Microstructural characterization of AlZnO thin films with various Al concentrations grown on Si substrates by atomic layer deposition
Ju Ho Lee1, Jae-Won Lee2, Sooyeon Hwang1, Sang Yun Kim1, Jeong Yong Lee1, and Jin- Seong Park2*
1 Department of Materials Science and Engineering, KAIST, Daejeon 305-701, Republic of Korea 2 Materials Science and Engineering, Dankook University, Anseo-Dong, Cheonan, 330-714, Republic of Korea
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Transparent conducting oxides (TCOs) are widely used in various applications such as display panels, solar cells, defrosters, and transparent thin film transistors. There are many representative TCO materials, for example, indium tin oxide, copper oxide, nickel oxide, and zinc oxide (ZnO) [1]. Many of these TCO materials, ZnO has been widely studied due to its abundance, wide direct bandgap of 3.37 eV, and large exciton binding energy of 60 meV under room-temperature. However, undoped non-stoichiometric ZnO thin film is unstable at high temperature and shows low conductivity [2]. Therefore, to enhance a stability and an electrical properties of ZnO thin films, group III elements in periodic table such as B, Al, Ga, In are doped in ZnO matrix.
Among the group III elements doped ZnO thin films, Al-doped ZnO (AZO) thin films show relatively superior electrical properties compared to that of B- or Ga-doped ZnO thin films [3]. Al atoms in ZnO matrix located to Zn sites as substitutional atoms or interstitial sites, and thus, as Al concentration of AZO thin films increased, the conductivity of the films increased. However, due to the differences of physical and chemical properties between Zn and Al, microstructural characteristics of AZO thin films changed depending on the Al concentration.
In this study, we present microstructural characterization of the AZO thin films with various Al concentrations (0 ~ 12.62 at%) grown on Si substrates at 250°C by atomic layer deposition. Interestingly, high-resolution transmission electron microscopy investigations reveal that slightly Al-doped ZnO thin film (~ 2.54 at%) shows better crystallinity than pure ZnO and heavily Al-doped ZnO thin films.
References
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(2) J. H. Lee, Y. Y. Kim, H. K. Cho and J. Y. Lee, J. Cryst. Growth 311, 4641 (2009).
(3) H. Kim, A. Piqué, J. S. Horwitz, H. Mattoussi, H. Murata, Z. H. Kafafi and D. B.
Chrisey, Appl. Phys. Lett. 74, 3444 (1999).
