Optical properties of silicon carbide thin films deposited by atomic substitution on porous silicon

Silicon carbide films on porous-Si/Si substrates have attracted considerable attention due to their potential use in modern high-power electronic devices. Here, SiC/porous-Si/Si heterostructures fabricated by an atomic substitution method are investigated. Scanning electron microscopy shows the formation of a continuous about 40 nm thick film of SiC, with a sharp interface to the porous Si sublayer. Energy-dispersive x-ray spectroscopy confirmed that Si, C, and O are the only constituents of the SiC film and the porous-Si underlayer. Raman spectroscopy indicated 3C and 6H polytypes in the SiC film. Spectroscopic ellipsometry in the range of 0.6–5.1 eV was performed in order to determine the refractive index (n), extinction coefficient (k), and bandgap (Eg) of the SiC layer. Macro-FTIR transmission spectra showed the expected absorption features of SiC. IR reflectance maps measured with nano-resolution reveal lateral inhomogeneities of the intensity, which we attribute to the morphology of the porous silicon sublayer. Numerical simulations of the local near-field response were performed for regions, where the SiC layer lay directly on silicon and for regions where it is free-standing over pores. The simulation results are in close agreement with the experimental observations obtained by nanoFTIR and confirm that the porous substrate plays a decisive role in determining the local optical and structural properties of the SiC/porous-Si/Si heterostructures.