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7 Dec 1998

Volume 73, Issue 23, pp. 3321-3467

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Ultrafast phase dynamics of coherent carriers in GaAs

X. Y. Yu, Q. Luo, W. L. Li, Q. Li, Z. R. Qiu, and J. Y. Zhou

Appl. Phys. Lett. 73, 3321 (1998); http://dx.doi.org/10.1063/1.122708 (3 pages) | Cited 8 times

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Ultrafast phase dynamics of free-induction decay for carriers in bulk GaAs is studied with differential-phase spectroscopy. The instantaneous phase shifts of the free-induction decay with respect to the excitation pulses are extracted from simultaneously recorded laser pulse autocorrelation and free-induction decay in GaAs. Ultrafast phase dynamics during and immediately after the femtosecond pulse excitation are numerically evaluated with optical Bloch equations using pump pulse and semiconductor exciton parameters as input. Good agreement of the theory with experiment is obtained. © 1998 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
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Self-consistent Green’s function approach to the analysis of dielectrically apertured vertical-cavity surface-emitting lasers

B. Klein, L. F. Register, K. Hess, D.G. Deppe, and Q. Deng

Appl. Phys. Lett. 73, 3324 (1998); http://dx.doi.org/10.1063/1.122710 (3 pages) | Cited 12 times

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Dielectrically apertured vertical-cavity surface-emitting lasers are modeled using a Green’s-function-based optical solver that allows calculation of the full-vector lasing modes and their threshold conditions. The laser is separated into subsystems consisting of a planar microcavity, a dielectric aperture, and an active gain medium. The exact Green’s function solution for a radiating point source in the planar microcavity is then used to construct an eigenvalue equation for the self-consistent lasing modes. The derived eigenvalue equation is numerically solved to evaluate threshold dependence on aperture and cavity design. Results show a low threshold for thin oxide apertures placed at field antinodes, as well as for tapered oxides with thin tapers placed at field nodes. © 1998 American Institute of Physics.
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42.55.Sa Microcavity and microdisk lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Px Semiconductor lasers; laser diodes
02.10.Ud Linear algebra
02.10.Xm Multilinear algebra
02.30.Sa Functional analysis

Efficient contour generation and tracking of a moving object with a rhodium-doped BaTiO3 crystal working in the near infrared

Pierre Mathey, Pierre Jullien, and Daniel Rytz

Appl. Phys. Lett. 73, 3327 (1998); http://dx.doi.org/10.1063/1.122709 (3 pages) | Cited 1 time

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The depletion efficiencies and their corresponding constant times are investigated in four differently doped barium titanate crystals at the near-infrared wavelength of 854 nm. It is shown that the rhodium-doped crystal offers the best results. Satisfactory motion tracking and edge enhancement are demonstrated with an optical photorefractive novelty filter. © 1998 American Institute of Physics.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.79.Pw Imaging detectors and sensors
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
78.20.-e Optical properties of bulk materials and thin films
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Optical engineering with Fibonacci dielectric multilayers

Enrique Maciá

Appl. Phys. Lett. 73, 3330 (1998); http://dx.doi.org/10.1063/1.122759 (3 pages) | Cited 59 times

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We study the resonant transmission of light through Fibonacci dielectric multilayers (FDM). Making use of a transfer matrix renormalization technique [E. Maciá and F. Domínguez-Adame, Phys. Rev. Lett. 76, 2957 (1996)] we obtain closed analytical expressions for the transmission coefficient under arbitrary incidence angle conditions. We analyze the relationship between the resonant wavelengths and the quasiperiodic structure of the substrate, suggesting the potential use of arrays containing FDMs of different sizes in the design of optical microcavities. © 1998 American Institute of Physics.
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78.66.-w Optical properties of specific thin films
02.20.-a Group theory
42.79.Wc Optical coatings

An application of the apertureless scanning near-field optical microscopy: Imaging a GaAlAs laser diode in operation

R. Bachelot, G. Wurtz, and P. Royer

Appl. Phys. Lett. 73, 3333 (1998); http://dx.doi.org/10.1063/1.122760 (3 pages) | Cited 7 times

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The imaging of a commercial GaAlAs semiconductor laser emitting at 0.78 μm has been performed by apertureless scanning near-field optical microscopy using a sharp metallic tip. This tip was used as an optical and force probe simultaneously. In stimulated emission, we observed the single transverse laser mode whose dimensions are in good agreement with theoretical results. In spontaneous emission, an optical contrast linked to the known laser layers structure was observed. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
07.79.Fc Near-field scanning optical microscopes

Direct fabrication of polyimide waveguide grating by synchrotron radiation

Junya Kobayashi, Tohru Maruno, Tetsuyoshi Ishii, Toshiaki Tamamura, and Toshiyuki Horiuchi

Appl. Phys. Lett. 73, 3336 (1998); http://dx.doi.org/10.1063/1.122761 (3 pages) | Cited 2 times

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Synchrotron radiation induces a change in the refractive index of a fluorinated polyimide by an order of 10−2, which is about ten times larger than the change it induces in silica glass irradiated by ultraviolet light, presumably due to fluorine detachment and subsequent volume compaction. We have fabricated a 0.51-μm-period grating structure in an embedded waveguide through a 15-μm-thick overcladding by using an x-ray mask with a spatially modulated pattern. The grating is fabricated at a dose of 160 A s and shows a reflectivity of 60% and a full width at half maximum as narrow as 0.25 nm at around a wavelength of 1.55 μm. © 1998 American Institute of Physics.
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42.70.Jk Polymers and organics
42.79.Gn Optical waveguides and couplers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.79.Dj Gratings
42.65.Wi Nonlinear waveguides
42.82.Et Waveguides, couplers, and arrays

A phase jump phenomenon in interferometry

Weidong Zhou and Lilong Cai

Appl. Phys. Lett. 73, 3339 (1998); http://dx.doi.org/10.1063/1.122762 (3 pages) | Cited 3 times

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A phase jump phenomenon in interferometers is reported. When the intensity of one arm of an interferometer changes from greater to less (or less to greater) than that of another, a phase jump of 180° will take place if the phase difference between two beams is fixed as π. We name this phenomenon “phase jump.” Both theoretical analysis and experimental verification are conducted and the results are presented here. The slope of the phase jump is infinite and highly stable. Therefore, this phase jump phenomenon can be used as optical comparators, reference mark, position indexes, pulse generators, edge detection, etc. © 1998 American Institute of Physics.
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07.60.Ly Interferometers

Measurement of temperature gradient in diode-laser-pumped high-power solid-state laser by low-coherence reflectometry

S. L. Huang, W. L. Wu, and P. L. Huang

Appl. Phys. Lett. 73, 3342 (1998); http://dx.doi.org/10.1063/1.122763 (3 pages) | Cited 2 times

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A noninvasive technique was developed to measure the temperature distribution in laser gain medium. Both axial and radial temperature distributions of a diode-laser-pumped and intracavity frequency-doubled high-power Nd:YVO4/KTP laser were characterized using a high dynamic range, low-coherence reflectometer. This measurement is important to the design of high-power solid-state lasers both in terms of mode matching and laser-rod doping selection. © 1998 American Institute of Physics.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.70.Hj Laser materials
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Electroabsorption spectroscopy study of an azopolymer film fabricated by electrostatic adsorption

Ke Yang, Srinivasan Balasubramanian, Xiaogong Wang, Jayant Kumar, and Sukant Tripathy

Appl. Phys. Lett. 73, 3345 (1998); http://dx.doi.org/10.1063/1.122764 (3 pages) | Cited 8 times

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Electroabsorption spectroscopy measurements are reported on a multilayer thin film of a prototypical azopolymer. The sample was prepared by sequentially dipping the substrate into aqueous solutions containing the polycation poly(diallyl dimethyl ammonium chloride) and the polyanion CH-1A-NS, an epoxy based polymer with azobenzene chromophore. The measured ratio of χ3333(3) to χ1133(3) for the electrostatically assembled film is 4, which indicates that the chromophores in this film are oriented preferentially perpendicular to the film plane instead of an isotropic distribution in three-dimensional space. For comparison, a spin coated film of CH-1A-NS was studied by the same method. The ratio of χ3333(3) to χ1133(3) for the spin coated film is found to be 1.9, indicating that the same chromophores in the spin coated film are oriented preferentially in the film plane. These results imply that the process of electrostatic layer-by-layer adsorption leads to a preferred orientation of the chromophores, perpendicular to the film plane, while the same chromophores in the spin coated film lie predominately in the plane of the substrate. © 1998 American Institute of Physics.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
61.41.+e Polymers, elastomers, and plastics
68.55.-a Thin film structure and morphology
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
42.70.Jk Polymers and organics
78.20.Jq Electro-optical effects
78.40.Me Organic compounds and polymers
78.66.Qn Polymers; organic compounds

Effect of well number on organic multiple-quantum-well electroluminescent device characteristics

Jingsong Huang, Kaixia Yang, Zhiyuan Xie, Baijun Chen, Hongjin Jiang, and Shiyong Liu

Appl. Phys. Lett. 73, 3348 (1998); http://dx.doi.org/10.1063/1.122765 (3 pages) | Cited 22 times

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A doping technique for fabricating organic multiple-quantum-well electroluminescent (EL) devices is demonstrated. This device consists of N,N′-Bis(3-methyphenyl)-N,N′-diphenylbenzidine used as a hole transporter, undoped tris(8-quinolinolato) aluminum (Alq) as a barrier potential or electron transporter, and Alq doped with 5,6,11,12-tetraphenylnaphthacene as a potential well and an emitter. Our experimental results suggest that the double-quantum-well EL devices show the optimum emission characteristics. The efficiency and the luminance of the device achieve 15.7 lm/W and 7500 cd/m2, respectively. © 1998 American Institute of Physics.  
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73.61.Ph Polymers; organic compounds
85.60.Jb Light-emitting devices
78.66.Qn Polymers; organic compounds
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Lasing from InGaAs/GaAs quantum dots with extended wavelength and well-defined harmonic-oscillator energy levels

G. Park, O. B. Shchekin, D. L. Huffaker, and D. G. Deppe

Appl. Phys. Lett. 73, 3351 (1998); http://dx.doi.org/10.1063/1.122766 (3 pages) | Cited 45 times

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Data are presented on the lasing transitions from InGaAs/GaAs quantum dots that exhibit four well-resolved energy transitions, with the electronic state density of a two-dimensional harmonic oscillator. Lasing has been obtained on the second and third transitions, depending on the cavity (gain) length, with the longest lasing wavelength measured to be 1.19 μm. The temperature dependence of threshold is studied and regions of nearly temperature-independent threshold are found. Interesting aspects of the unique electronic state density for lasers are discussed. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
73.20.At Surface states, band structure, electron density of states
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Optical fiber temperature sensor using a gain-switched Fabry–Perot semiconductor laser self-seeded from a linearly chirped fiber Bragg grating

Shenping Li and K. T. Chan

Appl. Phys. Lett. 73, 3354 (1998); http://dx.doi.org/10.1063/1.122767 (3 pages) | Cited 2 times

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We present a highly sensitive fiber temperature sensor based on a gain-switched Fabry–Perot semiconductor laser self-seeded from a linearly chirped fiber Bragg grating. A temperature resolution of better than 0.1 °C was demonstrated. This sensor not only has the advantage of robustness against fluctuating light levels, but also obviates the need for fine wavelength discrimination. © 1998 American Institute of Physics.
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07.20.Dt Thermometers
42.81.Pa Sensors, gyros
42.55.Px Semiconductor lasers; laser diodes
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
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Observation of vibrational modes of irregular drums

Olivier Haeberlé, Bernard Sapoval, Kristen Menou, and Holger Vach

Appl. Phys. Lett. 73, 3357 (1998); http://dx.doi.org/10.1063/1.122768 (3 pages) | Cited 6 times

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Vibrational modes of irregular or prefractal drums have been calculated using a correspondence between the wave propagation and the diffusion equations. The resonance frequencies and the vibrational-mode structures measured on low thickness plastic film membranes using a holographic setup are found to be in good agreement with theoretical predictions. © 1998 American Institute of Physics.
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63.50.-x Vibrational states in disordered systems
61.43.Hv Fractals; macroscopic aggregates (including diffusion-limited aggregates)
05.45.-a Nonlinear dynamics and chaos
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Platinum nanodot formation by atomic point contact with a scanning tunneling microscope platinum tip

D. H. Huang, T. Nakayama, and M. Aono

Appl. Phys. Lett. 73, 3360 (1998); http://dx.doi.org/10.1063/1.122769 (3 pages) | Cited 14 times

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Using a platinum tip of a scanning tunneling microscope, ultrasmall nanodots of about 1 to 2 nm in diameter are reproducibly created on the Si(111)7×7 surface at room temperature by applying appropriate voltage pulses between tip and sample. Dynamic processes of the nanodot formation have been monitored by means of the displacement of the tip and the current through the tip. The experimental data suggest that a nanometer-scale bridge is formed between tip and sample, and that the created nanodot is a part of the nanobridge left on the surface. We have also observed relaxation of the tip apex and the created nanodots after the nanobridge is broken. © 1998 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
61.46.-w Structure of nanoscale materials
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Ion induced disordering and dissolution of Ni3Al precipitates

J. C. Ewert, G. Schmitz, F. Harbsmeier, M. Uhrmacher, and F. Haider

Appl. Phys. Lett. 73, 3363 (1998); http://dx.doi.org/10.1063/1.122770 (3 pages) | Cited 3 times

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The disordering of homogeneous Ni3Al and decomposed Ni(Al) alloys under irradiation with 300 keV 58Ni ions is studied at room temperature. In order to determine the development of the long-range order parameter, electron diffraction patterns are quantitatively evaluated taking into account dynamical diffraction effects. Although postulated by a recent model based on the thermal spike concept, no finite rest order is observed in the high-dose limit. The disordering rate of Ni3Al precipitates is much higher than that of homogeneous Ni3Al which is explained by the additional chemical dissolution of the particles due to ballistic mixing. © 1998 American Institute of Physics.
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64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation
61.80.Jh Ion radiation effects
61.82.Bg Metals and alloys

Activation fields in ferroelectric thin film capacitors: Area dependence

T. K. Song, S. Aggarwal, Y. Gallais, B. Nagaraj, R. Ramesh, and J. T. Evans

Appl. Phys. Lett. 73, 3366 (1998); http://dx.doi.org/10.1063/1.122771 (3 pages) | Cited 37 times

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We report the activation field characteristics of (La,Sr)CoO3/Pb(Nb,Zr,Ti)O3/(La,Sr)CoO3 capacitors with areas varying from 13 to 9600 μm2. Switching properties such as maximum current and switching time depend on the capacitor area and measuring circuit elements, but the activation field is independent of capacitor area and measuring circuit parameters. Area independence of activation fields is also confirmed in (Pb,La)(Zr,Ti)O3 thin film capacitors. Two different approaches have been used to determine the activation field, yielding similar results. It is concluded that activation field is an intrinsic property and is a good quantitative measure of the ferroelectric switching properties. © 1998 American Institute of Physics.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.32.Tt Capacitors
77.80.Fm Switching phenomena

Room-temperature diffusivity of self-interstitials and vacancies in ion-implanted Si probed by in situ measurements

Salvatore Coffa and Sebania Libertino

Appl. Phys. Lett. 73, 3369 (1998); http://dx.doi.org/10.1063/1.122753 (3 pages) | Cited 13 times

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We have determined the room-temperature diffusivity of self-interstitials and vacancies in Si. Silicon p+−n junctions were realized in n-type epitaxial Si wafers, having an O and C content ⩽ 1015/cm3, and implanted at room temperature with 2.5 MeV He ions to fluences in the range 1×109–1×1012/cm2. The junctions were reverse biased at −30 V, in order to embody the entire damage profile of the ion in the depletion layer, and in situ leakage measurements were performed during and just after implantation. It is found that the leakage current increases monotonically during implantation while, at the beam turn off, it decreases by about a factor of 2 for times as long as 1 day. Ex situ deep level transient spectroscopy measurements show that the main contribution to leakage current is due to the deep levels introduced in the band gap by phosphorous–vacancy and divacancy complexes. This allowed us to associate the leakage current reduction at the beam turn off to the recombination of vacancy-type complexes by residual free interstitials. When, for a fixed fluence, the ion flux is increased, an initial faster transient, lasting up to ∼1000 s, is observed and has been attributed to the annihilation of residual free vacancies. Diffusivity values of 1.5×10−15 and 3.0×10−13 cm2/s for interstitials and vacancies, respectively, have been achieved from the analysis of these data. © 1998 American Institute of Physics.
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66.30.J- Diffusion of impurities
66.30.Lw Diffusion of other defects
61.72.J- Point defects and defect clusters
61.72.uf Ge and Si
61.82.Fk Semiconductors
85.40.Ry Impurity doping, diffusion and ion implantation technology

A method for liquid crystal alignment using in situ ultraviolet exposure during imidization of polyimide

Jae-Hoon Kim, Bharat R. Acharya, Satyendra Kumar, and Ki Ryong Ha

Appl. Phys. Lett. 73, 3372 (1998); http://dx.doi.org/10.1063/1.122754 (3 pages) | Cited 17 times

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Homogeneous alignment of liquid crystals can be achieved by a technique using polyimide films and in situ exposure to linearly polarized ultraviolet (LPUV) light during imidization. The alignment layers prepared by this method exhibit higher thermal stability while requiring shorter processing time than the conventional UV alignment method which employs UV exposure after the imidization of polyimide is complete. Multidomain cells can be easily fabricated with the use of a photomask and multistep in situ LPUV exposure during hard bake. © 1998 American Institute of Physics.
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61.30.-v Liquid crystals
83.80.Xz Liquid crystals: nematic, cholesteric, smectic, discotic, etc.
82.35.-x Polymers: properties; reactions; polymerization
68.60.Dv Thermal stability; thermal effects

Metal–insulator transition in SrRuO3 induced by ion irradiation

Z. Sefrioui, D. Arias, M. A. Navacerrada, M. Varela, G. Loos, M. Lucía, J. Santamaría, F. Sánchez-Quesada, and M. A. López de la Torre

Appl. Phys. Lett. 73, 3375 (1998); http://dx.doi.org/10.1063/1.122772 (3 pages) | Cited 15 times

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We have studied the effect of He+ irradiation on the electrical resistivity and Curie temperature of ferromagnetic SrRuO3 thin films. An evolution from metallic to insulating behavior is observed when He+ ion fluence is increased, suggesting a metal–insulator transition. Damage by ion irradiation produces a strong decrease of the Curie temperature. On the other hand, no significant change in Tc (∼160 K) takes place in fresh samples grown at different substrate temperatures. We discuss the possible correlation between structural changes induced by irradiation, which reflect in an increase of the pseudocubic lattice parameter, and the observed depression of Tc.© 1998 American Institute of Physics.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Cc Other ferromagnetic metals and alloys
71.30.+h Metal-insulator transitions and other electronic transitions
61.80.Jh Ion radiation effects
75.70.Ak Magnetic properties of monolayers and thin films

Hydrogen desorption and adsorption measurements on graphite nanofibers

C. C. Ahn, Y. Ye, B. V. Ratnakumar, C. Witham, R. C. Bowman, and B. Fultz

Appl. Phys. Lett. 73, 3378 (1998); http://dx.doi.org/10.1063/1.122755 (3 pages) | Cited 76 times

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Graphite nanofibers were synthesized and their hydrogen desorption and adsorption properties are reported for 77 and 300 K. Catalysts were made by several different methods including chemical routes, mechanical alloying, and gas condensation. The nanofibers were grown by passing ethylene and H2 gases over the catalysts at 600 °C. Hydrogen desorption and adsorption were measured using a volumetric analysis Sieverts’ apparatus, and the graphite nanofibers were characterized by transmission electron microscopy and Brunauer–Emmett–Teller surface area analysis. The absolute level of hydrogen desorption measured from these materials was typically less than the 0.01 H/C atom, comparable to other forms of carbon. © 1998 American Institute of Physics.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
61.46.-w Structure of nanoscale materials

Transient thermochromism during ArF excimer laser ablation of poly(3-dodecylthiophene) films

Katsunori Tsunoda, Keiko Kakinuma, Hirofumi Yajima, and Tadahiro Ishii

Appl. Phys. Lett. 73, 3381 (1998); http://dx.doi.org/10.1063/1.122773 (3 pages)

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The photothermal effects involved in ArF (193 nm) laser ablation of poly(3-dodecylthiophene) (PDT) films, which have the characteristics of fusibility and thermochromism, were studied using atomic force microscopy and transient absorption spectroscopy. A molten layer was observed in the irradiated region of the PDT films. The behavior of the transient absorption spectra corresponding to the thermochromism showed a rapid increase in temperature during laser duration. A heating rate of approximately 5×109 deg/s was obtained. The obtained findings reveal that photothermal effects are significantly involved in the ablation process. © 1998 American Institute of Physics.
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78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
79.20.Ds Laser-beam impact phenomena
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.66.Qn Polymers; organic compounds
61.41.+e Polymers, elastomers, and plastics

Scale dependence of submicron polycrystals due to configurational entropy

Qiang Yang and Wei Yang

Appl. Phys. Lett. 73, 3384 (1998); http://dx.doi.org/10.1063/1.122774 (3 pages) | Cited 5 times

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It is well known that polycrystals exhibit abnormal Hall-Petch dependence when their grain sizes fall into the submicron range. A plausible explanation is that the scale dependence of the yield stress of submicron polycrystals is mediated not only by the internal energy of the dislocation patterns, but also by their configurational entropy. Two-level dislocation arrangements are explored which naturally embed a grain size. Detailed calculations of the internal energy and the configurational entropy are facilitated by the dislocation pileup theory and the Ashby model of geometric necessary dislocations. It is shown that the present model is capable of interpreting the abnormal Hall-Petch dependence for grain sizes in the submicron range. © 1998 American Institute of Physics.
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65.20.-w Thermal properties of liquids
65.40.gd Entropy
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
61.72.Bb Theories and models of crystal defects
61.72.Lk Linear defects: dislocations, disclinations

Thermal diffusivity measurements of sub-micron organic dye thin films using a high temperature superconductor bolometer

Steven M. Savoy, Cyndi A. Wells, John T. McDevitt, and Timothy A. Rhodes

Appl. Phys. Lett. 73, 3387 (1998); http://dx.doi.org/10.1063/1.122775 (3 pages)

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The thermal diffusivity of a thin organic dye layer deposited atop thin films of the high temperature superconductor YBa2Cu3O7−δ is measured using a pulsed laser flash method. Here, the underlying superconductor acts as a highly sensitive temperature transducer after appropriate conversion of the transient voltage response from 7 ns optical pulses. Film surface temperature decays for several thicknesses of the dye layers were evaluated; these decays exhibited a linear dependence of the time at half temperature maximum versus thickness squared. Three dimensional finite difference modeling was used to study and extract the thermal diffusivity values of the thin organic layers as well as to investigate the transient temperature distributions within the dye and superconductor areas. © 1998 American Institute of Physics.
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07.20.-n Thermal instruments and apparatus
68.60.Dv Thermal stability; thermal effects
85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
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Photoluminescence of localized excitons in pulsed-laser-deposited GaN

M. Cazzanelli, D. Cole, J. F. Donegan, J. G. Lunney, P. G. Middleton, K. P. O’Donnell, C. Vinegoni, and L. Pavesi

Appl. Phys. Lett. 73, 3390 (1998); http://dx.doi.org/10.1063/1.122776 (3 pages) | Cited 14 times

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Continuous-wave photoluminescence (PL) and time-resolved photoluminescence of gallium nitride layers grown by pulsed laser deposition are compared. The temperature dependence of the photoluminescence decay time and the PL-integrated intensity allows a determination of radiative and nonradiative time constants of GaN. We find that luminescence peaks centered at 3.360 and 3.305 eV at low temperature can be attributed to recombination of excitons localized at extended defects. The photoluminescence radiative lifetime at room temperature is on the order of tens of ns. © 1998 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Fg Pulsed laser ablation deposition

Silica capping for Al0.3Ga0.7As/GaAs and In0.2Ga0.8As/GaAs quantum well intermixing

G. Li, S. J. Chua, S. J. Xu, X. C. Wang, A. Saher Helmy, Mao-Long Ke, and J. H. Marsh

Appl. Phys. Lett. 73, 3393 (1998); http://dx.doi.org/10.1063/1.122777 (3 pages) | Cited 20 times

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Spin-on silica capping has been demonstrated to be an effective dielectric encapsulant layer for quantum well (QW) intermixing at temperatures significantly lower than for conventionally deposited silica. A blueshift of up to 125 meV was observed in the photoluminescence (PL) peak energy of both GaAs and InGaAs QWs after annealing for less than 60 s at 850 °C, without noticeable degradation in the PL emission intensity. A threshold temperature was identified below which no significant QW disordering took place. The activation energy for Al diffusion in Al0.3Ga0.7As/GaAs QWs was about 2.55 eV. Broadly similar effects were seen for In0.2Ga0.8As/GaAs QWs but, in addition, strain effects appear to enhance disordering during the early stages of the anneal. © 1998 American Institute of Physics.
Show PACS
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
81.05.Ea III-V semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
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