Reliability of InGaAsP light emitting diodes at high current density

InGaAsP LED's emitting at 1.3 µm are attractive sources for long distance transmission systems. These devices have been shown to have excellent reliability at 8 kA/cm
²
. In order to launch more power into the optical fiber it is desirable to operate at the highest possible current densities consistent with system reliability requirements. In this work, the high temperature aging behavior of these LED's has been studied at current densities from 20 to 40 kA/
²
. Both the standard LED structure, where the small diameter p-contact is isolated with a dielectric layer, and a structure in which a Schottky barrier is used for isolation are examined. Dark spot defect (DSD) formation is greatly enhanced at these high current densities in devices with dielectric isolation, limiting MTTF at
T_{J} = 70\degC to 2 \times 10^{5}
h. In contrast, devices with Schottky-barrier isolation remain essentially free of DSD's and have
MTTF > 10^{7}
h at 70°C. These results suggest that stress from the dielectric layer promotes the growth of DSD's. Schottky-barrier devices in which the dielectric layer is eliminated are, thus, better suited for high current-density operation.