X-ray and Raman Characterization of Bi-Sb Thin Films Grown by Molecular Beam Epitaxy*

The material Bi x Sb 1−x  is a promising candidate for spin-orbit torque (SOT) applications due to its potentially high figure of merit for spin-charge interconversion [Nature Mater. 17, 808 (2018)]. This is due to the strong spin-orbit coupling and topological features in the electronic band structure in the appropriate composition range. We describe the synthesis of Bi x Sb 1−x thin films using molecular beam epitaxy and their detailed structural characterization via x-ray diffraction, transmission electron microscopy, and reflection high energy electron diffraction. We discuss the crystalline defects in these films over a wide range of alloy compositions. Finally, we use Raman spectroscopy to investigate the phonon modes in these thin films and compare the results with those from bulk-grown Bi x Sb 1−x  crystals previously reported in the literature.