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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/63990

    Title: 自聚性砷化銦鎵量子點之光電特性;Electronic and Optical Properties of InxGa1-xAsSelf-Assembled Quantum Dots
    Authors: 張文豪;Chang,Wen-Hao
    Contributors: 物理研究所
    Date: 2001-07-05
    Issue Date: 2014-05-08 15:59:51 (UTC+8)
    Publisher: 國立中央大學
    Abstract: 本論文旨於探討自聚性砷化銦鎵量子點的光電特性,其主要研究內容涵蓋兩
    ;This dissertation is devoted to the electronic and optical properties of InxGa1-xAs
    self-assembled quantum dots. The main focus of this dissertation can be divided into
    two parts. First, we present optical investigations with regard to the physical features of
    the confined states in InxGa1-xAs quantum dots. Three optical spectroscopes have been
    employed: photoluminescence, photocurrent and electroreflectance. These
    spectroscopes in principle can all be utilized to probe the interband transitions in the
    InxGa1-xAs quantum dots, but possess characteristic features specific to the different
    physical mechanisms involved in each. The general features of the quantum-dot
    photoluminescence, including the state-filling effect and its interplay with carrier
    dynamics, and the temperature effects on carrier distributions, are comprehensively
    discussed. The photoluminescence spectroscopy was further utilized to study the tuning
    of confined energy levels in InAs self-assembled dots via rapid thermal annealing.
    Intense and sharp interband transitions were observed, which demonstrates
    unambiguously that the investigated quantum dots retained their optical quality and
    zero-dimensional properties even after the strongest condition of interdiffusion.
    Photocurrent spectroscopy was used to investigate both temperature and electric-field
    effects on the InAs dots. The path for thermal escapes of photogenerated electron-hole
    pair from the dot states is clarified. Low-temperature photocurrent also revealed a clear
    feature of field-induced escapes via direct tunneling out of the quantum dots. The
    applied electric field not only leads to an energy shift due to quantum-confined Stark
    effects, but also causes a size selective tunneling. A more detailed study of electric-field
    effects on the quantum dot interband transitions was presented by electroreflectance
    spectroscopy. Asymmetric Stark shifts in transitions energies were observed, implying
    that the optically excited electron-hole pairs exhibit built-in dipole moments in the
    quantum dots.
    After having the idea of confined states in the InxGa1-xAs self-assembled dots, in
    the second part of this dissertation, we present how to manipulate and corral electrons in
    these confined states. The quantum dots were incorporated into a space-charge structure,
    so that the charging of quantum dots can be achieved by suitably applied bias voltage,
    forming charged quantum dots. We developed a novel spectroscopic technique, called
    electron-filling modulation reflectance (EFR), to study the charging of InxGa1-xAs
    self-assembled dots. The EFR technique is essentially a new kind of electroreflectance,
    but possessing characteristic features that are more similar to the conventional
    space-charge techniques, such as capacitance-voltage and admittance spectroscopes.
    Electron distribution and level occupation in quantum dot ensemble were investigated
    by combining the EFR with the capacitance-voltage spectroscopy. We used the
    capacitance-voltage characteristics to construct the electronic structures of the
    investigated In0.5Ga0.5As quantum dots. The Coulomb-charging energy required for
    adding electrons into the dots were also deduced from the capacitance-voltage
    characteristics. The electron level occupations were investigated by monitoring the
    measured EFR intensity. We found that the electron distribution in the dot ensemble was
    inhomogeneous near the Fermi level, which was attributed to the correlated charge
    transfer among different dots. The temperature effects on electron thermal population in
    the dots are demonstrated. We also present a combination of EFR with admittance
    spectroscopy to study the charging of InAs quantum dots. Charging dynamics of the
    InAs dots were characterized by the admittance spectroscopy. Clear features for
    different electronic shells of the InAs dots were resolved, enabling a separate
    investigation of the electron escape behaviors in different dot shells. The interband
    transitions of charged quantum dots were obtained from EFR measurements. We
    demonstrate clear Pauli blocking of the transition strength caused by the electrons being
    charged into the quantum dots. Remarkable energy modification due to the formation of
    negatively charged exciton was observed. The experimental determined energy shifts
    were finally compared with the theoretical calculation of Coulomb interactions in a
    quantum dot with a parabolic confining potential.
    Appears in Collections:[物理研究所] 博碩士論文

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