Volume 84, Issue 12, 22 March 2004
- lasers, optics, and optoelectronics
- structural, mechanical, thermodynamic, and optical properties of condensed matter
- electronic transport and semiconductors
- magnetism and superconductivity
- dielectrics and ferroelectricity
- nanoscale science and design
- device physics
- applied biophysics
- interdisciplinary and general physics
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS
84(2004); http://dx.doi.org/10.1063/1.1682678View Description Hide Description
We report theoretical investigations of a superlatticephotonic crystal(PC)waveguide in which the holes in the PC are infiltrated with an electro-optic medium and alternate rows biased so as to produce a superlatticestructure. The three-dimensional simulations fully incorporate the finite thickness of the PCstructure and show that the optical properties become strongly dependent on the direction of light propagation. Depending on the degree of index modulation the light experiences switching, out-coupling, or giant refraction and dispersion.
84(2004); http://dx.doi.org/10.1063/1.1687981View Description Hide Description
The use of strain-compensated InGaAsSb/AlGaAsSb quantum wells for the fabrication of type I mid-infrared laser devices grown on GaSb substrates by molecular-beam epitaxy is reported. The creation of a tensile strain in the barriers by the incorporation of an arsenic fraction greater than 2% allows to reduce the average strain in the active region and increase the valence band offset to improve hole confinement in the wells. A 2.82 μm emission wavelength in pulsed mode along with a threshold current density are obtained at room temperature for a type I InGaAsSb/AlGaAsSb double-quantum-well laser diode. By further increasing the indium and arsenic compositions into the wells and barriers, respectively, pulsed lasing at a wavelength of 2.89 μm at room temperature has also been achieved.
84(2004); http://dx.doi.org/10.1063/1.1669062View Description Hide Description
Emission of coherent light at 5.75 μm wavelength has been obtained by intracavity frequency doubling of a GaAs-based quantum cascade laser. This nonlinearity originates from the second-order susceptibility of the bulk material hosting the heterostructure and can be exploited by growing the quantum cascade laser on a 〈111〉 substrate.
Systematic design of photonic crystal structures using topology optimization: Low-loss waveguide bends84(2004); http://dx.doi.org/10.1063/1.1688450View Description Hide Description
Topologyoptimization is a promising method for systematic design of optical devices. As an example, we demonstrate how the method can be used to design a bend in a two-dimensional photonic crystal waveguide with a transmission loss of less than 0.3% in almost the entire frequency range of the guided mode. The method can directly be applied to the design of other optical devices, e.g., multiplexers and wave splitters, with optimized performance.
84(2004); http://dx.doi.org/10.1063/1.1689395View Description Hide Description
Nanoscale photochemical and photophysical etching of Si in atmosphere is demonstrated by means of an optical near-field setup. With 351 nm -laser radiation and low intensities, the etching mechanism is purely photochemical. In this regime, the width of patterns—which is about 115 nm at full width at half maximum (FWHM)—corresponds, approximately, to the diameter of the fiber tip. The vertical etch rate is of the order of 1 nm/s. With 514.5 nm -laser light etching is observed only at significantly higher laser-light intensities. Patterns with width down to about 30 nm at FWHM have been achieved. Here, the lateral resolution corresponds to about 1/18 of the laser wavelength employed.
84(2004); http://dx.doi.org/10.1063/1.1688456View Description Hide Description
Photoinduced birefringence in bacteriorhodopsin films was investigated using pump–probe method and its application for photonic switching explored. A diode-pumped second-harmonic YAG laser was used as a pumping beam and a diode laser at was used as a probing beam. The pump and probe beams overlap at the sample. Without the pumping beam, the probing light cannot transmit the analyzer to the detector. However, due to the photoinduced anisotropy, a portion of the probing light is detected when the pumping beam is present. Since is far from the absorption peak of the ground state, the photoinduced birefringence predominates. Using the intensity-dependent photoinduced birefringence in a bacteriorhodopsin film, we have demonstrated a photonic switch with contrast ratio, rise time and decay time.
84(2004); http://dx.doi.org/10.1063/1.1688981View Description Hide Description
In this letter, we show that photonic crystals with geometries of lower symmetry, such as the rectangular geometry, are uniquely suited for applications involving the superprism effect. The extra degree of freedom provided by the anisotropy of the unit cell allows more freedom in searching for suitable iso-frequency curves. Also, the appearance of multiple orders of diffraction allows more than one incident plane wave to couple to the same Bloch mode. This extra degree of freedom is decisive when trying to optimize the transmission. We illustrate these ideas on a particular rectangular configuration which ensures a strong angular superprism effect, a well collimated transmitted beam, and power transmissions of up to 80%.
84(2004); http://dx.doi.org/10.1063/1.1688983View Description Hide Description
We demonstrate the simultaneous generation of the three basal red–green–blue colors from a lone bi-functional laser and optical nonlinear crystal. The laser works in a dual-wavelength operation in the two (near 1062 nm) and (near 1338 nm) channels, under a fixed wavelength pumping (at 744.7 nm) and with a fixed crystal orientation. Red and green results from self-frequency doubling of the two laser channels, blue results of self-sum frequency mixing of the pump and the 1338 nm laser.
84(2004); http://dx.doi.org/10.1063/1.1686894View Description Hide Description
We report on the surface passivation of Type-II InAs/GaSb superlatticephotodetectors using various ammonium sulfide solutions. Compared to unpassivated detectors, zero-bias resistance of treated 400 μm×400 μm devices with 8 μm cutoff wavelength was improved by over an order of magnitude to at 80 K. Reverse-bias dark current density was reduced by approximately two orders of magnitude to less than at −2 V. Dark current modeling, which takes into account trap-assisted tunneling, indicates greater than 70 times reduction in bulk trap density for passivated detectors.
Surface-topography-induced enhanced transmission and directivity of microwave radiation through a subwavelength circular metal aperture84(2004); http://dx.doi.org/10.1063/1.1688001View Description Hide Description
Strongly enhanced transmission of microwave radiation is observed through a single subwavelength circular aperture of diameter in a metallic plate. The phenomenon is caused by resonant excitation of electromagneticsurface waves supported by four concentric grooves surrounding the aperture on the illuminated side of the sample. It is also shown that similar surface patterning on the output face of the sample results in very strong angular confinement (directivity) of the transmitted beam. A finite element code is used to investigate the electromagnetic fields on both the illuminated and the exit side of the structure, the predictions from which show excellent agreement with the experimental results.
Excitation and recording of morphology-dependent resonances in spherical microresonators by hollow light guiding fibers84(2004); http://dx.doi.org/10.1063/1.1688976View Description Hide Description
We report the excitation and simultaneous recording of morphology-dependent resonances in dye-doped microresonators by a single hollow fiber. The spherical microresonator was plugged in the tapered end of a light guiding flexible hollow fiber. Light from a frequency-doubled laser was coupled via a beam splitter into one end of the hollow fiber and transported to the resonator mounted on the tapered end of the fiber. Fluorescence was excited in the resonator. This fluorescence was partly coupled in the hollow fiber and guided back to the untapered end. Here, the fluorescence was separated from the laser light by a beam splitter and analyzed spectroscopically. The tapered fiber was prepared by heating with a laser.
Metal nanoparticle precipitation in periodic arrays in -doped glass by two interfered femtosecond laser pulses84(2004); http://dx.doi.org/10.1063/1.1688004View Description Hide Description
We report on the precipitation control of Aunanoparticles in periodic arrays in silicate glass.-doped glass samples were first irradiated by two 800 nm interfered femtosecond laser pulses at room temperature and then heat treated at for the Aunanoparticleprecipitation in the laser irradiation areas. One-dimensional periodic arrays of the Aunanoparticles were controlled by changing the pulse energy and the incident angle between the interfered laser pulses. The smallest dimension in the obtained arrays was a width of 300 nm. The mechanism of the metal nanoparticleprecipitation by this technique was discussed. Only two pulses are required to encode these periodic microstructures, which are applicable to emerging nanostructure devices such as optical memory with ultrahigh storage density, micrograting with high diffractive efficiency and integrative micro-optical switches.
Generation and detection of terahertz pulses using post-process bonding of low-temperature-grown GaAs and AlGaAs84(2004); http://dx.doi.org/10.1063/1.1688977View Description Hide Description
We present an electro-optical method to measure very high frequency characteristics of planar electronic devices. This method allows one to generate and detect subpicosecond electrical pulses on a coplanar stripline using photoconduction and electroabsorption sampling in transferred low-temperature-grown epitaxial layers. The epitaxial lifted-off films are directly van der Waals bonded on the transmission line under test. Good switching efficiency and short electrical rise time are measured. A bandwidth of 2.5 THz with 60 dB of dynamic range is obtained. This confers to the technique a large field of applications in ultrahigh-speed electronic measurements.
- STRUCTURAL, MECHANICAL, THERMODYNAMIC, AND OPTICAL PROPERTIES OF CONDENSED MATTER
Electrochemical gating of individual single-wall carbon nanotubes observed by electron transport measurements and resonant Raman spectroscopy84(2004); http://dx.doi.org/10.1063/1.1666997View Description Hide Description
Metal electrodespatterned lithographically on top of individual single-wall carbon nanotubes are used to gate the nanotubes with respect to a reference electrode in an electrolyte drop. The gating is found to have a dramatic effect on both the Raman spectra and electron transport of the nanotubes. Current through metallic nanotubes is found to increase sharply with electrochemical gate voltage, indicating that the Fermi energy reaches valence and conduction band van Hove singularities. Using resonant confocal micro-Raman spectroscopy, we observe a upshift of the tangential mode vibrational frequency, as well as a 90% decrease in intensity, by applying 1 V between an individual nanotube and a silver reference electrode in a dilute solution. The mechanisms for the shifts of the Raman mode frequencies are discussed on the basis of changes in the lattice constant of heavily charged nanotubes.
84(2004); http://dx.doi.org/10.1063/1.1682697View Description Hide Description
We investigate the thermal stability of boron-doped junctions formed by Ge preamorphization and solid phase epitaxial regrowth. Isochronal annealing and characterization by sheet resistance, secondary-ion mass spectrometry, and spreading-resistance measurement are used to extract detailed information on the thermal stability of the boron activation. Using a previously established model of self-interstitial defect evolution from clusters to dislocation loops, we perform simulations of the release of interstitials from the end-of-range region. The simulations indicate that the measured deactivation is driven by interstitials emerging from the end-of-range defect region.
84(2004); http://dx.doi.org/10.1063/1.1669067View Description Hide Description
We describe optical and structurecharacteristics of InAs quantum dashes grown on a GaAs substrate using an AlGaAsSb metamorphic buffer. The metamorphic buffer increases the lattice constant of the growth matrix from 5.653 to 5.869 Å. The increased lattice constant of the growth matrix yields a lattice mismatch with the InAs active region of only 3.2% and accommodates a large In content to access emission wavelengths From our comparison with quantum dotstructures, we conclude that the elongated quantum dash formation is due to asymmetric surfacebonds in the zinc blende crystal structure that control surface migration in low strain conditions.
84(2004); http://dx.doi.org/10.1063/1.1667260View Description Hide Description
Small-angle x-ray scattering (SAXS) intensities measured in a series of natural zircons, from fully crystalline to fully amorphous, give evidence for nanoscale density fluctuations within the amorphous phase produced by α-decay self-irradiation. At low amorphous fractions the SAXS intensity is dominated by the signal associated with the sharp crystalline/amorphous interphase. At high amorphous fractions a peak at develops, indicating the presence of 1 nm diameter regions that show a high-density contrast with the surrounding matrix. Density fluctuations are interpreted in terms of nanometer size voids.
Crystallization kinetics and microstructure-dependent leakage current behavior of ultrathin dielectrics: In situ annealing studies84(2004); http://dx.doi.org/10.1063/1.1667621View Description Hide Description
The crystallization kinetics of ∼3 nm filmsgrown by atomic layer deposition(ALD) on -passivated Si (100) wafers were investigated using an in situ transmission electron microscope (TEM) with heating capability. Through gray-scale analysis of dark-field TEM images, it was found that a two-dimensional nucleation and growth mechanism with a decreasing of nucleation rate could account for the observed transformation rate behavior. The effects of crystalline defects (e.g., grain boundaries) on the leakage current were studied using a reduced pressure in situ postdeposition anneal in the ALD system to avoid interfacial growth. The leakage current magnitude and temperature dependence were found to be essentially independent of the microstructural changes that accompany crystallization of the films.
84(2004); http://dx.doi.org/10.1063/1.1669060View Description Hide Description
The polarity of the ZnO film grown on sapphire using an ultrathin Ga wetting layer has been investigated by electron holography. Spontaneous polarization of the ZnO film leads to localized charges in the surface, which change the potential distribution in the vacuum side of the film. The potential distribution depends on the nature of the bounded charges and change as a function of the distance from the film surface. By studying the dependence of the potential change on the distance from the film surface, the ZnO film with very thin Ga wetting layer is determined to have the  polarity.
84(2004); http://dx.doi.org/10.1063/1.1650031View Description Hide Description
Enhancement of cathodoluminescence of manganese-activated zinc gallate thin-filmphosphor by energetic particle bombardment is reported. The thin-filmphosphor was grown at room temperature on silicon (100) substrates by rf magnetron sputter deposition from a 2 mol % Mn-doped target in an oxygen–argon mixture. After the deposition, the films were annealed at for 3 h in air. The influence of energetic particle bombardment on cathodoluminescent (CL) properties of films was investigated by varying a gas pressure during the sputter growth. Our results have shown that CLbrightness from filmsgrown at 2 mTorr was more than eight times higher than that of filmsgrown at 20 mTorr. The remarkable improvement in CLbrightness from filmsgrown at a low pressure is presumably due to the energetic particle bombardment of the growingfilm surface yielding a densely packed microstructure and a better crystalline quality with a highly -textured structure.