Effect of ion bombardment and hydrogen pressure during deposition on the optical properties of hydrogenated amorphous carbon thin films

• Published in: Diamond and related materials 2011-02, Vol.20 (2), p.109-114
• Main Authors: Kassavetis, S., Laskarakis, A., Logothetidis, S.
• Format: Article
• Language: English
• Subjects: Applied sciences; Carbon; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Deposition; Deposition by sputtering; Electronics; Exact sciences and technology; Hydrogen storage; Hydrogenated amorphous carbon; Ion bombardment; Materials science; Mathematical models; Methods of deposition of films and coatings; film growth and epitaxy; Optical properties; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of specific thin films; Optoelectronic devices; Physical radiation effects, radiation damage; Physics; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Spectroscopic ellipsometry; Structure of solids and liquids; crystallography; Thin films
• ISSN: 0925-9635; 1879-0062
• DOI: 10.1016/j.diamond.2010.11.008

Carbon-based thin films are ideal materials for several state-of-the-art applications, such as protective materials and as active films for organic electronics, medical, optoelectronic devices. In this work, we study in detail the effect of the ion-bombardment and the hydrogen partial pressure during deposition on the optical properties of hydrogenated amorphous carbon (a-C:H) thin films grown onto c-Si substrates by rf magnetron sputtering. The optical properties of the a-C:H films were investigated by phase modulated Spectroscopic Ellipsometry in a wide spectral region from the NIR to the Vis-far UV (0.7–6.5 eV). A dispersion model based on two Tauc-Lorentz oscillators, has been applied for the analysis of the measured < ε(ω)> of the a-C:H films to describe the π–π* and σ–σ* interband electronic transitions, that can describe accurately the optical properties of all amorphous carbons. The applied V b influences the bombardment of the growing thin films with Ar ions affecting the content of sp 2 and sp 3 hybridized carbon bonds in the films. As it was found, the increase of the applied negative voltage reduces the optical transparency of the a-C:H films. Also, the H incorporation has been found to change only the energy position of the σ–σ* transitions. Finally, from the study of the refractive index n(ω = 0 eV) it has been found that the increase of the ion bombardment during the films deposition is correlated to an increase in the films density. ► Accurate estimation of the π–π* and σ–σ* interband electronic transitions. ► Substrate negative bias voltage increase results to less transparent a-C:H films and affects the energy position of the π–π* and σ–σ* transitions and the bonded H fraction in the films.