Volume 92, Issue 9, 03 March 2008
- lasers, optics, and optoelectronics
- plasmas and electrical discharges
- structural, mechanical, thermodynamic, and optical properties of condensed matter
- electronic transport and semiconductors
- magnetism and superconductivity
- dielectrics and ferroelectricity
- nanoscale science and design
- organic electronics and photonics
- device physics
- applied biophysics
- interdisciplinary and general physics
Index of content:
Single-electron transistor (SET)-based multivalued (MV) not-AND (NAND) and not-OR (NOR) logic cells were implemented on a silicon-on-insulator chip. Depending on the ways of connecting two SETs with a field-effect transistor, the voltage transfer characteristics show typical NAND or NOR gate functions for various input voltages, which are binary, MV, and binary-MV mixed. Moreover, the switching functionality of our NAND (NOR) can convert to OR (AND) operation by simply adjusting their initial input voltages. These flexible two-input logic gates are expected to provide four basic arithmetic cells for the SET MV logic gate family.
- LASERS, OPTICS, AND OPTOELECTRONICS
92(2008); http://dx.doi.org/10.1063/1.2889448View Description Hide Description
The strong influence of the complex reverse flow phenomenon on the dynamic temperature behavior of vertically aligned liquid crystal displays (VA-LCDs) has been demonstrated. Good agreement was obtained between theoretical and experimental switching profiles over a wide temperature range . This was achieved using the Leslie–Ericksen theory in a one-dimensional model with material viscosity coefficients obtained from an improved estimation procedure. Such accurate numerical simulations can have a large impact on further improvements of VA-LCDs (e.g., the development of temperature-compensating driving schemes).
92(2008); http://dx.doi.org/10.1063/1.2889495View Description Hide Description
Doping a minute amount of photocurable monomers in a liquid crystal(LC) cell, we can stabilize the LC alignment after UV exposure by forming a LC pretilt layer on the substrate surface. By varying the UV exposure time, we can control the pretilt angle of the LCs continuously. A single-cell-gap transflective LC cell was fabricated through a photomask. The LC molecules at the transmissive and reflective pixels are pretilted at 54° and 65°, respectively, at which optimal phase retardations of half and quarter wavelengths are achieved. This type of transflective LC display shows an excellent electro-optical match between the two subpixels.
Direct modulation of electroluminescence from silicon nanocrystals beyond radiative recombination rates92(2008); http://dx.doi.org/10.1063/1.2889499View Description Hide Description
We propose a light emitting transistor based on siliconnanocrystals provided with built-in modulation. Suppression of electroluminescence from siliconnanocrystals embedded into the gate oxide of a field effect transistor is achieved by fast Auger quenching. In this process, a modulating drain signal causes heating of carriers in the channel and facilitates the charge injection into the nanocrystals. This excess of charge enables fast nonradiative processes that are used to obtain 100% modulation depths at modulating voltages of .
92(2008); http://dx.doi.org/10.1063/1.2889501View Description Hide Description
Microwave guiding was demonstrated over in air using a large diameter hollow plasma waveguide. The waveguide was generated with the femtosecond laser system at the Advanced Laser Light Source facility. A deformable mirror was used to spatially shape the intense laser pulses in order to generate hundreds of filaments judiciously distributed in a cylindrical shape, creating a cylindrical plasma wall that acts as a microwave waveguide. The microwaves were confined for about , which corresponds to the free electron plasma wall recombination time. The characteristics of the plasma waveguide and the results of microwave guiding are presented.
Optical polarization characteristics of light-emitting diodes fabricated on GaN substrates oriented between and planes92(2008); http://dx.doi.org/10.1063/1.2890050View Description Hide Description
Optical polarizationcharacteristics of light-emitting diodes(LEDs) were studied. Light-emitting diode samples were fabricated on four types of GaN substrates near orientation with intentional off-axis cuts of 0°, 5°, 10°, and 27° towards . A confocal microscope was used to characterize the optical polarization of electroluminescence at various currents. The highest polarization ratio of 0.91 was measured on samples fabricated on a 5° off-cut substrate. First moments were calculated on emission spectra to assess emission peak shifts of two polarization components. We drew a conclusion that substrate off-axis cut is a technique to improve optical polarizationcharacteristics of nonpolar-oriented LEDs.
Continuous-wave room temperature operated type I GaSb-based lasers with quinternary AlInGaAsSb barriers92(2008); http://dx.doi.org/10.1063/1.2890053View Description Hide Description
Diode lasers emitting at were designed and fabricated. Device active region contained two compressively strained InGaAsSbquantum wells incorporated in quinternary AlInGaAsSb barriers. Laser output power at room temperature was in continuous wave regime and more than in pulse.
92(2008); http://dx.doi.org/10.1063/1.2890166View Description Hide Description
We report on electrically pumped high-quantum dot-micropillar cavities with quality factors of up to 16.000. A special current injection scheme using a ring-shaped upper contact is presented which ensures an efficient light out-coupling through the uncapped upper surface of the micropillar. The devices feature excellent single-quantum dot cavity quantum electrodynamic effects with a Purcell enhancement of about 10 for a micropillar with a diameter of .
Improving the operation temperature of semiconductor-based terahertz photodetectors: A multiphoton design92(2008); http://dx.doi.org/10.1063/1.2890167View Description Hide Description
We propose and theoretically investigate a semiconductor-based terahertz-detector design exploiting a multiphoton absorption strategy through a bound-to-bound-to-continuum scheme. Our results demonstrate that such a multisubband architecture may access values of the background-limited infrared photodetection temperature, significantly higher than those of conventional quantum well infrared photodetectors operating at the same frequency, and therefore could represent a better alternative to the latter in the terahertz spectral region.
92(2008); http://dx.doi.org/10.1063/1.2890487View Description Hide Description
We present a femtosecond third-harmonic generation Maker fringes technique capable of simultaneously providing the magnitude of the cubic nonlinearity and the refractive indexdispersion of optical materials. This technique takes advantage of the high intensity and broad spectral band of femtosecond pulses, but requires the use of a spectrometer to deconvolute the information contained in Maker fringes produced by the broad band light.
92(2008); http://dx.doi.org/10.1063/1.2890492View Description Hide Description
A phosphor-free white light-emitting diode (LED) was fabricated with laterally distributed blue and green multiple quantum wells (MQWs) grown by a selective area growth method. Photoluminescence and electroluminescence (EL) spectra of the LED showed emission peaks corresponding to the individual blue and green MQWs. The integrated EL intensity ratio of green to blue emission varied from 2.5 to 6.5 with the injection current below , but remained constant at high injection currents above . The stability of the emission color at high currents is attributed to parallel carrier injection into both MQWs.
92(2008); http://dx.doi.org/10.1063/1.2890717View Description Hide Description
Raman-type stimulated emission at frequencies between 5.0 and as well as between 6.1 and has been realized in silicon crystals doped by phosphorus donors. The Raman laser operates at around under optical excitation by a pulsed, frequency-tunable infrared free electron laser. The frequencies of the observed laser emission are close to the frequencies of the intracenter laser lines which originate from the and phosphorus states. The Stokes shift of is equal to the difference between the energies of the phosphorus ground state, , and the excited state.
White-light light-emitting device based on surface plasmon-enhanced nanocrystal wavelength conversion on a blue/green two-color light-emitting diode92(2008); http://dx.doi.org/10.1063/1.2890730View Description Hide Description
The authors demonstrate the implementation of a white-light device by spin-coating nanocrystals (NCs) on the top of a blue/green two-color quantum-well light-emitting diode for converting blue and green emissions into red light through the absorption/reemission process. Meanwhile, Au nanoparticles are mixed with NCs for generating localized surface plasmon (LSP) modes to couple with the NCs. The LSP modes can absorb green emission and effectively transfer the energy into the NCs through the coupling process for enhancing red emission. With the LSP coupling process, the conversion efficiency from the blue/green range into red light can be increased by around 30%. The conversion quantum efficiency can reach 52.8%.
Improving spatial resolution and reducing aspect ratio in multiphoton polymerization nanofabrication92(2008); http://dx.doi.org/10.1063/1.2841042View Description Hide Description
The authors investigate the phenomena affecting lateral spatial resolution (LSR) and aspect ratio (AR) in multiphotonpolymerization (MPP) nanofabrication. A LSR of and an AR of 1.38 were achieved for photocured polymer lines on the surface of a substrate by continuing scanning mode. Theoretical analysis based on the distribution of light intensity in this setup indicates that the LSR could be improved to better than . The asymmetric shrinkage of voxel in the axial and lateral directions has a significant impact for obtaining features of low AR, which are a critical requirement for construction of micro/nanodevices by MPP nanofabrication.
92(2008); http://dx.doi.org/10.1063/1.2883873View Description Hide Description
Despite progress in the performance of image sensors, comparatively little work has focused on overcoming the limitations of planar image sensor arrays. We present a technique to construct curved monolithic silicon structures that can be processed using standard silicon processing prior to curving. The process relies on microstructuring of a monolithic silicon die using a deep reactive ion etch process. This technique can be used to build curved integrated circuits such as image sensors for more compact cameras with improved optical performance.
92(2008); http://dx.doi.org/10.1063/1.2890713View Description Hide Description
We describe the design, fabrication, and characterization of a narrow band tunable guided mode resonance (GMR) reflectance filter that is actuated by optically induced trans-cis isomerization of an azobenzene liquid crystal. Constructing a plastic replica-molded containment cell with a rubbed polyimide film to initially direct the liquid crystal molecular orientation parallel to the grating lines of the GMR filter, isomerization caused by exposure to a laser results in a shift of the resonant reflected wavelength.
92(2008); http://dx.doi.org/10.1063/1.2890727View Description Hide Description
(BBO) was found to have huge birefringence in the frequency region. Polarized terahertz transmission spectroscopy revealed a value of about . This result could be related to a polarization-dependent absorption that was observed at about ; in close agreement with first principles-calculations, showing this to be due to low-frequency phonon modes of the -rings. These findings suggest the utilization of the birefringent properties of BBO for optical parametric devices including amplifiers and oscillators, operating in the terahertz regime.
92(2008); http://dx.doi.org/10.1063/1.2891082View Description Hide Description
We present terahertz reference-free phase imaging for identification of three explosive materials (HMX, RDX, and DNT. We propose a feature extraction technique to locate the spectral position of an unknown material’s absorption lines without using the reference signal. The samples are identified by their absorption peaks extracted from the negative first-order derivative of the sample signal phase divided by the frequency at each pixel. This technique will greatly benefit the future development of standoff distance, large size focal-plane terahertz imaging system.
92(2008); http://dx.doi.org/10.1063/1.2841713View Description Hide Description
We develop an open-aperture (OA) scan and nonlinear transmission theory of two-photon-induced excited-stateabsorption, under the excitation of spatial Gaussian laser pulses with temporal Gaussian and hyperbolic secant profiles. The found analytic expressions allow us to straightforwardly fit the OA -scan trace and the nonlinear transmission curve, for convenient extraction of the nonlinear absorption coefficients. As a test, the two-photon-induced excited-stateabsorption in a chalcone derivative of 3,4-dimethoxy--fluorochalcone is explored by performing femtosecond -scan measurement and is analyzed by our theory.
92(2008); http://dx.doi.org/10.1063/1.2883953View Description Hide Description
A spin-polarized vertical cavity surface emitting laser, with self-organized quantum dots as the active gain media, has been fabricated and characterized. Electron spin injection is achieved via a Schottky tunnel contact. The laser is operated at and, at this temperature, the degree of circular polarization in the output is 8% and the maximum threshold current reduction is 14%. These effects are not observed in identical control devices with nonmagnetic contacts.
92(2008); http://dx.doi.org/10.1063/1.2884684View Description Hide Description
Bragg-type gratings were prepared by femtosecond laser irradiation in a series of optical polymers. The diffraction efficiency of polymethylpentene (PMP) was an order of magnitude higher than those of other polymers. Repeated scanning irradiation with femtosecond laser light formed gratings by refractive index changes inside the polymers. In PMP, whose density was the lowest among the polymers examined, large volume contraction by femtosecond laser irradiation was observed by transmission electron microscopy. The larger refractive index change of PMP was attributed to its large volume contraction based on its low density.