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Atomic Scale Characterization of Point Defects in the Ultra-Wide Band Gap Semiconductor β-Ga2O3

Johnson, Jared M
http://rave.ohiolink.edu/etdc/view?acc_num=osu1577916628182296

Abstract Details

2020, Doctor of Philosophy, Ohio State University, Materials Science and Engineering.
Precisely controlled point defects are vital to the manipulation of important electronic properties in semiconductor materials. Point defects and their complexes display a wide range of atomic structures and functional states that critically influence a semiconductor’s unique properties. Therefore, gaining insight on the exact nature of their formation and role in determining properties is key to advancing these materials for application. This type of characterization requires obtaining experimental information on the atomic scale structure of point defects. The emerging ultra-wide band gap semiconductor β-Ga2O3, which displays excellent properties for high-performance electrical, optical, and power device applications, lacks the detailed understanding of point defects needed for its development. In this work, point defects are characterized in β-Ga2O3 bulk crystals and thin films. Centered around high-resolution scanning transmission electron microscopy (STEM), several characterization techniques are collectively used to uncover point defect formation and to link theoretical predictions to measured properties. First, an unusual formation of point defect complexes within the atomic-scale structure of β-Ga2O3 is directly observed using STEM. These complexes, which involve one cation interstitial atom paired with two cation vacancies, correlate directly with structures predicted by density functional theory. The divacancy-interstitial complexes are shown to act as compensating acceptors by a comparison between STEM data and deep level optical spectroscopy results. This comparison also reveals that the development of the complexes is facilitated by Sn doping through increased vacancy concentration. Additionally, a different stable complex is shown to form via the relaxation of a specific Ga atom near two adjacent divacancy-interstitial complexes. Molecular dynamics simulations confirm the energetic stability of the new structure. Point defects in β-(AlxGa1-x)2O3 films are investigated using quantitative STEM to explain the inability to achieve epitaxial growth of high Al concentration films. A quantitative STEM analysis of Al site occupancy indicates that 54% of the incorporated Al occupies the Ga2 site, conflicting with density function theory formation energy calculations. This result suggests that the growth of a higher energy structure leads to the difficulty in β-(AlxGa1-x)2O3 film growth. The aforementioned divacancy-interstitial complexes are also observed in the films, showing an increase in concentration with Al. Finally, a new STEM technique is proposed for the three-dimensional characterization of vacancies, lighter and heavier dopants. Using multislice STEM simulations of β-Ga2O3, the contrast of vacancies and lighter defects is shown to become enhanced when selecting a small range of low scattering angles. The origin of this effect is the de-channeling of electrons due to the point defect in the atomic column. The three-dimensional characterization of the point defects can be realized by capturing the de-channeling signal in the 20–40 mrad detection angle range.
Jinwoo Hwang (Advisor)
Roberto Myers (Committee Member)
Wolfgang Windl (Committee Member)
177 p.
Materials Science
wide band gap semiconductor; point defects; electron microscopy

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Citations

  • Johnson, J. M. (2020). Atomic Scale Characterization of Point Defects in the Ultra-Wide Band Gap Semiconductor β-Ga2O3 [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1577916628182296

    APA Style (7th edition)

  • Johnson, Jared. Atomic Scale Characterization of Point Defects in the Ultra-Wide Band Gap Semiconductor β-Ga2O3 . 2020. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1577916628182296.

    MLA Style (8th edition)

  • Johnson, Jared. "Atomic Scale Characterization of Point Defects in the Ultra-Wide Band Gap Semiconductor β-Ga2O3 ." Doctoral dissertation, Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1577916628182296

    Chicago Manual of Style (17th edition)

osu1577916628182296
509
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