Modulation of surface states in Sb2 Te3/ Bi2 Te3 topological insulator heterostructures: The crucial role of the first adlayers

Abstract

The hunt for an ideal topological insulator, where the Dirac point is situated in a desirable energetic position and the bulk remains insulating, has motivated experiments on band structure engineering in these materials. To achieve this, Sb2Te3 and Bi2Te3 are commonly combined in ternary compounds or, less frequently, in heterostructures. Here we report on the growth of Sb2Te3/Bi2Te3 heterostructures by means of molecular-beam epitaxy. Using angle-resolved photoelectron spectroscopy, we are able to differentiate between the shift of the chemical potential and the changes in the electronic structure, causing the lift-off of the Dirac point away from the bulk valence band when varying the Sb2Te3 adlayer thickness. Our paper demonstrates that the important modulation of the surface states takes place for the very first Sb2Te3 layers, while thicker adlayers only cause a gradual change of the bulk states and a rigid shift of the chemical potential. Furthermore, we observe the occurrence of diffusion between the Bi2Te3 and Sb2Te3 layers and conclude that a growth at room temperature, followed by annealing, maintains an acceptable crystalline quality while substantially reducing the interdiffusion.