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    ULTRAFAST OPTICAL SPECTROSCOPIC STUDY OF SEMICONDUCTORS IN HIGH MAGNETIC FIELDS

    By

    XIAOMING WANG

    A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT

    OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

    UNIVERSITY OF FLORIDA

    2008

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    2008 Xiaoming Wang

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    To my wife and my daughter

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    ACKNOWLEDGMENTS

    First of all, I would like to express my deep gratitude to my advisor, Professor David

    Reitze, for his supervision, instruction, encouragement, tremendous support and friendship

    during my Ph.D. He guided me into a beautiful world of ultrafast optics. His profound

    knowledge of ultrafast optics, condensed matter physics and his teaching style always impress

    me and will help me all through my life.

    I wish to thank my supervisory committee, Prof. Stanton, Prof. Tanner, Prof. Rinzler and

    Prof. Kleiman, for their instructions for my thesis and finding errors in my thesis manuscript.

    I would like to give my sincere thanks to the visible optics staff scientists at the National

    High Magnetic Field Laboratory, Dr. Xing Wei and Dr. Stephen McGill, for their excellent

    technical support for our experiments. I learned plenty of knowledge about spectrometers, fibers,

    cryogenics, magnets and LabView program from them. Also I give my special thanks to Dr.

    Brandt, former director of DC facility at NHMFL, for his great administrative assistance.

    I appreciate the experimental and theoretical supervisions we received for our research

    projects from Prof. Stanton from University of Florida, Prof. Kono from Rice University and

    Prof. Belyanin from Texas A&M University. Special thanks should be given to my research

    collaborators, Dr. Young-dahl Cho and Jinho Lee. Our research projects would not be so

    successful without their contribution.

    This work is supported by National Science Foundation and In House Research Program at

    the National High Magnetic Field Laboratory.

    Finally I want to send my warmest thanks to my wife and my daughter, my parents and

    parents in law for their endless love and support. I could not complete my studies without their

    emotional and financial support.

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    TABLE OF CONTENTS page

    ACKNOWLEDGMENTS ...............................................................................................................4

    LIST OF TABLES...........................................................................................................................8

    LIST OF FIGURES .........................................................................................................................9

    ABSTRACT...................................................................................................................................14

    CHAPTER

    1 INTRODUCTION AND OVERVIEW ..................................................................................16

    1.1 Semiconductors and Quantum Wells ............................................................................17 1.2 Magneto-spectroscopy in High Magnetic Fields ..........................................................18 1.3 Motivation for Performing Ultrafast Spectroscopy in High Magnetic Fields ..............19

    1.3.1 Quantum Optical Processes in Semiconductors--Superfluorescence ................19 1.3.2 Studies of Technologically Interesting Materials ..............................................20

    2 HIGH FIELD MAGNETO-OPTICAL TECHNIQUES AND FUNDAMENTALS OF MAGNETO-OPTICAL SPECTROSCOPY...........................................................................24

    2.1 Introduction...................................................................................................................24 2.2 Basic Background of Optical Response of Solids.........................................................24 2.3 Magneto-spectroscopy of Semiconductors--Methods...................................................27

    2.3.1 Transmission Spectroscopy ...............................................................................27 2.3.2 Reflection Spectroscopy ....................................................................................28 2.3.3 Photoluminescence (PL) Spectroscopy..............................................................29

    2.4 Time-resolved Spectroscopy of Semiconductors..........................................................29 2.5 CW Optical Experimental Capabilities at the NHMFL ................................................32 2.6 Development of Ultrafast Magneto-optical Spectroscopy at NHMFL.........................34

    2.6.1 Introduction of Ultrafast Optics .........................................................................34 2.6.2 Magnet and Cryogenics for Ultrafast Optics at NHMFL ..................................35 2.6.3 Ultrafast Light Sources ......................................................................................36

    2.6.3.1 Ti:Sapphire femtosecond oscillator..........................................................36 2.6.3.2 Chirped pulse amplifier ............................................................................37 2.6.3.3 Optical parametric amplifier ....................................................................38 2.6.3.4 Streak camera ...........................................................................................39

    3 ELECTRONIC STATES OF SEMICONDUCTOR QUANTUM WELL IN MAGNETIC FIELD...............................................................................................................57

    3.1 Introduction...................................................................................................................57 3.2 Band Structure of Wurzite and Zinc Blend Structure Bulk Semiconductors................57 3.3 Selection Rules..............................................................................................................60

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    3.4 Quantum Well Confinement .........................................................................................61 3.5 Density of States in Bulk Semiconductor and Semiconductor Nanostructures ............63 3.6 Magnetic Field Effect on 2D Electron Hole Gas in Semiconductor Quantum Well ....64 3.7 Excitons and Excitons in Magnetic Field......................................................................66

    3.7.1 Excitons..............................................................................................................66 3.7.2 Magneto excitons .............................................................................................67

    4 MAGNETO-PHOTOLUMINESCENCE IN INGAAS QWS IN HIGH MAGNETIC FIELDS...................................................................................................................................78

    4.1 Background ...................................................................................................................78 4.2 Motivation for Investigating PL from InGaAs MQW in High Magnetic Fields

    Using High Power Laser Excitation..............................................................................81 4.3 Sample Structure and Experimental Setup....................................................................82 4.4 Experimental Results and Discussion ...........................................................................82

    4.4.1 Prior Study of InxGa1-xAs/GaAs QW Absorption Spectrum .............................82 4.4.2 PL Spectrum Excited with High Peak Power Ultrafast Laser in High

    Magnetic Field ..................................................................................................84 4.5 Summary .......................................................................................................................87

    5 INVESTIGATIONS OF COOPERATIVE EMISSION FROM HIGH-DENSITY ELECTRON-HOLE PLASMA IN HIGH MAGNETIC FIELDS .........................................98

    5.1 Introduction to Superfluorescence (SF) ........................................................................98 5.1.2 Spontaneous Emission and Amplified Spontaneous Emission..........................99 5.1.3 Coherent Emission Process--Superradiance or Superfluorescence .................101 5.1.4 Theory of Coherent Emission Process--SR or SF in Dielectric Medium ........106

    5.2 Cooperative Recombination Processes in Semiconductor QWs in High Magnetic Fields ...........................................................................................................................109 5.2.1 Characteristics of SF Emitted from InGaAs QW in High Magnetic Field. .....110 5.2.2 Single Shot Random Directionality of PL Emission .......................................112 5.2.3 Time Delay between the Excitation Pulse and Emission.................................113 5.2.4 Linewidth Effect with the Carrier Density.......................................................113 5.2.5 Emission intensity Effect with Carrier Density ...............................................113 5.2.6 Threshold Behavior..........................................................................................114 5.2.7 Exponential Growth of Emission Strength with the Excited Area ..................114

    5.3 Experiments and Setup................................................................................................115 5.4 Experimental Results and Discussion .........................................................................117

    5.4.1 Magnetic Field and Power Dependence of PL ................................................117 5.4.2 Single Shot Experiment

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