  We demonstrate the capability of growing high quality ultrathin 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 (ARPES), 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 EF . We conclude that thermal cracking of Te and Se in our growth
leads to higher quality thin films, paving the way for future improvements in
growth of topological insulators.
