Structural properties of Bi_2Te_3 topological insulator thin films grown by molecular beam epitaxy on (111) BaF_2 substrates

摘要

Structural properties of topological insulator bismuth telluride films grown epitaxially on (111) BaF_2 with a fixed Bi_2Te_3 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 Bi_2Te_3 and Bi_4Te_5, 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 Bi_2Te_3 films. Line width of the L= 18 Bi_2Te_3 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 Bi_2Te_3 films with thickness from 165 to 8 nm exhibited well defined interference fringes, evidencing homogeneous layers with smooth surface. Our results demonstrate that Bi_2Te_3 films with very well controlled structural parameters can be obtained. High structural quality Bi_2Te_3 films as thin as only eight quintuple layers grown here are promising candidates for intrinsic topological insulator.