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

The dependence of electrical, optical, structural, and surface properties on the thickness of Ga-doped ZnO (GZO) thinfilms 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 −3 Ohm-cm to 4.9×10 −4 Ohm-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 microscopeexaminationsshowedthattheCMRS-grownGZOfilmhasastrongly(002)preferredorientationwithincreasingthickness eventhoughit was sputtered at lowsubstrate temperature below230 ◦ C.Byusing 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.