Effect of defects on the degradation of ZnSe-based white LEDs

A white LED based on II–VI compound materials has been developed. The optical output power and forward voltage of a typical ZnSe-based white LED lamp at a drive current of 20 mA are 4.3 mW and 2.6 V, respectively. Device lifetime (half-time) at IF=5 mA have exceeded 2 500 h at 60 °C, corresponding to an estimated lifetime of over 20 000 h at 20 °C. The most important defects limiting the lifetime are the dislocations and the stacking faults penetrating the active layer. Origins of these defects are the dislocations in the substrate as well as lattice irregularities at the epilayer/substrate interface. Though we have not yet found any evidence for microscopic defects in the cladding layers to take part in the degradation of our white LEDs, its possibility cannot be neglected.