Growth, structure, and electronic properties of epitaxial bismuth telluride topological insulator films on BaF₂ (111) substrates

Epitaxial growth of topological insulator bismuth telluride by molecular beam epitaxy onto BaF₂ (111) substrates is studied using Bi ₂Te₃ and Te as source materials. By changing the beam flux composition, different stoichiometric phases are obtained, resulting in high quality Bi₂Te₃ and Bi₁Te₁ epilayers as shown by Raman spectroscopy and high-resolution X-ray diffraction. From X-ray reciprocal space mapping, the residual strain, as well as size of coherently scattering domains are deduced. The Raman modes for the two different phases are identified and the dielectric functions derived from spectroscopic ellipsometry investigations. Angular resolved photoemission reveals topologically protected surface states of the Bi₂Te₃ epilayers. Thus, BaF ₂ is a perfectly suited substrate material for the bismuth telluride compounds.