Spatially resolved EELS of GaAs/GaAlAs heterostructures

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)Al(x)As 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 less-than-or-equal-to 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.