Dresden 2011 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 29: Topical Session TEM VIII
MM 29.2: Vortrag
Mittwoch, 16. März 2011, 16:00–16:15, IFW B
Determination of Nitrogen Concentration in Dilute GaNAs by STEM HAADF Z-Contrast Imaging — •Tim Grieb1, Knut Müller1, Oleg Rubel2, Rafael Fritz2, Marco Schowalter1, Kerstin Volz2, and Andreas Rosenauer1 — 1Universität Bremen, D-28359 Bremen — 2Universität Marburg, D-35032 Marburg
Incorporation of small amounts of nitrogen into III-V semiconductors such as GaAs reduces their band gaps which makes these alloys interesting for diverse applications. As only low N-concentrations are needed, composition analyses require highly sensitive methods. In this contribution we show that high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) allows accurate determination of composition in diluted GaNAs, based on comparison of experimental with simulated reference images. HAADF intensity is affected by atomic number (Z-contrast), thermal-diffuse scattering (TDS), and Huang scattering at static atomic displacements (SADs). For GaNAs, conventional simulations based on frozen lattice multislice algorithms that include TDS let expect a lower HAADF-STEM contrast compared to pure GaAs, but experimental results show a contrary ratio. The observed contrast can be obtained by taking SADs into account that are caused by the comparatively small covalent radius of N atoms. The SADs are computed by relaxation of super cells via valence force field calculations and implemented into the STEMsim simulation software. Considering SADs we present quantitative evaluation of concentration in GaNx<0.05As1−x quantum wells that agree with strain state analysis and X-ray diffraction measurements.