An explanation for catastrophic failures of GaN-based vertical structure LEDs subjected to thermoelectric stressing

摘要

Both accelerated life tests and engineering practices present a common behavior: LED products may encounter catastrophic failure under thermo-electric co-stressing. The present work proposes that the applied thermoelectric stresses themselves are not necessary conditions but pre-conditions for LED breakdown. The deformation and sliding of the metal lines on n-GaN under thermoelectric co-stressing cause electrodes to become dilapidated. Such dilapidated electrodes with rough edges will help to generate localized high electrical fields. The catastrophic failure occurs during the de-trapping process of space charges in and around threading dislocations when the applied electric field is removed and short circuits form between the charged dislocation cores and the tips of the dilapidated electrodes. A phenomenological relationship is given to describe the interactions between temperatures and applied electric currents on the diffusion-flux-accommodated sliding and deformation of patterned metal electrodes on vertical LEDs. Such a law is coincident with the practical trend of LED failure rates observed in accelerated life tests and engineering applications.