  The microstructure of Bi2Se3 topological-insulator thin films grown by
molecular beam epitaxy on InP(111)A and InP(111)B substrates that have
different surface roughnesses has been studied in detail using X-ray
diffraction, X-ray reflectivity, atomic force microscopy and probe-corrected
scanning transmission electron microscopy. The use of a rough Fe-doped
InP(111)B substrate results in complete suppression of twin formation in the
Bi2Se3 thin films and a perfect interface between the films and their
substrates. The only type of structural defects that persist in the "twin-free"
films is an antiphase domain boundary, which is associated with variations in
substrate height. It is also shown that the substrate surface termination
determines which family of twin domains dominates.
