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