Microstructure and residual strain in (formula presented) thin films on (formula presented)-buffered (formula presented) substrates

The microstructure and residual strain of bilayer films of (formula presented) on (formula presented) substrates are investigated by means of electron-diffraction analysis and high-resolution transmission electron microscopy. In two samples containing (formula presented) buffer layers with thicknesses of 37 and 75 nm, a compressive strain is measured in the (formula presented) layers. From the presence of lattice defects close to interface imperfections it can be concluded that the thickness of these (formula presented) layers is close to the critical value for mismatch-strain relaxation. The strain level in the layer on the 37-nm-thick buffer is lower than that in the layer on the 75-nm buffer. A high density of planar shear defects is observed which can be introduced by steps of the substrate surface and by stacking faults in the film. Interfacial stacking faults are found at the interface between the (formula presented) and the (formula presented) layers. Interface roughening can hinder the formation of these faults. In addition, a strong roughness of the interface is found to induce strong lattice bending and extra strain in the (formula presented) layer.