Reliability And Degradation Modes Of 280 Nm Deep Uv Leds On Sapphire

In this paper, we report a study of the degradation of AlGaN-based 280 nm LEDs, which were grown on sapphire substrates using migration-enhanced metalorganic chemical vapor deposition process (MEMOCVD). Electroluminescence (EL), atomic force microscopy (AFM), cathodoluminescence (CL), and scanning electron microscopy (SEM) observations showed that the degradation of deep UV LEDs generally fell into two categories: catastrophic degradation and gradual degradation. The catastrophic degradation was found to be mostly caused by the non-uniformity of surface morphology. The gradual power reduction had two characteristic time constants indicating two possible degradation mechanisms as found from temperature and bias dependent LED power degradation measurements. The faster time constant was bias dependent and virtually constant with temperature whereas the second time constant (slower) varied exponentially with junction temperature. For this temperature dependent part, the activation energies of degradation were determined to be 0.23 eV and 0.27 eV under injected current density of 100 A/cm(2) and 200 A/cm(2) respectively.