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Effect of post-annealing on the optoelectronic properties of ZnO:Ga films prepared by pulsed direct current magnetron sputtering 指導老師：林克默 學 生：吳仕賢 報告日期：2010.04.09 W.T. Yen a, Y.C. Lin a, P.C. Yao b, J.H. Ke a, Y.L. Chen a, Thin Solid Films (2009). a Department of Mechatronics Engineering, National Changhua University of Education, Changhua 50007, Taiwan b Department of Materials Science and Engineering, DaYeh University, Changhua 515, Taiwan. 大綱 前言 實驗流程 結果與討論 結論 前言 The resemblance in atomic radius (Ga:0.062 nm and Zn:0.083 nm) and bond lengths result in less lattice deformation for Ga-doping during high temperature processing. However, the low resistive, visible transparent GZO thin films with high near-infrared reflectivity has potential employment in “solar control” or “low-emittance” windows. In this study, we illustrate the results of our investigations on the effect of post-annealing on the optoelectronic properties of ZnO:Ga films prepared by pulsed direct current magnetron sputtering. 實驗流程 A sintered ceramic target with a mixture of ZnO and Ga2O3 (99.999% purity) was employed. The content of Ga2O3 added to the target was 3 wt.%. Argon was admitted as the sputtering gas after the sputtering chamber was pumped down to 6.6×10−4 Pa. The working distance between the target and substrate was 5.5 cm. The deposition were performed by the following settings: direct current power, 150W; substrate temperature, 250±3°C; pulse frequency of 10 kHz. After deposition, the pristine GZO samples were further annealed by varying 300 to 500 °C under ambient atmosphere. 結果與討論 In summary, the XRD characterization exhibits that the GZO thin films have well crystallinity with identical preferred crystal orientation irrelevant to the annealing temperatures. This result is somewhat different to those published elsewhere for the sputtered ZnO:Al films. Nevertheless, as proved by Fig. 1, the grain size of the films did not alter significantly by annealing. In that case, the density of the grain boundary was kept constant so that the grain boundary limited transport effect did not alter substantially by annealing. The XPS spectra of the GZO films (Fig. 3) shows that the binding energy (BE) of each constituent element is positioned at 1117.72 eV (Ga2p3/2), 1022.23 eV (Zn2p3/2) and 530.9 eV (O1s), respectively as calibrated to 285.43 eV (C1s). Recent study shows that hydroxide species originating during deposition is not the source of adsorbed oxygen. However, peroxide species (O22−) is believed to be the origins of surface component. During deposition, the surface is exposed mainly to Zn and O2 species. Furthermore, there are other more reactive oxygen species in the gas phase. To deposit ZnO film, O2 is unfavorable to dissociate directly, instead, peroxide intermediates are formed. Additionally, the absorption band edge will move toward the long wavelength side (red shift), i.e., the Burstein–Moss effect weakens because the carrier concentration is lowered by rising in annealing temperature. With that, the optical band gap falls between 3.53 and 3.82 eV. Furthermore, Eopt decreases slightly by the annealing temperature as consequence of dropping in carrier concentration at elevated annealing temperature. On the other hand, the poor crystalline and small grain size of pristine GZO films without annealing or annealing at low temperature leads to more grain boundaries and defects which bring about GZO films with greater near-infrared absorption, and thereby, lower nearinfrared reflectivity. Rising in the annealing temperature improves the crystallinity and grain size of GZO thin films while the grain boundaries and defects decreases, 結論 Annealing is beneficial in improving the crystalline and conductivity of thin film. The film has lowest resistivity of 1.36×10−4Ω cm with optical band gap around 3.82 eV by annealing at 300 °C for 0.5h. Besides, the average optical transmittance in the visible region for all films reaches 88%.