Institute of Solid State Physics, University of Bremen, 28359 Bremen, Germany, EMAT, University of Antwerp, 2020 Antwerp, Belgium, CEA, LETI, Minatec Campus, Grenoble, France, University Grenoble Alpes, 38000 Grenoble, France

The chemical composition of four Si1?xGex layers grown on silicon was determined from quantitative scanning transmission electron microscopy (STEM). The chemical analysis was performed by a comparison of the high-angle annular dark field (HAADF) intensity with multislice simulations. It could be shown that amorphous surface layers originating from the preparation process by focused-ion beam (FIB) at 30 kV have a strong influence on the quantification: the local specimen thickness is overestimated by approximately a factor of two, and the germanium concentration is substantially underestimated. By means of simulations, the effect of amorphous surface layers on the HAADF intensity of crystalline silicon and germanium is investigated. Based on these simulations, a method is developed to analyze the experimental HAADF-STEM images by taking the influence of the amorphous layers into account which is done by a reduction of the intensities by multiplication with a constant factor. This suggested modified HAADF analysis gives germanium concentrations which are in agreement with the nominal values. The same TEM lamella was treated with low-voltage ion milling which removed the amorphous surface layers completely. The results from subsequent quantitative HAADF analyses are in agreement with the nominal concentrations which validates the applicability of the used frozen-lattice based multislice simulations to describe the HAADF scattering of Si1?xGex in STEM. © 2017 Elsevier B.V.

Amorphous layers, Chemical analysis, Quantitative HAADF STEM, SiGe

Chemical analysis, Germanium, Germanium compounds, High resolution transmission electron microscopy, Ion beams, Scanning electron microscopy, Silicon compounds, Specimen preparation, Transmission electron microscopy, Amorphous layer, Amorphous surface layers, Germanium concentration, High-angle annular dark fields, Multislice simulations, Quantitative haadf stems, Scanning transmission electron microscopy, SiGe, Amorphous silicon, germanium, silicon, accuracy, Article, chemical analysis, chemical composition, high angle annular dark field, material state, scanning transmission electron microscopy, simulation, surface property, thickness