P-N Junctions in Ultrathin Topological Insulator Sb2Te3/Bi2Te3 Heterostructures Grown by Molecular Beam Epitaxy

We fabricated topological insulating Sb2Te3/Bi2Te3 p-n heterostructures by means of molecular beam epitaxy and characterized the topography of the films by scanning tunneling microscopy. Due to the van der Waals growth mode of the layered Te compounds, X-ray diffraction measurements show that the heterostructure is fully relaxed on the Si(111) substrate. Furthermore, scanning transmission electron microscopy measurements unveil the crystalline structure of the p-n interface. Energy dispersive X-ray spectroscopy and atom probe tomography enable the mapping of the chemical element distribution. We conclude that a diffusion of Sb and Bi during growth causes the formation of ternary compounds. In addition a Sb and Te accumulation at the substrate interface could be detected. Transport measurements prove the tunability of the carrier concentration via thickness variation of the p-n heterostructure.