Enhanced Seebeck coefficient of bismuth telluride compounds with graded doping profiles

Thermoelectric properties of Bi-Sb-Te and Bi-Se-Te compounds with graded Ag doping profiles are reported. A junction structure with graded doping is formed in the Bi-Te based compounds through thermally driven Ag diffusion, which has demonstrated a greatly enhanced Seebeck coefficient when a thermal gradient is applied in the same direction of carrier concentration gradient. A mechanism based on the spatial variation of bandgap narrowing induced by heavy-doping effect is proposed to explain the anomalous thermoelectric property of Bi-Te based compounds with graded doping profiles.