University of PardubiceFaculty of Chemical Technology

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High Resolution X-ray Diffraction from Epitaxial Layers and Bulk Crystals of BimTen and BimSen

Authors: Holý Václav | Kriegner Dominik | Wimmer Stefan | Bauer Gunther | Groiss Heiko | Springholz Gunther | Albu M | Hofer F | Caha Ondřej | Drašar Čestmír | Čermák Patrik

Year: 2017

Type of publication: ostatní - přednáška nebo poster

Page from-to: nestránkováno

Titles:

Language	Name	Abstract	Keywords
eng	High Resolution X-ray Diffraction from Epitaxial Layers and Bulk Crystals of BimTen and BimSen	Bismuth telluride (Bi2Te3) and bismuth selenide Bi2Se3 are prototypical examples for a three-dimensional topological insulator with a gapped bulk band structure and a topological two-dimensional surface state with Dirac-like energy–momentum dispersion and spin–momentum locking. The surface states are protected by time-reversal symmetry and are immune to surface impurities and backscattering. In contrast to conventional III-V, II-VI or IV-VI compound semiconductors, bismuth telluride (as well as bismuth selenide) can exist in multiple phases with different chemical compositions. Moreover, the rhombohedral lattices of these compounds suffer from twinning; in a twinned domain the usual ABCABC… stacking of basal (0001) planes is replaced by ACBACB…. Therefore, these materials contain various defects the structure of which can be investigated by high-resolution x-ray diffraction. Using the reciprocal mapping technique we measured the reciprocal-space distributions of the diffracted intensity along the symmetric rod 000L for series of Bi2Te3 epitaxial layers deposited by molecular-beam epitaxy onto BaF2(111) substrates. We found that the phase structure of the layers substantially depend on the growth condition, especially on the excess flux of the group VI-elements (Te or Se). If the chemical composition of the layer is non-stoichiometric, the lattice structure of the layer can be described as a random sequence of structural motifs, namely Bi-Bi double layers and XBiXBiXBi quintuple layers, (X= Te or Se). X-ray diffraction from such a structure was modelled using the approach of random Markow chains. We determined the parameters of these chains and their dependence on the growth conditions and determined the optimum conditions under which an almost perfect lattice can be obtained.