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7 Nov 1994

Volume 65, Issue 19, pp. 2377-2495

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Time‐resolved decay of the blue emission in porous silicon

C. I. Harris, M. Syväjärvi, J. P. Bergman, O. Kordina, A. Henry, B. Monemar, and E. Janzén

Appl. Phys. Lett. 65, 2451 (1994); http://dx.doi.org/10.1063/1.112704 (3 pages) | Cited 23 times

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The technologically interesting blue emission from porous silicon has been studied using time‐resolved photoluminescence. In as‐etched samples prepared using the standard electrochemical method, the decay time is shown to be extremely fast (τ=0.86 ns). This decay time remains unchanged from room temperature down to 77 K. The porous material giving the blue emission is unstable and degrades rapidly under UV photoexcitation. A corresponding increase in red intensity with decreasing blue intensity is observed, demonstrating a correlation between the two types of emission. Under ambient light conditions at room temperature the material is more stable and remains emissive for a number of days. © 1994 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.47.-p Spectroscopy of solid state dynamics

Self‐consistent calculation of the modulation response for quantum well laser diodes

Matt Grupen and Karl Hess

Appl. Phys. Lett. 65, 2454 (1994); http://dx.doi.org/10.1063/1.112705 (3 pages) | Cited 4 times

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Modulation responses for a set of strained‐layer InGaAs quantum well lasers as calculated by a new version of Minilase are presented and compared to experiment. Based upon the agreement with measured data, Minilase is used further to associate gain saturation and low frequency rolloff with carrier capture in the quantum well. The capture rates, therefore, influence the modulation response in a significant way even if the time constants are much shorter than the inverse frequency of the modulation signal. © 1994 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Photoluminescence determination of the nitrogen doping concentration in 6H‐SiC

A. Henry, O. Kordina, C. Hallin, C. Hemmingsson, and E. Janzén

Appl. Phys. Lett. 65, 2457 (1994); http://dx.doi.org/10.1063/1.112706 (3 pages) | Cited 19 times

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The intensity of impurity and intrinsic luminescence lines reflects the impurity doping concentration. A calibration procedure is presented for the nitrogen impurity in 6H–SiC. The calibration is valid for a large range of n‐type doping from 1014 to 1016 cm−3. Effects of excitation density, temperature during the photoluminescence experiments as well as the observation of acceptor related lines are discussed. © 1994 American Institute of Physics.
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61.72.up Other materials
71.55.Ht Other nonmetals
78.55.Hx Other solid inorganic materials

Strain relief in linearly graded composition buffer layers: A design scheme to grow dislocation‐free (<105 cm−2) and unstrained epilayers

S. I. Molina, F. J. Pacheco, D. Araújo, R. García, A. Sacedón, E. Calleja, Z. Yang, and P. Kidd

Appl. Phys. Lett. 65, 2460 (1994); http://dx.doi.org/10.1063/1.112707 (3 pages) | Cited 21 times

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The strain relaxation in linearly graded composition InGaAs layers grown on (001) GaAs substrates by molecular beam epitaxy is studied by transmission electron microscopy (TEM) and double crystal x‐ray diffraction (DCXRD). The dislocation distribution in these layers does not coincide with the predicted equilibrium dislocation distribution [J. Tersoff, Appl. Phys. Lett. 62, 693 (1993)]. The dislocation density in the dislocation‐rich layer thickness is slightly smaller than the equilibrium density. The thickness of the dislocation‐rich region is different in the [110] and [110] directions. A good correspondence exists between the TEM and DCXRD strain measurements. The dislocation distribution observed by TEM has made it possible to design a scheme to grow dislocation‐free and unstrained top layers on linearly graded composition buffer layers. © 1994 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Tunneling hot electron transistor as a high power source at terahertz frequencies

M. W. Dellow, N. J. Cronin, and S. J. Bending

Appl. Phys. Lett. 65, 2463 (1994); http://dx.doi.org/10.1063/1.112708 (3 pages) | Cited 4 times

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A novel device is proposed, based upon a tunneling hot electron transfer amplifier, which exhibits the characteristics of negative differential resistance (NDR) coupled with high current gain. The mechanism which produces the NDR is known to be extremely fast. The combination of these features suggests that such a device could be used as a high power source of terahertz radiation. © 1994 American Institute of Physics.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
73.40.Gk Tunneling
72.20.Ht High-field and nonlinear effects

Picosecond luminescence dynamics in CdS/CdSe Stark superlattices

W. Langbein, M. Hetterich, M. Grün, C. Klingshirn, and H. Kalt

Appl. Phys. Lett. 65, 2466 (1994); http://dx.doi.org/10.1063/1.112709 (3 pages) | Cited 8 times

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Screening of the intrinsic piezoelectric fields in hexagonal, strained layer CdS/CdSe type II superlattices by optically generated electron‐hole pairs leads to a shift of the optical transitions of up to 400meV. After intense picosecond excitation, the transition energy follows a logarithmic law as a function of time. This temporal behavior is consistent with model calculations of the density dependent transition‐matrix elements in the tilted bandstructure. © 1994 American Institute of Physics.
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78.55.Et II-VI semiconductors
78.47.-p Spectroscopy of solid state dynamics
78.66.Hf II-VI semiconductors

Laser heating and photoluminescence in GaAs and AlxGa1−xAs

P. S. Dobal, H. D. Bist, S. K. Mehta, and R. K. Jain

Appl. Phys. Lett. 65, 2469 (1994); http://dx.doi.org/10.1063/1.112710 (3 pages) | Cited 3 times

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Low‐temperature band‐to‐band photoluminescence of GaAs and AlGaAs excited by the 514.5 nm line of an argon ion laser beam was used as a probe to measure the temperature at the focused laser spot. A combined study of the dependence of band‐gap energy on increasing laser power density and temperature was undertaken. The band‐gap variation with temperature has been correlated with laser induced temperature at the focused laser spot as a function of laser power density. The induced temperature is lower than anticipated from the theories for cw laser heating. This disagreement can be explained by the contribution of photoexcited carriers to the thermal conductivity, which is not considered by theories available for laser heating in semiconductors. © 1994 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
72.40.+w Photoconduction and photovoltaic effects

Thick c‐axis textured (Tl,Pb)(Ba,Sr)2Ca2Cu3O9/Ag0.37 superconducting tapes by an ink spray pyrolysis method using a Tl‐free precursor

Douglas L. Schulz, Philip A. Parilla, David S. Ginley, James A. Voigt, and E. Peter Roth

Appl. Phys. Lett. 65, 2472 (1994); http://dx.doi.org/10.1063/1.112711 (3 pages) | Cited 9 times

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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. © 1994 American Institute of Physics.
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84.71.Mn Superconducting wires, fibers, and tapes
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
74.72.-h Cuprate superconductors

dc SQUIDs based upon YBa2Cu3O7 nanobridges

J. Schneider, M. Mück, and R. Wördenweber

Appl. Phys. Lett. 65, 2475 (1994); http://dx.doi.org/10.1063/1.113037 (3 pages) | Cited 9 times

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Superconducting quantum interference devices (dc SQUIDs) were fabricated from high‐temperature superconducting YBa2Cu3O7 thin films, using nanobridges as weak links. The weak link behavior in these devices caused by coherent motion of vortices was observed for bridges with dimensions smaller than the effective penetration depth, which was approximately 400–600 nm for the films. The dc SQUIDs consisted of two parallel nanobridges with widths of 100–500 nm. The size of the SQUID hole ranged from 2×2 to 2×10 μm2. The SQUIDs were operated in the temperature range from liquid helium up to 85 K and showed voltage modulations as a function of an applied magnetic field. At 75 K peak‐to‐peak values of 15 μV were observed. The flux noise at 4.2 K was determined to be smaller than 8×10−5 ϕ0 /√Hz. © 1994 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
74.78.-w Superconducting films and low-dimensional structures
74.50.+r Tunneling phenomena; Josephson effects

Eye‐diagram and scattering parameter characterization of superconducting and gold coplanar transmission lines

J. Kruse, W. H. Chang, D. Scherrer, M. Feng, M. Scharen, A. Cardona, and R. Forse

Appl. Phys. Lett. 65, 2478 (1994); http://dx.doi.org/10.1063/1.112712 (3 pages) | Cited 8 times

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We report the gigahertz experimental results of time and frequency performance on YBCO high‐temperature superconductor and gold coplanar transmission lines. An on‐wafer direct probing measurement system was used to collect data at cryogenic temperatures on both YBCO and gold coplanar lines. The insertion loss of the 6 cm lines at a frequency of 2.5 GHz was measured to be −0.03 dB for the superconducting line compared to −10.4 dB for the gold line at 80 K. Eye‐diagram measurements were performed on the packaged lines and show the correlation between the insertion loss of the line and the attenuation of a pseudorandom bit sequence. The measured eye height was 170 mV for the YBCO compared to 90 mV for a gold line at 1 Gbit/s and a temperature of 77 K for the packaged 6 cm lines. © 1994 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.25.Qc Superconducting surface acoustic wave devices and other superconducting devices

Growth and properties of La2−xSrxCuO4 films

I. E. Trofimov, L. A. Johnson, K. V. Ramanujachary, S. Guha, M. G. Harrison, M. Greenblatt, M. Z. Cieplak, and P. Lindenfeld

Appl. Phys. Lett. 65, 2481 (1994); http://dx.doi.org/10.1063/1.112671 (3 pages) | Cited 25 times

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Single‐crystalline films of La2−xSrxCuO4 have been grown epitaxially on SrTiO3, NdGaO3, and LaSrAlO4 substrates by laser ablation. We show that record values of the superconducting transition temperature may be achieved by high‐pressure annealing in oxygen. The films exhibit values of Tco above 38 K, as well as a linear variation of the resistivity with T and excellent crystal quality. © 1994 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
81.15.Fg Pulsed laser ablation deposition
74.72.-h Cuprate superconductors

Giant magnetoresistance in magnetic multilayered nanowires

L. Piraux, J. M. George, J. F. Despres, C. Leroy, E. Ferain, R. Legras, K. Ounadjela, and A. Fert

Appl. Phys. Lett. 65, 2484 (1994); http://dx.doi.org/10.1063/1.112672 (3 pages) | Cited 229 times

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Giant magnetoresistance (GMR) is observed in a new type of nanostructured material consisting of magnetic multilayered nanowires formed by electrodeposition into nanometer‐sized pores of a template polymer membrane. The composition of these nanowires is modulated over nanometer length scales with distinct magnetic and nonmagnetic metallic layers. Magnetoresistance measurements with the current perpendicular to the layers were performed on the array of parallel nanowires. GMR of about 15% was observed at room temperature on Co/Cu multilayered nanowires. © 1994 American Institute of Physics.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
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

Densification, anisotropic deformation, and plastic flow of SiO2 during MeV heavy ion irradiation

E. Snoeks, A. Polman, and C. A. Volkert

Appl. Phys. Lett. 65, 2487 (1994); http://dx.doi.org/10.1063/1.112646 (3 pages) | Cited 46 times

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The response of SiO2 thin films and implantation masks to 4.0 MeV Xe irradiation is studied. Trenches in silica deform dramatically after irradiation with 3×1015 ions/cm2. In situ wafer curvature measurements show that thin planar silica films first densify by 3.6% during irradiation. The resulting stress then relaxes viscously by radiation‐enhanced Newtonian flow. At a flux of 3×1010 Xe ions/cm2s the measured shear viscosity was 6×1013Pa s. We find evidence that an irradiation induced anisotropic deformation mechanism is present in the silica films. In equilibrium, this deformation leads to an average compressive saturation stress as large as 4.5×107 Pa. © 1994 American Institute of Physics.
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61.80.Jh Ion radiation effects

Novel technique for growth‐etch cycling of flame‐deposited diamond films

T. P. Thorpe, R. A. Weimer, and J. A. Freitas

Appl. Phys. Lett. 65, 2490 (1994); http://dx.doi.org/10.1063/1.112647 (3 pages) | Cited 2 times

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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. © 1994 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Low‐energy‐electron diffraction by nano‐objects in projection microscopy without magnetic shielding

Vu Thien Binh, V. Semet, and N. Garcia

Appl. Phys. Lett. 65, 2493 (1994); http://dx.doi.org/10.1063/1.112648 (3 pages) | Cited 27 times

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This paper shows that by using nanotips as nanosources of electrons, Fresnel diffraction by nano‐objects is observed in a low‐energy‐electron projection microscope without any magnetic field shielding. The results shown are consistent with the Aharonov‐Bohm effect and Lorentz force deviation due to the magnetic stray fields. © 1994 American Institute of Physics.
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61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
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
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