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    Molecular Beam Epitaxy-Grown InGaN Nanowires and Nanomushrooms for Solid State Lighting

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    Anwar Gasim_Final Thesis.pdf
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    Type
    Thesis
    Authors
    Gasim, Anwar A.
    Advisors
    Ooi, Boon S. cc
    Committee members
    Alsunaidi, Mohammad A.
    Foulds, Ian G.
    Program
    Electrical Engineering
    KAUST Department
    Computer, Electrical and Mathematical Science and Engineering (CEMSE) Division
    Date
    2012-05
    Embargo End Date
    2015-01-01
    Permanent link to this record
    http://hdl.handle.net/10754/229251
    
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    Show full item record
    Access Restrictions
    At the time of archiving, the student author of this thesis opted to temporarily restrict access to it. The full text of this thesis became available to the public after the expiration of the embargo on 2015-01-01.
    Abstract
    InGaN is a promising semiconductor for solid state lighting thanks to its bandgap which spans the entire visible regime of the electromagnetic spectrum. InGaN is grown heteroepitaxially due to the absence of a native substrate; however, this results in a strained film and a high dislocation density—two effects that have been associated with efficiency droop, which is the disastrous drop in efficiency of a light-emitting diode (LED) as the input current increases. Heteroepitaxially grown nanowires have recently attracted great interest due to their property of eliminating the detrimental effects of the lattice mismatch and the corollary efficiency droop. In this study, InGaN nanowires were grown on a low-cost Si (111) substrate via molecular beam epitaxy. Unique nanostructures, taking the form of mushrooms, have been observed in localized regions on the samples. These nanomushrooms consist of a nanowire body with a wide cap on top. Photoluminescence characterization revealed that the nanowires emit violet-blue, whilst the nanomushrooms emit a broad yellow-orange-red luminescence. The simultaneous emission from the nanowires and nanomushrooms forms white light. Structural characterization of a single nanomushroom via transmission electron microscopy revealed a simultaneous increase in indium and decrease in gallium at the interface between the body and the cap. Furthermore, the cap itself was found to be indium-rich, confirming it as the source of the longer wavelength yellow-orange-red luminescence. It is believed that the nanomushroom cap formed as a consequence of the saturation of growth on the c-plane of the nanowire. It is proposed that the formation of an indium droplet on the tip of the nanowire saturated growth on the c-plane, forcing the indium and gallium adatoms to incorporate on the sidewall m-planes instead, but only at the nanowire tip. This resulted in the formation of a mushroom-like cap on the tip. How and why the indium droplets formed is not entirely clear, but a localized temperature dip may have been the cause. Ultimately, the simultaneous growth of nanowires and nanomushrooms on the same substrate may pave the way to the development of a phosphor-free, efficient, inherent white LED.
    Citation
    Gasim, A. A. (2012). Molecular Beam Epitaxy-Grown InGaN Nanowires and Nanomushrooms for Solid State Lighting. KAUST Research Repository. https://doi.org/10.25781/KAUST-3YPIA
    DOI
    10.25781/KAUST-3YPIA
    ae974a485f413a2113503eed53cd6c53
    10.25781/KAUST-3YPIA
    Scopus Count
    Collections
    MS Theses; Electrical and Computer Engineering Program; Computer, Electrical and Mathematical Science and Engineering (CEMSE) Division

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