  We show that a number of transport properties in topological insulator (TI)
Bi2Se3 exhibit striking thickness-dependences over a range of up to five orders
of thickness (3 nm - 170 \mu m). Volume carrier density decreased with
thickness, presumably due to diffusion-limited formation of selenium vacancies.
Mobility increased linearly with thickness in the thin film regime and
saturated in the thick limit. The weak anti-localization effect was dominated
by a single two-dimensional channel over two decades of thickness. The
sublinear thickness-dependence of the phase coherence length suggests the
presence of strong coupling between the surface and bulk states.
