Volume 91, Issue 20, 12 November 2007
- 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
- device physics
- applied biophysics
- interdisciplinary and general physics
Index of content:
We show, first, that the charge relaxation (response) time of resonant-tunnelingdiode (RTD) can be significantly shorter or longer than the resonant-state lifetime, depending on RTD operating point and RTD parameters. Coulomb interaction between electrons is responsible for the effect. Second, it is also demonstrated that the operating frequencies of RTDs are limited neither by resonant-state lifetime nor by relaxation time; particularly in the RTDs with heavily doped collector, the differential conductance can stay negative at the frequencies far beyond the limits imposed by the time constants. We provide experimental evidences for both effects.
- LASERS, OPTICS, AND OPTOELECTRONICS
91(2007); http://dx.doi.org/10.1063/1.2809606View Description Hide Description
A simple local patterning laser-assisted method to transform bulk metallic Zn into a highly efficient ZnO-based random lasing medium is reported. The method uses the plasma of laser-induced air breakdown to treat the surface of a Zn target and thus transform it into a porous, nanostructured ZnO layer, which exhibits a strong exciton photoluminescence band in the UV . We show that the synthesized ZnO-based material can work as an efficient random lasing medium, simultaneously strongly scattering and amplifying pumping light, leading to a mirrorless generation of few laser emission narrow lines within the exciton band.
91(2007); http://dx.doi.org/10.1063/1.2809614View Description Hide Description
We present direct observations of electromagnetic fields localized in disordered photonic crystal waveguides and report the modal volumes and quality factors of the confined modes. Geometrical perturbations distributed uniformly throughout the crystal lattice were introduced by changing orientations of the polygonal lattice elements. Cavities in the disordered waveguides were excited by resonant coupling through a chain of random open resonators. Localized optical resonances with sub- modal volumes and quality factors of up to were observed.
91(2007); http://dx.doi.org/10.1063/1.2811713View Description Hide Description
Nonlinear refractive index and nonlinear absorption coefficient of high-quality Mn:ZnSe nanocrystals are measured by -scan technique at wavelength. The synthesized nanocrystals with nucleation doping have tunable wavelength (between ), high quantum yield , and high thermal as well as photochemical stabilities. The unique nanocrystal structure (with a MnSe core, diffusion region, and an outer ZnSe layer) shows size-dependent nonlinear effects, which can be qualitatively explained by a simple model using crystal field. Studies of nonlinear optical properties are very important and necessary for high-power optical applications (such as light-emitting diodes and lasers) of such Mn-doped ZnSenanocrystals.
91(2007); http://dx.doi.org/10.1063/1.2812549View Description Hide Description
We report a time-resolved study of the recombination dynamics in molecular beam epitaxygrown single quantum wells(SQWs) of width. The SQWs exhibit different emission properties, depending on both the well width and defect density. Stimulated emission has been achieved at room temperature in a separate confinement double heterostructure having a wide SQW as an active region. It has been found that a critical parameter for the lasing is the inhomogeneous broadening of both QW and barrier emission bands.
91(2007); http://dx.doi.org/10.1063/1.2805813View Description Hide Description
We discuss the influence of current-induced heating on the current-voltage characteristics and the spectral behavior in quantum well and quantum wire intersubband emitter structures. A conventional quantum cascade laser structure in the material system with undoped cladding layers and an undoped active region is examined. This heterostructure serves as a first growth step for quantum wire intersubband emitters fabricated by the cleaved-edge overgrowth technique. We discuss the influence of electrons supplied by a remote -silicon doping. Duty-cycle dependent measurements on the quantum wire structures confirm the influence of current-induced heating on the characteristics as well as on the emission spectra.
91(2007); http://dx.doi.org/10.1063/1.2805816View Description Hide Description
photodiode was fabricated on (000l) substrate by plasma-assisted molecular beam epitaxy. and In metals deposited using vacuum evaporation were used as -type and -type contacts, respectively. Current-voltage measurements on the device showed weak rectifying behavior. The photodetectors exhibited a peak responsivity at around . The ultraviolet-visible rejection ratio of four orders of magnitude was obtained at bias. The photodetector showed fast photoresponse with a rise time of and fall time of . In addition, the thermally limited detectivity was calculated as at , which corresponds to a noise equivalent power of at room temperature.
91(2007); http://dx.doi.org/10.1063/1.2813619View Description Hide Description
The optical upconversion of infrared light to visible light has been achieved in photosensitizer-doped organic light-emitting diodes, where poly(-vinylcarbazole) doped with infrared photosensitizer of 2,4,7-trinitro-9-fluorenylidene)malonitrile was used as hole-transporting layer, and tris(8-hydroxyquinoline) aluminum acted as both emitting and electron-transporting layers. Both electroluminescent intensity and current were enhanced under infrared illumination. The enhancement ratio was obtained as 2.45 times for electroluminescent emission and 1.45 times for current. This work brought forth a prototype design for novel flexible organic optical upconversion device used in near infrared field.
91(2007); http://dx.doi.org/10.1063/1.2814040View Description Hide Description
We report an entanglement generation experiment that utilizes a siliconwaveguide. Using spontaneous four-wave mixing in a -long silicon wire waveguide, we generated , high-purity time-bin entangled photons without temperature control and observed a two-photon interference fringe with visibility.
91(2007); http://dx.doi.org/10.1063/1.2814041View Description Hide Description
Waveguides based on line defects in pillar photonic crystals have been fabricated in technology. Transmission measurements of different line defects are reported. The results can be explained by comparison with two-dimensional band diagram simulations. The losses increase substantially at mode crossings and in the slow light regime. The agreement with the band diagrams implies a good control on the dimensions of the fabricated features, which is an important step in the actual application of these devices in photonic integrated circuits.
91(2007); http://dx.doi.org/10.1063/1.2814886View Description Hide Description
We demonstrate optical limiting using the self-lensing effect of a higher-order Laguerre-Gaussian beam in a thin dye-doped polymer sample, which we find consistent with our model using Gaussian decomposition. The peak phase shift in the sample required for limiting is smaller than that for a fundamental Gaussian beam with the added flexibility that the nonlinear medium can be placed either in front of or behind the beam focus.
91(2007); http://dx.doi.org/10.1063/1.2812576View Description Hide Description
We demonstrate an electrically tunable two dimensional photonic crystal nanocavity containing InAs self-assembled quantum dots(QDs).Photoluminescence and electroluminescence measurements are combined to probe the cavity mode structure and demonstrate a local electrical contact to the quantum dots. Measurements performed as a function of the electric field enable us to probe the capture, relaxation, and recombination dynamics of photogenerated carriers inside the quantum dots emitting into a modified photonic environment. Furthermore, the two dimensional photonic crystal is probed by spatially dependent photocurrent spectroscopy indicating a enhancement of the local radiative lifetime of the QDs inside the photonic crystal environment.
Fabrication and characterization of two-dimensional photonic crystal microcavities in nanocrystalline diamond91(2007); http://dx.doi.org/10.1063/1.2813023View Description Hide Description
Diamond-based photonic devices offer exceptional opportunity to study cavity quantum electrodynamics at room temperature. Here we report fabrication and optical characterization of high quality photonic crystalmicrocavities based on nanocrystallinediamond. Fundamental modes near the emission wavelength of negatively charged nitrogen-vacancy centers with quality factors as high as 585 were observed. Three-dimensional finite-difference time-domain simulations were carried out, having excellent agreement with the experimental results in the values of the mode frequencies. Polarization of the modes was measured; their anomalous behavior provides important insights to scattering loss in these structures.
Influence of electric field on spectral positions of dislocation-related luminescence peaks in silicon: Stark effect91(2007); http://dx.doi.org/10.1063/1.2813024View Description Hide Description
Spectral positions of dislocation-related luminescence (DRL) peaks from dislocation loops located close to a junction in silicon were shifted by carrier injection level. We suppose that the excitonic transition energies of DRL were reduced by an effective electric field at dislocation sites due to quadratic Stark effect (QSE). The field results from built-in junction field reduced by carrier injection. A constant of the shift, obtained from fitting of the data with QSE equation, was . The effect can explain the diversity of DRL spectra in silicon and may allow tuning and modulation of DRL for future photonic applications.
Free-running avalanche photodiode with active quenching for single photon counting at telecom wavelengths91(2007); http://dx.doi.org/10.1063/1.2815916View Description Hide Description
We present an avalanche photodiode with an active quenching circuit on an application specific integrated circuit (ASIC) that is capable of operating in both gated and free-running modes. The ASIC chip is fabricated using complementary metal oxide semiconductortechnology guaranteeing long-term stability, reliability, and compactness. In the free-running mode, we find a single photon detection efficiency of 10% with of noise.
91(2007); http://dx.doi.org/10.1063/1.2807273View Description Hide Description
Aggregate nonlinear response of silicon is determined by the competition between the free carrier absorption (FCA) and two-photon absorption(TPA). We show that the front end of optical pulses is always exposed to TPA dominated nonlinear regime, whereas the trailing edge can be seen at FCA dominated regime at high intensities. These two losses can be used for pulse compression if the center of the pulse is in FCA dominated nonlinear regime. To reach this operation regime, energy of wide pulses has to be larger than . Competition phenomenon is observed experimentally in a mode locked laser setup to generate pulse of .
91(2007); http://dx.doi.org/10.1063/1.2805031View Description Hide Description
The authors present microlasers on the material system. These microlasers are equipped with one dimensional or two dimensional photonic crystals (PhCs) acting as highly reflecting microscaled mirrors. Hence, microlasers with cavity lengths as short as could be realized, exhibiting output powers per facet of up to and side mode suppression ratios of in continuous wave operation.
Spectrally narrowed emissions occurring near an interface between a single crystal thiophene/phenylene co-oligomer and a glass substrate91(2007); http://dx.doi.org/10.1063/1.2815642View Description Hide Description
Polarized emission microspectroscopy has been investigated on a single crystal of a thiophene/phenylene co-oligomer. We measured polarized emissions occurring from the thin cloven facets of the crystal mounted on a glass substrate. The polarized UV light from a mercury lamp was used for the excitation. The spectrally narrowed emissions have been observed with an unusually low excitation intensity at the parts of the substrate very close to the interface between the crystal and the substrate.
91(2007); http://dx.doi.org/10.1063/1.2815652View Description Hide Description
The polarity is a special property for III-nitride materials with wurtzite structure along different orientations. The influence of normal and reversed polarizations on laser performance of the violet laser diodes with Ga-face and N-face configurations is studied numerically. Specifically, the laser performance, band diagram, carrier confinement, and emission wavelength are investigated. The results show that the threshold current is improved and emission wavelength is redshifted when the laser diode is with reversed polarization.
- PLASMAS AND ELECTRICAL DISCHARGES
91(2007); http://dx.doi.org/10.1063/1.2811711View Description Hide Description
A metallic slab lens featured with specially designed nano slits is presented to realize imaging for arbitrary object and image distances. Based on the particular propagation properties of surface plasmonpolaritons in nanostructures, slits perforated in silver slab are designed with variant widths to produce desired optical phase retardations. Numerical simulation of an illustrative lens is performed through finite-difference time-domain method and shows that subwavelength imaging is realized at the designed position.
91(2007); http://dx.doi.org/10.1063/1.2812567View Description Hide Description
A method for the measurements of electron temperature in the plasma using cutoff frequency and surface wave absorption frequency is described. The cutoff frequency, which gives directly the plasma density, is obtained from the transmission spectrummeasured between two antennas exposed to the plasma. The surface wave absorption frequency, which has the information of the sheath determined by the electron density and the electron temperature, is obtained from the reflection spectrummeasured at radiating antenna. The electron temperature is derived from the dispersion equation of the surface wave with the electron density measured from cutoff frequency.