Abstract
The thermal conductivities of c- and a-axis-oriented zinc oxide (ZnO) thin films with nominal thicknesses of 100, 200, and 300 nm are investigated. The c- and a-axis-oriented ZnO thin films were synthesized by radio frequency magnetron sputtering on the c- and r-plane sapphire substrates, respectively. The epitaxial relationship between the ZnO thin film and the c-plane sapphire substrate is (0001) [1 1 00] || (0001) [11 2 0], and that between the ZnO thin film and the r-plane sapphire substrate is (11 2 0) [1 1 00] || (01 1 2) [11 2 0]. The c-axis-oriented ZnO thin film has a columnar structure, whereas the a-axis-oriented ZnO thin film has a single domain-like structure and a significantly flat surface. The thermal conductivity of the c-axis-oriented ZnO thin film is in the range of 18-24 W m -1 K -1 , whereas for the a-axis-oriented ZnO thin film, it is in the range of 24-29 W m -1 K -1 . For the c-axis-oriented ZnO thin films, the phonon scattering on both the out-of-plane and in-plane grain boundaries affects the thermal conductivity. In contrast, the thermal conductivity of the a-axis-oriented ZnO thin films decreases with the decrease of the film thickness. The distribution of the normalized cumulative thermal conductivity of the a-axis-oriented ZnO thin films suggests that the heat transport carrier mostly consists of phonons with the mean free paths between 100 nm and 1 μm.
| Original language | English |
|---|---|
| Article number | 035101 |
| Journal | Journal of Applied Physics |
| Volume | 125 |
| Issue number | 3 |
| DOIs | |
| Publication status | Published - 2019 Jan 21 |
| Externally published | Yes |
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ASJC Scopus subject areas
- Physics and Astronomy(all)
Cite this
Thermal conductivity of hetero-epitaxial ZnO thin films on c - And r -plane sapphire substrates : Thickness and grain size effect. / Yamashita, Yuichiro; Honda, Kaho; Yagi, Takashi; Jia, Junjun; Taketoshi, Naoyuki; Shigesato, Yuzo.
In: Journal of Applied Physics, Vol. 125, No. 3, 035101, 21.01.2019.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Thermal conductivity of hetero-epitaxial ZnO thin films on c - And r -plane sapphire substrates
T2 - Thickness and grain size effect
AU - Yamashita, Yuichiro
AU - Honda, Kaho
AU - Yagi, Takashi
AU - Jia, Junjun
AU - Taketoshi, Naoyuki
AU - Shigesato, Yuzo
PY - 2019/1/21
Y1 - 2019/1/21
N2 - The thermal conductivities of c- and a-axis-oriented zinc oxide (ZnO) thin films with nominal thicknesses of 100, 200, and 300 nm are investigated. The c- and a-axis-oriented ZnO thin films were synthesized by radio frequency magnetron sputtering on the c- and r-plane sapphire substrates, respectively. The epitaxial relationship between the ZnO thin film and the c-plane sapphire substrate is (0001) [1 1 00] || (0001) [11 2 0], and that between the ZnO thin film and the r-plane sapphire substrate is (11 2 0) [1 1 00] || (01 1 2) [11 2 0]. The c-axis-oriented ZnO thin film has a columnar structure, whereas the a-axis-oriented ZnO thin film has a single domain-like structure and a significantly flat surface. The thermal conductivity of the c-axis-oriented ZnO thin film is in the range of 18-24 W m -1 K -1 , whereas for the a-axis-oriented ZnO thin film, it is in the range of 24-29 W m -1 K -1 . For the c-axis-oriented ZnO thin films, the phonon scattering on both the out-of-plane and in-plane grain boundaries affects the thermal conductivity. In contrast, the thermal conductivity of the a-axis-oriented ZnO thin films decreases with the decrease of the film thickness. The distribution of the normalized cumulative thermal conductivity of the a-axis-oriented ZnO thin films suggests that the heat transport carrier mostly consists of phonons with the mean free paths between 100 nm and 1 μm.
AB - The thermal conductivities of c- and a-axis-oriented zinc oxide (ZnO) thin films with nominal thicknesses of 100, 200, and 300 nm are investigated. The c- and a-axis-oriented ZnO thin films were synthesized by radio frequency magnetron sputtering on the c- and r-plane sapphire substrates, respectively. The epitaxial relationship between the ZnO thin film and the c-plane sapphire substrate is (0001) [1 1 00] || (0001) [11 2 0], and that between the ZnO thin film and the r-plane sapphire substrate is (11 2 0) [1 1 00] || (01 1 2) [11 2 0]. The c-axis-oriented ZnO thin film has a columnar structure, whereas the a-axis-oriented ZnO thin film has a single domain-like structure and a significantly flat surface. The thermal conductivity of the c-axis-oriented ZnO thin film is in the range of 18-24 W m -1 K -1 , whereas for the a-axis-oriented ZnO thin film, it is in the range of 24-29 W m -1 K -1 . For the c-axis-oriented ZnO thin films, the phonon scattering on both the out-of-plane and in-plane grain boundaries affects the thermal conductivity. In contrast, the thermal conductivity of the a-axis-oriented ZnO thin films decreases with the decrease of the film thickness. The distribution of the normalized cumulative thermal conductivity of the a-axis-oriented ZnO thin films suggests that the heat transport carrier mostly consists of phonons with the mean free paths between 100 nm and 1 μm.
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U2 - 10.1063/1.5055266
DO - 10.1063/1.5055266
M3 - Article
VL - 125
JO - Journal of Applied Physics
JF - Journal of Applied Physics
SN - 0021-8979
IS - 3
M1 - 035101
ER -