Site Preference of Se and Te in Bi_2Se_3-xTe_x Thin Films

The ternary topological insulators Bi_2Se_3-xTe_x have attracted a great deal of attention due to their exotic physical and chemical properties. While most of the studies focus on the properties of these ternary TIs, limited research was performed to investigate the dynamic atomic stack of its crystal structure. We prepared high-quality Bi_2Se_3-xTe_x thin films on GaAs(111)B substrates using molecular beam epitaxy, characterized with Raman spectroscopy, x-ray diffraction and photoelectron spectroscopy. It is found that when Se is replaced by Te, the preferred substituting sites are the middle layer at 0 < x < 1, and this is also valid for Se substituting Te at 2 < x < 3. In the middle region, the substituting atoms prefer to go to the first and the fifth layer.