ZnSSe-based/GaAs heterostructures have been becoming very important materials for blue-green light emitting diodes (LEDs) and lasers. However, the applications of these heterostructures are still limited by two main types of defects including dark line defects (DLDs) and dark patches.
Figure 2110 shows an example of cathodoluminescence (CL) images. This image was taken from a ZnSe/GaAs heterostructure. The dark-line defects (DLDs) formed primarily along (100) directions ( and ) in the area (labeled A) photodegraded by an argon laser. Some DLDs marked by arrowheads are misoriented by 5 to 25 degrees from the <100> directions. "M" in the figure marks a misfit dislocation.
Figure 2110. Cathodoluminescence (CL) image taken from a ZnSe/GaAs heterostructure. Adapted from 
 L. Salamanca-Riba and L.H. Kuo, Observation of  and  Dark Line Defects in Optically Degraded ZnSSe-Based LEDs by Transmission Electron Microscopy, Journal of Electronic Materials, 25 (2) (1996) 239.