Volume 89, Issue 15, 09 October 2006
- 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:
Siliconnanoparticles embedded in silica show promising optoelectronic properties, due to quantum confinement and/or radiative interface states that should correlate with the particles’ average size and shape. Here the authors report the combination of electron tomography with plasmon-filtered microscopy in order to reconstruct the three-dimensional morphology of siliconnanoparticles. They find that particles with complex morphologies and high surface to volume ratios are dominant, rather than the commonly assumed near-spherical structures. These results should affect quantum-confined excitons and the interface density of states. Their findings may help to explain the physical origin of the unusually broad photoluminescence bands and efficiencies.
- LASERS, OPTICS, AND OPTOELECTRONICS
89(2006); http://dx.doi.org/10.1063/1.2358118View Description Hide Description
This letter reports on the observation of resonant enhancement by intersubband transitions of the second-harmonic generation of radiation in quantum wells grown on -sapphire templates. Quantum wells with a nominal well thickness of 10 ML have been investigated in terms of intersubband linear and nonlinear optical properties. A strong increase of the second-harmonic conversion is observed at a pump wavelength of , which is attributed to double-resonance enhancement of the nonlinear susceptibility by intersubband transitions. The second-order susceptibility at resonance is of the order of , in good agreement with calculations.
All-angle negative refraction and evanescent wave amplification using one-dimensional metallodielectric photonic crystals89(2006); http://dx.doi.org/10.1063/1.2360187View Description Hide Description
The authors numerically demonstrate all-angle negative refraction for propagating waves, as well as evanescent wave amplifications, using a one-dimensional photonic crystal consisting of metal-dielectric multilayers. Their structure has uniform surfaces parallel to the object plane and operates at the visible wavelength range. Using realistic material parameters including loss, they design a multilayer structure and verified its subwavelength resolution in the image formation process.
89(2006); http://dx.doi.org/10.1063/1.2360218View Description Hide Description
The authors present evidence for a distinct optical phonon progression in the nonlinear intersubband absorption spectra of electrons in a superlattice. Femtosecond two-color pump-probe experiments in the near infrared show spectral holes separated by the longitudinal optical (LO) phonon frequency and a homogeneous line broadening of approximately . The nonlinear bleaching signal decays with a time constant of due to intersubband scattering of delocalized electrons, followed by a weak picosecond component attributed to the relaxation of electrons from longer-lived localized states.
89(2006); http://dx.doi.org/10.1063/1.2358296View Description Hide Description
The authors theoretically investigate the effects of isotropic composition interdiffusion on the optical transition energy of quantum-dot (QD) structures under an electric field. Their three-dimensional QD calculation is based on coupled QDs arranged periodically in a tetragonal superlattice, taking into account the effects of finite band offset, valence-band mixing, strain, effective mass anisotropicity, and different QD shapes. The electron and hole Hamiltonians with the interdiffusioneffect are solved in the momentum space domain. The enhanced Stark shifts and the reduced built-in dipole moment have been found for the interdiffused QD structures.
Asymmetric long period fiber gratings fabricated by use of laser to carve periodic grooves on the optical fiber89(2006); http://dx.doi.org/10.1063/1.2360253View Description Hide Description
An asymmetric long period fiber grating (LPFG) with a large attenuation of and a low insertion loss of is fabricated by use of focused laser beam to carve periodic grooves on one side of the optical fiber. Such periodic grooves and the stretch-induced periodic microbends can effectively enhance the refractive index modulation and increase the average strain sensitivity of the resonant wavelength of the LPFG to . The resonant wavelength and the peak attenuation of the LPFG can be tuned by and , respectively, by the application of a stretching force.
Determining the temporally and radially resolved temperature distribution inside a pulsed broad-area vertical-cavity surface-emitting laser cavity89(2006); http://dx.doi.org/10.1063/1.2361164View Description Hide Description
The authors experimentally determine temporally and radially resolved profiles of the temperature distribution within the cavity of a broad-area vertical-cavity surface-emitting laser in pulsed operation. For this, the recently discovered state of spatially incoherent emission [M. Peeters et al., Opt. Express13, 9337 (2005)] is harnessed. Using single-shot measurements of spectrally resolved near field profiles acquired by a fast-gated charge coupled devicecamera, the wavelength shift due to heating of the device is temporally and radially resolved. From the wavelength shift the temperature shift is extracted, which finally allows for determination of absolute temperature profiles.
89(2006); http://dx.doi.org/10.1063/1.2361186View Description Hide Description
The authors report on a quantum well infrared detector embedded in a surface-plasmonwaveguide and processed into a deeply etchedphotonic crystal structure. The device was characterized by collecting the polarization dependent response spectra at different angles of incidence. With this method it is possible to map the photonicband structure by directly detecting the modes of the photonic crystal. It therefore represents a new and direct characterization procedure for photonic crystals. The device shows a strong mixing between TE and TM polarized modes, which is caused by the asymmetric vertical waveguide design.
89(2006); http://dx.doi.org/10.1063/1.2356380View Description Hide Description
Human IgG interactions with surface bound protein A are monitored label-free using microinterferometric backscatter detection. An electromagnetic wave-based model is developed and used to quantitatively describe the change in interference pattern as a consequence of the molecular interaction with the affinity layer on the fused silica capillary. Within the framework of the model it is of paramount importance to establish a valid stop criterion for the infinite summations involved in the fringe pattern computations. The high sensitivity towards surface changes, ease of changing the surface chemistry to other specific interacting layers, and simplicity of the optical sensor make this technique a powerful tool in biosensing.
89(2006); http://dx.doi.org/10.1063/1.2360235View Description Hide Description
This letter presents a type of infrared detector named the detector. The design essentially eliminates Shockley-Read-Hall generation currents. The result is greatly reduced dark current and noise, compared to other midwave infrared detectors, such as photodiodes. This enables the to operate at background-limited infrared photodetection conditions at significantly higher temperatures than conventional midwave infrared detectors and have greater detectivity near room temperature. The is demonstrated in InAs and InAsSb materials, exhibiting cutoff wavelengths of 3.4 and , respectively.
89(2006); http://dx.doi.org/10.1063/1.2358323View Description Hide Description
In this letter, the authors report the design, fabrication, and characterization of a silicon micromachined periodic structure for optical applications at . The microstructure, which can be envisioned as a one-dimensional photonic crystal, is composed of a periodic array of -thick silicon walls and -wide air gaps, each one corresponding to a different odd number of quarter wavelength at (hybrid quarter wavelength). The fabrication is based on the electrochemicaletching of silicon, yielding parallel trenches with depths up to . Preliminary reflectivity measurements show the presence of a band gap at , as theoretically expected.
89(2006); http://dx.doi.org/10.1063/1.2355455View Description Hide Description
A simple and easy method of the fabrication of one-dimensional magnetic gratingstructure is developed. By using the interference pattern of two femtosecond laser beams, a selective-area annealing of as-deposited film was achieved and one-dimensional magnetic gratingstructures were fabricated. The as-deposited films exhibit no magnetic response at room temperature. Several microscopies were applied to confirm the periodic crystalline and magnetic structures. The Faraday-like rotation of the polarization of the zeroth- and first-order diffracted beams were measured, and that of the first-order diffracted beam is nearly six times larger than that of the zeroth-order beam.
89(2006); http://dx.doi.org/10.1063/1.2358929View Description Hide Description
Intersubband transitions in short period superlattices prepared by molecular beam epitaxy were investigated using the optical absorption technique. The peak position wavelengths of these transitions are found to span the spectral range of for samples cut into 45° waveguides with GaNquantum well thicknesses ranging between 1.70 and . The Fermi energy levels are estimated from the carrier concentrations, which were measured using an electrochemical capacitance-voltage profiler. The well widths were inferred from comparing the measured peak position energy of the intersubband transitions and the bound state energy levels calculated using the transfer matrix method.
Individual classification of buried transistors in live microprocessors by functional infrared emission spectral microscopy89(2006); http://dx.doi.org/10.1063/1.2358935View Description Hide Description
The authors classify good, leaky, and broken field effect transistors (FET’s) in a live flip-chip microprocessor using functional infrared emission spectralmicroscopy. The FET’s are in the active layer that is sandwiched between a thick heat-absorbing silicon material and a highly reflecting grid of metal interconnects. Together they are optically imaged only as a single bright blob. They classify FET’s individually from their distinct electroluminescencespectra that are recovered efficiently by spectral decomposition of the detected composite spectrum. Leaky FET’s have no apparent structural damage and are detectable only in live microprocessors.
89(2006); http://dx.doi.org/10.1063/1.2358936View Description Hide Description
The authors studied the current-voltage characteristics of the organic superlattices of an ITO/1,3,5-tris-(3-methylphenylphenylamino) triphenylamine (-MTDATA) . The thickness of -MTDATA was varied from with the fixed Bphen thickness at . The current-voltage characteristics of the organic superlattice show a peak and a valley between 3 and when the thickness of -MTDATA is , which is due to the resonant tunneling currents. It is found that there is no luminance by the resonant tunneling currents.
Utilization of water/alcohol-soluble polyelectrolyte as an electron injection layer for fabrication of high-efficiency multilayer saturated red-phosphorescence polymer light-emitting diodes by solution processing89(2006); http://dx.doi.org/10.1063/1.2358942View Description Hide Description
Highly efficient multilayer red polymer light-emitting diodes were fabricated by solution process-ing from iridium complex, bis(1-(3-(9,9-dimethyl-fluorene-2-yl)phenyl)isoquinoline-) iridium(III)acetylacetonate, doped into polyfluorene as a host and with a water/alcohol-soluble polymer, poly[(9,9-bis(-((-dimethyl)--ethylammonium)propyl)-2,7-fluorene)-2,7-(9,9-dioctylfluorene)-4,7-(2,1,3-benzoselenadiazole)]dibromide (PFN) as electron injection layer. The device with the structure showed an external quantum efficiency of 18.0% and luminance efficiency of at a current density of , a peak emission at , and Commission International de I’Eclairage coordinates of (0.665, 0.319). The efficiency remained as high as , and , at a current density of , and a luminance of .
89(2006); http://dx.doi.org/10.1063/1.2360896View Description Hide Description
The authors propose to exploit the unique properties of surface plasmons to enhance the signal-to-noise ratio of midinfrared photodetectors. The proposed photodetector consists of a slit in a metallic slab filled with absorptive semiconductor material. Light absorption in the slit is enhanced due to Fabry-Perot resonances. Further absorption enhancement is achieved by surrounding the slit with a series of periodic grooves that enable the excitation of surface plasmons that carry electromagnetic energy towards the slit. Using this scheme, they design and optimize a photodetector operating at with a roughly 250 times enhancement in the absorption per unit of volume of semiconductor material compared to conventional photodetectors operating at the same wavelength.
89(2006); http://dx.doi.org/10.1063/1.2357598View Description Hide Description
The authors examined band absorption saturation properties of 150 stacked InAsquantum dot layers on InP substrate. The transmission change at the vertical incidence based on the saturable absorption of the quantum dots was as much as 1%. Theoretical prediction shows that the transmission change could be greatly increased by removing the InP substrate. After grinding the substrate and antireflection coating on both surfaces, transmittance change was build up to 3%. It is thus concluded that highly stacked quantum dot layers are potentially applicable to a planar-type mode locker for short optical pulse generation in the band.
89(2006); http://dx.doi.org/10.1063/1.2361167View Description Hide Description
The authors measure the temperature dependence of the components of threshold current of undoped and -doped quantum dot lasers and show that the temperature dependence of the injection level necessary to achieve the required gain is the largest factor in producing the observed negative in -doped quantum dot lasers.
89(2006); http://dx.doi.org/10.1063/1.2361179View Description Hide Description
The continuous-wave (cw) operation of GaInNAsSb lasers at is reported. Light-current measurements were made before and after a cw burn in at , during which a device with initial threshold current and maximum output power experienced a 15% drop in peak output power. These preliminary lifetime results provide insight into the reliability of GaInNAsSb active regions and reinforce the promise of this material for C-band devices. High-resolution modal gain spectra were extracted from the amplified spontaneous emissionspectra acquired after the burn in, providing reliable values for the internal loss, transparency current, and differential gain.
89(2006); http://dx.doi.org/10.1063/1.2359580View Description Hide Description
Results of a study of different gain section designs in nonresonantly optically pumped vertically emitting semiconductor disk lasers (SCDLs) are presented. Clear superiority of structures with barriers based on graded-gap layers is demonstrated. This finding is assigned to the lack of absorption saturation within the barriers caused by the efficient carrier collection capabilities of graded structures compared to ungraded ones. Transient photoluminescence experiments providing direct access to the carrier transfer from the barrier to the quantum-well active region confirm this explanation. Consequently, the authors propose graded designs for SCDLs.