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Structure and composition of bismuth telluride topological insulators grown by molecular beam epitaxy
Author(s) -
Steiner Hubert,
Volobuev Valentine,
Caha Ondřej,
Bauer Günther,
Springholz Gunther,
Holý Václav
Publication year - 2014
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s1600576714020445
Subject(s) - stacking , molecular beam epitaxy , diffraction , lattice (music) , materials science , crystallography , bismuth , lattice constant , epitaxy , topological insulator , neutron diffraction , crystal structure , condensed matter physics , chemistry , optics , physics , layer (electronics) , nanotechnology , organic chemistry , acoustics , metallurgy
The structure and composition of Bi 2 Te 3−δ topological insulator layers grown by molecular beam epitaxy is studied as a function of beam flux composition. It is demonstrated that, depending on the Te/Bi 2 Te 3 flux ratio, different layer compositions are obtained corresponding to a Te deficit δ varying between 0 and 1. On the basis of X‐ray diffraction analysis and a theoretical description using a random stacking model, it is shown that for δ≥ 0 the structure of the epilayers is described well by a random stacking of Te–Bi–Te–Bi–Te quintuple layers and Bi–Bi bilayers sharing the same basic hexagonal lattice structure. The random stacking model accounts for the observed surface step structure of the layers and compares very well with the measured X‐ray data, from which the lattice parameters a and c as a function of the chemical composition were deduced. In particular, the in‐plane lattice parameter a is found to continuously increase and the average distance of the (0001) hexagonal lattice planes is found to decrease from the Bi 2 Te 3 to the BiTe phase. Moreover, the lattice plane distances agree well with the linear interpolation between the Bi 2 Te 3 and BiTe values taking the strain in the epilayers into account. Thus, the chemical composition Bi 2 Te 3−δ can be directly determined by X‐ray diffraction. From analysis of the X‐ray diffraction data, quantitative information on the randomness of the stacking sequence of the Bi and Te layers is obtained. According to these findings, the layers represent random one‐dimensional alloys of Te–Bi–Te–Bi–Te quintuple and Bi–Bi bilayers rather than a homologous series of ordered compounds.