Investigation on structural, morphological and optical properties of Co-doped ZnO thin films

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This paper reports the structural, morphological and optical properties of undoped and cobalt doped (1, 10 atomic wt% Co) ZnO thin films on glass substrates prepared by a simple cost effective sol-gel spin coating technique. The effect of cobalt doping on the optical properties like transmittance, refractive index, extinction coefficient, etc. was investigated. X-ray diffraction (XRD) and Raman spectra confirm the formation of wurtzite ZnO structure with (100) as the preferred orientation. Atomic force microscopy (AFM) images of ZnO and Co-doped ZnO films show smooth surfaces with a uniform distribution of spherical grains on the surface. The morphological changes from undoped to doped samples are more evident from the correlation images obtained using MATLAB software. All the films show more than 80% of transparency in the entire visible region while 10% Co-doped ZnO film has the highest transparency (>94%). Spectroscopic ellipsometry was used to study the refractive index and extinction coefficient which indicates the highest refractive index and lower extinction coefficient for 10% Co-doped ZnO thin films. High transparency in the visible region along with a high refractive index and lower extinction coefficient in Co-doped ZnO films can be useful for optoelectronic devices.