Recombination mechanisms and thermal droop in AlGaN-based UV-B LEDs

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.