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21 Dec 1998

Volume 73, Issue 25, pp. 3629-3786

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Pressure and temperature dependence of the absorption edge of a thick Ga0.92In0.08As0.985N0.015 layer

Piotr Perlin, Sudhir G. Subramanya, Dan E. Mars, Joachim Kruger, Noad A. Shapiro, Henrik Siegle, and Eicke R. Weber

Appl. Phys. Lett. 73, 3703 (1998); http://dx.doi.org/10.1063/1.122869 (3 pages) | Cited 51 times

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We have studied the pressure and temperature dependence of the absorption edge of a 4-μm-thick layer of the alloy Ga0.92In0.08As0.985N0.015. We have measured the hydrostatic pressure coefficient of the energy gap of this alloy to be 51 meV/GPa, which is more than a factor two lower than that of GaAs (116 meV/GPa). This surprisingly large lowering of the pressure coefficient is attributed to the addition of only ∼1.5% nitrogen. In addition, the temperature-induced shift of the edge is reduced by the presence of nitrogen. We can explain this reduction by the substantial decrease of the dilatation term in the temperature dependence of the energy gap. © 1998 American Institute of Physics.
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78.66.Fd III-V semiconductors
71.20.Nr Semiconductor compounds
85.60.-q Optoelectronic devices

Intraband absorption in the 8–12 μm band from Si-doped vertically aligned InGaAs/GaAs quantum-dot superlattice

Q. D. Zhuang, J. M. Li, H. X. Li, Y. P. Zeng, L. Pan, Y. H. Chen, M. Y. Kong, and L. Y. Lin

Appl. Phys. Lett. 73, 3706 (1998); http://dx.doi.org/10.1063/1.122870 (3 pages) | Cited 22 times

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Normal-incident infrared absorption in the 8–12-μm-atmospheric spectral window in the InGaAs/GaAs quantum-dot superlattice is observed. Using cross-sectional transmission electron microscopy, we find that the InGaAs quantum dots are perfectly vertically aligned in the growth direction (100). Under the normal incident radiation, a distinct absorption peaked at 9.9 μm is observed. This work indicates the potential of this quantum-dot superlattice structure for use as normal-incident infrared imaging focal arrays application without fabricating grating structures. © 1998 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.30.Fs III-V and II-VI semiconductors
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
42.79.Pw Imaging detectors and sensors
85.60.Gz Photodetectors (including infrared and CCD detectors)

Si δ-layers embedded in GaAs

P. O. Holtz, B. Sernelius, A. V. Buyanov, G. Pozina, H. H. Radamson, L. D. Madsen, J. P. McCaffrey, B. Monemar, J. Thordson, and T. G. Andersson

Appl. Phys. Lett. 73, 3709 (1998); http://dx.doi.org/10.1063/1.122871 (3 pages) | Cited 1 time

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An ultrathin, 1–6 monolayers (MLs) thick, Si δ layer, is embedded in bulk GaAs. The normally observed self-assembling with resulting phase separation can be avoided until δ-layer thickness of 4 MLs, which opens the possibility to study two-dimensional (2D) properties of this III–V/IV heterostructure. Optical, electrical, transport, and structural characterization of the Si δ layer has been carried out. In luminescence, two novel emission bands are observed, which are blueshifted as the width of the Si δ layer is reduced, indicating pronounced 2D properties. The derived results on transition energies and electronic structure are compared with theoretical predictions obtained by a self-consistent approach. © 1998 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
68.35.Ct Interface structure and roughness
73.20.At Surface states, band structure, electron density of states
73.61.Cw Elemental semiconductors
73.61.Ey III-V semiconductors

Direct tunneling diode structure with a multilayer charge injection barrier

E. M. Dons, C. S. Skowronski, and K. R. Farmer

Appl. Phys. Lett. 73, 3712 (1998); http://dx.doi.org/10.1063/1.122872 (3 pages) | Cited 7 times

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We report the fabrication and testing of a silicon-based tunnel diode structure that incorporates a multilayer tunneling dielectric. The barrier consists of two thermally grown silicon oxide layers of direct tunneling thickness, ∼3.5 nm each, separated by an ultrathin nanocrystalline silicon layer approximately 5 nm thick. The diode displays current–voltage characteristics that are similar to those of a Fowler–Nordheim device, with a strong current turn-on beyond threshold positive and negative biases, and a “window” region between these two levels where charge transport across the barrier is negligible. In contrast to Fowler–Nordheim devices, the barrier does not appear to degrade significantly when biased in either of its conduction regimes. This property is attributed to the intrinsic degradation resistance of direct tunnel oxides. Additionally, capacitance–voltage characteristics show that the structure is of high quality. Because of its current–voltage and endurance capabilities, this structure shows promise for nonvolatile memory and other applications which require improved endurance and charge retention. © 1998 American Institute of Physics.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
06.60.Mr Testing and inspecting procedures

Intensity-invariant subpicosecond absorption saturation in heavy-ion irradiated bulk GaAs

N. Stelmakh, J. Mangeney, A. Alexandrou, and E. L. Portnoi

Appl. Phys. Lett. 73, 3715 (1998); http://dx.doi.org/10.1063/1.122873 (3 pages) | Cited 11 times

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We demonstrate that bulk GaAs irradiated by heavy Au+ ions shows efficient saturable absorption with subpicosecond recovery time and without any relaxation rate saturation up to excitation densities as high as 1.6 mJ/cm2. A comparison with other types of ion irradiation shows that heavy-ion-irradiated GaAs is a very promising material for ultrafast optoelectronics and optical processing at high repetition rates. © 1998 American Institute of Physics.
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78.47.-p Spectroscopy of solid state dynamics
61.82.Fk Semiconductors
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
78.40.Fy Semiconductors
81.05.Ea III-V semiconductors
61.80.Jh Ion radiation effects

Cation vacancy formation and migration in the AlGaAs heterostructure system

P. Mitev, S. Seshadri, L. J. Guido, D. T. Schaafsma, and D. H. Christensen

Appl. Phys. Lett. 73, 3718 (1998); http://dx.doi.org/10.1063/1.122874 (3 pages) | Cited 3 times

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A simple experimental approach has been employed to obtain thermochemical parameters for cation vacancy formation and migration in the AlGaAs heterostructure system. Cation vacancies are injected into the free surface by annealing under an arsenic-rich ambient. Their presence is detected by monitoring the local rate of Al–Ga interdiffusion at imbedded quantum well markers. The sample is unusually thick allowing us to separately identify contributions from the vapor, epilayer, and substrate phases. The entropies and enthalpies of vacancy formation and migration are (5.2±5.7) kB and (1.8±0.5) eV and (11.3±4.4) kB and (3.3±0.4) eV, respectively. © 1998 American Institute of Physics.
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61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
65.20.-w Thermal properties of liquids
65.40.gd Entropy
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
66.30.Lw Diffusion of other defects

Mechanism of silicon exfoliation induced by hydrogen/helium co-implantation

M. K. Weldon, M. Collot, Y. J. Chabal, V. C. Venezia, A. Agarwal, T. E. Haynes, D. J. Eaglesham, S. B. Christman, and E. E. Chaban

Appl. Phys. Lett. 73, 3721 (1998); http://dx.doi.org/10.1063/1.122875 (3 pages) | Cited 53 times

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Infrared spectroscopy and secondary ion mass spectrometry are used to elucidate the mechanism by which co-implantation of He with H facilitates the shearing of crystalline Si. By studying different implant conditions, we can separate the relative contributions of damage, internal pressure generation, and chemical passivation to the enhanced exfoliation process. We find that the He acts physically as a source of internal pressure but also in an indirect chemical sense, leading to the reconversion of molecular H2 to bound Si–H in “VH2-like” defects. We postulate that it is the formation of these hydrogenated defects at the advancing front of the expanding microcavities that enhances the exfoliation process.
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61.72.uf Ge and Si
81.05.Cy Elemental semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Far-infrared (λ = 88 μm) electroluminescence in a quantum cascade structure

Michel Rochat, Jérôme Faist, Mattias Beck, Ursula Oesterle, and Marc Ilegems

Appl. Phys. Lett. 73, 3724 (1998); http://dx.doi.org/10.1063/1.122895 (3 pages) | Cited 85 times

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Intersubband electroluminescence has been investigated in a quantum cascade structure based on vertical transition designed for far-infrared (λ = 88 μm) emission. A narrow luminescence peak with a full width at half maximum of 0.7 meV is measured at low excitation currents (30 A/cm2) and low temperature (T = 5 K). The electroluminescence efficiency exhibits a strong temperature and current dependence, consistent with an interplay between electron–electron and optical phonon scattering. © 1998 American Institute of Physics.
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78.60.Fi Electroluminescence
63.20.K- Phonon interactions
71.38.-k Polarons and electron-phonon interactions
42.55.Px Semiconductor lasers; laser diodes

Fine structure in the secondary electron emission peak for diamond crystal with (100) negative electron affinity surface

V. M. Asnin and I. L. Krainsky

Appl. Phys. Lett. 73, 3727 (1998); http://dx.doi.org/10.1063/1.122876 (3 pages) | Cited 10 times

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A fine structure was discovered in the low-energy peak of the secondary electron emission spectra of the diamond surface with negative electron affinity. We studied this structure for the (100) surface of the natural type-IIb diamond crystal. We have found that the low-energy peak consists of a total of four maxima. The relative energy positions of three of them could be related to the electron energy minima near the bottom of the conduction band. The fourth peak, having the lowest energy, was attributed to the breakup of the bulk exciton at the surface during the process of secondary electron emission. © 1998 American Institute of Physics.
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79.20.Hx Electron impact: secondary emission
73.20.At Surface states, band structure, electron density of states
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.35.-y Excitons and related phenomena

Injection lasers with vertically aligned InP/GaInP quantum dots: Dependence of the threshold current on temperature and dot size

T. Riedl, E. Fehrenbacher, A. Hangleiter, M. K. Zundel, and K. Eberl

Appl. Phys. Lett. 73, 3730 (1998); http://dx.doi.org/10.1063/1.122877 (3 pages) | Cited 15 times

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We report on threefold-stacked vertically aligned InP/GaInP quantum dot injection lasers emitting in the visible part of the spectrum (690–705 nm) with a low threshold current density of jth = 172 A/cm2 at 90 K showing a thermally activated increase towards higher temperatures. We derived an activation energy for this behavior, which is found to be just one half of the energetic distance between the dot transition energy and the wetting layer band gap. Thus, we identify thermal evaporation of carriers out of the dots and into the wetting layer states as the process responsible for the increase in the threshold current. The nonradiative carrier lifetime in the wetting layer (τnrWL) is estimated to be approximately 250–400 ps. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ey III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Anomalous high carrier mobility in smectic E phase of a 2-phenylnaphthalene derivative

Masahiro Funahashi and Jun-ichi Hanna

Appl. Phys. Lett. 73, 3733 (1998); http://dx.doi.org/10.1063/1.122896 (3 pages) | Cited 53 times

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Ambipolar carrier transport properties in different phases of a liquid-crystalline photoconductor, 2-(4-octylphenyl)–6-n-butoxynaphthalene, were investigated by a time-of-flight technique. Carrier mobilities were increased stepwise when phase transition took place as the temperature decreased. The smectic E phase in the range of 55–125 °C exhibited nondispersive ambipolar carrier transport with an anomalous high carrier mobility of 1.0×10−2 cm2/V s, while the smectic A phase between 125 and 129 °C had similar carrier transport with a smaller mobility of 4×10−4 cm2/V s. In contrast to the crystalline phase, structural defects in the smectic E phase, which were obvious under microscopic observation with polarized illumination, did not deteriorate the carrier transport properties. © 1998 American Institute of Physics.
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72.20.Fr Low-field transport and mobility; piezoresistance
61.30.Jf Defects in liquid crystals
64.70.M- Transitions in liquid crystals
72.40.+w Photoconduction and photovoltaic effects

Strain relaxation in InAs/GaSb heterostructures

Brian R. Bennett

Appl. Phys. Lett. 73, 3736 (1998); http://dx.doi.org/10.1063/1.122878 (3 pages) | Cited 7 times

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Lattice strain relaxation in InAs/GaSb heterostructures was investigated by x-ray diffraction. Two types of structures, grown by molecular beam epitaxy, are compared. In the first, GaSb buffer layers were grown on GaAs substrates, followed by 0.05–1.0 μm thick InAs layers. In the second, InAs layers were grown directly on GaSb substrates. For a given thickness, the InAs layers retain significantly more strain when grown on GaSb substrates, reflecting the lower threading dislocation density in the GaSb substrates relative to the GaSb buffer layers grown on GaAs.
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68.60.Bs Mechanical and acoustical properties
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Highly efficient electron emission from diode-type plane emitters using chemical-vapor-deposited single-crystalline diamond

Toshimichi Ito, Masaki Nishimura, and Akimitsu Hatta

Appl. Phys. Lett. 73, 3739 (1998); http://dx.doi.org/10.1063/1.122879 (3 pages) | Cited 17 times

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A highly efficient electron emitting diode with a flat emission surface has been fabricated using a 600 nm single-crystalline diamond film homoepitaxially grown on high-pressure synthesized (100) diamond by means of chemical-vapor deposition and ion-implantation techniques. The emitter contains a buried injection electrode layer and a hydrogenated diamond surface. When driving voltages ranging from 0.3 to 1.1 kV were applied between them, very efficient electron emissions were observed. The emission efficiency, defined as the ratio of the emission current to the injection diode current, reached 100% for emission currents on the order of 10−7 A and did not significantly depend on the currents. © 1998 American Institute of Physics.
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85.45.Db Field emitters and arrays, cold electron emitters
79.70.+q Field emission, ionization, evaporation, and desorption
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.40.Ry Impurity doping, diffusion and ion implantation technology
61.72.up Other materials

Effect of heating rate on positive-temperature-coefficient-of-resistivity behavior of conductive composite thin films

S. Hirano and A. Kishimoto

Appl. Phys. Lett. 73, 3742 (1998); http://dx.doi.org/10.1063/1.122880 (3 pages) | Cited 12 times

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A phenomenon was discovered that leads to the selective detection of abrupt increases in the temperature of conductive composite thin films consisting of conductive ceramic fillers and an insulating polymer matrix. Examining the heating rate dependence of the positive-temperature–coefficient-of-resistivity (PTCR) effect provided information about this intelligent phenomenon. The anomalous PTCR effect was observed above 0.3 °C min−1 for all the prepared films. However, the magnitude of the anomaly decreased when the heating rate decreased below 0.1 °C min−1, and when the heating rate further decreased below 0.04 °C min−1, the anomalous resistivity–temperature relationship disappeared. The results suggest that these thin films can selectively detect abrupt increases in temperature, which could lead to an intelligent mechanism. Our results also suggest a PTCR mechanism, in which the expansion of crosslinked polymers in the thermodynamic nonequilibrium state essentially produces the anomaly. © 1998 American Institute of Physics.  
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73.61.-r Electrical properties of specific thin films
84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)

Electrical characterization of two deep electron traps introduced in epitaxially grown n-GaN during He-ion irradiation

F. D. Auret, S. A. Goodman, F. K. Koschnick, J-M. Spaeth, B. Beaumont, and P. Gibart

Appl. Phys. Lett. 73, 3745 (1998); http://dx.doi.org/10.1063/1.122881 (3 pages) | Cited 42 times

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Epitaxial n-GaN was irradiated with 5.4-MeV He ions. Capacitance–voltage (C–V) measurements showed that 5.4-MeV He ions remove free carriers at a rate of 6200±300 cm−1 in the first micron below the surface. Deep level transient spectroscopy (DLTS) revealed that, in addition to the radiation-induced defects previously detected by DLTS at 0.18–0.20 eV below the conduction band, He-ion irradiation introduced two additional prominent defects, ER4 (EC-0.78 eV) and ER5 (EC-0.95 eV) at rates of 1510±300 and 3030±500 cm−1, respectively. Capture cross-section measurements revealed that electron capture kinetics of ER5 is similar to that of a line defect. © 1998 American Institute of Physics.
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71.55.Eq III-V semiconductors
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
73.61.Ey III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

{311} defects in silicon: The source of the loops

Jinghong Li and Kevin S. Jones

Appl. Phys. Lett. 73, 3748 (1998); http://dx.doi.org/10.1063/1.122882 (3 pages) | Cited 48 times

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The annealing kinetics of extended defects in Si+-implanted Si have been investigated by in situ annealing plan-view transmission electron microscopy (TEM) samples in a TEM. A 〈100〉 Czochralski-grown silicon wafer was implanted with 100 keV Si+ at the subamorphizing dose of 2×1014 cm−2. Following implantation, the effect of annealing of 800 °C was studied by in situ annealing. After 5 min of annealing at 800 °C, a dense collection of both {311} defects (3×1011/cm2) and small subthreshold dislocation loops (1×1011/cm2) were observed. Upon subsequent annealing, the {311} defect density decreased rapidly and the loop density increased. The evolution of approximately 500 {311} defects could be followed as a function of annealing time. The unfaulting of a {311} defect was observed to be the source of every subthreshold loop observed to from (about 150 loops in the monitored region). After the initial 5 min anneal at 800 °C, the probability of a {311} unfaulting into a loop was about 50%. Based on these observations, it is concluded that unfaulting of the {311} defects is the source of the subthreshold dislocation loops in nonamorphized ion-implanted silicon. 70% of the loops formed were determined to have a Burgers vector of a/3〈111〉, while 30% were perfect with a Burgers vector of a/2〈110〉. © 1998 American Institute of Physics.
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61.72.Nn Stacking faults and other planar or extended defects
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.Lk Linear defects: dislocations, disclinations

A mechanically flexible tunneling contact operating at radio frequencies

A. Erbe, R. H. Blick, A. Tilke, A. Kriele, and J. P. Kotthaus

Appl. Phys. Lett. 73, 3751 (1998); http://dx.doi.org/10.1063/1.122883 (3 pages) | Cited 43 times

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We report on a nanomachined electromechanical resonator applied as a mechanically flexible tunneling contact. The resonator was machined out of a single-crystal silicon-on-insulator substrate and operates at room temperature with frequencies up to some 73 MHz, transferring electrons by mechanical motion. © 1998 American Institute of Physics.
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07.10.Cm Micromechanical devices and systems
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
77.65.-j Piezoelectricity and electromechanical effects
85.35.Ds Quantum interference devices
81.65.Cf Surface cleaning, etching, patterning
85.40.Hp Lithography, masks and pattern transfer

Nitrogen radical adsorption on InAs (001) surface studied by scanning tunneling microscopy and x-ray photoelectronic spectroscopy

M. Kasu, N. Kobayashi, H. Tanaka, and O. Mikami

Appl. Phys. Lett. 73, 3754 (1998); http://dx.doi.org/10.1063/1.122884 (3 pages)

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The adsorption of nitrogen (N) radicals (nitridation) on InAs (001) surfaces has been studied by ultrahigh-vacuum scanning tunneling microscopy and x-ray photoelectronic spectroscopy. The nitridation proceeds as Langmuir adsorption. The N adsorption at 350 °C is faster than that at 100 °C, but N adsorption rates at 100 °C on InAs and GaAs are almost the same. These results are explained as follows: at 350 °C, N radicals bond mainly with the topmost In atoms on an In-stabilized surface, and at 100 °C, N radicals replace As atoms in the topmost layer on an As-stabilized surface, and subsequently bond with In atoms in the second layer. The amorphous 100 °C nitrided surface layer is found to have an insulating characteristic without surface states. © 1998 American Institute of Physics.
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81.05.Ea III-V semiconductors
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
79.60.Dp Adsorbed layers and thin films
82.20.Pm Rate constants, reaction cross sections, and activation energies
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.65.-b Surface treatments

Zero-dimensional excitonic properties of self-organized quantum dots of CdTe grown by molecular beam epitaxy

Yoshikazu Terai, Shinji Kuroda, Kôki Takita, Tsuyoshi Okuno, and Yasuaki Masumoto

Appl. Phys. Lett. 73, 3757 (1998); http://dx.doi.org/10.1063/1.122885 (3 pages) | Cited 39 times

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The successful growth of self-organized quantum dots (QDs) of CdTe on ZnTe (100) surface by molecular beam epitaxy is reported. Atomic force microscope measurements on the uncapped samples revealed the formation of CdTe QDs with typical dot diameters of 20±2 nm and heights of 2.7±0.3 nm at 3.5-ML-thick CdTe deposited. The intensity of photoluminescence (PL) from the capped QDs was higher than CdTe/ZnTe single quantum wells (SQWs) by a few orders of magnitude at 4.2 K, and exhibited a thermal quenching with an activation energy of 110 meV, which is about twice as large as those in SQWs. In time-resolved PL measurements, the decay time was almost independent of temperature below 20 K. This is interpreted as due to the zero-dimensional excitonic properties in QDs. © 1998 American Institute of Physics.
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71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Magneto-optics of InAs/Ga1−xInxSb infrared superlattice diodes

F. Fuchs, E. Ahlswede, U. Weimar, W. Pletschen, J. Schmitz, M. Hartung, B. Jager, and F. Szmulowicz

Appl. Phys. Lett. 73, 3760 (1998); http://dx.doi.org/10.1063/1.122886 (3 pages) | Cited 9 times

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Spectrally resolved measurements of the responsivity of infrared photodiodes based on InAs/(GaIn)Sb superlattices (SL) were performed in applied magnetic fields. For the field oriented parallel to the growth axis, interband Landau transitions related to both the center and the edge of the SL Brillouin zone in the growth direction were observed, in accordance with the parity selection rules that are expected for the type II system under consideration. For the field oriented perpendicular to the growth axis, the interband Landau resonances are broadened and the widening of the band gap is smaller. © 1998 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.70.Sq Magnetooptical devices
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Nanocrack junctions in unidirectionally twinned thin films of YBa2Cu3O7−δ on (001) NdGaO3

G. Koren, E. Polturak, N. Levy, G. Deutscher, and N. D. Zakharov

Appl. Phys. Lett. 73, 3763 (1998); http://dx.doi.org/10.1063/1.122887 (3 pages) | Cited 16 times

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We found unidirectional nanocracks in unidirectionally twinned films of YBa2Cu3O7−δ on NdGaO3 which are normal to the twin planes. In 70–250 nm thick films, transmission electron and atomic force microscopy show that these unidirectional nanocracks are found to be 1–2 μm apart and have 2–4 nm width. Microbridges that cross these nanocracks behave as natural Josephson junctions. They show Shapiro steps under microwave irradiation and suppression of the critical current Ic in magnetic fields. A very large in-plane anisotropy of the resistivities and Ic was observed and this was correlated with the nanocracks orientation, length, and film thickness. The observed anisotropy of Ic near Tc is shown to be consistent with a d+is wave symmetry of the order parameter in YBa2Cu3O7−δ. © 1998 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.50.+r Tunneling phenomena; Josephson effects
74.25.Sv Critical currents
74.78.-w Superconducting films and low-dimensional structures
61.72.Mm Grain and twin boundaries
62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
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Micromagnetic tailoring of periodic antidot permalloy arrays for high density storage

L. Torres, L. Lopez-Diaz, and J. Iñiguez

Appl. Phys. Lett. 73, 3766 (1998); http://dx.doi.org/10.1063/1.122888 (3 pages) | Cited 51 times

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A micromagnetic study on antidot permalloy arrays is carried out in order to delimit their possibilities for high density storage. The dependence of the recorded bit quality on antidot size, separation distance, and film thickness is reported as well as hysteresis loops and coercivities. The simulations show a limit for the antidot size around 80 nm leading to maximum areal storage densities of about 10 Gbits/in2. The results are interpreted in terms of demagnetizing, anisotropy, and exchange energies’ balance. © 1998 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Ss Magnetic recording materials
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.30.Gw Magnetic anisotropy
75.30.Et Exchange and superexchange interactions

Nonlinear magneto-optical Kerr effect and second harmonic generation interferometry in Co–Cu granular films

T. V. Murzina, E. A. Ganshina, S. V. Guschin, T. V. Misuryaev, and O. A. Aktsipetrov

Appl. Phys. Lett. 73, 3769 (1998); http://dx.doi.org/10.1063/1.122889 (3 pages) | Cited 11 times

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Magnetoinduced effects in second harmonic (SH) generation are experimentally studied in the CoxCu1−x granular films. Significant nonlinear magneto-optical Kerr effect (NOMOKE) is observed both in longitudinal and transverse configurations. The interference of the SH fields generated by the interface and bulk, nonmagnetic and magnetoinduced nonlinear polarizations is discussed as a mechanism of NOMOKE enhancement. The bulk nonmagnetic dipole quadratic susceptibility of Co nanocrystals stems from the lack of inversion symmetry in the Co granules. © 1998 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.66.Bz Metals and metallic alloys
78.20.Ls Magneto-optical effects
75.50.Kj Amorphous and quasicrystalline magnetic materials

Neutron diffraction evidence for a new ferromagnetic phase in Cr doped Pr0.5Ca0.5MnO3

F. Damay, C. Martin, A. Maignan, M. Hervieu, B. Raveau, F. Bourée, and G. André

Appl. Phys. Lett. 73, 3772 (1998); http://dx.doi.org/10.1063/1.122890 (3 pages) | Cited 47 times

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Cr doping in Pr0.5Ca0.5MnO3 is known to destroy the low-temperature antiferromagnetic charge-ordered state and to induce a ferromagnetic component as well as colossal magnetoresistance properties. Effects of Cr doping on the magnetic and nuclear structures are studied here by neutron diffraction for Pr0.5Ca0.5Mn0.95Cr0.05O3. It is shown that, at low temperature, the strongly distorted charge ordered structure usually observed in Pr0.5Ca0.5MnO3 is replaced by a ferromagnetic phase in which the basal-plane distortion of the MnO6 octahedra has disappeared, in agreement with the restoration of the double–exchange interactions. © 1998 American Institute of Physics.
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75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.50.Ee Antiferromagnetics
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
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Bulk and surface characterization of a dewetting thin film polymer bilayer

H. Ade, D. A. Winesett, A. P. Smith, S. Anders, T. Stammler, C. Heske, D. Slep, M. H. Rafailovich, J. Sokolov, and J. Stöhr

Appl. Phys. Lett. 73, 3775 (1998); http://dx.doi.org/10.1063/1.122891 (3 pages) | Cited 17 times

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We have monitored the progression of the dewetting of a partially brominated polystyrene (PBrS) thin film on top of a polystyrene (PS) thin film with scanning transmission x-ray microscopy (STXM) as well as photoemission electron microscopy (PEEM). We mapped the projected thickness of each constituent polymer species and the total thickness of the film with STXM, while we determined the surface composition with PEEM. Our data show that the PBrS top layer becomes encapsulated during the later stages of dewetting and that atomic force microscopy topographs cannot be utilized to determine the contact angle between PBrS and PS. © 1998 American Institute of Physics.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.70.Dm X-ray absorption spectra
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