Enhanced thermoelectric properties of atomic-layer-deposited ZnO-Based superlattice thin films by tuning the composition and structure of interlayers
Journal
Ceramics International
Date Issued
2021
Author(s)
Abstract
Superlattice thin films composed of a lightly Hf-doped ZnO matrix and various periodically inserted interlayers—including TiO2, ZrO2, HfO2, and their combinations, with various thicknesses—were prepared by atomic layer deposition (ALD) and characterized in terms of thermoelectric properties. The effects of interlayer type and thickness on the comprehensive thermoelectric properties of the superlattice films were determined, including electron mobility (μe), electron concentration (ne), electrical conductivity (σ), Seebeck coefficient (S), power factor (PF), thermal conductivity (κ), and ZT value. The TiO2, ZrO2, and HfO2 interlayers provided different potential barriers (HfO2 > ZrO2 ? TiO2) and atomic-mass mismatches (HfO2 > ZrO2 > TiO2) with the matrix, resulting in differing trade-off's among energy filtering (raising S), carrier blocking (lowering σ), and phonon scattering (reducing κ) effects. Favorable balances of the effects were obtained by combining the single-content interlayers into composite interlayers, where the ALD preparation method enabled precise tuning of the interlayer composition and structure for optimal thermoelectric properties of the superlattice films. Specifically, superlattice films with a composite interlayer consisting of an alternating 1 cycle TiO2/1 cycle HfO2 structure at 1.5 nm thickness achieved a maximum of approximately 17-fold increase in ZT over that of bulk ZnO films. The results presented a quantitative guide for designing interlayer structures in superlattice films for enhanced thermoelectric properties. ? 2021
Subjects
Atomic layer deposition
Energy filtering
Superlattice
Thermoelectric
Transparent conductive oxides
Atoms
Composite films
Economic and social effects
Film preparation
II-VI semiconductors
Semiconductor doping
Structural optimization
Thermoelectricity
Thin films
Titanium dioxide
Tuning
Zinc oxide
Zirconia
Atomic-layer deposition
Composite interlayers
Interlayer structure
Super-lattice films
Superlattice thin films
Thermoelectric properties
Thermoelectric equipment
Type
journal article