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Applied Physics Letters

Issue 23 • Date Jun 2001

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Displaying Results 1 - 25 of 65
  • Issue Cover

    Page(s): c1
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    Freely Available from IEEE
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Terahertz repetition frequencies from harmonic mode-locked monolithic compound-cavity laser diodes

    Page(s): 3571 - 3573
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    Compound-cavity laser diodes are mode locked at a harmonic of the fundamental round-trip frequency to achieve repetition rates of up to 2.1 THz. The devices are fabricated from GaAs/AlGaAs material at a wavelength of 860 nm and incorporate two gain sections with an etched slot reflector between them, and a saturable absorber section. Autocorrelation studies are used to investigate device behavior for different reflector types and reflectivity. These lasers may find applications in terahertz imaging, medicine, ultrafast optical links, and atmospheric sensing. © 2001 American Institute of Physics. View full abstract»

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  • Characteristics of polarization switching from the low to the high frequency mode in vertical-cavity surface-emitting lasers

    Page(s): 3574 - 3576
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    Polarization selection in small-area vertical-cavity surface-emitting lasers is studied experimentally in dependence of injection current and substrate temperature in the vicinity of the minimum threshold condition. Polarization switching from the low to the high frequency fundamental spatial mode is demonstrated. The effective birefringence displays a minimum in the transition region. The observation of dynamical transition states hints to the relevance of nonlinear effects. A comparison to the predictions of the San Miguel–Feng–Moloney model based on phase-amplitude coupling is given. © 2001 American Institute of Physics. View full abstract»

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  • Intensity noise in quantum-dot laser diodes

    Page(s): 3577 - 3579
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    We present intensity noise studies of a self-organized InAs/GaAs quantum-dot laser. The noise power measured for the full emission spectrum was found to be smaller than that for separate longitudinal mode groups. This noise cancellation indicates that the intensity fluctuations of the mode groups were anticorrelated, with typical values of the normalized correlation coefficient of around -0.50. This surprisingly high value is not consistent with the model of the quantum-dot laser as an inhomogeneous ensemble of independent microlasers. © 2001 American Institute of Physics. View full abstract»

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  • Intersubband Raman Laser

    Page(s): 3580 - 3582
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    An intersubband Raman laser has been realized in an artificial GaAs/AlGaAs three-level quantum-well structure. A CO2 laser in resonance with the one-to-three level transition is used as the pump, while the lasing emission occurs via the three-to-two level transition. The one-to-two level spacing is designed to be in resonance with the AlAs-like longitudinal optical phonon mode, favoring the Raman process. This work presents an alternative mechanism for realizing intersubband lasers and opens up new possibilities in reaching the far infrared region and achieving room-temperature operation. © 2001 American Institute of Physics. View full abstract»

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  • Tunable narrow-band terahertz generation from periodically poled lithium niobate

    Page(s): 3583 - 3585
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    We describe a technique for generating tunable narrow-band terahertz radiation via optical rectification in periodically-poled lithium niobate. Frequency tuning is accomplished by spatially chirping the domain width laterally to the beam propagation direction, and adjusting the temperature of the sample. We demonstrate tuning over a continuous range from 0.8 to 2.5 THz. The bandwidth of the terahertz waveforms is as narrow as 0.02 THz. © 2001 American Institute of Physics. View full abstract»

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  • 72 W Nd:Y3Al5O12 ceramic laser

    Page(s): 3586 - 3588
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    A high-power continuous-wave polycrystalline 1% Nd:Y3Al5O12 (Nd:YAG) ceramic rod laser was demonstrated. With 290 W/808 nm laser diode pumping, cw laser output of 72 W was obtained at 1064 nm. The optical-to-optical conversion efficiency is 24.8%. Thermally induced birefringence properties of Nd:YAG ceramic was also investigated. © 2001 American Institute of Physics. View full abstract»

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  • Refraction contrast imaging with a scanning microlens

    Page(s): 3589 - 3591
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    We demonstrate subwavelength spatial resolution with a scanning microlens operating in collection mode with a large-area detector. Optical contrast is created by refraction of off-axis light rays at angles larger than the maximum collection angle. With a microfabricated silicon microlens 10 μm in diameter, we measure spatial resolution due to refraction contrast of λ/4.3 at a wavelength of λ=10.7 μm. A model based on ray tracing is developed to explain our result, and we show that lens diameter and index of refraction limit resolution for large emission and collection angles. © 2001 American Institute of Physics. View full abstract»

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  • Monolithically integrated, flexible display of polymer-dispersed liquid crystal driven by rubber-stamped organic thin-film transistors

    Page(s): 3592 - 3594
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    This letter describes the monolithic integration of rubber-stamped thin-film organic transistors with polymer-dispersed liquid crystals (PDLCs) to create a multipixel, flexible display with plastic substrates. We report the electro-optic switching behavior of the PDLCs as driven by the organic transistors, and we show that our displays operate robustly under flexing and have a contrast comparable to that of newsprint. © 2001 American Institute of Physics. View full abstract»

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  • Hydrostatic pressure effect on photoluminescence from a GaN0.015As0.985/GaAs quantum well

    Page(s): 3595 - 3597
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    Photoluminescence from a GaN0.015As0.985/GaAs quantum well has been measured at 15 K under hydrostatic pressure up to 9 GPa. Both the emissions from the GaNAs well and GaAs barrier are observed. The GaNAs-related peak shows a much weaker pressure dependence compared to that of the GaAs band gap. A group of new peaks appear in the spectra when the pressure is beyond 2.5 GPa, which is attributed to the emissions from the N isoelectronic traps in GaAs. The pressure dependence of the GaNAs-related peaks was calculated using the two-level model with the measured pressure coefficients of the GaAs band gap and N level as fitting parameters. It is found that the calculated results deviate seriously from the experimental data. An increasing of the emission intensity and the linewidth of the GaNAs-related peaks was also observed and briefly discussed. © 2001 American Institute of Physics. View full abstract»

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  • Electromigration threshold in copper interconnects

    Page(s): 3598 - 3600
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    The electromigration threshold in copper interconnects is reported in this study. The length-dependent electromigration degradation rate is observed and quantified in the temperature range of 295–400 °C. Based on the Blech electromigration model [I. A. Blech, J. Appl. Phys. 47, 1203 (1976)], a simplified equation is proposed to analyze the experimental data from various combinations of current density and interconnect length, as well as to estimate the electromigration threshold product of current density and line length, (jL)th, at a certain temperature. The resulting (jL)th value appears to be temperature dependent, decreasing with increasing temperature in the tested range between 295 and 400 °C. © 2001 American Institute of Physics. View full abstract»

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  • Initial stages of SiC oxidation investigated by ion scattering and angle-resolved x-ray photoelectron spectroscopies

    Page(s): 3601 - 3603
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    Initial stages of oxidation of single-crystal, Si-faced silicon carbide were investigated using ion scattering and angle-resolved x-ray photoelectron spectroscopies. The very first oxidation products are shown to be silicon oxycarbides (SiCxOy), while, for longer oxidation times, a mixture of SiCxOy and SiO2 is formed in the near-surface region of the growing oxide film. The composition of the near-surface region of such thin films is very similar to that reported in previous investigations for the near-interface region when thicker oxides films are grown on SiC. © 2001 American Institute of Physics. View full abstract»

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  • Structure, interface roughness, and growth mechanism of reactive deposition epitaxy of CoSi2 on Si(100) substrates

    Page(s): 3604 - 3606
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    Thin CoSi2 films have been grown on Si(100) substrates using the relative deposition epitaxy method. The structure of the silicide films have been analyzed using x-ray diffraction, transmission electron microscopy (TEM), and Rutherford backscattering spectrometry and channeling, and the interface roughness of the CoSi2/Si(100) is analyzed using specular x-ray reflectivity and cross-sectional TEM. The structure and interface roughness of CoSi2/Si(100) is found to be dependent on the substrate temperature. Highly epitaxial CoSi2 with minimum interface roughness is obtained when the film is grown at substrate temperatures around 900 K. The observed interface roughness is a parabolic function of temperature. The achievement of the best silicide at a substrate temperature around 900 K is explained on the basis of the instantaneous diffusion of Co through growing CoSi2. © 2001 American Institute of Physics. View full abstract»

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  • Simple chemical routes to diamond-cubic germanium–tin alloys

    Page(s): 3607 - 3609
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    We report the development of a simple chemical route to growing Ge1-xSnx semiconductors using ultrahigh-vacuum chemical vapor deposition and the molecular precursor (Ph)SnD3 as the source of Sn atoms. Thin films were deposited on oxidized and oxide-free Si by reactions of (Ph)SnD3 with Ge2H6 at 350 °C. The composition, microstructure, and bonding properties of the films were characterized by Rutherford backscattering, high-resolution analytical electron microscopy, and Raman spectroscopy. As-deposited Ge1-xSnx on oxidized Si displayed good crystallinity which improved significantly by annealing at 400 °C. High-resolution electron microscopy and diffraction indicated a diamond-cubic structure with lattice constants intermediate to those of Ge and α-Sn. As-deposited Ge1-xSnx on pure Si was monocrystalline and epitaxial. Nanoprobe analysis in plan view and cross section revealed that the as-deposited and annealed materials were homogeneous with good chemical purity. The Raman spectra showed bands corresponding to Ge–Ge and Sn–Ge vibrations with frequencies consistent with a random tetrahedral alloy. © 2001 American Institute of Physics. View full abstract»

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  • Influence of temperature on luminescence of terbium ions in LiNbO3

    Page(s): 3610 - 3611
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    Single crystals of LiNbO3 doped with terbium were grown by the Czochralski method and their optical properties were examined. It has been found that, in contrast to isostructural LiTaO3:Tb, the terbium ions in LiNbO3 exhibit intense luminescence at low temperatures only, up to about 150 K. At this temperature, a luminescence quenching mechanism with activation energy of 0.22 eV is switched on. As a consequence, the luminescence of LiNbO3:Tb is reduced to a negligible level at room temperature. © 2001 American Institute of Physics. View full abstract»

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  • Nucleation and growth kinetics of AlN films on atomically smooth 6H–SiC (0001) surfaces

    Page(s): 3612 - 3614
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    Nucleation and growth kinetics of AlN films on atomically smooth 6H–SiC (0001) surfaces, which were obtained by HCl etching at elevated temperatures prior to growth, were investigated. The surface morphology and the defect density of AlN films on such surfaces were significantly improved compared to those on as-received SiC surfaces. This is due to enhanced diffusion length and reduced incoherent boundaries at the coalescence regions of the AlN islands. AlN nuclei on the as-received SiC surface were crystallographically misaligned and thus induced incoherent boundaries at the coalescence stage, resulting in the delay of the two-dimensional growth mode transition and defect formation in AlN films. © 2001 American Institute of Physics. View full abstract»

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  • In situ observation of stress relaxation in CdTe/ZnTe heterostructures by reflectance-difference spectroscopy

    Page(s): 3615 - 3617
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    The first stages of epitaxial growth of CdTe on ZnTe and ZnTe on CdTe are monitored with reflectance difference spectroscopy. Spectroscopic reflectance difference data show strong optical anisotropy responses at the critical points of the bulk dielectric function at the E0, E1, and E11 interband transitions of ZnTe, respectively, CdTe, which indicate that anisotropic in-plane strain occurs during epitaxial growth. Applying a model it is possible to determine the in-plane strain due to the disbalance of 60° dislocations along [11¯0] and [110]. Kinetic reflectance difference data taken at the E1 transition of the respective material exhibit with an accuracy of one monolayer the onset of the formation of misfit dislocations for these material systems. © 2001 American Institute of Physics. View full abstract»

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  • Nanocrystallization of amorphous-Ta40Si14N46 diffusion barrier thin films

    Page(s): 3618 - 3620
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    The nanocrystallization process in thin amorphous-Ta40Si14N46 films, annealed in the range between 800 and 1000 °C for 1 h, is investigated by high-resolution transmission electron microscopy and high-angle annular dark-field and energy-dispersive x-ray analyses. At 800 °C clusters of about 2 nm in size indicate that compositional inhomogeneities have developed while the film has still remained structurally amorphous. The sample annealed at 900 °C contains a high density of nanograins of TaN measuring about 2 nm as well as amorphous structures measuring 75–100 nm having a high tantalum content. After annealing at 1000 °C, an almost entirely crystalline structure is observed with 4-nm-sized particles of cubic TaN and 15-nm-sized grains of Ta5Si3. Possible mechanisms driving these structural changes are discussed. © 2001 American Institute of Physics. View full abstract»

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  • Investigation on morphological stability of ultrathin Pb films

    Page(s): 3621 - 3623
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    Ultrathin Pb films supported by Al film were made by using cold-rolling and ion-beam thinning techniques. The morphological instability of the Pb film under electron-beam irradiation was investigated by means of in situ transmission electron microscopy observations. It has been found that under electron-beam irradiation, Pb films with an incoherent Pb/Al interface spheroidized into Pb particles, but those with a semicoherent Pb/Al interface were stable in morphology. The morphological stability of thin films depends on the microstructure and the thermodynamic property of the interphase boundary. A critical interfacial energy for the spheroidization of thin films was determined based on a thermodynamics analysis. © 2001 American Institute of Physics. View full abstract»

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  • Conductance peak splitting in hole transport through a SiGe double quantum dot

    Page(s): 3624 - 3626
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    We have observed the splitting of Coulomb oscillation peaks in coupled Si0.9Ge0.1 double quantum dots at 4.2 K. The quantum dots are formed by trench isolation, which means that the dots can be made much smaller than possible with the surface-gated approach. A dot diameter of 50 nm or less increases the charging energy and, therefore, the operating temperature of the device compared to previous approaches. A simulation of the results using parameters calculated from the lithographic dimensions of the device shows that a good fit to the experimental data can be achieved with a realistic interdot capacitance value. © 2001 American Institute of Physics. View full abstract»

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  • Fabrication of an all-oxide thermoelectric power generator

    Page(s): 3627 - 3629
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    An oxide thermoelectric device was fabricated using Gd-doped Ca3Co4O9 p-type legs and La-doped CaMnO3 n-type legs on a fin. The power factors of p legs and n legs were 4.8×10-4Wm-1 K-2 and 2.2×10-4Wm-1 K-2 at 700 °C in air, respectively. With eight p–n couples the device generated an output power of 63.5 mW under the thermal condition of hot side temperature Th=773 °C and a temperature difference ΔT=390 °C. This device proved to be operable for more than two weeks in air showing high durability. © 2001 American Institute of Physics. View full abstract»

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  • Microcathodoluminescence of impurity doping at gallium nitride/sapphire interfaces

    Page(s): 3630 - 3632
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    We have used low-temperature cathodoluminescence spectroscopy (CLS) to probe the spatial distribution and energies of electronic defects near GaN/Al2O3 interfaces grown by hydride vapor phase epitaxy (HVPE). Cross sectional secondary electron microscopy CLS shows systematic variations in impurity/defect emissions over a wide range of HVPE GaN/Sapphire electronic properties. These data, along with electrochemical capacitance–voltage profiling and secondary ion mass spectrometry, provide a consistent picture of near-interface doping by O diffusion from Al2O3 into GaN, over a range 100–1000 nm. © 2001 American Institute of Physics. View full abstract»

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  • Detection of two dangling bond centers with trigonal symmetry at and below a (100) Si/SiO2 interface

    Page(s): 3633 - 3635
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    Using electrical detection of electron paramagnetic resonance (EDEPR), two defect centers located at the Si (100)/SiO2 interface and in regions several μm below the silicon surface have been observed at a low temperature. Improvements in the EDEPR measurement technique enabled the experimental detection of the g-factor anisotropy of two centers, labeled Pba and Pbb. Both appear with a [111]-oriented, trigonally symmetric g-tensor with g||=2.0008/g=2.0098 and g||=1.9974/g=2.0160, respectively (Δg=±0.0004). The data of the Pba center are very similar to those of the well known Pb0 center occurring on (100) oriented silicon. The location of the center which is significantly below the (100)Si/SiO2 interface is discussed. © 2001 American Institute of Physics. View full abstract»

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  • Correlation between current–voltage characteristics and dislocations for n-GaN Schottky contacts

    Page(s): 3636 - 3638
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    We directly evaluated the effect of dislocations on current–voltage (I–V) characteristics of Au/Ni/n-GaN Schottky contacts. A submicrometer Schottky dot array was formed by electron beam lithography, and I–V measurements were conducted using atomic force microscopy with a conductive probe. The sample, which has a free electron concentration of 5.8×1017cm-3, showed that neither dislocations nor steps affect the I–V characteristics. These results indicate that, in fabricating short-gate FETs, gate Schottky contacts containing dislocations should not be considered a problem with respect to uniformity and reproducibility. © 2001 American Institute of Physics. View full abstract»

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Applied Physics Letters, published by the American Institute of Physics, features concise, up-to-date reports on significant new findings in applied physics.

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Nghi Q. Lam
Argonne National Laboratory