films*

Bi₂Te₃ and Sb₂Te₃ are semiconductors that also behave as topological insulators when they are thin films. The topological properties mean that the surface conducting states have carriers that have spins locked normal to their momentum states. We have studied the growth of thin films grown by molecular beam epitaxy containing Bi₂Te₃, Sb₂Te₃ and alloys of (Bi_1-xSb_x)₂Te₃. As was discovered earlier¹, this allows the chemical potential to be tuned from p-type to n-type by varying the relative composition. We have also grown short period superlattices and thin bilayers of the tellurides to study how this occurs when the binary phases are kept in separate layers. The growth on c-plane sapphire crystallizes into a flatter film when Bi₂Te₃ is the interfacial layer. Like in the case of alloys, the carrier type in the bilayers can be tuned by modifying layer thickness. In bilayers with different thicknesses we have studied how the conductivity depends on layer thickness.

1. Zhang, J. et al. Band structure engineering in (Bi_1−xSb_x)₂Te₃ ternary topological insulators. Nature Communications 2:574 ; 10.1038/ncomms1588 (2011).