  We identify the multi-layered compound GeBi4Te7 to be a topological insulator
with a freestanding Dirac point, slightly above the valence band maximum, using
angle-resolved photoemission spectroscopy (ARPES) measurements. The spin
polarization satisffies the time reversal symmetry of the surface states,
visible in spin-resolved ARPES. For increasing Sb content in GeBi(4-x)SbxTe7 we
observe a transition from n- to p-type in bulk sensitive Seebeck coefficient
measurements at a doping of x = 0.6. In surface sensitive ARPES measurements a
rigid band shift is observed with Sb doping, accompanied by a movement of the
Dirac point towards the Fermi level. Between x = 0.8 and x = 1 the Fermi level
crosses the band gap, changing the surface transport regime. This difference of
the n- to p-type transition between the surface region and the bulk is caused
by band bending effects which are also responsible for a non-coexistence of
insulating phases in the bulk and in the near surface region.
