Rapid degradation phenomenon in heterojunction GaAlAs--GaAs lasers

The rapid degradation phenomenon in Ga1−xAlxAs–GaAs DH lasers has been associated with the growth of a dislocation network during the device operation. The nature of these defects has been analyzed by transmission electron microscopy in an effort to understand their origin and growth mechanism. The propagation of the dislocation network is found to take place by successive climb of a dislocation crossing the n-Ga1−xAlxAs, p-GaAs, and p-Ga1−xAlxAs layers in the stripe area. The climb process leads to the formation of a three-dimensional dislocation dipole network which extends through the three epitaxial layers and remains confined to the stripe area. A tentative model which discusses the network growth process is presented. The source of the very large vacancy concentration involved in the climb process has been attributed to the interfaces between the binary and ternary layers. The fast climb rate has been related to large drift forces acting on the vacancies during the device operation. The dominant drift forces are thought to be electrical and elastic in nature.