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25 Jun 2001

Volume 78, Issue 26, pp. 4065-4199

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High-speed 1.55 μm Fe-doped multiple-quantum-well saturable absorber on InP

A. Marceaux, S. Loualiche, O. Dehaese, and B. Lambert

Appl. Phys. Lett. 78, 4065 (2001); http://dx.doi.org/10.1063/1.1381410 (3 pages) | Cited 3 times

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Excitonic saturable absorption on iron-doped InGaAs/InP multiple-quantum-well structures is studied by Fourier transform infrared spectroscopy and pump-probe measurement in the 1.55 μm wavelength range. The recovery time of the excitonic absorption bleaching is improved by iron doping and is found to vary from 7 ns on the undoped sample to 7 ps on the highest doped sample. The samples exhibit high optical switching with a differential optical transmission coefficient of more than 20% and a saturation fluence smaller than 47 μJ/cm2. Furthermore, we notice no degradation of the contrast ratio due to iron doping. © 2001 American Institute of Physics.
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42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
78.67.De Quantum wells
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.65.Pc Optical bistability, multistability, and switching, including local field effects
73.21.Fg Quantum wells
78.30.Fs III-V and II-VI semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.47.-p Spectroscopy of solid state dynamics

InGaAsNSb/GaAs quantum wells for 1.55 μm lasers grown by molecular-beam epitaxy

X. Yang, J. B. Héroux, L. F. Mei, and W. I. Wang

Appl. Phys. Lett. 78, 4068 (2001); http://dx.doi.org/10.1063/1.1379787 (3 pages) | Cited 47 times

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InGaAsNSb/GaAs quantum wells (QWs) were grown by solid-source molecular-beam epitaxy using a N2 radio frequency plasma source. The effect of adding Sb during growth of InGaAsN/GaAs QWs was studied. X-ray diffraction, reflection high-energy electron diffraction and transmission electron microscopy studies indicate that Sb suppresses the three-dimensional growth and improves the interface of the QWs. X-ray diffraction and secondary ion mass spectroscopy analysis show that Sb gets incorporated into the quantum well, which becomes a quinternary compound that was previously unexplored. The introduction of Sb during growth of InGaAsN/GaAs QWs significantly enhances the optical properties of the QWs. 1.53 μm room-temperature photoluminescence was obtained from InGaAsNSb/GaAs QWs, which demonstrates the potential of fabricating 1.55 μm InGaAsNSb/GaAs QW lasers for long-haul applications. © 2001 American Institute of Physics.
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81.07.St Quantum wells
78.67.De Quantum wells
68.65.Fg Quantum wells
42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Cr III-V semiconductors

High spatial resolution subsurface microscopy

S. B. Ippolito, B. B. Goldberg, and M. S. Ünlü

Appl. Phys. Lett. 78, 4071 (2001); http://dx.doi.org/10.1063/1.1381574 (3 pages) | Cited 68 times

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We present a high-spatial-resolution subsurface microscopy technique that significantly increases the numerical aperture of a microscope without introducing an additional spherical aberration. Consequently, the diffraction-limited spatial resolution is improved beyond the limit of standard subsurface microscopy. By realizing a numerical aperture of 3.4, we experimentally demonstrate a lateral spatial resolution of better than 0.23 μm in subsurface inspection of Si integrated circuits at near infrared wavelengths. © 2001 American Institute of Physics.
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07.60.Pb Conventional optical microscopes
42.79.Bh Lenses, prisms and mirrors
42.15.Eq Optical system design
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Ultrashort InGaAsP/InP lasers with deeply etched Bragg mirrors

M. Kamp, J. Hofmann, A. Forchel, and S. Lourdudoss

Appl. Phys. Lett. 78, 4074 (2001); http://dx.doi.org/10.1063/1.1377623 (2 pages) | Cited 4 times

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We have fabricated short cavity lasers with deeply etched Bragg mirrors based on 1.55 μm emitting InGaAsP/InP laser structures. Continuous-wave operation has been obtained for devices with a length of 40 μm, showing threshold currents of 12 mA. The dynamic properties of the lasers were studied by measurements of the relative intensity noise (RIN). A maximum modulation frequency of 8.4 GHz was extracted from the RIN data. © 2001 American Institute of Physics.
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42.55.Sa Microcavity and microdisk lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Mi Dynamical laser instabilities; noisy laser behavior
42.60.Fc Modulation, tuning, and mode locking
42.79.Bh Lenses, prisms and mirrors

Ionic and electronic dark decay of holograms in LiNbO3:Fe crystals

Yunping Yang, Ingo Nee, Karsten Buse, and Demetri Psaltis

Appl. Phys. Lett. 78, 4076 (2001); http://dx.doi.org/10.1063/1.1380247 (3 pages) | Cited 16 times

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The lifetimes of nonfixed holograms in LiNbO3:Fe crystals with doping levels of 0.05, 0.138, and 0.25 wt % Fe2O3 have been measured in the temperature range from 30 to 180 °C. The time constants of the dark decay of holograms stored in crystals with doping levels of 0.05 and 0.25 wt % Fe2O3 obey an Arrhenius-type dependence on absolute temperature T, but yield two activation energies: 1.0 and 0.28 eV, respectively. For these crystals, two different dark decay mechanisms are prevailing, one of which is identified as proton compensation and the other is due to electron tunneling between sites of Fe2+ and Fe3+. The dark decay of holograms stored in crystals with the doping level of 0.138 wt % Fe2O3 is the result of a combination of both effects. © 2001 American Institute of Physics.
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42.40.Ht Hologram recording and readout methods
42.70.Ln Holographic recording materials; optical storage media
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Gi Light-sensitive materials

Direct observation of longitudinal spatial hole burning in semiconductor optical amplifiers with injection

J.-N. Fehr, M.-A. Dupertuis, T. P. Hessler, L. Kappei, D. Marti, P. E. Selbmann, B. Deveaud, J. L. Pleumeekers, J.-Y. Emery, and B. Dagens

Appl. Phys. Lett. 78, 4079 (2001); http://dx.doi.org/10.1063/1.1382623 (3 pages) | Cited 10 times

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Measurements of spontaneous emission from InGaAsP semiconductor optical amplifiers provide information on both the carrier density and temperature. By spatially resolving the light emitted along the active layer of the device, we find evidence of longitudinal spatial hole burning which results from amplified spontaneous emission in the structure and is modified by the injected optical signal. Under injection, we also observe pronounced asymmetry of the amplified spontaneous emission intensity from the two facets which we relate to the carrier density profile. The experimental results are in good agreement with numerical simulations. An analysis of the measured spectra reveals an unexpected very high temperature (400 K) and its decrease by at least 35 K in the middle of the device when light is injected. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

Amplified spontaneous emission in active channel waveguides produced by electron-beam lithography in LiF crystals

R. M. Montereali, M. Piccinini, and E. Burattini

Appl. Phys. Lett. 78, 4082 (2001); http://dx.doi.org/10.1063/1.1381568 (3 pages) | Cited 22 times

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In this letter we report the observation of amplified spontaneous emission of the red light from LiF:F2 centers in active channel waveguides realized by electron-beam lithography in lithium fluoride crystals. Low pumping power densities have been used in quasi-continuous-wave regime at room temperature; the appreciable values of the gain coefficients, 4.67 cm−1 with an exciting power density of 0.31 W/cm2 at 458 nm, make this material a good candidate for the realization of active integrated optical devices. © 2001 American Institute of Physics.
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78.45.+h Stimulated emission
42.79.Gn Optical waveguides and couplers
61.72.J- Point defects and defect clusters

Observation of stimulated emission in an ultrashort-period nonsymmetric GaAs/AlAs superlattice

V. G. Litovchenko, D. V. Korbutyak, A. I. Bercha, Yu. V. Kryuchenko, S. G. Krylyuk, H. T. Grahn, R. Hey, and K. H. Ploog

Appl. Phys. Lett. 78, 4085 (2001); http://dx.doi.org/10.1063/1.1379985 (3 pages) | Cited 5 times

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Nonsymmetric short-period GaAs/AlAs superlattices, for which the well thickness is at least a factor of 2 larger than the barrier thickness, have been shown to exhibit a direct band gap for any well thickness. These superlattices are characterized by an enhanced intensity of the luminescence as compared to their symmetric indirect-gap counterparts with the same well width, and, thus, may be used as light-emitting devices, in particular, as low-threshold lasers in the red visible spectrum. This conjecture is supported by the observation of stimulated emission at T = 80 K for a GaAs/AlAs superlattice with six monolayers well and three monolayers barrier width. © 2001 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.45.+h Stimulated emission
78.55.Cr III-V semiconductors
78.67.De Quantum wells
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Surface-emitting, single-lobe operation from second-order distributed-reflector lasers with central grating phaseshift

Gunawan Witjaksono and Dan Botez

Appl. Phys. Lett. 78, 4088 (2001); http://dx.doi.org/10.1063/1.1382633 (3 pages) | Cited 12 times

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Surface-emitting diode lasers containing a second-order Bragg grating with a central phaseshift, Δϕ, of values around π are found to fundamentally favor lasing in a mode of symmetric near-field amplitude profile, which in turn provides emission in a single-lobed beam orthonormal to the surface. Devices of 500 μm long distributed-feedback (DFB) active region (λ = 0.98 μm) and 500 μm long distributed feedback reflector passive regions provide, for Δϕ = π, a surface-emitted beam pattern with 88% central-lobe power content, and external differential quantum efficiency, ηD, of 51%. Since the guided field is antisymmetric to start with, and a central π phaseshift causes two grating-outcoupled beams to be out-of-phase with each other, the net result is a single-lobed far-field pattern. The guided-field peak-to-valley (intensity) ratio, R, in the active (i.e., DFB) region is only 2, which insures single-mode operation to high powers, since the intermodal discrimination is high (⩾100 cm−1). Over a wide range in Δϕ:60°; ηD remains high (>50%) and the degree of guided-field uniformity remains low (R<2). © 2001 American Institute of Physics.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.Dj Gratings
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Photopumped red-emitting InP/In0.5Al0.3Ga0.2P self-assembled quantum dot heterostructure lasers grown by metalorganic chemical vapor deposition

J. H. Ryou, R. D. Dupuis, G. Walter, D. A. Kellogg, N. Holonyak, D. T. Mathes, R. Hull, C. V. Reddy, and V. Narayanamurti

Appl. Phys. Lett. 78, 4091 (2001); http://dx.doi.org/10.1063/1.1382622 (3 pages) | Cited 16 times

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We report the 300 K operation of optically pumped red-emitting lasers fabricated from InP self-assembled quantum dots embedded in In0.5Al0.3Ga0.2P layers on GaAs (100) substrates grown by metalorganic chemical vapor deposition. Quantum dots grown at 650 °C on In0.5Al0.3Ga0.2P layers have a high density on the order of 1010 cm−2 and the dominant size of individual quantum dots ranges from ∼5 to ∼10 nm for 7.5 monolayer “equivalent growth.” These InP/In0.5Al0.3Ga0.2P quantum dot heterostructures are characterized by atomic force microscopy, high-resolution transmission electron microscopy, and photoluminescence. Laser structures are prepared from wafers having two vertically stacked InP quantum dot active layers within a 100-nm-thick In0.5Al0.3Ga0.2P waveguide and upper and lower 600 nm InAlP cladding layers. We observe lasing at λ∼680 nm at room temperature in optically pumped samples. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Opal photonic crystals infiltrated with chalcogenide glasses

V. N. Astratov, A. M. Adawi, M. S. Skolnick, V. K. Tikhomirov, V. Lyubin, D. G. Lidzey, M. Ariu, and A. L. Reynolds

Appl. Phys. Lett. 78, 4094 (2001); http://dx.doi.org/10.1063/1.1380729 (3 pages) | Cited 7 times

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Composite opal structures for nonlinear applications are obtained by infiltration with chalcogenide glasses As2S3 and AsSe by precipitation from solution. Analysis of spatially resolved optical spectra reveals that the glass aggregates into submillimeter areas inside the opal. These areas exhibit large shifts in the optical stop bands by up to 80 nm, and by comparison with modelling are shown to have uniform glass filling factors of opal pores up to 40%. Characterization of the domain structure of the opals prior to infiltration by large area angle-resolved spectroscopy is an important step in the analysis of the properties of the infiltrated regions. © 2001 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.40.Pg Disordered solids
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
42.70.Ce Glasses, quartz

Fast modulation scheme for a two laterally coupled laser diode array

G. Carpintero, H. Lamela, M. Leonés, C. Simmendinger, and O. Hess

Appl. Phys. Lett. 78, 4097 (2001); http://dx.doi.org/10.1063/1.1378806 (3 pages) | Cited 1 time

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The present letter reports a modulation scheme that takes advantage of the unique characteristics of a two laterally coupled laser diode (also known as twin stripe array) to overcome the limit on the modulation imposed by the laser’s relaxation oscillation frequency. Through the use of the rate equation description of the device we uncover the device dynamics behind the modulation scheme generating 35 ps (full width at half maximum) laser pulses at 8 Gb/s modulation rate. Our scheme relies on the fast dynamics of the phase difference, controlled by means of the current injection on each stripe. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking

Charge-separation effects in 1.3 μm GaAsSb type-II quantum-well laser gain

W. W. Chow and H. C. Schneider

Appl. Phys. Lett. 78, 4100 (2001); http://dx.doi.org/10.1063/1.1379784 (3 pages) | Cited 12 times

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A microscopic laser theory is used to investigate gain and threshold properties in a GaAsSb quantum-well laser. Depending on the geometry of the type-II quantum-well gain region, there may be appreciable band distortions due to electron–hole charge separation. The charge separation and accompanying band distortions lead to interesting optical behaviors, such as excitation-dependent oscillator strength and band edge energies. Implications to laser operation include significant blueshift of the gain peak with increasing injection current, and inhibition of spontaneous emission, which may result in threshold current reduction. © 2001 American Institute of Physics.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.Fg Quantum wells
78.67.De Quantum wells

Detection of picosecond electrical pulses using the intrinsic Franz–Keldysh effect

J. F. Lampin, L. Desplanque, and F. Mollot

Appl. Phys. Lett. 78, 4103 (2001); http://dx.doi.org/10.1063/1.1381030 (3 pages) | Cited 14 times

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We report time-resolved measurements of ultrafast electrical pulses propagating on a coplanar transmission line using the intrinsic Franz–Keldysh effect. A low-temperature-grown GaAs layer deposited on a GaAs substrate allows generation and also detection of ps pulses via electroabsorption sampling (EAS). This all-optical method does not require any external sampling probe. A typical rise time of 1.1 ps has been measured. EAS is a good candidate for use in THz characterization of ultrafast devices. © 2001 American Institute of Physics.
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78.47.-p Spectroscopy of solid state dynamics
78.20.Jq Electro-optical effects
84.40.Az Waveguides, transmission lines, striplines
06.60.Jn High-speed techniques (microsecond to femtosecond)
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)

Nonreciprocal transmission in a direct-bonded photorefractive Fe:LiNbO3 buried waveguide

Corin B. E. Gawith, Ping Hua, Peter G. R. Smith, and Gary Cook

Appl. Phys. Lett. 78, 4106 (2001); http://dx.doi.org/10.1063/1.1381028 (3 pages) | Cited 1 time

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We report the fabrication of a 20-μm-thick photorefractive Fe:LiNbO3 planar waveguide buried in MgO:LiNbO3 by direct bonding of precision polished surfaces. Nonreciprocal transmission measurements were performed in a 3-mm-long device with a continuous wave 532 nm frequency-doubled YAG laser source. A Fresnel-reflection-based counterpropagating beam arrangement was used to measure a relative change in optical density of approximately 2 within the waveguide, with a photorefractive response time of 4.9 ms. © 2001 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
42.70.Gi Light-sensitive materials
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.82.Et Waveguides, couplers, and arrays

Small-signal impedance characteristics of quantum-well laser structures

G. E. Giudice, D. V. Kuksenkov, and H. Temkin

Appl. Phys. Lett. 78, 4109 (2001); http://dx.doi.org/10.1063/1.1382651 (3 pages)

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Small-signal impedance characteristics of quantum-well laser structures are analyzed. A simple analytical expression for the frequency dependence of below-threshold small-signal impedance is derived and verified experimentally. It is shown that the differential carrier lifetime and quantum-well transport and capture times can be extracted from electrical impedance measurements. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
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Spontaneous polarization-vector-reorientation photorefractive effect in ferroelectric liquid crystals

Takeo Sasaki, Yuji Kino, Minoru Shibata, Naoko Mizusaki, Atsushi Katsuragi, Yuichi Ishikawa, and Takeshi Yoshimi

Appl. Phys. Lett. 78, 4112 (2001); http://dx.doi.org/10.1063/1.1379595 (3 pages) | Cited 12 times

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The photorefractive effect of a ferroelectric liquid crystal doped with a photoconductive compound was investigated. The photorefractive effect appeared only at the temperature at which the sample exhibits ferroelectricity. The refractive index grating formation time was measured to be ∼ 30 ms. In the ferroelectric phase, reorientation of the spontaneous polarization vector was found to be induced by the internal space-charge field. © 2001 American Institute of Physics.
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77.80.-e Ferroelectricity and antiferroelectricity
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
77.22.Ej Polarization and depolarization
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order

Terahertz radiation from magnetoresistive Pr0.7Ca0.3MnO3 thin films

Noriaki Kida and Masayoshi Tonouchi

Appl. Phys. Lett. 78, 4115 (2001); http://dx.doi.org/10.1063/1.1381573 (3 pages) | Cited 19 times

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Terahertz (THz) radiation with its spectrum extending up to 1 THz has been observed by an illumination of femtosecond optical pulses to optical switching devices fabricated on magnetoresistive manganite thin films; Pr0.7Ca0.3MnO3. The THz radiation strongly depends on temperature T and its T trend reverses sign across charge-orbital and spin-ordering T. © 2001 American Institute of Physics.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
42.65.Pc Optical bistability, multistability, and switching, including local field effects
75.47.Gk Colossal magnetoresistance

Picosecond Z-scan measurements on bulk GaN crystals

V. Pačebutas, A. Stalnionis, A. Krotkus, T. Suski, P. Perlin, and M. Leszczynski

Appl. Phys. Lett. 78, 4118 (2001); http://dx.doi.org/10.1063/1.1380248 (3 pages) | Cited 11 times

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Bulk GaN crystals were characterized by using picosecond laser pulses at λ = 0.527 μm and Z-scan techniques. The role of the free-carrier absorption was evaluated by a dynamical, pump-and-probe-type transmitivity measurement. The values of two-photon absorption coefficient (17–20 cm/GW) and refractive index changes at high optical irradiances due to bound (n2 = −4×10−12 esu) and free (σr = −1.0×10−20 cm3) electrons in that material were determined. © 2001 American Institute of Physics.
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78.47.-p Spectroscopy of solid state dynamics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Room-temperature visible electroluminescence of Al-doped silicon oxide films

X. M. Wu, Y. M. Dong, L. J. Zhuge, C. N. Ye, N. Y. Tang, Z. Y. Ning, W. G. Yao, and Y. H. Yu

Appl. Phys. Lett. 78, 4121 (2001); http://dx.doi.org/10.1063/1.1382629 (3 pages) | Cited 5 times

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A series of Al-doped amorphous silicon oxide films have been grown on p-type silicon (100) substrates by a dual ion beam cosputtering method. Visible electroluminescence (EL) from the devices, made by films with different contents of Al, can be seen with the naked eye under forward bias and reverse bias for films containing sufficient amounts of Al. The EL spectra are found to have a luminescence band peaked at 510 nm (2.4 eV), which is the same result as that obtained from silicon oxide films. With the increase in the amounts of Al, the peak position does not shift, the onset of the bias decreases, and the intensity of EL peak increases. Experiment results show that the doping of Al is beneficial to improving the conduction condition of films while the structure of the films associated with luminescence centers is affected hardly at all. © 2001 American Institute of Physics.
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78.60.Fi Electroluminescence
78.66.Nk Insulators
85.60.Jb Light-emitting devices

Optical investigation of strain in Si-doped GaN films

J. Sánchez-Páramo, J. M. Calleja, M. A. Sánchez-García, and E. Calleja

Appl. Phys. Lett. 78, 4124 (2001); http://dx.doi.org/10.1063/1.1379063 (3 pages) | Cited 5 times

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The effects of Si doping on the growth mode and residual strain of GaN layers grown on Si(111) substrates by plasma-assisted molecular beam epitaxy are studied by Raman scattering and photoluminescence. As the Si concentration increases a progressive decrease of the high-energy E2 mode frequency is observed, together with a redshift of the excitonic emission. Both effects indicate an enhancement of the biaxial tensile strain of thermal origin for increasing doping level, which is confirmed by x-ray diffraction measurements. Beyond Si concentrations of 5×1018 cm−3 both the phonon frequency and the exciton emission energy increase again. This change indicates a partial strain relaxation due to a change in the growth mode. © 2001 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
78.55.Cr III-V semiconductors
68.60.Bs Mechanical and acoustical properties
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
52.77.Dq Plasma-based ion implantation and deposition
63.20.-e Phonons in crystal lattices

Effects of substrate micropatterning on nonlinear optical properties of polar self-assembling films

Leiming Li and Samuel I. Stupp

Appl. Phys. Lett. 78, 4127 (2001); http://dx.doi.org/10.1063/1.1379988 (3 pages) | Cited 2 times

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Self-assembling triblock molecules were previously shown to form thin films with polar order. These films are also known to contain polar supramolecular aggregates that are layered in head-to-tail fashion. In this work, glass substrates were prepared using a focused-ion-beam system to generate 1 mm×1 mm areas containing periodic arrays of squares with lateral dimensions of 7 and 17 μm. The squares were defined by 3 μm wide and 10 nm deep troughs created by Ga ion beams. Using second-harmonic-generation measurements, the average molecular tilt angle was found to be smaller in patterned films, suggesting that micropatterning enhances overall polarization in these films. © 2001 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Jk Polymers and organics
42.65.An Optical susceptibility, hyperpolarizability
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.66.Qn Polymers; organic compounds
81.16.Dn Self-assembly

Mass transport growth and optical emission properties of hydride vapor phase epitaxy GaN

T. Paskova, E. M. Goldys, P. P. Paskov, Q. Wahab, L. Wilzen, M. P. de Jong, and B. Monemar

Appl. Phys. Lett. 78, 4130 (2001); http://dx.doi.org/10.1063/1.1381421 (3 pages) | Cited 2 times

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The optical emission properties of mass-transport regions of GaN grown by hydride vapor phase epitaxy are studied by cathodoluminescence imaging and spectroscopy. A strong donor–acceptor pair emission is observed from the mass-transport regions. Spatially resolved cathodoluminescence reveals a strong intensity contrast between the exciton and donor–acceptor bands from mass-transport and nontransport regions. Focused Auger electron and x-ray photoelectron spectroscopies were employed to investigate the impurity incorporation in the different regions. A preferential moderate increase of residual impurity incorporation or redistribution in mass-transport regions is suggested to be responsible for the observed change of the dominant radiative mechanism. © 2001 American Institute of Physics.
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78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.60.Hk Cathodoluminescence, ionoluminescence
79.20.Fv Electron impact: Auger emission
71.35.-y Excitons and related phenomena
79.60.Bm Clean metal, semiconductor, and insulator surfaces
71.55.Eq III-V semiconductors

Structural characterization of InAs/GaAs quantum-dot nanostructures

D. Pal, E. Towe, and S. Chen

Appl. Phys. Lett. 78, 4133 (2001); http://dx.doi.org/10.1063/1.1382855 (3 pages) | Cited 9 times

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We have performed high-resolution x-ray diffraction measurements on vertically aligned InAs/GaAs quantum-dot nanostructures. The measurements were carried out for both the symmetric (004) and asymmetric (113) and (224) Bragg reflections. Theoretical simulations of the rocking curves indicate that the x-ray signal is primarily from the pseudomorphically strained (In,Ga)As wetting layers. The average thickness and indium composition in the wetting layers, as determined from simulations of the rocking curves, were, respectively, 0.72 nm and 88%. Transmission electron microscopy studies show the creation and annihilation of quantum dots with no observable dislocations. © 2001 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
61.05.cp X-ray diffraction
68.37.Lp Transmission electron microscopy (TEM)

Recrystallization in polyvinylidene fluoride upon low fluence swift heavy ion impact

A. Biswas, R. Gupta, N. Kumar, D. K. Avasthi, J. P. Singh, S. Lotha, D. Fink, S. N. Paul, and S. K. Bose

Appl. Phys. Lett. 78, 4136 (2001); http://dx.doi.org/10.1063/1.1376664 (3 pages) | Cited 13 times

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Thin films (9 μm) of polyvinylidene fluoride (PVDF) are irradiated by swift heavy ions (180 MeV Ag14+) in the fluence range 1×1010–1×1012ions/cm2 with an electronic linear energy transfer LET∼11 keV/nm. In sharp contrast to the previous results, the most characteristic crystalline asymmetric and symmetric CH2 doublets (located at 3025 and 2985 cm−1), have shown remarkable increase in their respective Fourier transform infrared (FTIR) absorbance intensities upon low fluence ion impact (1010 ions/cm2). This increase in absorbance is in consonance with the simultaneous decrease of the transmission intensities of other crystalline bending vibration bands located at 532 (CF2 bending), 614, 796, and 975 cm−1 (all due to CH2 bending) at the similar ion fluence. It appears most probable from the results that, being a polar polymer, the molecular dipoles in PVDF forming a hydrogen bond network get realigned upon irradiation into a highly ordered state of chain molecules in the crystalline regions and create volume elements as crystallites. © 2001 American Institute of Physics.
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61.41.+e Polymers, elastomers, and plastics
61.82.Pv Polymers, organic compounds
78.66.Qn Polymers; organic compounds
68.55.-a Thin film structure and morphology
61.80.Jh Ion radiation effects
78.35.+c Brillouin and Rayleigh scattering; other light scattering
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