Spectroscopic ellipsometry studies of sol-gel-derived Cu-doped ZnO thin films

Undoped and Cu-doped ZnO (Zn_1−xCu_xO: x = 0.00, 0.03, 0.06, 0.10) films were prepared on Si(100) substrates by the sol-gel method, and the effects of Cu content on the structural, and optical properties of these films were investigated by X-ray diffraction (XRD) and UV–visible spectroscopic ellipsometry (SE). XRD patterns revealed that all the films were monophasic and had wurtzite structure with (002) preferential orientation along c-axis, indicating there were not any secondary phases. The measured UV–visible SE spectra were analyzed with an appropriate procedure to accurately determine the thickness and the optical constants. We found that the refractive index and the extinction coefficient increase with Cu content increasing. The optical band gap (E_g) has been calculated by classical Tauc formula, and the E_g values decrease as Cu content increasing. The variation in E_g with different Cu content revealed that the E_g value was affected by doping Cu. These mean that we can control the optical properties of the ZnO films by varying Cu content, which might be important in view of designing integrated optic devices. - Highlights: • Undoped and Cu-doped ZnO thin films were prepared by the sol-gel method. • The structural and optical properties of Cu-doped ZnO films were investigated. • Band gap Eg decreases as Cu content increasing. • The optical constants (n and k) increase with Cu content increasing