High spatial resolution transmission electron microscopy studies of semiconductor heterostructures

In the last few months a resolution of 0.07 nm has been demonstrated in a high angle annular dark field (HAADF) image recorded with a scanning transmission electron microscope (STEM) equipped with spherical aberration coefficient correctors . In the last ten years HAADF imaging has demonstrated the capability to achieve atomic resolution in a solid with several advantages relative to other TEM imaging techniques, such as phase contrast high-resolution transmission electron microscopy (HRTEM) . The capabilities of new FEG TEM instruments equipped with STEM attachment allow us to obtain at the same time z-contrast results, comparable with dedicated STEM, and TEM capabilities . We have used HAADF experiments to directly obtain chemical information with atomic resolution on semiconductor heterostructures. Si-GaAs superlattices fabricated by molecular beam epitaxy (MBE) were used as samples. The 10 period superlattices were grown on GaAs (001) wafers and included Si quantum wells of nominal thickness of one monolayer separated by 30 nm thick GaAs barriers. Cross-sectional scanning tunneling microscopy (XSTM) experiments were also conducted for comparison on the same specimens. The TEM results are compared with XSTM experiment on the same samples.