Volume 85, Issue 17, 25 October 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:
nanopyramids and nanocolumns and their photoluminescence properties" title="Direct synthesis of single crystalline nanopyramids and nanocolumns and their photoluminescence properties" />
Single crystalline indium oxide pyramid and column structures were synthesized by a simple physical evaporation technique. The pyramidstructure was obtained without any catalytic action while the column structure was produced using gold as the catalyst. The nanostructures were characterized by x-ray diffraction, scanning electron microscopy and transmission electron microscopy. A blue-green photoluminescence band in the visible region was observed in the structures which could be ascribed to the existence of a large amount of singly ionized oxygen vacancies, confirmed by electron paramagnetic resonance.
- LASERS, OPTICS, AND OPTOELECTRONICS
85(2004); http://dx.doi.org/10.1063/1.1808888View Description Hide Description
We fabricated two-dimensional photonic crystalstructures in zinc oxide films with focused-ion-beam etching. Lasing is realized in the near-ultraviolet frequency at room temperature under optical pumping. From the measurement of lasing frequency and spatial profile of the lasing modes, as well as the photonicband structure calculation, we conclude that lasing occurs in the strongly localized defect modes near the edges of photonic band gap. These defect modes originate from the structure disorder unintentionally introduced during the fabrication process.
85(2004); http://dx.doi.org/10.1063/1.1808878View Description Hide Description
Current pumped terahertz (THz) emitting devices have been fabricated from galliumdopedsilicon. The time resolved peak power was per facet at a peak pumping current of , and the emission was observed up to temperatures near . The spectra occurred in two distinct series at , and at . The emission was attributed to the radiative transitions of holes from the split sublevels of the excited state to the sublevels of the ground state and the ground state, yielding an energy separation of between the two ground states. These results indicated that emitters based on Ga impurity transitions open up a range of THz frequencies, and the properties of their spectra can improve the understanding of impurity level physics.
85(2004); http://dx.doi.org/10.1063/1.1808881View Description Hide Description
We have fabricated and characterized a light emitting photonic crystal slab in the blue near , based on quantum well active material. A multilayer nanopattern transfer technique was developed to fabricate these optical structures. The dependence of the photoluminescence enhancement on specific pattern dimension, coupled with distinct polarization characteristics of emission, was found to be in good agreement with theoretical simulations, thereby supporting the existence of photonic crystalband gap. The results suggest that practical fabrication of photonic crystal slabtype light emitting diodes for enhanced external quantum efficiency in the blue and ultraviolet is feasible.
85(2004); http://dx.doi.org/10.1063/1.1807967View Description Hide Description
We have utilized hybrid zinc oxide∕silica microdisk lasers to sense volatile organic compounds, such as toluene and nitrobenzene. Nonspecific adsorption of these organic molecules onto the microdisk surface causes an increase in the disk refractive index, ultimately resulting in a redshift of the observed lasing wavelengths. The monitoring of these shifts provides the sensing modality. Microdisk lasers were found to respond rapidly and reversibly to the investigated chemicals demonstrating, in principal, the chemical and biological sensing capabilities of such devices.
85(2004); http://dx.doi.org/10.1063/1.1807970View Description Hide Description
Fabrication of a planar semiconductor microcavity, composed of cylindrical Bragg reflectors surrounding a radial defect, is demonstrated. A versatile polymer bonding process is used to transfer active InGaAsPresonators to a low-index transfer substrate. Vertical emission of in-plane modes lasing at telecom wavelengths is observed under pulsed optical excitation with a submilliwatt threshold.
85(2004); http://dx.doi.org/10.1063/1.1807948View Description Hide Description
We report on micro-photoluminescence studies of single quantum wires which were grown by molecular beam epitaxy. Employing the cleaved edge overgrowth technique, quantum wires located in an overgrown (011) oriented GaAs quantum well originate purely from the tensile strain field of InAlAs layers grown along the  direction. These stressor layers are separated by -wide AlGaAs barriers so that the photoluminescence signals of different quantum wires can be resolved individually. Their confinement energy varies systematically with the widths of the stressor and overgrown layers, reaching values as high as . The quantum wire signals are characterized by a smooth line shape even for the lowest excitation powers, indicating the absence of pronounced exciton localization.
85(2004); http://dx.doi.org/10.1063/1.1812365View Description Hide Description
The growth conditions for quantum dots(QDs) have been optimized and QDs of high luminescence efficiency and the room temperature operation of QD lasers emitting at have been demonstrated. Lattice-matched InGaAsP was used as a barrier layer for the InGaAsQDs and the emission wavelength was controlled by the QD composition. High-density InGaAsQDs with an areal density as high as have been grown. The integrated and peak intensity of the photoluminescence(PL) spectra at room temperature are as high as 25% and 10% of those at , respectively. The room temperature PL peak intensity is about 50% that of a high-quality quantum well. Room temperature, pulsed operation at has been achieved from broad area lasers with a cavity length. Threshold current density per QD stack of is measured for the five-, seven-, and ten-stack QD lasers.
Femtosecond time-resolved dispersion relation of complex nonlinear refractive index in a semiconductor quantum well85(2004); http://dx.doi.org/10.1063/1.1808225View Description Hide Description
We present simultaneous measurement of femtosecond time-resolved nonlinear phase and amplitude changes around the excitonic resonance of the quantum well using polarization-division Sagnac interferometer. The nonlinear complex refractive index of the semiconductor material for all-optical devices is successfully determined from directly measured nonlinear phase and amplitude changes.
85(2004); http://dx.doi.org/10.1063/1.1812375View Description Hide Description
Three-dimensional artificial crystals with periodicity corresponding to terahertz wave lengths were fabricated by self-assembling monosized metal spherical particles. The metal crystals were weakly sintered to utilize them as templates. The metal templates were inverted to air spheres crystal embedded in dielectric resin though infiltration and etching. The resulting resin inverted crystals clearly presented the photonic stop gaps within terahertz wave region and the frequencies of the gaps were confirmed to agree well with calculation by plane wave expansion method.
85(2004); http://dx.doi.org/10.1063/1.1812595View Description Hide Description
This letter develops a method that is able to optimize the grating pivot position to obtain maximum continuous tuning range for a Littrow laser, and also verifies the method by implementation of a single-chip integrated laser using the microelectromechanical systems(MEMS)technology. The laser consists of a semiconductor gain chip, a microlens, and a MEMS blazed grating arranged in the Littrow configuration. The laser is integrated onto a single silicon chip while maintaining the ability of continuous tuning in a large range. It has a compact size of , and has obtained a tuning range of with a resolution of , a maximum power of and a side mode suppression ratio of . Other merits include fast tuning speed, improved mechanical/wavelength stability, batch fabrication, and low cost.
85(2004); http://dx.doi.org/10.1063/1.1810626View Description Hide Description
We investigate the optical nonlinearity of a ferroelectric thin film using the top-hat Z scan technique at a wavelength of with duration pulses. The film exhibits the fast and giant optical nonlinearities having the two-photon absorption coefficient of and the nonlinear refraction coefficient of , respectively. The mechanism of the optical nonlinearity is discussed in detail. In particular, we also give two important formulas for the top-hat Z scan, which are very valuable and helpful for estimating the nonlinear optical coefficients when the material possesses the simultaneous nonlinear absorption and nonlinear refraction.
85(2004); http://dx.doi.org/10.1063/1.1806278View Description Hide Description
Hollow-core photonic-crystal fibers (PCFs) capable of transporting sub-100-fs pulses of Ti:sapphire laser radiation in one of their transmission peaks centered around 800 nm have been designed and demonstrated. These fibers are shown to enhance self-phase modulation of submicrojoule 100-fs Ti:sapphire laser pulses, allowing a spectral bandwidth of 35 nm to be achieved with an 8-cm PCF sample.
85(2004); http://dx.doi.org/10.1063/1.1811378View Description Hide Description
High refractive index contrast optical microdisk resonators fabricated from silicon-on-insulator wafers are studied using an external silica fiber taper waveguide as a wafer-scale optical probe. Measurements performed in the wavelength band show that these silicon microdisks can support whispering-gallery modes with quality factors as high as , limited by Rayleigh scattering from fabrication induced surface roughness. Microdisks with radii as small as are studied, with measured quality factors as high as for an optical mode volume of .
85(2004); http://dx.doi.org/10.1063/1.1808501View Description Hide Description
White-light-emitting diodes are fabricated by using emitting chip with (blue and yellow) or , (blue, yellow, and red). At a color temperature of , the color coordinates are , , and the color rendering index is 84%; at a color temperature of , the color coordinates are , , and the color rendering index is 92%. The blue and yellow emission bands are originated from ions, while the red (680) emission band is originated from ions in host. The energy transfer among three bands occurs due to the spectral overlap between emission and absorption bands. It is confirmed by the faster decay time of the energy donor. Our white-light-emitting diodes show higher color reproducibility, higher color stability on forward-bias current, and excellent color rendering index in comparison with a commercial -based white-light-emitting diode.
85(2004); http://dx.doi.org/10.1063/1.1811382View Description Hide Description
Two practically fully relaxed AlN domains were identified by x-raydiffractometry for AlNgrown on (100) diamond. The epitaxial orientation relationships diamond for the predominant AlN domain (type I) and diamond for the second domain (type II) are obtained. Surface morphology measurements corroborate the good structural quality of the AlN film. In addition, the intrinsic built-in voltage of a -diamond diode was determined as . By spectrally resolved photocurrent measurements, the ultraviolet electroluminescence emission was confirmed to originate at the heterojunction interface, and is most probably due to a defect center.
Surface acoustic wave ultraviolet photodetectors using epitaxial multilayers grown on -plane sapphire85(2004); http://dx.doi.org/10.1063/1.1811383View Description Hide Description
A surface acoustic wave(SAW) ultraviolet (UV) photodetector is made of a zinc oxide based epitaxial multilayer structure on an -plane sapphire substrate. Piezoelectric and semiconducting layers are used for SAW excitation and photodetection, respectively. A thin layer grown between the two layers isolates the semiconducting layer from the piezoelectric one. In contrast to previously reported SAWUV detectors on and , the Sezawa SAW mode in the system is used for its high acoustic velocity and large maximum effective piezoelectric coupling constant. The interaction of the SAW with the photogenerated carriers in the semiconducting layer results in a phase shift and an insertion loss change, as functions of light wavelength and power. The SAWUV detector can be used as a passive zero-power remote wireless UV sensor.
85(2004); http://dx.doi.org/10.1063/1.1811384View Description Hide Description
High-order correction to the fields of ultrashort, tightly focused laser pulses expressed in power series of and ( the central oscillatory frequency, the pulse duration for half period, the beam waist radius at the central frequency ), are derived. These expressions can be used to describe accurately the fields of laser pulses, and are suitable for practical calculations. The first-order correction terms to the fields based on paraxial approximation are explicitly given. They are applied to a simulation study of electron dynamics in laser pulse field with special attention given to the vacuum laser acceleration scheme. We found that as long as , the zeroth-order approximation (long pulse approximation) is adequate for describing the interaction. For , higher-order corrections have to be taken into account.
85(2004); http://dx.doi.org/10.1063/1.1807019View Description Hide Description
We first analyze why most of the photonic crystals produced by two-photon photopolymerization technique exhibit no photonic band gap effect. And then subdiffraction-limited resolution-enabled finely quantified pixel writing, a scheme that has been used in micromachine fabrication, is adopted as the solution. As a result, higher accuracy in depicting and better reproducibility in both fabrication and photonic band gap effect observation are obtained. More important, the method allows for precise precompensation of the structure shrinkage induced by photochemical reactions of polymerization, which may pave the way to high-fidelity fabrication of polymerphotonic and optoelectronic devices that require strictly the structural parameters.
85(2004); http://dx.doi.org/10.1063/1.1810215View Description Hide Description
A bistable liquid crystal display based on the bend and splay configurations has been demonstrated. This display can be switched between the bend and splay deformation in a three-electrode configuration and has infinite bistable lifetime. It also has wide viewing angles, excellent contrast ratios, and very fast selection. Selection electric pulse duration of can be used to switch this display, implying the possibility of a high information content applications.
- STRUCTURAL, MECHANICAL, THERMODYNAMIC, AND OPTICAL PROPERTIES OF CONDENSED MATTER
85(2004); http://dx.doi.org/10.1063/1.1807032View Description Hide Description
A figure of merit is proposed in order to optimize the self-organized growth of nanoscale elements into one-/two-dimensional arrays via a fine selection of the deposition/annealing conditions. This figure of merit has been designed to account for the most significant defects inherent in such arrays. Its versatility has been studied by kinetic Monte Carlo simulations of self-organized growth of metal clusters on the reconstructed surface. The optimization relationships between deposition/annealing conditions and characteristics of the metal-on- systems are obtained and analyzed within the framework of competition between thermodynamical tendencies and kinetic limitations.