Fabrication of near-ultraviolet light-emitting diodes for white light source applications using fluorescent-silicon carbide

Li Lin

    Research output: Book/ReportPh.D. thesis

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    Abstract

    This thesis focuses on the fabrication of a hybrid fluorescent silicon carbide (fSiC) based warm white light-emitting diode (LED). This type of white LED employs a near-ultraviolet (NUV) LED as the excitation source and a donoracceptor-pair (DAP) co-doped f-SiC substrate as the wavelength-conversion material. In comparison with the commonly used wavelength-conversion material like phosphors, the f-SiC based white LED does not contain any rareearth element and has a longer material lifetime.
    This work starts with the fabrication of the NUV LED device which functions as the excitation source in the f-SiC based white LED. Then, to enhance the electroluminescence (EL) output of the NUV LED, the work of performance optimization on aluminum-doped zinc oxide (AZO) as a current spreading layer (CSL) is demonstrated. In the end, to produce a hybrid f-SiC based warm white LED, a bonding method for combination of the NUV LED and a nitrogen (N)-boron (B) co-doped f-SiC epi-layer is presented.
    To make a NUV LED device, standard post-growth fabrication process including the formation of mesas, CSLs and pads is carried out on NUV LED epi-wafers. In addition, to obtain strong output light of the NUV LED, it is critical to employ a proper CSL with both good conductivity and high transparency in the NUV wavelength region. Therefore, transparent conductive oxide AZO is studied and optimizations are carried out on the AZO based CSLs. It turns out in the end that a graphene interlayer can improve the performance of the AZO based CSL by decreasing the Schottky barrier height between the CSL and the semiconductor. On the other hand, to fabricate a hybrid f-SiC based warm white LED by combining the NUV LED and the f-SiC epi-layer, an adhesive bonding approach is employed. Hydrogen silsesquioxane (HSQ) is used as the bonding material due to its high transparency in the NUV wavelength region. By using this method, a NUV LED grown on a 4H-SiC substrate is successfully bonded to a free-standing B-N co-doped f-SiC epi-layer. EL emission from the NUV LED on the top excites the bottom f-SiC epi-layer to generate light finally presenting a warm white emission.
    Original languageEnglish
    PublisherTechnical University of Denmark
    Number of pages119
    Publication statusPublished - 2018

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