Structural properties of Bi₂Te₃ topological insulator thin films grown by molecular beam epitaxy on (111) BaF₂ substrates

Structural properties of topological insulator bismuth telluride films grown epitaxially on (111) BaF₂ with a fixed Bi₂Te₃ beam flux were systematically investigated as a function of substrate temperature and additional Te flux. A layer-by-layer growth mode is observed since the early stages of epitaxy and remains throughout the whole deposition. Composition of the epitaxial films produced here stays between Bi₂Te₃ and Bi₄Te₅, as determined from the comparison of the measured x-ray diffraction curves with calculations. The substrate temperature region, where the growth rate remains constant, is found to be the most appropriate to obtain ordered Bi₂Te₃ films. Line width of the L = 18 Bi₂Te₃ diffraction peaks as low as 140 arcsec was obtained, indicating high crystalline quality. Twinning domains density rises with increasing growth temperature and reducing Te extra flux. X-ray reflectivity curves of pure Bi₂Te₃ films with thickness from 165 to 8 nm exhibited well defined interference fringes, evidencing homogeneous layers with smooth surface. Our results demonstrate that Bi₂Te₃ films with very well controlled structural parameters can be obtained. High structural quality Bi₂Te₃ films as thin as only eight quintuple layers grown here are promising candidates for intrinsic topological insulator.