Transmission electron microscope observation of lattice image of AlxGa1−xAs-AlyGa1−yAs superlattices with high contrast

Publisher Website
Google Scholar
Abstract
High‐resolution transmission electron microscope (TEM) observation is made on cross sections including the growth direction of MBE‐grown AlxGa1−xAs‐AlyGa1−yAs superlattice samples. Lattice images with contrast high enough to distinguish each of the constituent layers in superlattices are important for the study of heterointerfaces on an atomic scale, and two methods are developed in order to obtain them. One is to use superlattices with large difference Δx=y−x in Al composition. It is found that the degree of abruptness at the heterointerface is one or two monolayers and that the heterointerface of the ternary AlGaAs grown on the binary AlAs is smoother than that of the binary grown on the ternary. The other is to observe superlattices by using an electron beam incident along a [100] crystal axis. A theoretical consideration based on both kinematical and dynamical theory of diffraction is given, which suggests that, in obtaining lattice images with high contrast, an electron beam along a [100] crystal axis is more favorable than one incident along the [110] axis which is conventionally used. This is confirmed experimentally by using a GaAs‐AlGaAs superlattice sample.