Characterisation of optical band gap energies of amorf hydrogeneted carbon thin films (a-C: H) produced by single RF plasma method

In this study, optical band gap energies of a-C: H thin films produced by the plasma coating method were investigated. Thin films used in the study were produced within 15 minutes of coating time and under 0.2 torr chamber pressure. The plasma used in the production of thin films was generated under 40 MHz plasma frequency for different samples and under electric powers of 100, 150 and 200 W. The thicknesses of the produced thin films were found to be 798, 850 and 946 Ao for the thin films produced under the electric powers of 100, 150 and 200 W, respectively by an ellipsometer. Analyzes have shown that changing the plasma frequency has no significant effect on the film thickness, and increasing the plasma power and duration of the coating has increased the thin film thickness. The optical properties of thin films were examined by means of light transmittance experiments and the optical transmittance data of thin films produced under electric powers of 100, 150 and 200 W were obtained with respect to wavelength and light energy. Using this data, the wavelength-dependent absorption coefficients of the films were calculated. By using the absorption coefficients, the optical band gap energies of the films were found to be 1.36, 1.23 and 0.86 eV, respectively. Analyzes have revealed that the role of plasma frequency in the production of thin films is important, and that the changes in plasma frequency affect directly produced film's bond structure, which in turn leads to differences in optical band energies. Utilizing the results of the calculations, the optical band gap changes depending on the production conditions of the thin films are theoretically modeled. The obtained model was used to calculate the production parameters for thin films which are potentially usable in the production of devices which will work efficiently at some known color wavelengths.