  Three-dimensional topological insulators (3D-TIs) are a new generation of
materials with insulating bulk and exotic metallic surface states that
facilitate a wide variety of ground-breaking applications. However, utilization
of the surface channels is often hampered by the presence of crystal defects,
such as antisites, vacancies and twin domains. For terahertz device
applications, twinning is shown to be highly deleterious. Previous attempts to
reduce twins using technologically important InP(111) substrates have been
promising, but have failed to completely suppress twin domains while preserving
high structural quality. Here we report growth of twin-free molecular beam
epitaxial Bi2Se3 and Sb2Te3 structures on ultra-thin In2Se3 layers formed by a
novel selenium passivation technique during the oxide desorption of smooth,
non-vicinal InP(111)B substrates, without the use of an indium source. The
formation of un-twinned In2Se3 provides a favorable template to fully suppress
twin domains in 3D-TIs, greatly broadening novel device applications in the
terahertz regime.
