Intrinsic ultrathin topological insulators grown via molecular beam epitaxy characterized by in-situ angle resolved photoemission spectroscopy

We demonstrate the capability of growing high quality ultrathin (10 or fewer quintuple layers) films of the topological insulators Bi₂Se₃ and Bi₂Te₃ using molecular beam epitaxy. Unlike previous growth techniques, which often pin the Fermi energy in the conduction band for ultrathin samples, our samples remain intrinsic bulk insulators. We characterize these films using in-situ angle resolved photoemission spectroscopy, which is a direct probe of bandstructure, and ex-situ atomic force microscopy. We find that the conduction band lies above the Fermi energy, indicating bulk insulating behavior with only the surface states crossing the Fermi energy. The use of a thermal cracker allows for more stoichiometric flux rates during growth, while still creating intrinsically doped films, paving the way for future improvements in growth of topological insulators.