Microsc. Microanal. Microstruct. 2, 293-300 (1991)
DOI: 10.1051/mmm:0199100202-3029300

Spatially resolved EELS of GaAs/GaAlAs heterostructures

Hubert Lakner, Ludwig Josef Balk et Erich Kubalek

Werkstoffe der Elektrotechnik, Sonderforschungsbereich 254, Universität Duisburg, Kommandantenstrasse 60, D-4100 Duisburg 1, Germany

Abstract
Using typical beam parameters of the STEM and a parallel detector for the EEL spectra it is possible to detect principally the Al-L and Al-K edge in a GaAs/Ga(1-x)AlxAs heterostructure with a spatial resolution better than 2 nm, if the relative Al concentration is higher than x = 0.2. However, quantification of the Al edges is difficult due to minor As edges in front of the Al edges and a weak signal to noise ratio of the Al edges. Thus, for quantitative microanalysis the Ga-L edge is much more suitable. After background subtraction it is possible to determine the Ga concentration with an accuracy of x ≤ 0.05 in (1 - x). Therefrom the Al concentration x can be calculated. The spectra taken with different probe currents demonstrate that very small probe currents (5 pA) and probe diameters down to the limit of 0.2 nm can be used to perform chemical analysis of GaAs/GaAlAs heterostructures.

PACS
3480D - Atomic excitation and ionization by electron impact.
7340L - Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions.
8280 - Chemical analysis and related physical methods of analysis.

Key words
EEL spectroscopy -- Spatial resolution -- Heterostructures -- Semiconductor materials -- Gallium arsenides -- Aluminium arsenides -- Scanning transmission electron microscopy -- Chemical composition -- Molecular beam epitaxy


© EDP Sciences 1991