Berlin 2015 – scientific programme

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DS: Fachverband Dünne Schichten

DS 36: Poster Session I

DS 36.40: Poster

Thursday, March 19, 2015, 09:30–12:00, Poster A

Structural ordering and phonon mode behavior in MBE-grown Bi₂Te_3−xSe_x layers — •Karl Brunner¹, Steffen Schreyeck¹, Adrian Kirchner¹, Claus Schumacher¹, Jean Geurts¹, Grzegorz Karczewski², and Laurens W. Molenkamp¹ — ¹Universität Würzburg, Exp. Physik III, Würzburg, Germany — ²Institute of Physics, Polish Academy of Sciences, Warsaw, Poland

Layers of Bi₂Te_3−xSe_x, a system with interesting topological and thermoelectrical properties, were grown by MBE on H-passivated Si(111). We varied the Se-flux at constant Bi and Te flux to obtain 70 nm layers with x = 0 to 3. Bi₂Te_3−xSe_x forms chemically bonded quintuple layers (QLs) VI(2)-V-VI(1)-V-VI(2) with Van-der-Waals bonds between the QLs. EDX, Raman spectroscopy and HRXRD reveal a nonlinear increase of Se content x with Se flux, as well as changes of phonon-mode and XRD properties at x = 1. All these results are well described based on a kinetic adsorption/incorporation/desorption growth model with an enhanced incorporation probability of Se vs. Te, which is by far most pronounced at the central site VI(1). This results in partial ordering, e.g. 75% of the Se atoms at site VI(1) in Bi₂Te₂Se.

The Raman-active phonon modes E_2g, A_1g¹ and A_1g² are described by coupled spring-mass systems. The nearly constant mode frequencies for Se-content x = 0 to 1 verify the preferential incorporation of Se at the center-of-mass site VI(1). XRD reveals peculiar variations of lattice parameter c and XRD peak intensities with x. They are directly related to ordering and the different changes in spacings of inequivalent lattice planes within a QL caused by Se on site VI(1) or VI(2).