Proceedings Volume 6902

Quantum Dots, Particles, and Nanoclusters V

cover
Proceedings Volume 6902

Quantum Dots, Particles, and Nanoclusters V

View the digital version of this volume at SPIE Digital Libarary.

Volume Details

Date Published: 7 February 2008
Contents: 5 Sessions, 10 Papers, 0 Presentations
Conference: Integrated Optoelectronic Devices 2008 2008
Volume Number: 6902

Table of Contents

icon_mobile_dropdown

Table of Contents

All links to SPIE Proceedings will open in the SPIE Digital Library. external link icon
View Session icon_mobile_dropdown
  • Front Matter: Volume 6902
  • Semiconducting Nanostructures
  • Metallic Nanostructures
  • Nanostructures for Photonic Applications I
  • Nanostructures for Photonic Applications II
Front Matter: Volume 6902
icon_mobile_dropdown
Front Matter: Volume 6902
This PDF file contains the front matter associated with SPIE Proceedings Volume 6902, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.
Semiconducting Nanostructures
icon_mobile_dropdown
Experimental verification of dielectric constant decrease in silicon nanostructures
During the design of devices using Si nanostructures, it is often important to precisely know the dielectric function ε, since it determines many of their electrical and optical properties. Several theoretical studies have predicted a reduction in the dielectric constant ε as the nanostructure size decreases. Two competing physical mechanisms have been proposed for the reduction: quantum confinement and surface effects (due to a breaking of polarizable bonds on the surface). There have been only a few experimental works on the size dependence of ε, in which ε was measured only for one particular average size. In our work, we have measured the size-dependent ε of thin crystalline slabs at different sizes using variable angle spectroscopic ellipsometry from 270 nm to 1700 nm at the incident angles of 65°, 70° and 75°. The thin crystalline slabs of different thicknesses (~ 15 nm to 2.5 nm) were fabricated by repeatedly subjecting the top Si layer of SOI wafers to plasma oxidation and BOE etching. Ellipsometry and surface profile measurements were performed between each etching step. At the wavelength of 1700 nm, for which silicon is transparent and bulk ε is 11.7, we found thatε was reduced to 7.5 for a 2.5 nm thick Si slab. Our results represent the first systematic measurement of the dielectric function of Si nanostructures as a function of size and represent the first test of the theories.
Length dependences of in-plane polarizations anisotropy in GaInAsP/InP quantum-wire structures fabricated by dry etching and regrowth process
D. Plumwongrot, Y. Tamura, Y. Nishimoto, et al.
Wire-length dependences of In-place polarization anisotropy in GaInAsP/InP quantum-wire (Q-wire) structures fabricated by dry-etching and regrowth processes were investigated using a photo luminescence (PL) measurement. The reduction of polarization anisotropy of Q-wires is expected in the shorter Q-Wires. A strain-compensated GaInAsP/InP single-quantum-well initial wafer was prepared by an organometallic-vapor-phase-epitaxy (OMVPE) system. Using electron beam lithography, Ti-mask lift-off, CH4/H2 reactive-ion-etching and OMVPE regrowth processes, various lengths (L) of the Q-wires were realized for wire-widths (W) of 11-, 14- and 18 nm. The Q-wires were measured the polarization property in normal and parallel to wire-length direction at room temperature. As a result, stronger polarization anisotropy was observed in narrower Q-Wires and reduced in shorter length of Q-Wires. Furthermore, polarization anisotropy of strained Q-Wires was predicted by taking in account of the dipole moment interaction between conduction and heavy-hole subbands optical transition. A 5-nm narrowed wire-width calculation results shows a good agreement with experimental results. This could be considered that a strain distribution in the Q-Wire induced the energy band deformation at the edge of the Q-Wire, which reduced the effective wire-width to much narrower than the actual size observed by an SEM image.
PbTe quantum dots in tellurite glass microstructured optical fiber
PbTe doped tellurite glass photonic optical fiber for non linear application were developed using rod in tube method in a draw tower. We follow the growth kinetics of the quantum dots in the optical fiber by High Resolution Transmission Electron Microscopy giving some results related with the growth kinetic of the same in function of time so much for optical fiber as for the glass bulk. Absorption peak near 1500 nm as observed and it was attributed the optical resonance due PbTe quantum dots in the core fiber.
Metallic Nanostructures
icon_mobile_dropdown
Surface properties of silver and aluminum nanoclusters
Igor Vasiliev, Bharat Medasani
We apply first-principles computational methods to study the surface energy and surface stress of silver and aluminum nanoparticles. The structures, cohesive energies, and lattice contractions of Ag and Al nanoclusters are analyzed using an ab initio density functional pseudopotential technique combined with the generalized gradient approximation for the exchange-correlation functional. Our calculations predict the surface energy of Ag and Al nanoclusters to be in the range of 1.1-2.2 J/m2 and 0.9-2.0 J/m2, respectively. These values are consistent with the surface energies of bulk silver and aluminum. The surface stress is estimated from the average lattice contraction by considering the hydrostatic pressure on the surface of a spherical particle. A comparison of the calculated surface energies and stresses indicates a significantly greater degree of surface reconstruction in Al clusters than in Ag clusters.
Geometry-dependent plasmon resonances of metallic nanostructures for enhancement of localized electromagnetic fields around the nanostructures
This paper describes theoretical and experimental evaluations of electromagnetic fields around metallic nanostructures, such as nanorods, nano-pillars, and a collection of nanorods separated by nano-scale distances. Nanostructures having different sizes and shapes were evaluated. The spacing between nanorods and elliptical nanopillars was varied such that the effect of nanoparticle spacing on the electromagnetic fields in the regions between the nanostructures could be studied. Gold was the metal employed in our work as it demonstrates substantial plasmon excitation and is chemically stable. Calculations of the electromagnetic fields in the vicinity of the different metallic nanostructures were made by employing Finite Difference Time Domain (FDTD). Refractive index of the media surrounding the nanostructures was varied for these calculations. These calculations were carried out at different wavelengths in the visible and near-infrared spectral regimes. In order to fabricate these nanostructures on silica substrates, focused ion beam (FIB) milling was employed. These structures were fabricated on gold-coated planar silica and mica substrates and tips of four mode and multimode optical fibers. In our experimental evaluations of the different metallic nanostructures, surface enhanced Raman scattering (SERS) signals from the different metallic nanostructures were obtained and were correlated to the spacing distance between the different metallic nanostructures.
Dynamics of exchange interactions in a one dimensional magnetic quantum dot chain
R. Amuda, A. Brinda
Small magnetic structures have attracted a great deal of attraction owing to their special transport and magnetic properties. In a magnetic quantum dot array, the interdot exchange interaction leads to alignment of individual magnetization. In this paper, starting from the interaction energy between the neighboring dots, we set up an equation of motion for the magnetization. We use bosonic operators combined with the Holstein-Primakoff transformations in the semiclassical limits and arrive at Nonlinear Schrodinger equation. Localized solutions called solitons are identified for the collective excitations, which could be harnessed for data transfer.
Nanostructures for Photonic Applications I
icon_mobile_dropdown
Light-current curve of a tunneling-injection quantum dot laser
Dae-Seob Han, Levon V. Asryan
The potential for high-power operation of a laser exploiting tunneling-injection of electrons and holes into quantum dots (QDs) from two separate quantum wells (QWs) is studied. An extended theoretical model is developed to account for out-tunneling leakage of carriers from QDs. Even in the presence of out-tunneling from QDs, the parasitic recombination flux outside QDs is shown to remain restricted with increasing injection current; correspondingly, the LCC becomes more and more linear and the slope efficiency closer to unity at high injection currents. The linearity is due to the fact that the current paths connecting the opposite sides of the structure lie entirely within QDs - in view of the threedimensional confinement in QDs, the out-tunneling fluxes of carriers from dots are limited.
Modulation and thermal properties of tunnel-coupled InAs QD 1.13µm VCSELs
Quantum dot (QD) -based vertical cavity surface emitting lasers (VCSELs) are predicted to have faster modulation response and better thermal stability as compared with quantum well (QW) VCSELs. QD size distribution, limited carrier capture and thermalization rates affect the maximum saturated gain of QD-based lasers. To address these problems, structures of tunnel coupled pairs consisting of InGaAs QW grown on top of self-assembled InAs QDs (QWon- QDs) were employed as a gain medium for VCSELs. Photoluminescence and transmission electron microscopy were used to study the properties of the "well-on-dots" active medium. We have developed a triple-pair tunnel QW-on-QDs structure with a QD transition which is red-shifted ~ 32 meV relative to QW ground state (GS). This optimized energy separation ▵E = EQW - EQDs was found to be close to the energy of the LO phonon. All-epitaxial tunnel-coupled QD VCSELs demonstrated continuous wave (CW) mode lasing in a wide temperature range from T = - 20°C to above 150°C. The room temperature lasing wavelength λ = 1131 nm corresponds to the QD GS transition. A minimum threshold current value Ith = 0.7 mA was measured in a 9 μm oxide aperture VCSEL. The maximum power from a single device was 2.5 mW and maximum differential efficiency was 0.16 W/A. Small signal modulation responses of these VCSELs showed a maximum resonance frequency of about 9 GHz. The damping-limited cut-off frequency for these tunnel QW-on-QDs VCSELs was estimated at 34 GHz from the dependence of damping factor and resonance frequency on driving current.
Nanostructures for Photonic Applications II
icon_mobile_dropdown
Quantum key distribution using a semiconductor quantum dot source emitting at a telecommunication wavelength
P. M. Intallura, M. B. Ward, O. Z. Karimov, et al.
We present the first demonstration of telecom fiber-based quantum key distribution using single photons from a quantum dot in a pillar microcavity. The source offers both telecommunication wavelength operation at 1.3 microns and Purcell enhancement of the spontaneous emission rate. Several emission lines from the InAs/GaAs quantum dot are identified, including the exciton-biexciton cascade and charged excitonic emission. We show an order of magnitude increase in the collected intensity of the emission from a charged excitonic state when temperature tuned onto resonance with the HE11 mode of the pillar microcavity, as compared to the off-resonance intensity. Above- and below-GaAs-bandgap optical excitation was used and the effect of the excitation energy on the photoluminescence investigated. Exciting below the GaAs-bandgap offers significant improvement in the quality of the single photon emission and a reduction of the multi-photon probability to 0.1 times the value for Poissonian light was measured, before subtraction of detector dark counts, the lowest value recorded to date for a quantum dot source at a fibre wavelength. We observe also the first evidence of Purcell enhancement of the spontaneous emission rate for a single telecommunication wavelength quantum dot in a pillar microcavity. We have incorporated the source into a phase encoded interferometric scheme implementing the BB84 quantum cryptography protocol and distributed a key, secure from the pulse splitting attack, over standard telecommunication optical fibre. We show a transmission distance advantage over that possible with (length-optimized) uniform intensity weak coherent pulses at 1310 nm in the same system.