Band structure engineering in short period Bi₂Se₃/Sb₂Te₃ superlattices grown by molecular beam epitaxy

When grown by molecular beam epitaxy (MBE) Bi₂Se₃ is n-type and Sb₂Te₃ is p-type due to selenium vacancies and anti-site defects, respectively. To capitalize on the unique topological surface properties of these materials it is essential to reduce the bulk carriers. Compensation doping is a way to do that, but that method requires accurate dopant incorporation levels that are difficult to achieve. In this work we explore the use of p-n-p-n short-period superlattices (SLs) to accomplish this goal. A series of Bi₂Se₃/Sb₂Te₃ short-period SLs with varying period thicknesses and Bi₂Se₃ to Sb₂Te₃ thickness ratios were grown by MBE. The samples were characterized by high resolution x-ray diffraction (HR-XRD) and transport measurements. Using HR-XRD we determine the change in effective composition and SL period for the samples. We observed a dependence of bulk background doping on the SL period thickness: lower carrier density for thinner SL period. We interpret this as the formation of a gap due to quantum confinement effects. A preservation of a weak anti-localization (WAL) cusp, typical of topological surface features, was observed by magnetoconductance.