Thermal Conductivity and Phonon Scattering Processes of ALD Grown PbTe–PbSe Thermoelectric Thin Films

Abstract

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.

Te Nanoneedles Induced Entanglement and Thermoelectric Improvement of SnSe

“…The introduction of Te nanoneedles into the SnSe resulted in the formation of heterointerfaces between the Te and SnSe, which acted as effective phonon scattering centers. Thus, the κ values of the Te nanoneedles(x)/SnSe composites were lower than that of pristine SnSe, in accordance with the previous reports on the phonon scattering in composite materials [30][31][32]. The κ value of the pristine SnSe was restricted efficiently by the scattering of phonons at the heterointerfaces for reaction times of up to 4 h. With reaction times greater than 4 h, the κ value subsequently increased as the higher volumetric fraction of Te nanoneedles in the composite (Table S1) [26][27][28][29].…”

Advances in Atomic Layer Deposition (ALD) Nanolaminate Synthesis of Thermoelectric Films in Porous Templates for Improved Seebeck Coefficient

“…Increased phonon scattering was believed to be attributed to compositional points defects and interface boundaries between PbTe and PbSe layers, or other scattering defects like dislocations. The Volmer-Weber growth mode of ALD deposited PbTe and PbSe results in a further reduction in thermal conductivity, especially as film thickness is reduced [78]. Additionally, the ALD nanolaminates grown on porous templates show slightly further reduction in thermal conductivity compared to the case of the planar nanolaminates samples.…”

“…The dotted lines are cumulative thermal conductivity with respect to phonon mean free path at room temperature, that were calculated by Tian's group at MIT [77]. For comparison, the overlaid dot symbols were individual measurements of cross-plane thermal conductivity of PbTe, PbSe and PbTe/PbSe nanolaminates, grown on planar and porous silicon substrates with respect to their total thickness, reported by our collaborators Mallory E. DeCoster et al at the University of Virginia (UVA) [78]. In general, PbTe/PbSe nanolaminates exhibited lower thermal conductivity, compared to parent PbTe and PbSe films.…”

“…The thermal conductivity data were measured by time domain thermo-reflectance (TDTR) at University of Virginia (UVA). The data were extracted from ref [78] and [73].…”

A Review on Fundamentals, Design and Optimization to High ZT of Thermoelectric Materials for Application to Thermoelectric Technology

“…For instance, the thermal conductivity of the thin film was reported below the alloy limit using long-period compositionally graded Si 1-x Ge x superlattices. 158 The phonon thermal conductivity was reduced in n-type PbTe-PbSe nanostructured thin films grown by atomic layer deposition 159 . Huang et al 160 reduced the thermal conductivity in a silicon thin film using nanocone.…”