  Band structure engineering and interfacial buffer layers have been
demonstrated as effective means to tune the Fermi level in topological
insulators (TI). In particular, the charge compensated compound (BixSb1-x)2Te3
(BST) plays a critical role in the molecular beam epitaxy growth of magnetic
TIs. Here we introduce a strategy of exploiting epitaxial Cr2O3 as a buffer
layer and amorphous Cr2O3 as a capping layer in the growth of BST films. These
films exhibit carrier density lower than 1012/cm2 over a wide range of Bi
contents and higher mobility than BST films directly grown on Al2O3 substrate,
shedding light on the importance of interfacial layers for TI films and paving
a new avenue to the application of magnetic BST films.
