Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2016)
    Thin Films Monday Sessions
       Session TF-MoE

Paper TF-MoE8
Crystal Growth Simulation of ZnO Thin Film on α-Al2O3 Substrate by Molecular Dynamics Simulation

Monday, December 12, 2016, 8:00 pm, Room Makai

Session: Nanostructured Surfaces & Thin Films I
Presenter: Shunsuke Kawagishi, Tohoku University, Japan
Authors: S. Kawagishi, Tohoku University, Japan
J. Xu, Tohoku University, Japan
Y. Ootani, Tohoku University, Japan
T. Nishimatsu, Tohoku University, Japan
Y. Higuchi, Tohoku University, Japan
N. Ozawa, Tohoku University, Japan
M. Kubo, Tohoku University, Japan
Correspondent: Click to Email
A ZnO thin-film semiconductor is used as light emitting devices and quantum hall effect devices because of its broad wide band gap of 3.2 eV and large exciton binding energy of 60 meV. In the previous research, optical properties of the ZnO thin film depend on the crystal orientation and quality [1]. Therefore, in order to obtain the high-quality thin film, it is necessary to understand crystal growth process such as physical vapor deposition. However, it is difficult to observe the crystal growth process at atomic scale by experiments. In this study, to elucidate the crystal growth process of ZnO, we performed crystal growth simulation of a ZnO thin film on an α-Al2O3 substrate by our molecular dynamics simulator and analyzed crystal quality of the formed ZnO thin film.

At first, to investigate crystal growth process of the ZnO thin film, we irradiated ZnO molecules on an α-Al2O3(0001)substrate at a velocity of 900 m/s at 700, 900, and 1200 K. The ZnO thin films are formed on the substrate at 700, 900, and 1200 K. Next, to evaluate crystal quality of the formed ZnO thin films, we analyzed radial distribution function of the formed thin films. The first and second peaks of the radial distribution function at 1200 K are sharper than those at 700 and 900 K. This indicates that crystallinity of the formed thin film at 1200K is higher than that at 700 and 900 K. Our simulation result is in good agreement with the experimental result in which crystal quality is improved by increasing the substrate temperature [2]. Next, we investigated the atomic behavior in the growth process. At only 1200 K, some of the irradiated ZnO molecules dissociate on the thin film. Then, the Zn and O atoms diffuse into the formed thin film. Finally, 6-membered rings are formed by diffusion of the Zn and O atoms in the formed thin film. This indicates that atomic mobility of the Zn and O atoms on the substrate is promoted due to raising substrate temperature and this high mobility of the Zn and O atoms contributes to the quality of the formed thin film. Thus, we succeeded in crystal growth simulation of a ZnO thin film on an α-Al2O3 substrate and found difference in the growth process of the thin film at 700, 900, and 1200 K.

[1] S. Dutta et al., Progress in Materials Science, 54, 89-136 (2009).

[2] A. El-shaer et al., Superlattices and Microstructures, 38, 265-271 (2005).