ELEMENTAL MAPPING IN ALGAAS/GAAS HETEROSTRUCTURES USING PARALLEL EELS

Parallel detection of EEL spectra in a field emission STEM allows the determination of the Ga-concentration in AlxGa1-xAs/GaAs heterostructures with a spatial resolution of 1 nm and an accuracy of +/- 0.05 in (1-x). The weak signal to noise ratio and problems in background estimation limit the direct measurement of the Al-concentration by means of the Al-K edge. Automation of EELS data acquisition enables the detection of up to 4096 spectra in one experiment. The spectra either represent a linescan or a 2 D map. In practice, the technique is very useful to record elemental compositions along line profiles. The detection of 2 D maps with associated long recording times is in principle possible but still limited by specimen contamination and system instabilities.