| AVS 57th International Symposium & Exhibition | |
| Spectroscopic Ellipsometry Focus Topic | Friday Sessions |
| Session EL+AS+EM+MS+TF-FrM |
| Session: | Spectroscopic Ellipsometry - Inorganic Thin Films |
| Presenter: | H. Makino, Kochi University of Technology, Japan |
| Authors: | T. Yamada, Kochi University of Technology, Japan H. Makino, Kochi University of Technology, Japan N. Yamamoto, Kochi University of Technology, Japan T. Yamamoto, Kochi University of Technology, Japan |
| Correspondent: | Click to Email |
Transparent conductive Ga-doped ZnO (GZO) thin films was one of promising candidates as transparent electrodes in flat panel displays and thin film solar cells. In this study, we investigated contributions of intra-grain scattering and grain boundary scattering on Hall mobility of polycrystalline GZO thin films based on the analysis of spectroscopic ellipsometry measurements. The GZO films were deposited by ion-plating method with DC arc discharge. Samples with a wide range of thicknesses from 70 to 500 nm were deposited at 200 degree C on glass substrates by controlling the deposition time. Sintered ZnO ceramic tablets doped with 1 wt% and 4 wt% Ga2O3 were used as evaporation sources. A systematic study has been done on the structural, electrical and optical properties of GZO films. In the case of GZO films using 4wt% Ga2O3 doped tablet, the minimum resistivity of 1.8×10-4 Ωcm was obtained at the film thickness of around 350 nm. The carrier concentration and Hall mobility was 1.2×1021 cm-3 and 29 cm2/Vs, respectively. The GZO films showed c-axis preferential orientation nearly normal to the substrate surface with columnar grain structures. In XRD measurements, full width half maximum of (0002) omega rocking curve decreased with increasing the film thickness. It means that the fluctuation in the c-axis orientations among the grains improved with increasing the film thickness. Average grain size of columnar structure was estimated by Williamson-Hall plot on spectral width of in-plane XRD patterns. The average grain size increased with increasing film thickness. Optical mobility of the GZO films was estimated from analysis using the conventional Drude model on data obtained by spectroscopic ellipsometry. Differences between the optical mobility obtained by the spectroscopic ellipsometry and the Hall mobility obtained by Hall effect measurements suggest contribution from grain boundary scattering on the Hall mobility. It demonstrates that grain boundary scattering contributes to the Hall mobility in rather thinner film thickness. However, the very small contribution of grain boundary scattering to the Hall mobility was observed in the thick films. On the other hand, resistivity of 4.5×10-4 Ωcm with the carrier concentration of 3.6×1020 cm-3 and Hall mobility of 39 cm2/Vs was obtained for a 500 nm thick GZO film using the ZnO ceramic target doped with 1 wt% Ga2O3. The spectroscopic ellipsometry analysis on the GZO film suggests that the Hall mobility was dominated by intra-grain scattering.