The Reliability of Schottky Barrier Restricted GaAs/GaAlAs LEDs

Abstract

LEDs and diode lasers, using a Schottky barrier to restrict the current flow, have recently been reported. Devices with the current restricted by either a Schottky barrier (SB) or a dielectric layer have been shown to have similar performance but the reliability of SB devices has not been investigated. In this paper, the results of a reliability study on SB restricted GaAs/GaAlAs LEDs are presented. In comparison to the highly reliable dielectric isolated LEDs, SB restricted LEDs degrade fairly rapidly due to the interaction of Au and GaAlAs at the p-contact. During operation, Au from the heatsink migrates to the semiconductor and forms a AuGa alloy from which dark line defects initiate. By the use of a 1000 Å thick Pt or Pd barrier layer, Au migration is greatly reduced and the device lifetime increased. However, the thickness of the barrier metal must be further optimized before the SB device reliability is comparable to that of dielectric-isolated LEDs. In dielectric-isolated LEDs, degradation by Au–GaAlAs interaction is also shown to exist but only after long-term operation at elevated temperatures. Finally, since the processing and metallization for various stripe geometry lasers are similar to those used in our LEDs, GaAs/GaAlAs lasers should also degrade by these metal-semiconductor interactions.