Abstract
We fabricated the crystallized InGaZnO thin films by sol‐gel process and high‐temperature annealing at 900°C. Prior to the deposition of the InGaZnO, ZnO buffer layers were also coated by sol‐gel process, which was followed by thermal annealing. After the synthesis and annealing of the InGaZnO, the InGaZnO thin film on the ZnO buffer layer with preferred orientation showed periodic diffraction patterns in the X‐ray diffraction, resulting in a superlattice structure. This film consisted of nanosized grains with two phases of InGaO3(ZnO)1 and InGaO3(ZnO)2 in InGaZnO polycrystal. On the other hand, the use of no ZnO buffer layer and randomly oriented ZnO buffer induced the absence of the InGaZnO crystal related patterns. This indicated that the ZnO buffer with high c‐axis preferred orientation reduced the critical temperature for the crystallization of the layered InGaZnO. The InGaZnO thin films formed with nanosized grains of two‐phase InGaO3(ZnO)m superlattice showed considerably low thermal conductivity (1.14 Wm−1 K−1 at 325 K) due to the phonon scattering from grain boundaries as well as interfaces in the superlattice grain.
Highlights
The complex materials based on PbTe and SiGe have been considered for thermoelectric application due to high ZT values at mid- (500–900 K) and high- (>900 K) temperature range
The coating process was established with TG/differential thermal analysis (DTA) results, and hightemperature postannealing was performed for crystallization of these films
A more intense ZnO (0002) diffraction peak was observed in the InGaZnO thin film/flat ZnO buffer structure than in the InGaZnO thin film/rough ZnO buffer structure, as shown in Figures 4(b) and 4(c)
Summary
The complex materials based on PbTe and SiGe have been considered for thermoelectric application due to high ZT values at mid- (500–900 K) and high- (>900 K) temperature range. It was reported that nanosized inclusions (in bulk system) or nanocomposites (in low-dimensional system) in host material enhance dimensionless thermoelectric figure of merit, ZT = S2σT/κ (S: Seebeck coefficient, σ: electrical conductivity, T: temperature, and κ: thermal conductivity). Thermal conductivity is decreased due to more frequent phonon scattering by new generated interfaces, which is the main reason for the dramatic ZT increase [1]. P-type SiGe nanocomposite synthesized by sintering nanopowder showed a half of thermal conductivity (κnanocomposite = ∼2.3 Wm−1 K−1 at 1000 K) compared to that (κbulk = ∼4.5 Wm−1 K−1 at 1000 K) of SiGe bulk due to new generated grain boundaries [4]. The oxide thermoelectric materials such as Na0.75CoO2 [5], Ca3Co4O9 [6], and SrTiO3 [7] have been researched for thermoelectric application at high temperature due to high chemical and thermal stability as well as nontoxic elements
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