Reliability of DH Ga1-XAlX As LEDs For Lightwave Communications

Double heterostructure Gal-xAlXAs LEDs operated at high current densities (3 × 103 A/cm2) are being used as sources in lightwave communication systems, for example in optical data links. This paper discusses the reliability of these devices, distinguishing between catastrophic degradation due to Dark Line Defect (DLD) formation and gradual aging mechanisms. Two modes of DLD formation are observed: (1) A certain percentage of devices fail in relatively short times by DLD formation at threading dislocations. The growth of these DLDs is strongly current dependent, but independent of temperature. A 100h, 100 mA burn-in eliminates all of the devices which fail by this mode. Burn-in failures can be kept as low as 5%. (2) Under accelerated aging as many as 25% of the devices which passed the burn-in fail after 103h by a new mode of DLD formation. This mode is temperature dependent and related to stress at the dielectric-metal interface. Analysis shows that a 25% freak population gives ¿40 FITS at 70°C. Accelerated aging studies of clear devices are complicated by two competing processes: a slow degradation in light output and a slow increase which dominates at high temperatures. Activation energies for the two processes are 0.65 and 0.75 eV, respectively. Projected values of MTTF are 9 × 107h at 25°C and 4 × 106h at 70°C.