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Defect-generation and diffusion in (In)AlGaN-based UV-B LEDs submitted to constant current stress

The aim of this work is to analyze the degradation in (In)AlGaN-based UV-B LEDs, with a nominal emission wavelength of 310 nm, submitted to constant current stress at a high current density of 350 A/cm2. We observed two main degradation mechanisms that were studied by investigating the evolution of the main emission peak from the quantum well (QW) and of a parasitic peak centered at 340 nm. In the first 50 hours of stress the main peak decreases and the parasitic peak (probably related to radiative recombination in the quantum barrier next to the electron blocking layer) increases at drive currents between 5 mA and 50 mA. Secondly, after 50 hours of stress both the main and the parasitic peak decrease. The first degradation mode could be related to carrier escape from the QWs, since the increase in the parasitic peak is correlated with the decrease in the main peak. After 50 hours of stress, we observed that the current below the turn-on voltage at V = 2 V increases with a square-root of time dependence. This behavior indicates the presence of a diffusion process, probably by point defects causing an increase of non-radiative recombination in the LED.