Diffusion mechanism as cause of optical degradation in AlGaN-based UV-C leds investigated by TCAD simulations

We investigate the degradation physics of AlGaN-based UV-C LEDs emitting at 265 nm, by combined experimental measurements and numerical simulations. We demonstrate that: (i) during long-term operation, devices show degradation in the optical emission, which is more prominent at low measuring current levels; (ii) a strong correlation was found between the emission decrease and the increase in the forward leakage current, which suggests that the same process is responsible for the electrical and optical degradation; (iii) the observed long-term optical degradation was reproduced by numerical simulations, as being due to the increase in the defect density in the QW during the ageing, demonstrating the impacting role of SRH recombination on device reliability. (iv) The degradation kinetics follow the square-root of stress time. By solving Fick's differential equation near the quantum well, we ascribed degradation to the out-diffusion of hydrogen from the quantum well region, leading to the activation of non-radiative recombination centers, through the de-hydrogenation of point-defects.