Reliability of UVC LEDs fabricated on AlN/sapphire templates with different threading dislocation densities

Abstract

The impact of different AlN/sapphire template technologies [i.e., planar, epitaxial lateral overgrown (ELO), and high temperature annealed sputtered ELO] is studied with respect to the operation-induced degradation of 265 nm UVC LEDs. UVC LEDs with identical heterostructures were grown on templates providing different threading dislocation densities in the range of 0.8 × 109 cm−2 to 5.8 × 109 cm−2. A long-term stress experiment was performed on batches of LEDs, which were operated at a direct current of 200 mA corresponding to a current density of 60 A/cm2 and at a heat sink temperature of 20 °C. The UVC LEDs on templates with lower threading dislocation densities were found to provide a higher optical power and to degrade slower during 2000 h of operation. The experiment demonstrates an extrapolated L70 lifetime of more than 10 000 h for the high temperature annealed sputtered ELO technology. The results suggest that degradation is caused by operation-induced activation of defects whose density scales with the dislocation density.