Transmission electron microscopy was used to study (100) dark-line defects that were produced during the photo-degradation of heterostructures. The results showed that the dark-line defects were networks of elongated dislocation loops or half-loops that originated within the quantum-well region during operation. The loops lay on {111} planes. The results also showed that, after photo-degradation, Frank-type stacking faults became networks of dislocations while Shockley-type stacking faults remained unchanged. This indicated that Frank-type stacking faults were sources of degradation under the present experimental conditions. A mechanism for the degradation was proposed in which degradation was supposed to begin with the accumulation of charge on stacking faults, followed by the emission of a mobile defect from the fault and along <100> directions. It was thought that the mobile defect was probably a cluster of vacancies. As the mobile defect moved it left behind a trail of strained lattice along its path. Upon further electron-hole recombination, dislocation loops formed on the strained paths which were left by the mobile defects. The loops elongated via glide and cross-slip on the {111} planes, and became hair-pin type dislocation loops.

L.Salamanca-Riba, L.H.Kuo: Japanese Journal of Applied Physics, 1996, 35[1-10], 5333-7