Source: https://www.osapublishing.org/prj/abstract.cfm?uri=prj-5-2-A44
Timestamp: 2019-04-20 06:51:34+00:00

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This paper reports a comprehensive analysis of the origin of the electroluminescence (EL) peaks and of the thermal droop in UV-B AlGaN-based LEDs. By carrying out spectral measurements at several temperatures and currents, (i) we extract information on the physical origin of the various spectral bands, and (ii) we develop a novel closed-form model based on the Shockley–Read–Hall theory and on the ABC rate equation that is able to reproduce the experimental data on thermal droop caused by non-radiative recombination through deep levels. In the samples under test, the three EL bands are ascribed to the following processes: band-to-band recombination in the quantum wells (main EL peak), a parasitic intra-bandgap radiative transition in the quantum well barriers, and a second defect-related radiative process in the p-AlGaN superlattice.
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Fig. 1. Spectral distribution of the EL at various temperatures and a current of 1 mA. The four main emission peaks are labeled in the figure.
Fig. 2. Intensity of the QW emission for different temperatures and currents.
Fig. 3. Arrhenius plot of the intensity of the QW emission and fit according to Eq. (1).
Fig. 4. Temperature dependence of the peak wavelength of the QW emission. Inset: bandgap narrowing with increasing temperature in accordance with Varshni’s law.
Fig. 5. Intensity of the QW emission for different temperatures and currents fitted by Eqs. (3), (7), and (9).
Fig. 6. Numerical simulation of the band diagram and of electron and hole concentration at 140 and 300 K at a current of 10 mA.
Fig. 7. Arrhenius plot of the peak 3 intensity for different currents fitted by the complete SRH model [Eqs. (3), (7), and (9)].
Fig. 8. Arrhenius plot of the peak 4 intensity for different currents fitted by the complete SRH model [Eq. (7)].
Fig. 9. Intensity of the QW emission at different temperatures fitted by the complete SRH model [Eq. (7)] and the approximated model [Eq. (A3)], respectively.

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