric field as a bias. The optical switching behavior of NLC was largely affected by the chemical structures of PIs.
Local and external factors affecting the photodegradation of 4N,N′-dimethylamino-4′nitrostilbene polymer films
Authors: Galvan-Gonzalez Adriana , Canva Michael , Stegeman George I.
Published: July 2002

The photodegradation of the electro-optic chromophore 4N,N′-dimethylamino-4′nitrostilbene was investigated as a function of wavelength, temperature, local atmosphere, and local molecular environment, i.e., attached as a side chain to a polymer or dissolved as a guest in a host polymer.
Thermal conductivity of lateral epitaxial overgrown GaN films
Authors: Luo C.-Y. , Marchand H. , Clarke D. R. , DenBaars S. P.
Published: July 2002

The room-temperature thermal conductivity of lateral epitaxial overgrown metalorganic chemical vapor deposition GaN films is reported to be in excess of 155 W/m K. This compares with the reported value of 130 W/m K for bulk single crystals and a similar value (135 W/m K) for a thick (∼50 μm) GaN film grown, without a nucleation layer, on sapphire by hydride vapor phase epitaxy. The measurements were made by a third-harmonic electrical measurement.
Improved performance of electroluminescent devices based on an europium complex
Authors: Liang C. J. , Zhao D. , Hong Z. R. , Zhao D. X. , Liu X. Y. , Li W. L. , Peng J. B. , Yu J. Q. , Lee C. S. , Lee S. T.
Published: July 2002

Electroluminescent (EL) devices using an europium complex Eu(DBM)3 bath as the electron-transport emitting layer were fabricated. The quenching effect of the metal cathode and the unstable nature of the Eu complex under EL operation markedly influence the EL efficiency. By keeping the emitting area far from the metal cathode and partly doping the Eu(DBM)3 bath layer with a hole-transport material, the EL performance was significantly improved. Sharp-band red emissions with turn-on voltage of 3 V, brightness of 820 cd/m2, and external quantum efficiency of 1% were achieved.
Fused hollow cathode cold atmospheric plasma
Authors: Baránková H. , Bárdoš L.
Published: July 2002

A fused hollow cathode (FHC) plasma source is introduced. The system of radio-frequency (rf) generated hollow cathodes with flowing gas forms an integrated electrode source which operates in the pressure range from 1 Torr to atmospheric pressure. The diameter of the source is 3.5 cm. However, the construction perfectly enables further scaling up. The forward rf power to sustain the discharge at atmospheric pressure can be as low as 2 W. The discharge is stable, volume filling, silent, with no streamers. The FHC atmospheric plasma source is very promising for surface processing, specially on temperature sensitive substrates, and may substantially save costs by avoiding investments into the vacuum equipment.
Tl incorporation in InSb and lattice contraction of In1−xTlxSb
Authors: Lee J. J. , Razeghi M.
Published: July 2002

Ternary In1−xTlxSb thin films are grown by low pressure metalorganic chemical vapor deposition in the high In composition region. Infrared photoresponse spectra of the In1−xTlxSb epilayers show a clear shift toward a longer wavelength compared to that of InSb. Tl incorporation is confirmed by Auger electron spectroscopy. In contrast to the theoretical expectation, high resolution x-ray diffraction study reveals that the lattice of the In1−xTlxSb epilayers is contracted by the incorporation of Tl. As more Tl is incorporated, the lattice contraction is observed to increase gradually in the experimental range. A possible origin of this phenomenon is discussed. Our experimental results suggest that the Tl incorporation behavior in In1−xTlxSb differs from that of other group III impurities in III antimonides.
Coexistence of planar and three-dimensional quantum dots in CdSe/ZnSe structures
Authors: Strassburg M. , Deniozou Th. , Hoffmann A. , Heitz R. , Pohl U. W. , Bimberg D. , Litvinov D. , Rosenauer A. , Gerthsen D. , Schwedhelm S. , Lischka K. , Schikora D.
Published: July 2002

Two well distinguishable classes of nanoscale islands were identified in CdSe/ZnSe quantum dot structures by optical spectroscopy and transmission electron microscopy. For 2.1 to 3.1 monolayer CdSe deposition, coherent three-dimensional (3D) islands, formed in the Stranski–Krastanow (SK) mode, are found with typical diameters of ∼16 nm and a coverage-dependent density of up to 3×1010 cm−2. Simultaneously, small islands with lateral extensions below 10 nm and a density of ∼5×1011 cm−2 are formed by strain-modified island growth. Whereas the 3D SK islands dominate the emission properties at room temperature, the latter smaller islands determine the optical properties at temperatures below 120 K.
Intra-valence band photocurrent spectroscopy of self-assembled Ge dots in Si
Authors: Miesner C. , Röthig O. , Brunner K. , Abstreiter G.
Published: July 2002

Intra-valence band photocurrent investigations of self-assembled Ge dots in Si are reported. Boron-doped Ge dots of about 70 nm diameter and 6.5 nm height are deposited by molecular beam epitaxy in the Stranski–Krastanov growth mode within the intrinsic region of a p+-i-p+ Si structure. For a broad excitation wavelength range between about 2 μm (620 meV) and 6 μm (207 meV), interlevel photocurrent is observed in normal incidence and waveguide geometry. The absorption is attributed to transitions from hole states bound in the Ge dots to continuum states. The photocurrent can be measured up to T=100 K without any significant decrease of the responsivity.
Thermally activated electrical conductivity in thin GaN epitaxial films
Authors: Salzman J. , Uzan-Saguy C. , Kalish R. , Richter V. , Meyler B.
Published: July 2002

Temperature-dependent Hall measurements of thin GaN films subjected to He ion irradiation at ever increasing doses are used to study the electron transport in GaN. It is shown that electron transport is a thermally activated process with activation energies gradually increasing with reciprocal net carrier concentration, until a saturated value of the activation energy is reached. These experiments provide a direct verification that conductivity in thin GaN layers is controlled by potential barriers caused by depletion of carriers at grain boundaries in the material. Values of average grain size, density of surface states at the grain boundaries, and their energetics are extracted from the experiment.
Chemical ordering of epitaxial FePd deposited on ZnSe and the surfactant effect of segregated Se
Authors: Bourgognon C. , Tatarenko S. , Cibert J. , Carbonell L. , Etgens V. H. , Eddrief M. , Gilles B. , Marty A. , Samson Y.
Published: July 2002

We describe the experimental conditions under which a thin film (500 Å thick) of the ferromagnetic alloy FePd can be grown epitaxially onto a thin (100 nm thick) ZnSe(001) layer on a GaAs(001) substrate. A two-dimensional growth could be achieved by using a Pt seeding layer inserted between FePd and ZnSe. During the growth of the metallic layers, the segregation of Se atoms at the surface involves a dramatic effect on the formation of the uniaxial L10 FePd ordered phase. As a result, no perpendicular magnetic anisotropy was observed. The removal of the Se atoms from the Pt surface by a gentle ion bombardment, enables the growth of a FePd layer exhibiting a large anisotropy constant of about 1.2×107 erg/cm3 along the growth direction with a marked perpendicular magnetic domain configuration.