Thickness effects on the dielectric dispersion and optical conductivity parameters of CuO thin films

In this article, the effect of film thickness on the structural, optical, dielectric, and optical conductivity parameters of CuO thin films are reported. CuO thin films which are prepared by the physical vapor deposition technique under vacuum pressure of 10−5 mbar with various thicknesses in the range of 50 to 1000 nm are observed to exhibit amorphous nature of growth. The values of the energy bands gaps, the spectral response of the dielectric constant and of the optical conductivity parameters are highly sensitive to the film thickness. Particularly, while the 50 nm thick CuO films exhibits quantum confinement which forces the material to have wide band gap (2.70 eV), the thicker films display an energy band gap in the infrared range of spectrum. It was also observed that the thicker the films, the more pronounced the nonlinear dielectric response. In addition, analysis of the optical conductivity parameters using Drude-Lorentz approach for optical conduction has shown that the 50 nm thick films can display drift mobility value of 4.65 cm2/Vs accompanied with plasmon frequency of 1.20 GHz and free carrier density of 7.5×1017 cm3. The Drude-Lorentz analysis has also shown that the free carrier density and the plasmon frequency of CuO decreases with increasing film thickness. This decrement is accompanied with enhancement in the drift mobility values which reaches 12.56 cm2/V s as the film thickness exceeds 250 nm. Such features of the thin layer of CuO make them suitable for the production of nano/microthin film transistors.