Influence of oxygen partial pressure on transparency and conductivity of RF sputtered Al-doped ZnO thin films

Transparent conductive Al-doped ZnO thin films were prepared on glass substrates by radio frequency (RF) diode sputtering with Ar + O-2 gas at an Al2O3-mixed ZnO ceramic target. The samples, with constant thickness of 0.5 mu m, were prepared under various O-2 partial pressure ratios in the range of 0% to 3%, and then annealed at 400 degrees C for 4 h in a vacuum furnace. Their electrical, optical, and X-ray diffraction properties were evaluated. The resistivity of transparent films was in the range of 5 x 10(-3) tol X 10(-2) Omega.cm, the carrier concentration was 2 X 10(20) cm(-3), Hall mobility was 3-6 cm(2)/V s, and the property of infrared wavelength cutoff was confirmed. Introducing O-2 gas prevented the films from yellow coloration caused by lack of oxygen atoms, and improved the durability with respect to cracking and peeling caused by residual stress. Atomic force microscopy and X-ray diffraction measurements showed that the lateral grain size was 100-150 nm and vertical grain size was about 12 nm. (C) 2000 Elsevier Science B.V. All rights reserved.