We have carried out structural studies of nonluminescent areas developed by current injection in ZnMgSSe alloy-based II–VI blue light emitting diodes by electroluminescence topography and transmission electron microscopy. The nonradiative regions, which spread out in the 〈100〉 direction during current injection, consist of a high density of dislocation dipoles and dislocation loops. The source of these defects is the preexisting stacking faults originating at the substrate/epilayer interface. The dipoles themselves are aligned along both of the 〈110〉 directions lying in the {111} plane. Their Burgers vectors were of the type (a/2)〈011〉 inclined at 45° to the (001) junction plane.
GaInP epitaxial crystals grown on (001) GaAs at 660–700 °C by metalorganic chemical vapor deposition are examined by transmission electron microscopy. The computer-processed image of the high-resolution electron micrograph clearly reveals a lamellate-ordered domain structure of two variants of {111} superlattices, which is also investigated using cross-section and plan-view dark field electron micrographs. The spikes of well-defined superspots in the diffraction pattern were found to originate from the shape of the domains. The investigation of GaInP grown with different Zn concentrations showed that the disordering occurs as a result of a decrease in the density rather than the size of the domain.
Surface morphological changes in ZnSe-related II–VI epitaxial films grown by molecular beam epitaxy have been investigated by atomic force microscopy and transmission electron microscopy. We found that under group-II-rich conditions with c(2×2) surface reconstruction, the process of roughening gives rise to periodic elongated corrugations aligned in the [11̄0] direction. Under group-VI-rich conditions with (2×1) surface reconstruction, rounded grains form instead of corrugated structures. The surface morphology is dependent on the VI/II ratio and growth temperature, but is independent of the film strain. The observed morphological changes are mainly due to growth kinetics and are not stress driven. We propose a model to explain the changes in surface morphology under group-II-rich conditions and group-VI-rich conditions.
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