Dual ion beam grown silicon carbide thin films: Variation of refractive index and bandgap with film thickness

Abstract

Amorphous SiC thin films on a silicon substrate (Si) with different film thicknesses (about 20–450 nm) were deposited using dual ion beam sputtering deposition (DIBSD) at room temperature. These SiC thin films were of high quality showing high coverage (>90%) and low surface and interface roughness (<5 Å). The structure and morphology of these SiC/Si systems were explored by x-ray reflectivity, x-ray diffraction, scanning electron microscopy, and atomic force microscopy. The bonding configuration and compositional details of the SiC films were examined by Fourier-transform infrared and Raman spectroscopy. The optical constants (complex dielectric function and refractive index) and the bandgap of SiC thin films were analyzed through spectroscopic ellipsometry in the 0.55–6.3 eV energy range. An increase in the bandgap (5.15–5.59 eV) and a corresponding decrease in the refractive index (2.97–2.77) were noticed with the increase of SiC film thickness from about 20–450 nm. This thickness dependent trend in optical properties is attributed to the increase of the C to Si atomic concentration ratio in DIBSD grown SiC thin films with increasing film thickness, as observed from energy dispersive x-ray analysis measurements. The unique properties of amorphous SiC have already placed it as a suitable candidate for solar cells and photovoltaic applications in its thin film form. The results developed in this study for thickness dependent optical properties of SiC thin films can be used for further optimizing the performance of SiC in various applications through tuning of optical properties.