Degradation Studies of Diffused GaAs Electroluminescent Diodes Subjected to Mechanical Stress

The direct imposition of compressive mechanical stress during forward bias aging has been found to accelerate the degradation rate of diffused GaAs electroluminescent diodes by over an order of magnitude. The accelerated degradation occurs precipitously with increasing mechanical stress beyond the nominal threshold level of ~2×108 dyn/cm2, and is associated primarily with an increase in the initial rapid component of degradation rather than with the long term behavior. Complementary etching studies have established that dislocation generation can occur at the stress levels and temperatures which induce the accelerated degradation in the presence of forward bias. Moreover, both linear and extended defects are found in the substrate regions, remote from the p-n junction, of the diodes which exhibited accelerated degradation. However, the rapid aging behavior requires the presence of forward bias aging current and the continuous imposition of the mechanical stress, and cannot be induced by initial "prestress" aging under mechanical stress alone (without forward bias). These results demonstrate that the accelerated aging involves complicated interplay between electrical bias and mechanical stress, with the precise mechanisms for this behavior uncertain.