Electrical, Thermal, and Thermoelectric Characterizations of Vapor Solid Bi$_{2}$Te$_{3}$ Nanoplates

Single-crystal nanoplates of Bi$_{2}$Te$_{3}$ synthesized by the vapor solid method are characterized by electrical, thermal, and thermoelectrical measurements. The Bi$_{2}$Te$_{3}$ domains investigated are less than 12 nm thick and are suspended to remove substrate doping effects. A room temperature thermal conductivity of 1.5 Wm$^{-1}$K$^{-1}$ was measured, lower than the 1.8--3.3 Wm$^{-1}$K$^{-1}$ range reported for bulk crystals with different carrier types and concentrations. The room temperature electrical conductivity was measured at 1.5$\times $10$^{5}$ Sm$^{-1}$. Applying the Wiedemann-Franz Law, the electron contribution to the total thermal conductivity is nearly 40 {\%} at room temperature. The electrical conductivity is similar to that reported for bulk single crystals at an electron concentration of 3.5$\times $10$^{19}$ cm$^{-3}$.~ However, the room-temperature Seebeck coefficient of -66 $\mu $VK$^{-1}$ indicates $n$-type doping and is lower than that reported for $n$-type Bi$_{2}$Te$_{3}$ single crystals at an electron concentration as high as 14.6$\times $10$^{19}$ cm$^{-3}$. Consequently, the figure of merit is only 0.11 at room temperature, a factor of 7.9 lower than the highest ZT reported for $n$-type single crystals at the optimized doping level.