QUANTUM DOTS: OPTICS, ELECTRON TRANSPORT AND FUTURE APPLICATIONS

Transcription

1 QUANTUM DOTS: OPTICS, ELECTRON TRANSPORT AND FUTURE APPLICATIONS A comprehensive review of cutting-edge solid state research, focusing on its prominent example quantum dot nanostructures this book features a broad range of techniques for fabrication of these nano-structured semiconductors and control of their quantum properties. Written by leading researchers, the book considers advanced III V and II VI semiconductor quantum dots (QDs) realized by self-assembly, lithography and chemical synthesis; novel QD structures in nanowires and graphene; and transport and optical methods for control of single QDs. Significant attention is given to manipulation of single spins and control of their magnetic environment, generation of quantum light emitted by single dots in dielectric cavities, and dots coupled to plasmons in metallic structures. It is a valuable resource for graduate students and researchers new to this field. A LEXANDER TARTAKOVSKIIis a Reader in Experimental Semiconductor Physics in the Department of Physics and Astronomy, University of Sheffield. He has been working in quantum dot research since 2001, recently with a focus on high-sensitivity nano-nmr in ultra-small nuclear spin ensembles in individual quantum dots.

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3 QUANTUM DOTS: OPTICS, ELECTRON TRANSPORT AND FUTURE APPLICATIONS Edited by ALEXANDER TARTAKOVSKII University of Sheffield

4 CAMBRIDGE UNIVERSITY PRESS Cambridge, New York, Melbourne, Madrid, Cape Town, Singapore, São Paulo, Delhi, Mexico City Cambridge University Press The Edinburgh Building, Cambridge CB2 8RU, UK Published in the United States of America by Cambridge University Press, New York Information on this title: / c Cambridge University Press 2012 This publication is in copyright. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published 2012 Printed in the United Kingdom at the University Press, Cambridge A catalogue record for this publication is available from the British Library ISBN Hardback Cambridge University Press has no responsibility for the persistence or accuracy of URLs for external or third-party internet websites referred to in this publication, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate.

5 Contents List of contributors Preface page xi xv Part I Nanostructure design and structural properties of epitaxially grown quantum dots and nanowires 1 1 Growth of III V semiconductor quantum dots C. Schneider, S. Höfling and A. Forchel Introduction Properties of semiconductor quantum dots Epitaxial growth of quantum dots on GaAs substrates Quantum dot growth on InP substrates Conclusion 17 References 18 2 Single semiconductor quantum dots in nanowires: growth, optics, and devices M. E. Reimer, N. Akopian, M. Barkelid, G. Bulgarini, R. Heeres, M. Hocevar, B. J. Witek, E. P. A. M. Bakkers and V. Zwiller Introduction Nanowire quantum dot growth Optical properties of nanowire quantum dots Nanowire quantum dot devices 30 References 37 3 Atomic-scale analysis of self-assembled quantum dots by cross-sectional scanning, tunneling microscopy, and atom probe tomography J. G. Keizer and P. M. Koenraad Introduction Specimen preparation 41 v

6 vi Contents 3.3 Quantum dot analysis by X-STM Application to control of quantum dot formation Outlook: atom probe tomography Conclusion 58 References 58 Part II Manipulation of individual quantum states in quantum dots using optical techniques 61 4 Studies of the hole spin in self-assembled quantum dots using optical techniques B. D. Gerardot and R. J. Warburton Self-assembled quantum dots as host for spin qubits Motivating factors for hole spins Spectroscopy of few-level systems Hole spin sample design Spin initialization, manipulation, and read-out Strength of the hole hyperfine interaction Summary and outlook 80 Acknowledgements 80 References 81 5 Resonance fluorescence from a single quantum dot A. N. Vamivakas, C. Matthiesen, Y. Zhao, C.-Y. Lu and M. Atatüre Introduction Resonance fluorescence from a two-level system Observation of resonance fluorescence Conclusion 100 References Coherent control of quantum dot excitons using ultra-fast optical techniques: the role of acoustic phonons A. J. Ramsay and A. M. Fox Introduction Experimental methods Candidate mechanisms for the intensity damping Temperature-dependent measurements of Rabi rotations Model of LA-phonon induced dephasing Comparison of experiment to model Outlook 115 Acknowledgements 115 References 115

7 Contents vii 7 Holes in quantum dot molecules: structure, symmetry, and spin M. F. Doty and J. I. Climente Introduction Growth and spectroscopic characterization of QDMs Anticrossings and the formation of molecular states Spin projections and Zeeman splitting Antibonding molecular ground states Hole-spin mixing Summary 132 References 132 Part III Optical properties of quantum dots in photonic cavities and plasmon-coupled dots Deterministic light matter coupling with single quantum dots P. Senellart QDs in cavities: basics, motivation, first demonstrations Determininistic coupling of a QD to a cavity An ultrabright source of entangled photon pairs Some perspectives 149 References Quantum dots in photonic crystal cavities A. Faraon, D. Englund, I. Fushman, A. Majumdar and J. Vučković Introduction Quantum dots and photonic crystals Experimental techniques Probing the strong-coupling regime Nonlinear optics at the single photon level Applications and future directions 165 References Photon statistics in quantum dot micropillar emission M. Aßmann and M. Bayer Introduction Theoretical background Experimental approaches Experimental results Summary and outlook 182 References Nanoplasmonics with colloidal quantum dots V. V. Temnov and U. Woggon Introduction 185

8 viii Contents 11.2 Optical and electronic properties of colloidal semiconductor quantum dots Surface plasmons in low-dimensional metallic nanostructures Coupling of quantum dots to metal surfaces Practical application: QD-based all-optical plasmonic modulator Perspective: quantum optics with surface plasmons 197 References 197 Part IV Quantum dot nano-laboratory: magnetic ions and nuclear spins in a dot Dynamics and optical control of an individual Mn spin in a quantum dot L. Besombes, C. Le Gall, H. Boukari and H. Mariette Introduction II VI diluted magnetic semiconductor QDs Optical Mn spin orientation Resonant optical pumping of a single Mn spin Conclusion 218 References Optical spectroscopy of InAs/GaAs quantum dots doped with a single Mn atom O. Krebs and A. Lemaître Introduction The Mn acceptor impurity A Micro-photoluminescence setup in magnetic field Zero-field signature of Mn doping Energy levels for trions in zero field Photoluminescence in a longitudinal magnetic field Excitons versus trions Coupling to dark states due to anisotropic exchange Theoretical simulation of PL spectra Conclusion 234 References Nuclear spin effects in quantum dot optics B. Urbaszek, B. Eble, T. Amand and X. Marie Introduction Carrier spin decoherence Dynamic nuclear polarization Perspectives 250 References 251

9 Contents ix Part V Electron transport in quantum dots fabricated by lithographic techniques from III V semiconductors and graphene Electrically controlling single spin coherence in semiconductor nanostructures Y. Dovzhenko, K. Wang, M. D. Schroer and J. R. Petta Introduction Sample fabrication Measurement technology Quantum control Outlook 272 Acknowledgements 273 References Theory of electron and nuclear spins in III V semiconductor and carbon-based dots H. Ribeiro and G. Burkard The magnetic hyperfine Hamiltonian Nuclear nuclear interactions Hyperfine interaction in semiconductor-based quantum dots Hyperfine interaction in carbon-based quantum dots 290 References Graphene quantum dots: transport experiments and local imaging S. Schnez, J. Guettinger, F. Molitor, C. Stampfer, M. Huefner, T. Ihn and K. Ensslin Introduction Theoretical background Transport experiments Scanning-gate microscopy Summary and outlook 312 References 313 Part VI Single dots for future telecommunications applications Electrically operated entangled light sources based on quantum dots R. M. Stevenson, A. J. Bennett and A. J. Shields Introduction Electrically driven entangled light generation Electrical control of entangled light Interaction of entangled exciton photon states with nuclei Conclusion 337 References 337

10 x Contents 19 Deterministic single quantum dot cavities at telecommunication wavelengths D. Dalacu, K. Mnaymneh, J. Lapointe, G. C. Aers, P. J. Poole, R. L. Williams and S. Hughes Introduction Directed self-assembly Spectroscopy of site-controlled single quantum dots Integration of site-controlled quantum dots and cavities Conclusion 352 References 353 Index 356

11 Contributors M. Aßmann Experimentelle Physik 2, Technische Universität Dortmund, D Dortmund, Germany G. C. Aers Institute for Microstructural Sciences, National Research Council, Ottawa, Canada, K1A 0R6 N. Akopian Kavli Institute of Nanoscience, Delft University of Technology, 2628CJ Delft, The Netherlands T. Amand Université de Toulouse, INSA-CNRS-UPS, LPCNO, 135 Avenue de Rangueil, Toulouse, France M. Atatüre University of Cambridge, Cavendish Laboratory, J. J. Thomson Avenue, Cambridge CB3 0HE, UK E. P. A. M. Bakkers Kavli Institute of Nanoscience, Delft University of Technology, 2628CJ Delft, The Netherlands M. Barkelid Kavli Institute of Nanoscience, Delft University of Technology, 2628CJ Delft, The Netherlands M. Bayer Experimentelle Physik 2, Technische Universität Dortmund, D Dortmund, Germany A. J. Bennett Toshiba Research Europe Limited, 208 Cambridge Science Park, Cambridge CB4 0GZ, UK L. Besombes Institut Néel, CNRS & Université Joseph Fourier, 25 rue des Martyrs, Grenoble, France H. Boukari Institut Néel, CNRS & Université Joseph Fourier, 25 rue des Martyrs, Grenoble, France G. Bulgarini Kavli Institute of Nanoscience, Delft University of Technology, 2628CJ Delft, The Netherlands G. Burkard Department of Physics, University of Konstanz, D Konstanz, Germany J. I. Climente Department de Química Física i Analítica, Universitat Jaume I, E Castelló, Spain D. Dalacu Institute for Microstructural Sciences, National Research Council, Ottawa, Canada, K1A 0R6 xi

12 xii List of contributors M. F. Doty Department of Materials Science and Engineering, University of Delaware, Newark, Delaware 19716, USA Y. Dovzhenko Department of Physics, Princeton University, Princeton, New Jersey 08544, USA B. Eble Institut des NanoSciences de Paris, CNRS-UMR 7588, UPMC Univ. Paris 06, 140 Rue de Lourmel, Paris, France D. Englund Department of Electrical Engineering and Department of Applied Physics, Columbia University, New York, NY 10027, USA K. Ensslin Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland A. Faraon Hewlett Packard Laboratories, 1501 Page Mill Road, Palo Alto, CA 94304, USA A. Forchel Technische Physik, Physikalisches Institut and Wilhelm Conrad Röntgen Research Center for Complex Material Systems, Universität Würzburg, Am Hubland, D Würzburg, Germany A. M. Fox Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, UK I. Fushman Koshla Ventures, 3000 Sand Hill Road, Building 3, Suite 190, Menlo Park, CA 94025, USA B. D. Gerardot Heriot-Watt University, Edinburgh EH14 4AS, UK J. Guettinger Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland R. Heeres Kavli Institute of Nanoscience, Delft University of Technology, 2628CJ Delft, The Netherlands M. Hocevar Kavli Institute of Nanoscience, Delft University of Technology, 2628CJ Delft, The Netherlands M. Huefner Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland S. Hughes Department of Physics, Queen s University, Kingston, Canada, K7L 3N6 S. Höfling Technische Physik, Physikalisches Institut and Wilhelm Conrad Röntgen Research Center for Complex Material Systems, Universität Würzburg, Am Hubland, D Würzburg, Germany T. Ihn Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland J. G. Keizer COBRA Inter-University Research Institute, Eindhoven University of Technology, P.O. Box 513, NL-5600MB Eindhoven, The Netherlands P. M. Koenraad COBRA Inter-University Research Institute, Eindhoven University of Technology, P.O. Box 513, NL-5600MB Eindhoven, The Netherlands O. Krebs CNRS-Laboratoire de Photonique et de Nanostructures, Route de Nozay, Marcoussis, France J. Lapointe Institute for Microstructural Sciences, National Research Council, Ottawa, Canada, K1A 0R6 C. Le Gall Institut Néel, CNRS & Université Joseph Fourier, 25 rue des Martyrs, Grenoble, France A. Lemaître CNRS-Laboratoire de Photonique et de Nanostructures, Route de Nozay, Marcoussis, France

13 List of contributors xiii C.-Y. Lu University of Cambridge, Cavendish Laboratory, J. J. Thomson Avenue, Cambridge CB3 0HE, UK A. Majumdar Department of Electrical Engineering, Stanford University, Stanford, CA 94305, USA X. Marie Université de Toulouse, INSA-CNRS-UPS, LPCNO, 135 Avenue de Rangueil, Toulouse, France H. Mariette Institut Néel, CNRS & Université Joseph Fourier, 25 rue des Martyrs, Grenoble, France C. Matthiesen University of Cambridge, Cavendish Laboratory, J. J. Thomson Avenue, Cambridge CB3 0HE, UK K. Mnaymneh Institute for Microstructural Sciences, National Research Council, Ottawa, Canada, K1A 0R6 F. Molitor Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland J. R. Petta Department of Physics, Princeton University, Princeton, New Jersey 08544, USA P. J. Poole Institute for Microstructural Sciences, National Research Council, Ottawa, Canada, K1A 0R6 A. J. Ramsay Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, UK M. E. Reimer Kavli Institute of Nanoscience, Delft University of Technology, 2628CJ Delft, The Netherlands H. Ribeiro Department of Physics, University of Konstanz, D Konstanz, Germany C. Schneider Technische Physik, Physikalisches Institut and Wilhelm Conrad Röntgen Research Center for Complex Material Systems, Universität Würzburg, Am Hubland, D Würzburg, Germany S. Schnez Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland M. D. Schroer Department of Physics, Princeton University, Princeton, New Jersey 08544, USA P. Senellart Laboratoire de Photonique et de Nanostructures, CNRS, Route de Nozay, 91460, Marcoussis, France A. J. Shields Toshiba Research Europe Limited, 208 Cambridge Science Park, Cambridge CB4 0GZ, UK C. Stampfer Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland R. M. Stevenson Toshiba Research Europe Limited, 208 Cambridge Science Park, Cambridge CB4 0GZ, UK A. Tartakovskii Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, United Kingdom V. V. Temnov Institut des Molécules et Matériaux du Mans, UMR CNRS 6283, Université du Maine, 72085, Le Mans cedex, France B. Urbaszek Université de Toulouse, INSA-CNRS-UPS, LPCNO, 135 Avenue de Rangueil, Toulouse, France

14 xiv List of contributors A. N. Vamivakas University of Cambridge, Cavendish Laboratory, J. J. Thomson Avenue, Cambridge CB3 0HE, UK J. Vučković Department of Electrical Engineering, Stanford University, Stanford, CA 94305, USA K. Wang Department of Physics, Princeton University, Princeton, New Jersey 08544, USA R. J. Warburton Department of Physics, University of Basel, CH4056 Basel, Switzerland R. L. Williams Institute for Microstructural Sciences, National Research Council, Ottawa, Canada, K1A 0R6 B. J. Witek Kavli Institute of Nanoscience, Delft University of Technology, 2628CJ Delft, The Netherlands U. Woggon Technische Universität Berlin, Straße des 17. Juni 135, Berlin, Germany Y. Zhao University of Cambridge, Cavendish Laboratory, J. J. Thomson Avenue, Cambridge CB3 0HE, UK V. Zwiller Kavli Institute of Nanoscience, Delft University of Technology, 2628CJ Delft, The Netherlands

15 Preface Semiconductor quantum dots (QDs) have been extensively researched in the past 20 years or so. Over this period, the field has been stimulated by various motivating factors from fabrication of low-threshold temperature-insensitive QD lasers to the use of single spins for quantum computing and single dots for medical markers. In the past decade, refinement of fabrication and experimental techniques enabled researchers in the field to routinely use single QDs to access and control single electrons and holes and their spins, and to generate non-classical light. The focus of this book is on control of optical and transport properties of single and few QDs. The remarkable progress in this fast-developing field in the past three to five years is reported. The term quantum dot, widely used from late 1980s, usually refers to a semiconductor nano-structure. Typical sizes of a quantum dot range from a few nanometers in colloidal dots (also referred to as nano-crystals) to a few hundred nanometers in lithographically fabricated electrostatic structures, so that on average they contain from 10 3 to 10 6 atoms. The small physical size is the main common characteristic feature of quantum dots made from different materials and using various fabrication methods. It is usually combined with additional methods for electron energy engineering, for example, surrounding the dot with a higher band-gap semiconductor, applying gate-voltage creating a higher potential barrier around the dot, etc. This gives rise to the most important basic property of QDs: the motion of electrons and holes in QDs is suppressed in all three dimensions. This property gave quantum dots the name of zero-dimensional ( 0D ) structures. A result of the full confinement is the complete quantization or discretization of the energy spectrum of a confined charge carrier. This is in great contrast to higher-dimensionality structures such as quantum wells (QW), where the spectrum is continuous for the particle motion in the plane of the QW, and quantum wires where quantization is present only in two directions, and the third, along the wire, is described by an energy continuum. The quantized energy spectrum and complete localization also resembles the behavior of electrons in atoms, which gave quantum dots the title of artificial atoms. This description emphasizes the increased isolation of confined electrons and holes from the environment outside the dot, one of the most attractive properties widely exploited in applications ranging from quantum dot lasers for telecommunications to QD-based spin-qubits for quantum computing. xv

16 xvi Preface According to the Web of Science, studies of quantum dots have resulted in around publications since 1987, with increasing number of publications each year exceeding 2500 per year since Quantum dot research embraces variety of topics in physics, electrical and electronic engineering, chemistry, material science, biology and medicine, where, according to the demands of a specific application, different types of QD structures are employed. The work of the most prolific authors addresses topics such as QD design and growth, devices based on epitaxial self-assembled dots (lasers, photonic cavities, etc.), colloidal dots as fluorescent markers for biological and medical applications, optics of single epitaxial dots, spin qubits in optically active and gate-defined dots, single electron transport, optics of colloidal dots etc. This book will present the latest advances in QD research in the past three to five years, embracing some of these most active areas including fabrication, optical properties and electron transport. The material presented in this book is divided in to six parts describing: (1) nanostructure design and structural properties of epitaxially grown quantum dots and nanowires; (2) manipulation of individual quantum states in quantum dots using optical techniques; (3) optical properties of quantum dots in photonic cavities and plasmon-coupled dots; (4) magnetic ions and nuclear spins in a dot; (5) electron transport in quantum dots fabricated by lithographic techniques in III V semiconductors and graphene; (6) single dots for future telecommunications applications. Below I will briefly review each of these parts. (1) Nanostructure design and structural properties of epitaxially grown quantum dots and nanowires. The three chapters here will review epitaxial growth of III V quantum dots (Chapter 1), a relatively novel addition to the field QDs embedded in semiconductor nanowires enabling new flexibility with the material and substrate choice (Chapter 2), and finally ultra-sensitive techniques for structural characterization, delivering information on QD dimensions and material distribution inside nano-structures (Chapter 3). (2) Manipulation of individual quantum states in quantum dots using optical techniques. This part deals with advanced optical methods used for control and characterization of holes and electrons and importantly their spins in QDs. Chapter 4 presents applications of differential transmission for spectroscopy of spin- system, with a focus on manipulation of the hole spin a candidate for a decoherence free spin qubit, a basic building block for quantum computing. Chapter 5 focuses on resonance fluorescence describing the first application of this techniques to the atomic-like two-level system available in single QDs. Chapter 6 describes coherent control of excitons using ultra-fast optical pulses and photo-current detection in single QDs. This chapter focuses on fidelity of coherent operations and reasons leading to damping of exciton Rabi oscillations. Chapter 7 expands the description of hole properties in QDs presented in Chapter 4 to coupled QD structures, and reports on optical properties of these complex systems measured in photoluminescence of single QD molecules.

17 Preface xvii (3) Optical properties of quantum dots in photonic cavities and plasmon-coupled dots. Work presented in this part describes how optical properties of QDs are modified when they are inserted in optical cavities or interact with plasmons when positioned in proximity of a metal surface. Chapter 8 reports on efforts for deterministic light matter coupling using single quantum dots positioned in micropillar cavities fabricated using novel in-situ low-temperature lithography methods. Chapter 9 presents optical investigations carried out on another type of cavities comprising QDs: missing-hole defects in thin membrane photonic crystals made of GaAs. Chapter 10 discusses photon statistics in QD microlasers emission based on a GaAs micropillar design. Chapter 11 addresses a different type of QDs, the only example of colloidal dots, or nano-crystals, in this book. Taking advantage of their free surface, nano-crystals coupled to plasmon excitations in metallic nano-structures can easily be realized. Optical studies of such hybrid structures are presented in this chapter. (4) Quantum dot nano-laboratory: magnetic ions and nuclear spins in a dot. This chapter addresses spin effects related to behavior of nuclei in atoms constituting quantum dots, and spin effects related to transition-metal impurities located inside the dot. These phenomena effectively occur on the length-scales smaller than the physical dimensions of the dot. A QD acts as an enclosure, or a laboratory, where these nano-scale processes can be probed via the important changes they produce in the properties of the electrons and holes confined in QDs. Chapter 12 considers selfassembled CdTe/ZnTe QDs containing single Mn atoms. Optical manipulation of the spin of a single magnetic atom (Mn) in the solid-state environment is demonstrated. This chapter also provides a brief overview of II VI QDs fabrication. Chapter 13 considers a challenging goal of doping III V InGaAs dots with single Mn impurities, and reports on magneto-optics of such dots. Chapter 14 reports on optical manifestation of a variety of spin effects in QDs associated with nuclear spin polarization. (5) Electron transport in quantum dots fabricated by lithographic techniques from III V semiconductors and graphene. This section of the book touches on a very large field of electron transport in quantum dots fabricated using lithography. GaAs-based structures are considered in Chapter 15, where experiments are reported on electronspin control in laterally coupled double dots, work inspired by the Loss DiVincenzo proposal for spin-based quantum computing. The theory of quantum control of the singlet triplet qubit is outlined in Chapter 16, focusing specifically on the electron nuclear spin interaction in III V QDs and carbon-based structures. Chapter 17 reports on transport studies of single layer graphene nano-structures including spectroscopy in magnetic field and scanning-gate microscopy with high spatial resolution. (6) Single dots for future telecommunications applications. This part reports on work where single quantum dots are researched for possible future applications in secure optical communications and linear optics quantum computing. Chapter 18 addresses generation of entangled photon pairs using InGaAs/GaAs quantum dots: the first electrically driven entangled light source, and the first photon pair source where the entanglement of the emitted photons can be activated or deactivated

18 xviii Preface electrically is considered. Chapter 19 discusses a site-control technique for fabrication of self-assembled InAs/InP quantum dots emitting at telecommunication wavelengths enabling deterministic coupling of single dots to high finesse microcavities. Such devices will form the basis of efficient sources of single photons and entangled photon pairs for telecommunications applications. Alexander Tartakovskii