Enhanced Cross-Plane Thermoelectric Figure of Merit Observed in an Al₂O₃/ZnO Superlattice Film by Hole Carrier Blocking and Phonon Scattering

Abstract

We experimentally investigate the cross-plane figure of merit (ZT) for an Al2O3/ZnO (AO/ZnO) superlattice film by measuring cross-plane electrical and thermal conductivity and Seebeck coefficient using the 3-ω method and an in-house Seebeck coefficient measurement system recently developed for 300–500 K and examine how ZT factors depend on the AO layer inside the AO/ZnO superlattice film using measured thermoelectric properties. The AO/ZnO superlattice film exhibited maximum power factor of ∼276.2 μW/m K2 with low thermal conductivity (∼0.31 W/m K), producing ZT ≥ 0.45 at 500 K, which is approximately 2,650% improvement compared with an undoped ZnO film (∼0.017). The enhanced ZT performance of the AO/ZnO superlattice film can be explained by enhanced phonon scattering at the interface and minority carrier blocking at the interfacial barrier due to the AO layer, suggesting that the interfacial AO layer is important to enhance ZT in oxide-based films. These results open new applications for micro- or nanoscale thin film-based thermoelectric devices.

Enhanced Thermoelectric Transport and Stability in Atomic Layer Deposited-HfO2/ZnO and TiO2/ZnO-Sandwiched Multilayer Thin Films

“…One disadvantage of pure ALD ZnO, though, is its low electrical stability at high temperatures [20][21]. While this could be overcome by the incorporation of other elements, thermoelectric devices based on doped ALD ZnO thin films have been mainly limited to Al and Ga 3 [7,11,[22][23][24]. Although Al has been a well-established dopant, ALD Al-doped ZnO (AZO) has been reported to exhibit low doping efficiency of only about 13 % [19].…”

“…In addition, ALD allows high controllability over the amount and distribution of dopants. One disadvantage of pure ZnO synthesized by ALD, though, is its low electrical stability at high temperatures. , While this could be overcome by the incorporation of other elements, TE devices based on doped ZnO thin films synthesized by ALD have been mainly limited to Al and Ga. ,,− Although Al has been a well-established dopant, Al-doped ZnO (AZO) synthesized by ALD has been reported to exhibit a low doping efficiency of only about 13% . Additionally, group III elements have relatively low stability when doped in ZnO owing to the low electronegativity difference with O .…”

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

“…The Seebeck coefficient of undoped ZnO and doped AO/ZnO superlattices are −171 µV/K and −179 µV/K, respectively. But the Seebeck coefficient of doped AO/ZnO superlattice samples increased~337% more rapidly as the temperature increased and trended to become larger than the undoped ZnO sample [79]. The thermal conductivity of the AO/ZnO superlattice is 0.31 W/mK, which is about 1233% lower than that of the undoped ZnO sample.…”

“…Won-Yong Lee etc. at Chung-Ang University, S. Korea, investigated cross-plane thermoelectric properties of ALD deposited Al 2 O 3 /ZnO (AO/ZnO) superlattices over the temperature range of 300 K to 500 K [79]. The Seebeck coefficient of undoped ZnO and doped AO/ZnO superlattices are −171 µV/K and −179 µV/K, respectively.…”

Effects of Intermixing in Sb2Te3/Ge1+xTe Multilayers on the Thermoelectric Power Factor

“…For instance, both PbTe/Eu x Pb 1– x Te multilayers and Si/SiGe superlattices (SLs) show an increased PF inside the quantum wells, , and optimized growth direction of GaAs/AlAs SLs predicts superior ZT values (∼0.41) compared with the values for bulk GaAs . Furthermore, SL (multilayer) films of oxides, such as Al 2 O 3 /ZnO, LaNiO 3 /SrTiO 3 and Ca­(OH) 2 /Co 3 O 4 , have shown remarkably high ZT , − even though the values for the oxides themselves are relatively low. Chalcogenide materials, an extensively studied material class, exhibit favorable properties for high TE performance when structured in multilayer, e.g., Bi 2 Te 3 /Sb 2 Te 3 , PbSeTe/PbTe, Sb 2 Te 3 /MoS 2 , and GeTe/Sb 2 Te. ,− Among these, the highest ZT value of 2.4 at room temperature was obtained in Bi 2 Te 3 /Sb 2 Te 3 .…”