Thermal Conductivity And Phonon Scattering Processes Of Ald Grown Pbte-Pbse Thermoelectric Thin Films

This work studies the thermal conductivity and phonon scattering processes in a series of n-type lead telluride-lead selenide (PbTe-PbSe) nanostructured thin films grown by atomic layer deposition (ALD). The ALD growth of the PbTe-PbSe samples in this work results in nonepitaxial films grown directly on native oxide/Si substrates, where the Volmer-Weber mode of growth promotes grains with a preferred columnar orientation. The ALD growth of these lead-rich PbTe, PbSe, and PbTe-PbSe thin films results in secondary oxide phases, along with an increase microstructural quality with increased film thickness. The compositional variation and resulting point and planar defects in the PbTe-PbSe nanostructures give rise to additional phonon scattering events that reduce the thermal conductivity below that of the corresponding ALD-grown control PbTe and PbSe films. Temperature-dependent thermal conductivity measurements show that the phonon scattering in these ALD-grown PbTe-PbSe nanostructured materials, along with ALD-grown PbTe and PbSe thin films, are driven by extrinsic defect scattering processes as opposed to phonon-phonon scattering processes intrinsic to the PbTe or PbSe phonon spectra. The implication of this work is that polycrystalline, nanostructured ALD composites of thermoelectric PbTe-PbSe films are effective in reducing the phonon thermal conductivity, and represent a pathway for further improvement of the figure of merit (ZT), enhancing their thermoelectric application potential.