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 ele ctron microscopy (HRTEM). The dominant defect structures are {111} sta cking faults and interface mismatch dislocations. The distribution of stacking faults is limited to the first 70 nm thickness range of the g rown film, and almost no defects are observed in the thickness range b eyond 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 i nterface angle between the substrate and the film results in edge-type dislocations due to additional (002) ZnS layers (i.e. a low-angle bou ndary structure). Part of the stress created by these interface disloc ations is relaxed by generating stacking faults. Secondly mismatch dis locations with additional (111) layers, due to the lattice mismatch be tween GaAs and ZnS (4.4%), also favour the formation of stacking fault s at the interface. The structure models of these defects are given ba sed on the experimental HRTEM images.