MOVPE deposition and optical properties of thin films of a Bi₂Te_3-xSe_x topological insulator

A set of monocrystalline B₂Te_3-xSe_x films of various compositions were synthesized by metalorganic vapor epitaxy. The smooth films with thicknesses of about 500 nm were grown on (0001) Al₂O₃ substrates at 465 °C using trimethylbismuth, diethyltellurium and diisopropylselenium as meta-organic precursors. The epitaxial nature of the films and their rhombohedral crystal structure are confirmed by X-ray studies and Raman spectroscopy. The elemental composition of the films was determined by energy dispersive X-ray spectrometry. Optical properties of Bi₂Te_3-xSe_x films were examined in the 260-1000 nm range by multi-angle spectroscopic ellipsometry (SE). It was shown that the optical properties of Bi₂Te_3-xSe_x films vary monotonically depending on the ratio of selenium to tellurium. It is demonstrated that SE can be used for rapid assessment of the composition of Bi₂Te_3-xSe_x films. (paper)