  Topological insulators are novel quantum materials with metallic surface
transport, but insulating bulk behavior. Often, topological insulators are
dominated by bulk contributions due to defect induced bulk carriers, making it
difficult to isolate the more interesting surface transport characteristics.
Here, we report the synthesis and characterization of nanosheets of topological
insulator Bi2Se3 with variable Sb-doping level to control the electron carrier
density and surface transport behavior. (Bi1-xSbx)2Se3 thin films of thickness
less than 10 nm are prepared by epitaxial growth on mica substrates in a vapor
transport setup. The introduction of Sb in Bi2Se3 effectively suppresses the
room temperature electron density from ~4 \times 10^13/cm^2 in pure Bi2Se3 (x =
0) to ~2 \times 10^12/cm^2 in (Bi1-xSbx)2Se3 at x ~0.15, while maintaining the
metallic transport behavior. At x > ~0.20, a metal-insulator transition (MIT)
is observed indicating that the system has transformed into an insulator in
which the metallic surface conduction is blocked. In agreement with the
observed MIT, Raman spectroscopy reveals the emergence of vibrational modes
arising from Sb-Sb and Sb-Se bonds at high Sb concentrations, confirming the
appearance of Sb2Se3 crystal structure in the sample. These results suggest
that nanostructured chalcogenide films with controlled doping can be a tunable
platform for fundamental studies and electronic applications of topological
insulator systems.
