  Morphology of the interlayer van der Waals surface and differential tunneling
conductance in p-Bi2-xSbxTe3-ySey solid solutions were studied by scanning
tunneling microscopy and spectroscopy in dependence on compositions.
Topological characteristics of the Dirac fermion surface states were
determined. It is shown that the thermoelectric power factor and the material
parameter enhance with the shift of the Dirac point to the top of the valence
band with increasing of atomic substitution in these thermoelectrics.
Correlation between topological characteristics, power factor and material
parameter was found. A growth contribution of the surface states is determined
by an increase of the Fermi velocity for large atomic substitutions of Bi at
x>1.5 and small substitutions in the Te sublattice (y=0.06). In compositions
with smaller substitutions at x = (1-1.3) and y=(0.06-0.09), similar effect of
the surface states is determined by raise of the surface concentration of
charge carriers.
