(Invited) Spatially Resolved Study of the EQE Droop in InGaN QW LEDs: Interplay of Point Defects, Extended Defects, and Carrier Localization

We offer a concise overview for the mechanisms on the external quantum efficiency (EQE) droop in InGaN QW LEDs. We believe that non-radiative recombination due to extended defects and the deficiency in the electron blocking layer are most likely two primary mechanisms responsible for the droop. We perform spatially resolved electroluminescence (EL) measurements with varying injection current on an InGaN QW LED. The analyses of the EL mapping data reveal a correlation between carrier delocalization and EQE droop. In addition, we observe that at very low current, there is virtually no correlation between the local EL intensity and peak energy, reflecting very low carrier mobility; whereas with increasing current, an anti-correlation between the intensity and energy is eventually established, indicating substantial changes in the carrier mobility and diffusion length with increasing current. The results suggest the material inhomogeneity occur in different scales.