Large cooling differentials and high heat flux capability with p-type Bi$_{2}$Te$_{3}$/Sb$_{2}$Te$_{3}$ and n-type Bi$_{2}$Te$_{3}$/Bi$_{2}$Se$_{x}$Te$_{3-x}$ Superlattice Thermoelectric Devices

Thin film superlattice (SL) based thermoelectric (TE) devices offer the potential for improved efficiency and high heat flux cooling over conventional bulk materials. Recently, we have demonstrated external cooling of 55K and heat pumping capacity of 128 W/cm$^{2}$.\footnote{$^{.}$ G.E. Bulman, E. Siivola, B. Shen and R. Venkatasubramanian, Appl. Phys. Lett. 89, 122117 (2006).} These high heat fluxes in thin film devices, while attractive for cooling hot-spots in electronics, also make the device performance sensitive to various thermal resistances in the device structure. We will discuss advances in the cooling performance of Bi$_{2}$Te$_{3}$-based SL TE devices and describe a method to extract device material parameters, including thermal resistance, from measurements of their $\Delta $T-I-V characteristics. These parameters will be compared to values obtained through Hall and Seebeck coefficient measurement on epitaxial materials. Results will be presented for both single couple and multi-couple modules, as well as multi-stage cascaded devices made with these materials. Single stage cooling couples with $\Delta $T$_{max}$ of 57.8K (T$_{c} \quad \sim $242K) and multi-stage modules with $\Delta $T$_{max}\sim $92.2K (T$_{c} \quad \sim $209K) have been measured.