  Band engineering is an important mechanism to increase the thermopower of
thermoelectric materials by reconstructing the band structure near Fermi level.
PbTe and SnTe are the most representative systems in which band engineering
were achieved by various dopants. Starting with the elementary understanding of
the band structures, we established the phase diagram for the band engineering
in p-type PbTe/SnTe by constructing an s-p bonding model. We show that the
effects of band tuning are mainly determined by an inherent parameter of doping
element: the s orbital energy level. With the phase diagram, all the related
experimental observations can be consistently explained, moreover, undiscovered
effective dopants become foreseeable. Our study discovers an applicable
criteria to pick up proper dopants from the periodic table directly, and the
analytical method can be adopted to more thermoelectric materials.
