OBSERVATION OF [100] DARK LINE DEFECTS IN OPTICALLY DEGRADED ZNSXSE1-X-BASED LIGHT-EMITTING-DIODES BY TRANSMISSION ELECTRON-MICROSCOPY

We have used transmission electron microscopy to study the [100] dark Line defects (DLDs) produced during photodegradation of a ZnSxSe1-x-ba sed/GaAs heterostructure. Our results show that the DLDs are networks of elongated dislocation loops or half loops that originate in the qua ntum well region during device operation. The loops lie on {111} plane s. Our results also show that after photodegradation the Frank-type st acking faults become networks of dislocations while the Shockley-type stacking faults remain unchanged indicating that the Frank-type stacki ng faults are the sources for the degradation under our experimental c onditions. We propose a mechanism for the degradation process. The deg radation starts by the accummulation of charge on the stacking faults from the electron-hole recombination in the quantum well followed by t he emission of a mobile defect from the fault and along the [100] dire ctions. The mobile defect is probably a cluster of vacancies. As the m obile defect moves it leaves a trail of strained lattice along its pat h. Upon further electron-hole recombination dislocation loops form on the strained path left by the mobile defect. The loops elongate by gli de and cross-slip mechanism on {111} planes and become hair pin-like d islocation loops.