Experimental evidence of high power factors and low thermal conductivity in Bi2Te3/Sb2Te3 superlattice thin-films

Abstract

Thermoelectric properties of p-type Bi/sub 2/Te/sub 3//Sb/sub 2/Te/sub 3/ superlattice (SL) thin-films grown by organometallic vapor phase epitaxy (OMVPE) are described. The electrical and thermal transport properties including, hole mobility, Seebeck coefficient and power factor as a function of SL dimension are described. It is observed that the carrier mobility, Seebeck coefficient and power factor of the Bi/sub 2/Te/sub 3//Sb/sub 2/Te/sub 3/ SL structures are better than that of p-type Bi/sub x/Sb/sub 2-x/Te/sub 3/ alloys, with similar bandgap and electrical resistivity. The improvement in carrier mobility is attributed to avoiding or minimizing alloy scattering of carriers with SL structures while the enhanced Seebeck coefficient is related to the bandstructure difference between the alloy and the SL structures. Initial measurements indicate that power factor improvement of /spl sim/50%, over corresponding alloys, can be obtained in SL structures. We have measured the thermal conductivity of the SL structures by the 3-/spl omega/ method and have observed a factor of four to seven reduction in thermal conductivity of optimized structures, with respect to the alloys. The electrical conductivity and Seebeck coefficient are measured in the plane of the SL structures, while the 3-/spl omega/-measured thermal conductivity can potentially be dominated by a component perpendicular to the SL structures. Hence, the figure-of-merit (ZT) values are estimated with a correction for potential anisotropy of thermal conductivity. Including this correction, implying higher assumed thermal conductivities in the plane of SL's, the preliminary estimated ZT for some SL structures are in the range of 1.22 to 1.67 at 300 K.