Developing PbTe-based superlattice structures with enhanced thermoelectric performance

The fabrication of n-type PbTe/PbTe_0.75Se_0.25 structures using a simple evaporation technique has yielded high-quality superlattice films, a significant reduction in lattice thermal conductivity and potentially enhanced thermoelectric device performance, compared to standard PbTeSe alloys. The room temperature lattice thermal conductivity of PbTeSe alloys have been reduced by a factor of two or more using PbTe/PbTeSe superlattices in the cross-plane direction. Using this advantage, we have begun characterizing the cross-plane ZT of PbTe/PbTeSe superlattice devices, including the development of appropriate Ohmic contacts for the PbTe-material system. We will discuss various device process technologies for improved Ohmic contacts. The room-temperature measurement of cross-plane figure-of-merit in n-type PbTe/PbTe_0.75Se_0.25 device structure by the transient method will be reported. Also, these results will be combined with temperature dependent measurements of in-plane resistivity and Seebeck coefficient to yield evidence of enhanced thermoelectric performance. The results from similar p-type films, as well as preliminary data on heteroepitaxial films grown on Bi₂Te₃ will be discussed.