OBSERVATION OF [100] AND [010] DARK LINE DEFECTS IN OPTICALLY DEGRADED ZNSSE-BASED LEDS BY TRANSMISSION ELECTRON-MICROSCOPY

We have used transmission electron microscopy to study the [100] and [ 010] dark line defects (DLDs) produced after photodegradation of a ZnS Se-based/GaAs heterostructure. Our results show that the DLDs are netw orks of elongated dislocation loops or half-loops that originate in th e quantum well region during device operation. Our results also show t hat after photodegradation the grown-in or pre-existing Frank-type sta cking faults become tangles of dislocations. In contrast, the Shockley -type stacking faults remained unchanged for the photodegradation cond itions studied indicating that they are more resistant to photodegrada tion than the Frank-type stacking faults. Our results suggest that the Frank-type stacking faults are the sources of the DLDs. The mechanism for degradation probably starts by the emission of very small cluster s of vacancies from the Frank-type faults. Upon further illumination t he dislocation loops bounding the vacancies grow by gliding on {111} p lanes and become hairpin-like dislocation loops.