The effect of interstital Frank partial dislocations on the gradual degradation of 1.3-μm double-channel planar buried heterostructure laser diodes

The structure of defects occurring in degraded 1.3-μm double-channel planar buried heterostructure type laser diodes was studied in detail by conventional diffraction contrast, weak-beam dark-field microscopy and high-resolution lattice imaging in a transmission electron microscope. The electrical activity of the defects was analyzed by means of the electron-beam-induced current. Device degradation is associated with the presence of interstitial Frank partial dislocation loops with a Burgers vector of (a/3) {111} at the interfaces between the InGaAsP active layer exposed after the channel etching and the first p+-InP layer of the liquid-phase-epitaxy-grown current-blocking layers. No other types of defects were observed in the course of the present study. The implications of the latter finding are far-reaching and lead to a new degradation model for the microstrctural changes associated with the gradual degradation of long-wavelength lasers. A new degradation model is proposed, and laser diode design considerations for degradation-free operation are given. These consdierations are twofold: the device structure should (a) not favor Frank partial dislocation loop nucleation and (b) suppress the dissociation of the Frank partial dislocations.