Influences of Interfacial Misfit Dislocations on Cathodoluminescence of ZnS/GaAs(001) Studied by Transmission Electron Microscopy

The change in cathodoluminescence (CL) spectra of thin ZnS films grown by molecular beam epitaxy (MBE) on GaAs(001) has been examined by a low-temperature CL measurement system combined with a transmission electron microscope (TEM). It was found that structural defects such as dislocations and stacking faults formed in the ZnS films seriously affect CL intensity within a distance of 200 nm from the interface, and their effect becomes negligibly small at distances of more than 600 nm. The relative intensities of the exciton-associated emissions are small in comparison with the non-exciton-associated emissions for the thin samples that have relatively large stacking fault densities. This fact suggests that the stacking faults accompanying the partial dislocations suppress the generation of excitons. Moreover, the peak of the non-exciton-associated emission shifts markedly to long wavelengths, as the epitaxial layer thickness becomes less than 200 nm. The peak shift is attributed to the internal stress change in the ZnS film due to the stress caused by the lattice mismatch and the relaxation by the introduced defects.