  The compound Bi14Rh3I9 consists of ionic stacks of intermetallic
[(Bi4Rh)3I]2+ and insulating [Bi2I8]2- layers and has been identified to be a
weak topological insulator. Scanning tunneling microscopy revealed the robust
edge states at all step edges of the cationic layer as a topological
fingerprint. However, these edge states are found 0.25 eV below the Fermi level
which is an obstacle for transport experiments. Here, we address this obstacle
by comparing results of density functional slab calculations with scanning
tunneling spectroscopy and angle-resolved photoemission spectroscopy. We show
that the n-type doping of the intermetallic layer is intrinsically caused by
the polar surface and is well screened towards the bulk. In contrast, the
anionic "spacer" layer shows a gap at the Fermi level, both, on the surface and
in the bulk, i.e. it is not surface-doped due to iodine desorption. The well
screened surface dipole implies that a buried edge state, probably already
below a single spacer layer, is located at the Fermi level. Consequently, a
multilayer step covered by a spacer layer could provide access to the transport
properties of the topological edge states. In addition, we find a lateral
electronic modulation of the topologically non-trivial surface layer which is
traced back to the coupling with the underlying zigzag chain structure of the
spacer layer.
