Characterization and simulation of fluorescent silicon carbide: a study of donor-acceptor-pairs and intrinsic defects

    Research output: Book/ReportPh.D. thesis

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    Fluorescent silicon carbide (f-SiC) is an emerging luminescent material capable of displaying broadband and strong orange-yellowish light thanks to its extraordinarily high density of donor-acceptor-pairs (DAPs) introduced by the co-doping of nitrogen (N) and boron (B). This thesis describes the luminescent properties of f-SiC material by both theoretical and experimental approaches. The correlations between the radiative/non-radiative centers within the band gap of f-SiC introduced during its crystal growth and the particular luminescent behaviors have been established. DAP recombination is the major contributor of the photoluminescence (PL) in fSiC where the non-equilibrium electrons/holes on the N-induced donor levels and the B-induced acceptor levels, respectively, can have radiative recombination. In this thesis, several non-radiative recombination regimes corresponding to the inactive donors and the intrinsic defects are revealed to compete with the DAP recombination in fSiC. For instance, by combining the results of the thermally stimulated luminescence (TSL) measurements on f-SiC with the related TSL simulations, it is discovered that part of non-equilibrium electrons are trapped on the donors related to the hexagonal sites where these electrons are not enrolled in the spontaneous emission (i.e., PL). On the other hand, by measuring the temperature-dependent PL intensity spectra on f-SiC, the existence of a new B-induced deeper acceptor level (D∗-center) other than the well-known D-center (together called double D-centers) is confirmed. The D∗ -center is found to account for the dominating redshifted PL of f-SiC at low temperature. Meanwhile, the huge gap between the luminescence intensities of n-type and p-type f-SiC at elevated temperatures is explained by a two-step thermal activation procedure which involves the double D-centers and an hole trap with its energy level staying between those of the former two centers. Moreover, on the basis of the results from the time-resolved PL and static PL measurements at room temperature where the results are explained using a negative-U center related carrier dynamics model together with a steady-state DAP recombination model, it is believed that the fast non-radiative recombination channels involved with the intrinsic negative-U centers close to the conduction band minimum capture the majority of the non-equilibrium carriers, which causes the low internal quantum efficiency of f-SiC. Since f-SiC is anticipated to replace yellow phosphor for novel white light emitting diode (LED), the optimized thickness and optical incident power regarding to f-SiC material are investigated by measuring its PL quantum yield by using an integrating sphere. It is found that excessive incident power mainly contributes to the ultrafast non-radiative recombination, i.e., Auger recombination.
    The research outputs reported in this thesis have revealed that there still exists the possibility for the improvement of the luminescence efficacy of f-SiC, where the crystal growth conditions including dopants concentrations as well as thickness control of epilayer can be further optimized in order to reduce the densities of intrinsic defects and enhance DAP recombination in f-SiC.
    Original languageEnglish
    PublisherTechnical University of Denmark
    Number of pages186
    Publication statusPublished - 2019


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