Premature failure in Pt-GaAs IMPATTs - Recombination assisted diffusion as a failure mechanism

We have recently observed an aging anomaly in platinum-GaAs IMPATT diodes. The effect is observed during temperature stress aging of diodes operating in avalanche. At temperatures above about 300°C, the devices follow a log-normal failure distribution with an activation energy of 1.6 eV. At lower temperatures, however, a change in activation energy to the range of 0.2 to 0.4 eV is observed. The failures are caused by diffusion of defects from the platinum-GaAs interface into the diode during operation. Analysis of the diffusion leads to the conclusion that the defect motion is enhanced by recombination through the energy levels associated with the defects. The characteristics of this diffusion mechanism lead to the observed anomaly. This failure mechanism renders thick platinum-GaAs an unsuitable combination for IMPATT structures.