Films of pseudo-hexagonal Bi2 Te3, Bi2 Se3, and their alloys were successfully grown by molecular beam epitaxy (MBE) on GaAs (001) substrates. The growth mechanism and structural properties of these films were investigated by reflection high-energy electron diffraction (RHEED), atomic force microscopy (AFM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy and mapping. The results indicate that the epitaxial films are highly uniform and of high crystalline quality. The electronic band structure of these films was studied by angle-resolved photoemission spectroscopy (ARPES). The results confirm that these films are topological insulators, with a single Dirac cone for the topological surface states. Electric transport measurements were performed on the films, and weak anti-localization (WAL) was observed in the magnetoresistance. Tuning of conductance by gating was demonstrated in top-gated fi eld effect transistor (FET) devices fabricated from these fi lms.