Boston University Libraries OpenBU
    JavaScript is disabled for your browser. Some features of this site may not work without it.
    View Item 
    •   OpenBU
    • Theses & Dissertations
    • Boston University Theses & Dissertations
    • View Item
    •   OpenBU
    • Theses & Dissertations
    • Boston University Theses & Dissertations
    • View Item

    Optical and electronic properties of defective semiconductors from first principles calculations

    Thumbnail
    Date Issued
    2020
    Author(s)
    Lewis, David Kirk
    Share to FacebookShare to TwitterShare by Email
    Export Citation
    Download to BibTex
    Download to EndNote/RefMan (RIS)
    Metadata
    Show full item record
    Permanent Link
    https://hdl.handle.net/2144/41026
    Abstract
    Defects in semiconductors can play a vital role and even dominate the performance of optoelectronic devices. Thus, understanding the relationship between structural defects and optoelectronic properties is central to the design of new high-performance materials. In this dissertation, we apply state-of-the-art first-principles approaches based on density functional theory (DFT) and many-body perturbation theory (MBPT) to quantitatively describe trap state energies and optical excitation spectra of defective bulk gallium nitride (GaN) and monolayer germanium selenide (GeSe). GaN is a technologically important wide bandgap semiconductor used as a power electronics and blue light emitting material, and naturally contains performance-degrading defects. For GaN containing a charged nitrogen vacancy, we systematically study the trap-state energies and excitonic properties. We benchmark the accuracy of hybrid DFT by comparison to MBPT studies of defective bulk GaN and determine that the HSE functional (Heyd–Scuseria–Ernzerhof) predicts trap-state energies in excellent agreement with MBPT, and that a recently developed solid-state screened range-separated hybrid (SRSH) functional can quantitatively reproduce MBPT-predicted defect energetics, including optical excitations. Additionally, we utilize MBPT to quantify the localization of the Wannier-Mott exciton in the presence of a point defect, introducing an analysis technique of the exciton envelope and center-of-mass functions to extract the Wannier exciton Bohr radius and quantify the perturbation of the exciton wavefunction due to the defect. We then utilize (TD)SRSH to study the excited-state properties of three other important defects in GaN and predict that the carbon impurity may result in the well-known yellow luminescence in bulk GaN. Finally, we apply MBPT with the same analysis techniques developed for GaN to study the optoelectronic properties of defects in monolayer semiconducting GeSe, a material that has promising applications in next-generation optoelectronic devices; we determine that a selenium vacancy strongly modifies the optoelectronic properties of the material. Overall, this dissertation provides a recipe for performing quantitatively accurate MBPT and TDDFT calculations on defective semiconductors, with a systematic study of calculation convergence and defect-defect interactions. Additionally, by an analysis technique of the BSE-computed exciton wavefunction, we introduce a framework for describing defect-induced exciton localization that can be broadly applied to many classes of materials.
    Collections
    • Boston University Theses & Dissertations [6773]


    Boston University
    Contact Us | Send Feedback | Help
     

     

    Browse

    All of OpenBUCommunities & CollectionsIssue DateAuthorsTitlesSubjectsThis CollectionIssue DateAuthorsTitlesSubjects

    Deposit Materials

    LoginNon-BU Registration

    Statistics

    Most Popular ItemsStatistics by CountryMost Popular Authors

    Boston University
    Contact Us | Send Feedback | Help