Characterization of AlGaAs/GaAs interfaces by EELS and high‐resolution Z‐contrast imaging in scanning transmission electron microscopy (STEM)

Abstract

AbstractRecent developments in scannning transmission electron microscopy (STEM) instrumentation have pushed the limits of the achievable spatial resolution for analytical measurements into the subnanometer regime, which is necessary for the characterization of semiconducting heterostructures and interfaces. Z‐Contrast (or high‐angle annular dark field) imaging combines atomic resolution with chemical contrast. Such images are not affected by contrast reversals due to objective lens defocus or changes in specimen thickness, such as phase contrast images (bright field images). Parallel detection of electron energy‐loss spectra allows spatially resolved quantitative chemical information to be obtained even for high energy losses and when using a very fine electron probe diameter (down to < 0.3 nm). Examples demonstrating the performance of these techniques are given for AlGaAs/GaAs heterostructures used for very high speed and very high frequency devices. While high‐resolution Z‐contrast imaging is superior with respect to the spatial resolution achieved and the acquisition time needed, electron energy‐loss spectroscopy (EELS) can be used to record chemical line profiles with slightly decreased spatial resolution. In particular it can be used to quantify the Z‐contrast images by means of point analysis. Thus, the combination of Z‐contrast imaging and EELS can give information beyond the scope of either individual characterization technique.