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Applied Physics Letters

Issue 13 • Date Mar 2004

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Displaying Results 1 - 25 of 82
  • Issue Cover

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

    Page(s): toc1
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  • Highly directional emission from colloidally synthesized nanocrystals in vertical cavities with small mode spacing

    Page(s): 2223 - 2225
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    The optical properties of light emitting devices based on colloidally synthesized CdSe/CdS core/shell semiconductor nanocrystals embedded in vertical cavities are investigated. The cavities are several micrometers, thick and formed by a metallic mirror and a dielectric Bragg interference mirror deposited on the opposite surfaces of cleaved pristine mica sheets. Due to the large cavity length, up to 30 resonances are found within the Bragg mirror stop band. The corresponding small mode spacing allows one to extract a large portion of the broad nanocrystal luminescence band from the cavity upon optical excitation. The spontaneous emission of these cavities is highly forward directed with a beam divergence smaller than 1.3°. Furthermore, the emission is linearly polarized which is a result of the birefringent properties of the mica sheets. © 2004 American Institute of Physics. View full abstract»

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  • In-plane-type channel drop filter in a two-dimensional photonic crystal slab

    Page(s): 2226 - 2228
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    An in-plane-type channel-drop filtering device with input/output waveguides and a point defect cavity in a two-dimensional photonic crystal slab is investigated. The in-plane operation becomes possible by employing a point defect cavity with an extremely high Q factor to suppress the radiation loss for the out-of-plane direction. 60° bends are also introduced in the output waveguide to avoid interference between the input/output waveguides. The transmission frequency range of the output waveguide with bends is tuned by changing the size of the air holes at the apex of the corner so that the resonant frequency of the point defect cavity is within the transmission band. A channel drop operation with a very high resolution of 0.12 nm is successfully observed at 1.55 μm wavelengths. © 2004 American Institute of Physics. View full abstract»

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  • Terahertz-induced lensing and its use for the detection of terahertz pulses in a birefringent crystal

    Page(s): 2229 - 2231
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    We demonstrate terahertz-induced lensing (TIL), the focusing and defocusing of an ultrashort “probe” laser pulse induced by a collinearly traveling terahertz pulse in an electro-optic crystal. The intensity change on the axis of the probe beam after the crystal is shown to be linear with the terahertz (THz) electric field and can thus be used to measure the THz wave form. We show that the sensitivity of TIL is comparable to conventional electro-optic sampling, with the advantage of being applicable to all classes of electro-optic crystals, including strongly birefringent ones. The better sensitivity of TIL is demonstrated using the highly birefringent organic salt DAST (4-N,N-dimethylamino-4-N-methyl stilbazolium tosylate). © 2004 American Institute of Physics. View full abstract»

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  • Demonstration of a 256×256 middle-wavelength infrared focal plane array based on InGaAs/InGaP quantum dot infrared photodetectors

    Page(s): 2232 - 2234
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    We report a demonstration of an infrared focal plane array based on InGaAs/InGaP quantum dot infrared photodetectors. The middle-wavelength infrared quantum-dot infrared photodetector (QDIP) structure was grown via low-pressure metal organic chemical vapor deposition. A detectivity of 3.6×1010 cm Hz1/2/W was achieved at T=95 K and a bias of -1.4 V. The background limited temperature of our QDIP was 140 K with a 45° field of view. A 256×256 detector array was fabricated with dry etching, and hybridized to a Litton readout chip by indium bumps. Thermal imaging was achieved at temperatures up to 120 K. At T=77 K, the noise equivalent temperature difference was measured as 0.509 K with a 300 K background and f/2.3 optics. © 2004 American Institute of Physics. View full abstract»

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  • Coherent control of inhomogeneously broadened system by area-regulated pulse sequence

    Page(s): 2235 - 2237
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    We have proposed a coherent control method that is available even for inhomogeneously broadened systems, which uses an area-regulated laser pulse sequence. It is expected to be applied to ultrafast optical devices without restriction of energy relaxation time. © 2004 American Institute of Physics. View full abstract»

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  • High brightness GaInAs/(Al)GaAs quantum-dot tapered lasers at 980 nm with high wavelength stability

    Page(s): 2238 - 2240
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    High brightness (2 W with M2=3.4) is demonstrated at 980 nm using a gain-guided tapered GaInAs/(Al)GaAs quantum-dot laser. A remarkable low temperature shift (0.09 nm/K) of the emission wavelength is observed. Moreover, at 20 °C, the emission wavelength is quasiconstant as a function of the injected current. © 2004 American Institute of Physics. View full abstract»

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  • Ultracompact, multifunctional, and highly integrated 3×2 photonic switches

    Page(s): 2241 - 2243
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    An ultracompact, multifunctional, and highly integrated photonic switch with a 3×2 configuration has been designed and fabricated with SiGe/Si material by using silicon-optical bench technology. This kind of switch can be used in fiber optic communications systems, photonic integrated circuits and wavelength division multiplexed networks as an optical power splitter, optical crossconnect, optical add-drop multiplexer, and wavelength division multiplexer simultaneously or individually. The function of the device is to combine multiwavelengths from different input channels and to switch them to different output channels. The operating wavelength range of the device is designed in C band, i.e., 1530–1570 nm. The device was characterized at 1540, 1550, and 1560 nm wavelengths. The performance at these wavelengths is found satisfactory. The measured insertion loss is less than 2 dB, ON/OFF ratio is greater than 30 dB, crosstalk is between -20 and -25 dB, and switching speed is 100–200 ns. © 2004 American Institute of Physics. View full abstract»

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  • Partial focusing of radiation by a slab of indefinite media

    Page(s): 2244 - 2246
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    Negative refraction can occur at the interface between vacuum and an indefinite medium—an anisotropic medium for which not all elements of the permittivity and permeability tensors have the same sign. We show experimentally and via simulations that a metamaterial composed of split ring resonators, designed to provide a permeability equal to -1 along the longitudinal axis, will redirect s-polarized electromagnetic waves from a nearby source to a partial focus. The dispersion characteristics of indefinite media prohibit the possibility of true aplanatic points for a planar slab; however, by contouring the surfaces aplanatic points may be realized, as well as other geometrical optical behavior. © 2004 American Institute of Physics. View full abstract»

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  • Morphological properties of GaN quantum dots doped with Eu

    Page(s): 2247 - 2249
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    Morphological properties of Eu-doped GaN quantum dots grown by molecular beam epitaxy have been studied. Eu tends to segregate on the surface of AlN and GaN, leading to drastic changes in adatom kinetics. As a consequence, both size and density of Eu-doped GaN quantum dots strongly depend on the Eu flux used during the growth. © 2004 American Institute of Physics. View full abstract»

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  • Rewritable phase-change optical recording in Ge2Sb2Te5 films induced by picosecond laser pulses

    Page(s): 2250 - 2252
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    The phase transformation dynamics induced in Ge2Sb2Te5 films by picosecond laser pulses were studied using real-time reflectivity measurements with subnanosecond resolution. Evidence was found that the thermal diffusivity of the substrate plays a crucial role in determining the ability of the films to crystallize and amorphize. A film/substrate configuration with optimized heat flow conditions for ultrafast phase cycling with picosecond laser pulses was designed and produced. In this system, we achieved reversible phase transformations with large optical contrast (≫20%) using single laser pulses with a duration of 30 ps within well-defined fluence windows. The amorphization (writing) process is completed within less than 1 ns, whereas crystallization (erasing) needs approximately 13 ns to be completed. © 2004 American Institute of Physics. View full abstract»

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  • GaN micro-light-emitting diode arrays with monolithically integrated sapphire microlenses

    Page(s): 2253 - 2255
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    GaN micro-light-emitting diodes (micro-LEDs) with monolithically integrated microlenses have been demonstrated. Microlenses, with a focal length of 44 μm and a root mean square roughness of ∼1 nm, have been fabricated on the polished back surface of a sapphire substrate of an array of micro-LEDs by resist thermal reflow and plasma etching. The optical properties of the microlenses have been demonstrated to alter the emission pattern of the LED emitters. The cone of light emitted from this hybrid device is significantly less divergent than a conventional broad-area device. This combination of micro-LED and microlens technologies offers the potential for further improvement in the overall efficiency of GaN-based light emitters. © 2004 American Institute of Physics. View full abstract»

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  • Liquid-tin-jet laser-plasma extreme ultraviolet generation

    Page(s): 2256 - 2258
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    We demonstrate the applicability of liquid-metal jets in vacuum as regenerative targets for laser-plasma generation of extreme ultraviolet (EUV) and soft x-ray radiation. This extends the operation of liquid-jet laser-plasma sources to high-temperature, high-Z, high-density, low-vapor-pressure materials with new spectral signatures. The system is demonstrated using tin (Sn) as the target due to its strong emission around λ≈13 nm, which makes the material suitable for EUV lithography. We show a conversion efficiency of 2.5% into (2%BW×2π×sr) and report quantitative measurements of the ionic/atomic as well as particulate debris emission. © 2004 American Institute of Physics. View full abstract»

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  • Dependence of hard x-ray yield on laser pulse parameters in the wavelength-cubed regime

    Page(s): 2259 - 2261
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    Conversion efficiency and electron temperature scaling laws are experimentally studied in the wavelength-cubed 3) regime, where a single-wavelength focus allows low energy pulses incident on a Mo target to produce x rays with excellent efficiency and improved spatial coherence. Focused intensity is varied from 2×1016 to 2×1018 W/cm2. Conversion efficiency and electron temperature are best described by a power law for energy scaling while an exponential law best describes the scaling of these parameters with pulse duration. © 2004 American Institute of Physics. View full abstract»

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  • Extended shape evolution of low mismatch Si1-xGex alloy islands on Si(100)

    Page(s): 2262 - 2264
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    The sequence of shape transitions in low mismatch, dilute coherent Si1-xGex (x≪0.2) alloy islands was documented by scanning tunneling microscopy and cross-sectional transmission electron microscopy. In dilute Si1-xGex islands we observe an extended shape evolution involving a new “barn” shape formed by introduction of steep {111} facets not observed at higher mismatch strain. This extended shape evolution implies a delayed onset of plastic deformation as a result of an altered competition between strain relaxation via coherent islands and the introduction of dislocations in this regime. © 2004 American Institute of Physics. View full abstract»

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  • Free carrier absorption in heavily doped silicon layers

    Page(s): 2265 - 2267
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    The standard parametrization of free carrier absorption in silicon predicting a linear dependence of the absorption on carrier concentration is revised, finding that due to several simplifications, it is only applicable up to carrier densities of about 3×1016 cm-3. A parametrization applicable for both p- and n-type silicon and for doping densities as high as 1021 cm-3 is introduced. Using this parametrization, considerably better agreement between the emitter sheet resistance of diffused layers measured by IR transmission and electrical measurements is found, proving the applicability of the enhanced model even for heavily doped layers. Additionally, parameters for the dependence of the refractive index of silicon on doping concentration are given. © 2004 American Institute of Physics. View full abstract»

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  • GaN epitaxy on thermally treated c-plane bulk ZnO substrates with O and Zn faces

    Page(s): 2268 - 2270
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    ZnO is considered as a promising substrate for GaN epitaxy because of stacking match and close lattice match to GaN. Traditionally, however, it suffered from poor surface preparation which hampered epitaxial growth in general and GaN in particular. In this work, ZnO substrates with atomically flat and terrace-like features were attained by annealing at high temperature in air. GaN epitaxial layers on such thermally treated basal plane ZnO with Zn and O polarity have been grown by molecular beam epitaxy, and two-dimensional growth mode was achieved as indicated by reflection high-energy electron diffraction. We observed well-resolved ZnO and GaN peaks in the high-resolution x-ray diffraction scans, with no Ga2ZnO4 phase detectable. Low-temperature photoluminescence results indicate that high-quality GaN can be achieved on both O- and Zn-face ZnO. © 2004 American Institute of Physics. View full abstract»

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  • Mapping of multiple-quantum-well layers and structure of V defects in InGaN/GaN diodes

    Page(s): 2271 - 2273
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    Cathodoluminescence mapping reveals threading defects, frequently formed by the lattice misfit between GaN and sapphire substrate, as a dark contrast connected with changes in the energy state. Multiple quantum wells, 2.5 nm In0.25Ga0.75N and 13.9 nm GaN layers, are resolved in the secondary electron image as well as in the backscattered electron image. The backscattered electron image, providing compositional mapping without surface effects such as cleaved steps, reveals the presence of V defects and confirms the thin six-walled structure of the V defect with InGaN/GaN {1011¯} layers. These scanning electron microscopy observations can be performed after very simple specimen preparation, namely just cleaving the sapphire substrate with the epilayers. © 2004 American Institute of Physics. View full abstract»

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  • Mechanical response of KD2xH2(1-x)PO4 crystals during nanoindentation

    Page(s): 2274 - 2276
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    The deformation behavior of rapidly grown tetragonal KD2xH2(1-x)PO4 (KDP and DKDP) single crystals, with a deuteration degree x of 0.0, 0.3, and 0.6, is studied by nanoindentation with a 1 μm radius spherical indenter. Within experimental error, the deformation behavior is found to be independent of the deuterium content and different for (001) and (100) surfaces. Multiple discontinuities (so-called “pop-in” events) in force-displacement curves are observed during indentation loading, but not during unloading. Slip is identified as the major mode of plastic deformation in DKDP, and pop-in events are attributed to the initiation of slip. © 2004 American Institute of Physics. View full abstract»

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  • Passivation of Mn acceptors in GaMnAs

    Page(s): 2277 - 2279
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    The effects of hydrogen and deuterium on ferromagnetic GaAs doped with high concentrations of Mn (≈1021cm-3) are studied. Secondary ion mass spectroscopy depth profiles show that D is incorporated in the same concentration as Mn. The epilayers change from metallic to semiconducting behavior upon hydrogenation. Fourier transform infrared absorption measurements show the As–H and As–D local vibrational modes characteristic for the complexes of hydrogen with group-II acceptors in GaAs. © 2004 American Institute of Physics. View full abstract»

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  • Interpretation of anomalous temperature dependence of anti-Stokes photoluminescence at GaInP2/GaAs interface

    Page(s): 2280 - 2282
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    In this letter, we report on temperature-dependent anti-Stokes photoluminescence (ASPL) at an interface between partially ordered GaInP2 epilayer and GaAs substrate. It is found that the intensity of the ASPL depends strongly on temperature accompanying with a clear blueshift in energy. A localized-state luminescence model was employed to quantitatively interpret temperature dependence of the ASPL. Excellent agreement between the theory and experiment was obtained. Radiative recombination mechanism of the up-converted carriers was discussed. © 2004 American Institute of Physics. View full abstract»

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  • Mature InAs quantum dots on the GaAs(114)A surface

    Page(s): 2283 - 2285
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    InAs quantum dots (QDs), grown by molecular-beam epitaxy on GaAs(114)A surfaces, were studied in situ by atomically resolved scanning tunneling microscopy. At their mature stage, the QDs present a complicated but regular shape being bound by flat {110}, (111)A, and {2 5 11}A facets, and a steep part composed of rather variable combinations of {110}, (111)A, {1¯1¯1¯}B, and {2 5 11} surfaces. The QD shape can be derived from mature InAs QDs on GaAs(001). © 2004 American Institute of Physics. View full abstract»

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  • Clear quantum-confined luminescence from crystalline silicon/SiO2 single quantum wells

    Page(s): 2286 - 2288
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    Crystalline silicon single quantum wells (QWs) were fabricated by high-temperature thermal oxidation of ELTRAN® (Epitaxial Layer TRANsfer) silicon-on-insulator (SOI) wafers. The Si layer thicknesses enclosed by thermal SiO2 range from 0.8 to 5 nm. Luminescence energies from such QWs vary from 1.77 to 1.35 eV depending on the Si layer thickness, without evidence for interface-mediated transition seen in earlier work. The ability to detect quantum-confined luminescence seems to arise from the use of ELTRAN SOI wafers, from suppressed interface state luminescence by high-temperature oxidation and, possibly, from interface matching by crystalline silicon oxide. © 2004 American Institute of Physics. View full abstract»

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  • Energetic stability and magnetic properties of Mn dimers in silicon

    Page(s): 2289 - 2291
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    We present an accurate first-principles study of magnetism and energetics of single Mn impurities and Mn dimers in Si. Our results, in general agreement with available experiments, show that (i) Mn atoms tend to aggregate, the formation energy of dimers being lower than the sum of the separate constituents, (ii) ferromagnetic coupling is favored between the Mn atoms constituting the dimers in p-type Si, switching to an antiferromagnetic coupling in n-type Si, (iii) Mn atoms show donors (acceptor) properties in p-type (n-type) Si, therefore they tend to compensate doping, while dimers being neutral or acceptors allow for Si to be doped p-type. © 2004 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