Effect of Post-Annealing on Structural and Electrical Properties of ZnO:In Films

Indium-doped ZnO (ZnO:In) films are deposited on quartz substrates by rf magnetron sputtering. The effects of post-annealing on structural, electrical, optical and Raman properties are investigated by x-ray diffraction, Raman scattering, Hall measurement and first-principles calculation. The results indicate that all of the ZnO:In films have excellent crystallinity with a preferred ZnO (002) orientation. It is found that the incorporation of In can dramatically increase the intensity of the 274 cm^-1 Raman mode. However, both post-annealing treatment and increasing O_2 partial pressure in the process of preparing thin films can reduce the intensity of the 274 cm^-1 mode or even eliminate it, and relax compressive stress of the ZnO:In film judged by analyzing the shifts of the (002) Bragg peaks and E_2 (high) mode. Finally, the origin of the 274 cm^-1 mode is inferred to be the vibration of Zn interstitial (Zn_\rm i) defects, which play a crucial role in the high electron concentration and low resistivity of ZnO:In films annealed in an appropriate temperature range (450–600^\circ\!C).