title: Measurement of specimen thickness and composition in Al(x)Ga(1-x)N/GaN using high-angle annular dark field images.
abstract: In scanning transmission electron microscopy using a high-angle annular dark field detector, image intensity strongly depends on specimen thickness and composition. In this paper we show that measurement of image intensities relative to the intensity of the incoming electron beam allows direct comparison with simulated image intensities, and thus quantitative measurement of specimen thickness and composition. Simulations were carried out with the frozen lattice and absorptive potential multislice methods. The radial inhomogeneity of the detector was measured and taken into account. Using a focused ion beam (FIB) prepared specimen we first demonstrate that specimen thicknesses obtained in this way are in very good agreement with a direct measurement of the thickness of the lamella by scanning electron microscopy in the FIB. In the second step we apply this method to evaluate the composition of Al(x)Ga(1-x)N/GaN layers. We measured ratios of image intensities obtained in regions with unknown and with known Al-concentration x, respectively. We show that estimation of the specimen thickness combined with evaluation of intensity ratios allows quantitative measurement of the composition x. In high-resolution images we find that the image intensity is well described by simulation if the simulated image is convoluted with a Gaussian with a half-width at half-maximum of 0.07 nm.
authors.affiliation: Institut für Festkörperphysik, Universität Bremen, Otto-Hahn-Allee 1, D-28359 Bremen, Germany. rosenauer@ifp.uni-bremen.de
authors.forename: Andreas
authors.initials: A
authors.lastname: Rosenauer
authors.forename: Katharina
authors.initials: K
authors.lastname: Gries
authors.forename: Knut
authors.initials: K
authors.lastname: Müller
authors.forename: Angelika
authors.initials: A
authors.lastname: Pretorius
authors.forename: Marco
authors.initials: M
authors.lastname: Schowalter
authors.forename: Adrian
authors.initials: A
authors.lastname: Avramescu
authors.forename: Karl
authors.initials: K
authors.lastname: Engl
authors.forename: Stephan
authors.initials: S
authors.lastname: Lutgen