Proceedings Volume 7947

Quantum Dots and Nanostructures: Synthesis, Characterization, and Modeling VIII

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Proceedings Volume 7947

Quantum Dots and Nanostructures: Synthesis, Characterization, and Modeling VIII

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Volume Details

Date Published: 10 February 2011
Contents: 9 Sessions, 21 Papers, 0 Presentations
Conference: SPIE OPTO 2011
Volume Number: 7947

Table of Contents

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Table of Contents

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  • Front Matter: Volume 7947
  • Quantum Cavity Structures I
  • Quantum Cavity Structures II
  • Colloidal Quantum Dots
  • Quantum Wires
  • Quantum Dots I
  • Quantum Dots II
  • Novel Quantum Structures
  • Poster Session
Front Matter: Volume 7947
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Front Matter: Volume 7947
This PDF file contains the front matter associated with SPIE Proceedings Volume 7947, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.
Quantum Cavity Structures I
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Cavity quantum electrodynamics studies with site-controlled InGaAs quantum dots integrated into high quality microcavities
S. Reitzenstein, C. Schneider, F. Albert, et al.
Semiconductor quantum dots (QDs) are fascinating nanoscopic structures for photonics and future quantum information technology. However, the random position of self-organized QDs inhibits a deterministic coupling in devices relying on cavity quantum electrodynamics (cQED) effects which complicates, e.g., the large scale fabrication of quantum light sources. As a result, large efforts focus on the growth and the device integration of site-controlled QDs. We present the growth of low density arrays of site-controlled In(Ga)As QDs where shallow etched nanoholes act as nucleation sites. The nanoholes are located relative to cross markers which allows for a precise spatial alignment of the site-controlled QDs (SCQDs) and the photonic modes of high quality microcavites with an accuracy better than 50 nm. We also address the optical quality of the SCQDs in terms of the single SCQD emission mode linewidth, the oscillator strength and the quantum efficiency. A stacked growth of strain coupled SCQDs forming on wet chemically etched nanoholes provide the smallest linewidth with an average value of 210 μeV. Using time resolved photoluminescence studies on samples with a varying thickness of the capping layer we determine a quantum efficiency of the SCQD close to 50 % and an oscillator strength of about 10. Finally, single photon emission with associated with g(2)(0) = 0.12 of a weakly coupled SCQD - micropillar system will be presented.
Spectral tuning of site-selected single InAs/InP quantum dots via intermixing
K. Mnaymneh, D. Dalacu, P. J. Poole, et al.
In this paper, we present experimental results from site-selected single quantum dots that have undergone a number of intermixing process steps via rapid thermal annealing. We show that the intermixing process blueshifts the dot's emission spectrum without affecting the linewidth as well as decreasing its biexciton binding energy and s-p shell spacing. The anisotropic exchange splitting is shown to have undergone a sign inversion implying that the splitting had gone through zero. Intermixing provides another nanoengineering tool for the design of scalable solid-state photon and entangled photon pair sources.
Quantum Cavity Structures II
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Coherent coupling of the excitonic states in a single quantum dot
Anthony J. Bennett, Matthew A. Pooley, R. Mark Stevenson, et al.
A large vertical electric field can be used to linearly change the fine-structure splitting of a single InGaAs/GaAs quantum dot by over 100 μeV. In each single dot an avoided crossing is observed, where the magnitude of the splitting reaches a minimum value. We confirm in experiment that polarization-entangled photon pair emission occurs from quantum dots tuned in this manner.
Capture delay and modulation bandwidth in a quantum dot laser
Levon V. Asryan, Yuchang Wu, Robert A. Suris
We show that the carrier capture from the optical confinement layer into quantum dots (QDs) can strongly limit the modulation bandwidth ω-3 dB of a QD laser. Closed-form analytical expressions are obtained for ω-3 dB in the limiting cases of fast and slow capture. ω-3 dB is highest in the case of instantaneous capture into QDs, when the cross-section of carrier capture into a QD σn = ∞. With reducing σn, ω-3 dB decreases and becomes zero at a certain non-vanishing value σnmin. This σnmin presents the minimum tolerable capture cross-section for the lasing to occur at a given dc component j0 of the injection current density. The higher is j0, the smaller is σnmin and hence the direct modulation of the output power is possible at a slower capture. The use of multiple layers with QDs is shown to considerably improve the modulation response of the laser - the same ω-3 dB is obtained in a multi-layer structure at a much lower j0 than in a single-layer structure. At a plausible value of σn = 10-11 cm2, ω-3 dB as high as 19 GHz is attainable in a 5-QD-layer structure.
Colloidal Quantum Dots
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Single colloidal quantum dots as sources of single photons for quantum cryptography
Ferruccio Pisanello, Antonio Qualtieri, Godefroy Leménager, et al.
Colloidal nanocrystals, i.e. quantum dots synthesized trough wet-chemistry approaches, are promising nanoparticles for photonic applications and, remarkably, their quantum nature makes them very promising for single photon emission at room temperature. In this work we describe two approaches to engineer the emission properties of these nanoemitters in terms of radiative lifetime and photon polarization, drawing a viable strategy for their exploitation as room-temperature single photon sources for quantum information and quantum telecommunications.
Fabrication of the CdSeTe alloyed and CdSeTe/ZnS core-shell quantum dots
Guo-Xi Liang, Jun-Jie Zhu
The near-infrared (NIR)-emitting quantum dots (Qdots) have great potential for the use in biological imaging and diagnostic applications. In our work, a facile method was developed for the preparation of high quality, water-soluble, and NIR-emitting CdSeTe alloyed Qdots (A-Qdots) with L-cysteine (L-cys) as capping agent. By changing the size and the composition of the A-Qdots, the photoluminescent quantum yields (QYs) can reach as high as 53% and the emission color can be tuned between visible and NIR regions. Based on the fluorescence of the A-Qdots selectively quenched in the presence of Cu2+, the NIR-emitting CdSeTe A-Qdots were applied in ultrasensitive Cu2+ sensing. Furthermore, the prepared CdSeTe A-Qdots have been successfully applied for cell imaging, glucose and cholesterol assay, which demonstrates the great potential of the Qdots for biological applications. In order to improve the biocompatibility of the CdSeTe A-Qdots, new water-soluble CdSeTe/ZnS core-shell Qdots (CS-Qdots) with excellent NIR emission were synthesized in aqueous solution. The prepared CS-Qdots not only possessed high QYs but also exhibited excellent photobstability and favorable biocompatibility. Moreover, the CS-Qdots showed high electrogenerated chemiluminescence (ECL) signal. These characteristics showed their potential applications in cell imaging and biosensing with high sensitivity.
Probing oxygen consumption in epileptic brain slices with QDs-based FRET sensors
Chunfeng Zhang, Justin Ingram, Steven Schiff M.D., et al.
We developed ratiometric optical oxygen sensors to probe the oxygen consumption during epileptic events in rat brain slices. The oxygen sensors consist of the sensing part of phosphorescence dyes (Platinum (II) octaethylporphine ketone) and reference part of nanocystal quantum dots (NQDs) embedded in polymer blends, with pre-designed excitation through fluorescence resonance energy transfer (FRET) from NQDs to the oxygen sensitive dyes (OSDs). The ratiometric FRET sensors with fast temporal response and excellent bio-compatibility are suitable for real time quantitative dissolved oxygen (D.O.) probes in biological microenvironment. Coating the sensors onto the micro-pipettes, we performed simultaneous oxygen probes at pyramidal and oriens layers in rat hippocampal CA1. Different spatiotemporal patterns with maximum D.O. decreases of 9.9±1.1 mg/L and 4.9±0.7 mg/L during seizure events were observed in pyramidal and oriens layers, respectively.
Photothermal lens spectrometry of metallic nanoparticles colloids
We report on pump-probe mode-mismatched photothermal lens experiments of metallic nanoparticles water solutions. We show that metallic nanoparticles colloids exhibit nonlinear absorption effects related to attraction or repulsion forces that result from the interaction with the electromagnetic radiation. Gold and iron oxide nanoparticles show a double peak Z-scan shape that is associated to the presence of attraction forces. We calibrate the experiment using the linear absorption values of the samples obtaining their corresponding nonlinear absorption coefficients.
Quantum Wires
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Controlled formation of well-aligned GaAs nanowires with high aspect ratio on transparent substrates
In this study, we present a facile route to fabricate large-scale arrays of GaAs nanowires (NWs) with high aspect ratio on transparent substrates. It is demonstrated that the monolayer of SiO2 nanoparticles can be effectively used as etch masks for the inductively coupled plasma (ICP) etching process. To form the monolayer of SiO2 nanoparticles on the GaAs substrate, the concentration and temperature of the SiO2 colloidal dispersion solution as well as the interface wetting of the GaAs substrate are investigated. By adjusting the ICP etching conditions, the high-aspect-ratio GaAs NWs with lengths of 4.3μm and cross-sections of 70nm are successfully fabricated. Furthermore, the fabricated GaAs NWs are massively transferred onto the transparent substrate at low temperature. The SEM observation and the X-ray diffraction spectrum reveal that the transferred GaAs NWs have vertically aligned morphology and good crystal property.
Exciton states of quantum tetrapods
Kazuaki Sakoda, Yuanzhao Yao
Excitons of CdTe quantum tetrapods are theoretically analyzed. Individual electron and hole states are calculated by solving one-particle Schrödinger equation by the finite element method with the single-band effective-mass approximation and exciton states are obtained by exact diagonalization of the configuration interaction Hamiltonian. Spatial symmetries of the exciton states are related to those of the one-particle states by group theory and verified by numerical calculation. Then optical transition spectra are calculated and compared with available experimental data.
Positioned growth of InP nanowires
P. J. Poole, D. Dalacu, J. Lapointe, et al.
We describe two different approaches to growing precisely positioned InP nanowires on InP wafers. Both of these approaches utilize the selective area growth capabilities of Chemical Beam Epitaxy, one using the Au catalysed Vapour-Liquid-Solid (VLS) growth mode, the other being catalyst-free. Growth is performed on InP wafers which are first coated with 20 nm of SiO2. These are then patterned using e-beam lithography to create nanometer scale holes in the SiO2 layer to expose the InP surface. For the VLS growth Au is then deposited into the holes in the SiO2 mask layer using a self-aligned lift-off process. For the catalyst-free growth no Au is deposited. In both cases the deposition of InP results in the formation of InP nanowires. In VLS growth the nanowire diameter is controlled by the size of the Au particle, whereas when catalyst-free the diameter is that of the opening in the SiO2 mask. The orientation of the nanowires is also different, <111>B when using Au particles and <111>A when catalyst-free. For the catalysed growth the effect of the Au particle can be turned off by modifying growth conditions allowing the nanowire to be clad, dramatically enhancing the optical emission from InAs quantum dots grown inside the nanowire.
Quantum Dots I
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Antimony-based quantum dot memories
Dieter Bimberg, Andreas Marent, Tobias Nowozin, et al.
As a type-II heterostructure with exclusive hole confinement GaSb/(Al,Ga)As QDs are an ideal candidate for a QD based memory device operating at room temperature. We investigated different Antimony-based QDs in respect of localization energies and storage times with 8-band-k•p calculations as well as time-resolved capacitance spectroscopy. In addition, we present a memory concept based on self-organized quantum dots (QDs) which could fuse the advantages of today's main semiconductor memories DRAM and Flash. First results on the performance of such a memory cell are shown and a closer look at Sb-based QDs as a storage unit is taken.
GaSb/GaAs quantum dots with type-II band alignments prepared by molecular beam epitaxy for device applications
Shih-Yen Lin, Wei-Hsun Lin, Chi-Che Tseng, et al.
The growth procedures and device applications of GaSb/GaAs quantum dots (QDs) are investigated in this report. The influence of As flux on the GaSb QD morphologies and optical characteristics has revealed the importance of precise Sb/As flux control during Sb post-soaking procedures after GaSb deposition. With optimized GaSb QD growth conditions and long-term Sb post soaking procedure, room-temperature operation light-emitting diodes (LEDs) and high-temperature operation quantum-dot infrared photodetectors (QDIPs) are demonstrated. The results have revealed the possibilities of type-II GaSb QDs in the applications of optical devices.
Dense lying GaSb quantum dots on GaAs by Stranski-Krastanov growth
Thomas Henning Loeber, Dirk Hoffmann, Henning Fouckhardt
GaSb quantum dots (QDs) have been grown epitaxially on GaAs in the Stranski-Krastanov (SK) mode. By variation of the Sb/Ga-V/III flux ratio, the growth temperature, and the nominal coverage the QD dimensions and optoelectronic characteristics can be tuned. These modifications enable dense lying dots with a density up to 9.8 x 1010 cm-2. The position of the photoluminescence (PL) peak can be varied between 0.850 and 1.378 μm by precise control of growth parameters. To raise the PL intensity and QD laser output power samples with a stack of GaSb QD layers are grown on GaAs wafer. A GaSb-QD-laser with a 8-fold stack and an emission wavelength around 0.900 μm is realized with a differential quantum efficiency of 54%.
Quantum Dots II
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Real-time metrology of self assembled quantum dots by reflection high energy electron diffraction
Alexandre Freundlich, Chandani Rajapaksha
Based on atomistic analysis and kinematic diffraction theory, it has been previously predicted that quantum dot heights can be extracted from RHEED intensity profiles along the chevron tails (Feltrin A. and Freundlich A, J. Cryst. Growth 301-302, 38-41-2007). Here we report the existence of such periodic RHEED intensity fringes and demonstrate experimentally the possibility of monitoring real time the evolution of the average dot-size in the archetype InAs/GaAs system. The methodology when combined with RHEED information on the dot surface coverage and facet orientation is shown to provide a full metrology of self assembled quantum dots and could be valuable in assessing the QD growth kinetics and improving process reproducibility.
Fully coupled piezoelectric models on the optical properties of InGaN quantum dots
K. B. Hong, M. K. Kuo
This paper investigates the fully coupled piezoelectric models for determining strain fields, piezoelectric potentials, and optical properties of wurtzite InGaN quantum dots (QDs). Through the calculations, we find that the semi-coupled model clearly overestimates the piezoelectric potential, and the transition energy difference increased with increases in the dot size and indium composition. Consequently, the semi-coupled model causes a great amount of distortion in predicting the optical properties of InGaN QDs, compared to the fully coupled piezoelectric models.
Novel Quantum Structures
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Size, strain and band offset engineering in GaAs(Sb)(N)-capped InAs quantum dots for 1.3 - 1.55 μm emitters
J. M. Ulloa, M. del Moral, M. Montes, et al.
The optical and structural properties of InAs/GaAs quantum dots (QD) are strongly modified through the use of a thin (~ 5 nm) GaAsSb(N) capping layer. In the case of GaAsSb-capped QDs, cross-sectional scanning tunnelling microscopy measurements show that the QD height can be controllably tuned through the Sb content up to ~ 14 % Sb. The increased QD height (together with the reduced strain) gives rise to a strong red shift and a large enhancement of the photoluminescence (PL) characteristics. This is due to improved carrier confinement and reduced sensitivity of the excitonic bandgap to QD size fluctuations within the ensemble. Moreover, the PL degradation with temperature is strongly reduced in the presence of Sb. Despite this, emission in the 1.5 μm region with these structures is only achieved for high Sb contents and a type-II band alignment that degrades the PL. Adding small amounts of N to the GaAsSb capping layer allows to progressively reduce the QD-barrier conduction band offset. This different strategy to red shift the PL allows reaching 1.5 μm with moderate Sb contents, keeping therefore a type-I alignment. Nevertheless, the PL emission is progressively degraded when the N content in the capping layer is increased.
Poster Session
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Surface enhanced Raman radiation of crystal violet dye with a SiO2 buffer
Tung-Kai Liu, Wen-Chi Hung, Ming-Shan Tsai, et al.
Surface enhanced Raman radiation of crystal violet dye has been studied by modulating the localized surface plasmon effect of silver nanoparticles. In the experiment, a buffer layer of silicon dioxide (SiO2) was established between crystal violet dye and silver nanoparticles. With a probe of laser beam of 532 nm in wavelength, it was found that the intensity of the Raman scattering significantly depended on the thickness of SiO2 layer. A maximum Raman-radiation intensity occurred with a 10nm-thicked SiO2 layer. The experimental observation shows a possible modulation of surface enhanced Raman radiation by a proper dielectric buffer.
Synthesis of well-aligned and highly density nanopore arrays with the assistance of ultrasonic
Highly ordered and highly density nanopore arrays of anodic aluminum oxide template was prepared by a two-step anodization method and with the assistance of ultrasonic. Well-aligned nanopore arrays were obtained perpendicular to the surface of aluminum. The first step anodization was carried out under 0.4 M oxalic acid for one hour, and the anodized film was removed by chemical etching, than the sample was anodized again for 40 minute under the same conditions as the first anodization and with ultrasonic. The results of aluminum oxide films were characterized by scanning electron microscopy, and the microstructure of the anodic aluminum oxide membrane indicating that the nanochannel arrays prepared with the assistance of ultrasonic are better than those in ordinary way related to the pore aligned and pore density.
Synthesis and oxidation of silver nanoparticles
Hua Qi, D. A. Alexson, O. J. Glembocki, et al.
We demonstrated a fast and easy way to synthesize Ag nanoparticles (NPs) on ZnO nanowires (NWs) and silicon substrates by an electroless (EL) plating approach. ZnO NWs used here were grown via vapor-solid (VS) mechanism at 560 °C for 30 min. The stability to oxidation of these EL-produced homogeneous Ag NPs on ZnO nanowires was investigated by surface enhanced Raman spectroscopy (SERS), showing that the attachment of thiol to the Ag surface can slow down the oxidation process, and the SERS signal remains strong for more than ten days. Furthermore, we examined the surface oxidation kinetics of the Ag NPs as a function of NPs size and size distribution by monitoring the oxygen amount in the composites using energy dispersive x-ray (EDX). Results indicate that the EL plated Ag NPs show faster oxidation rates than those produced by e-beam (EB) evaporation in air. We attribute this to the fact that the EL produced silver particles are very small, in the 20 nm range, and thus have high surface energy, thus enhancing the oxidation. These studies provide extensive information related to the Ag NP oxidation rates, which can help in extending the Ag lifetime for various applications.