Dependence of Electrical, Optical, and Structural Properties on the Thickness of GZO Films Prepared by CRMS

Abstract

The dependence of electrical, optical, structural, and surface properties on the thickness of Ga-doped ZnO (GZO) thin films deposited on glass substrates by cylindrical rotating magnetron sputtering (CRMS) was investigated. The resistivity of the CMRS-grown GZO films gradually decreased from 7.4×10-3Ohm-cm to 4.9×10-4Ohm-cm with increasing its thickness, while the transparency of the GZO films in visible region were kept constant regardless of its thickness. Both x-ray diffraction and high resolution electron microscope examinations showed that the CMRS-grown GZO film has a strongly (002) preferred orientation with increasing thickness even though it was sputtered at low substrate temperature below 230°C. By using spectroscopic ellipsometry, we estimated accurately the dielectric function and band gap energy of the CRMS grown GZO film. Using absorption coefficient α(=4πk/λ) and linear extrapolation method, the band gap energy of the CRMS grown GZO film was estimated to be 3.67 × 0.04 eV, which is independent of its thickness. However, we found that it gave erroneous thickness-dependence of band gap energy when we used the absorbance (=-ln(T)/d) derived from transmission rather than the absorption coefficient. © 2011 The Electrochemical Society.