Properties of Bi₂Se₃ and Bi_xSb_(2-x)Te₃ grown by MBE

We have studied molecular beam epitaxy growth of Bi₂Se₃ and Bi_xSb_(2-x)Te₃. We have demonstrated that by using a two-step growth recipe, very flat films of both materials can be obtained. The film quality was confirmed using RHEED oscillations during growth and, post-growth XRD, AFM, and STEM. Under other growth and processing conditions, we have observed a more complicated film morphology in the growth of Bi_xSb(_2-x)Te₃, which we attribute to compositional phase segregation. Using different substrates strongly impacts the film morphology. By tuning the ratio of Bi to Sb, the carrier type can be tuned from p-type to n-type measured via the Hall effect. The films were also studied by ARPES using a flip-chip cleaving approach in which the film plane at the interface to the substrate is measured after cleaving. The Hall and ARPES results agreed with regard to carrier type.