Volume 94, Issue 8, 23 February 2009
- 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:
Current-driven domain wall (DW) motion has been studied in the NiFe layer of a Co/Cu/NiFe thin film ring using giant-magnetoresistance measurements in a four-point contact geometry. The NiFe layer is initially in an onion state configuration with two 180° DWs. An electric current drives the walls around the ring so that they annihilate and the NiFe layer forms a DW-free vortex state. The direction of motion of the two DWs is determined by the current polarity, enabling the vortex chirality to be selected.
94(2009); http://dx.doi.org/10.1063/1.3098974View Description Hide Description
- LASERS, OPTICS, AND OPTOELECTRONICS
94(2009); http://dx.doi.org/10.1063/1.3086333View Description Hide Description
We report on the fabrication and emission characteristics of InGaAs/GaAs quantum dot microtube ring resonators on Si substrates achieved using a simple but controllable substrate-on-substrate transfer process. We have observed three-dimensionally confined optical modes, including both radial and axial field distributions from quantum dot microtubes on Si with an engineered geometry at 77 K, which agrees well with results calculated using a photonic quasi-Schrödinger equation. An intrinsic -factor of is also derived.
94(2009); http://dx.doi.org/10.1063/1.3088851View Description Hide Description
We report that asymmetric c-shaped holes show mode switching between single- and double-resonance frequencies in the terahertz region, when the polarization direction of the incident light is controlled. The number of resonant frequencies is attributed to fundamental shape modes such as circle-, coaxial-, and rectangular-shaped holes activated under each polarization condition. All of these resonant peaks also show a transmission of over 90% with the assistance of the periodically arranged holes. These experimental results are in close agreement with theoretical simulations.
94(2009); http://dx.doi.org/10.1063/1.3075067View Description Hide Description
We have measured the infrared properties of optically transparent and electrically conductive single walled carbon nanotubethin films. We found that nanotubefilms with sheet resistance values of show outstanding transmittance in the infrared range up to at least , with an average transmittance greater than 90% over this range. The infrared properties of various materials were compared and we found that transparent nanotubeelectrodes and transparent grapheneelectrodes outperform the others in several key categories. This study opens another important application area for conductive nanotubethin films.
Unified explanation of the fluorescence decay and blinking characteristics of semiconductor nanocrystals94(2009); http://dx.doi.org/10.1063/1.3086297View Description Hide Description
Recently power law dynamics was observed in the fluorescence decay from semiconductornanocrystals and a model was proposed and analyzed on the basis the of Monte Carlo simulation to clarify the relation between the power law fluorescence decay and the power law blinking. However, analysis of the model on the basis of the Monte Carlo simulation is not decisive. In this paper we present the analytical solution of the model. The analytical result is used to prove rigorously that the exponent of the power law blinking and that of the power law fluorescence decay are the same.
94(2009); http://dx.doi.org/10.1063/1.3088850View Description Hide Description
We have observed negative optical torsional rigidity in an 80 m suspended high optical power cavity that would induce the Sidles–Sigg instability as a result of sufficient circulating power. The magnitude of the negative optical spring constant per unit power is a few as the result of the optical torsional stiffness in the yaw mode of a suspended mirror Fabry–Pérot cavity. It has been observed to depend on the -factor of the cavity which is in agreement with the Sidles–Sigg theory.
94(2009); http://dx.doi.org/10.1063/1.3088852View Description Hide Description
The microstructural changes associated with the formation of lithium tantalate waveguides after high repetition rate ultrafast laser inscription has been investigated by confocal micro-Raman experiments. While the laser beam focal volume is characterized by significant lattice damage, no reduction of Raman mode strength has been observed at the guiding region, suggesting the preservation of the nonlinear optical coefficient in the waveguide. A general blueshift of the Raman modes has been observed at the guiding region, suggesting lattice compression as the dominant mechanism of waveguide formation.
Low threshold current density of InAs quantum dash laser on InP (100) through optimizing double cap technique94(2009); http://dx.doi.org/10.1063/1.3088862View Description Hide Description
We report on the uniformity improvement of InAs quantum dashes (QDHs) grown by molecular beam epitaxy on InP (100) through optimizing double cap technique. Broad-area lasers were fabricated with an emission wavelength of . A threshold current density of was achieved for a five stack QDH structure and a cavity length of 1.2 mm. This results from a reduced inhomogeneous broadening (62 meV) and lower internal optical losses . The achievement paves the way toward ultralow threshold semiconductor laser for telecommunications.
94(2009); http://dx.doi.org/10.1063/1.3089359View Description Hide Description
A waveguide-integrated photodetector provides a small-footprint, low-capacitance design that overcomes the bandwidth-efficiency trade-off problem of free space optics. High performance silicon devices are critical to the emergence of electronic-photonic integrated circuits on the complementary metal oxide semiconductor platform. We have fabricated vertical siliconphotodetectors that are monolithically integrated with compact silicon oxynitride channel waveguides. We report over 90% coupling efficiency of 830 nm light from the silicon oxynitride channel waveguide to the siliconphotodetector. We analyze the dependence of coupling on waveguide index by comparing coupling from low index-contrast waveguides and high index-contrast waveguides.
Injectorless quantum cascade laser with low voltage defect and improved thermal performance grown by metal-organic chemical-vapor deposition94(2009); http://dx.doi.org/10.1063/1.3089362View Description Hide Description
We demonstrate a strain-compensated injectorless quantum cascade laser (I-QCL), grown by metal-organic chemical-vapor deposition, with a very low voltage defect operating up to room temperature. We experimentally study the effect of voltage defect on thermal performance by comparing the rise in core temperature over a 300 ns pulse width of I-QCL and conventional QCL, working in pulsed mode using time-resolved step scan. I-QCL shows approximately eight times lower rate of rise in core temperature compared to conventional QCL.
Measurement of gain and losses of a midinfrared quantum cascade laser by wavelength chirping spectroscopy94(2009); http://dx.doi.org/10.1063/1.3089570View Description Hide Description
We present an optimized technique for the measurement of gain and losses of semiconductor lasers. We optically inject the beam of a distributed feedback laser(DFB) inside the cavity of the lasers under study. The DFB laser operates in a pulsed mode and shifts its emission wavelength as a function of time. This frequency chirp creates the Fabry–Pérot fringes of the transmitted intensity that contains all the information on the cavity losses. The setup has been validated by a quantitative study of the losses as a function of the injected current, for a quantum cascade laser emitting at .
94(2009); http://dx.doi.org/10.1063/1.3089689View Description Hide Description
In this letter, we demonstrate a two step casting process to fabricate a bifunctional hydrogel-based microlens array, which responds to both temperature (becomes opaque above certain temperature) and (changes its focal length at different levels), and can be operated in air for an extended period of time. Each lens in the array is 1 mm in diameter and its focal length changes from 4.5 to 55 mm when the environmental is varied between 2.0 and 5.0. The light-switching capability is measured to be when temperature increases from 25 to .
94(2009); http://dx.doi.org/10.1063/1.3089380View Description Hide Description
We report on infrared quantum counting of photons at optical communication wavelengths based on nondegenerate two-photon absorption in a GaAs photomultiplier tube. The detected photonenergy is lower than the GaAsband gap and the energy difference is complemented by a high intensity pump field. This detection setup is simple, compact, has a broad spectral bandwidth, and benefits from the intrinsic low noise and dark counts of large band gap semiconductor junctions.
The origin of the high diode-ideality factors in GaInN/GaN multiple quantum well light-emitting diodes94(2009); http://dx.doi.org/10.1063/1.3089687View Description Hide Description
We report on a significant decrease in the diode-ideality factor of GaInN/GaN multiple quantum welllight-emitting diodes(LEDs), from 5.5 to 2.4, as Si-doping is applied to an increasing number of quantum barriers (QBs). The minimum ideality factor of 2.4 is obtained when all QBs are doped. It is shown that polarization-induced triangular band profiles of the undoped QBs are the major cause of the high ideality factors in GaInN/GaN LEDs. Numerical simulations show excellent agreement with the measured ideality factor value and its dependence on QB doping.
94(2009); http://dx.doi.org/10.1063/1.3089691View Description Hide Description
Recently, photoluminescence studies using resonant optical excitation in GaInN layers have been used to investigate the physical origin of efficiency droop in GaInN/GaN light-emitting diodes. In these studies, it has been assumed that in the case of resonant excitation, where electron-hole pairs are generated in the GaInN layers only, carrier transport effects play no role. We report that in contrast to this assumption, carrier escape from quantum wells does take place and shows strong dependence upon the duration of excitation and bias conditions. We also discuss the time scales required to reach steady-state conditions under pulsed optical excitation.
94(2009); http://dx.doi.org/10.1063/1.3089817View Description Hide Description
In the SiGe system, freedom in the design of quantum well(QW) devices is constrained by the 4.2% lattice mismatch between silicon and germanium. The substitution of the Si substrate by a SiGe pseudosubstrate customized to the respective QW structure’s requirements enables the growth of a -type SiGe QW infrared photodetector featuring interfaces between pure Si and SiGe layers of ultrahigh Ge content for a full exploitation of the band offset between the two materials. Our presented device realizes design concepts for narrowing the spectral response and reducing the noise gain made feasible by the utilization of a pseudosubstrate.
Subwavelength-resolved bidirectional imaging between two and three dimensions using a surface plasmon launching lens94(2009); http://dx.doi.org/10.1063/1.3089838View Description Hide Description
We demonstrate subwavelength-resolved bidirectional conjugate imaging between three-dimensional far-field and two-dimensional surface plasmon (SP) by using a SP launching lens (SPLL), which consists of multiple groove zones that is designed according to the Fresnel zone on a goldfilm. Resolvable separations between two SP point sources of 704 and 668 nm were obtained for far-field to SP and the contrary, respectively, at . The SPLL shows similar imaging properties to a traditional optical lens, which can be used to connect multiple channels between far-field and SP.
Optical bistability enhanced by highly localized bulk plasmon polariton modes in subwavelength metal-nonlinear dielectric multilayer structure94(2009); http://dx.doi.org/10.1063/1.3079408View Description Hide Description
Optical bistability of subwavelength metal-nonlinear dielectricmultilayerstructure is numerically studied in this letter. It is found that very low intensity thresholds for optical bistability can be achieved due to the excitation of highly localized bulk plasmonpolariton modes with TM polarized illumination. A bistability threshold of is obtained for mode, which is much lower than the recently reported results based on the large local field enhancement at the band edge of metal-dielectric photonic band gapstructure [A. Husakou and J. Herrmann, Phys. Rev. Lett.99, 127402 (2007)].
94(2009); http://dx.doi.org/10.1063/1.3088858View Description Hide Description
We experimentally studied the enhanced optical transmission of perforated silverfilms in the middle-infrared region. The optical transmission properties of the samples with classical inductive frequency selective surface structures are also affected by both the periodicity and the aperture shape. Our results indicate that the physical operating mechanisms are the same for the plasmon crystal and the frequency selective surface, and both surface plasmon polaritons due to the periodicity and waveguide modes that are present in single holes have effect in the optical transmission enhancement.
94(2009); http://dx.doi.org/10.1063/1.3089573View Description Hide Description
Based on recent improvements of growth of In-rich InGaN quantum wells with low defect density, we demonstrate current driven InGaN laser diodes at wavelengths as long as 500 nm. The laser structures are grown on -plane GaN substrate and are processed as broad oxide-insulated stripe laser diodes. We discuss the impact of the piezoelectric field on the emission energy of long wavelength laser diodes for this growth orientation. The combination of low threshold current density of with high slope efficiency of 650 mW/A enables high output powers up to several tens of milliwatts.