Dependence of Seebeck Coefficient on Carrier Concentration in Heavily B- and P-Doped Si1-xGex (x≦0.05) System

The electrical resistivity ρ, the Seebeck coefficient S and the carrier mobility µ were measured as a function of carrier concentration n for B- and P-doped Si, Si 0.97 Ge 0.03 and Si 0.95 Ge 0.05 prepared by arc melting. It was found that at a high carrier concentration of about 2×10 20 cm -3 , the S values of the Si 0.97 Ge 0.03 and Si 0.95 Ge 0.05 samples with dopant segregations are about 50% higher than those measured previously on Si 0.95 Ge 0.05 , Si 0.85 Ge 0.15 and Si 0.7 Ge 0.3 samples with little segregation, although the differences between their ρ values are very small. The most striking result is that the S curves of the doped Si samples have a hump at a concentration of about 3×10 19 cm -3 , while no hump was observed for the Si 0.97 Ge 0.03 samples, as in the case of Si 0.7 Ge 0.3 alloys. Such a hump is surprising because it conflicts with the conventional theory that predicts a monotonic decrease of S with increasing n . This phenomenon is related to a change in the effective mass which results from dopant segregation.