Formation of stacking faults in ZnS thin films epitaxially grown on GaAs(001)

The microstructure of single-crystal ZnS thin films epitaxially grown on GaAs(100) has been investigated by high resolution transmission electron microscopy (HRTEM). The dominant defect structures are {111} stacking faults and interface mismatch dislocations. The distribution of stacking faults is limited to the first 70 nm thickness range of the grown film, and almost no defects are observed in the thickness range beyond 100 nm. This could have important consequences in optoelectronic applications. The stacking faults of(lll) layers are generated at the substrate-film interface in the following two ways. Firstly a small interface angle between the substrate and the film results in edge-type dislocations due to additional (002) ZnS layers (i.e. a low-angle boundary structure). Part of the stress created by these interface dislocations is relaxed by generating stacking faults. Secondly mismatch dislocations with additional (111) layers, due to the lattice mismatch between GaAs and ZnS (4.4%), also favour the formation of stacking faults at the interface. The structure models of these defects are given based on the experimental HRTEM images.