Optical absorption spectra of hydrogenated microcrystalline silicon films by resonant photothermal bending spectroscopy

A resonant photothermal bending spectroscopy (PBS) is demonstrated for the measurement of absorption coefficient spectra in hydrogenated microcrystalline silicon (pc-Si:H) and hydrogenated microcrystalline cubic silicon carbide (mu c-3C-SiC:H) films. The resonant vibration technique utilized in PBS establishes the sensitivity as alpha d similar to 5 x 10(-5) in a vacuum measurement. Appling resonant PBS to pc-Si:H films, a new extra absorption coefficient alpha(ex) spectrum is observed from 0.6 to 1.2 eV. The alpha(ex) spectrum has a peak at similar to 1.0 eV, and the localized states inducing the alpha(ex) are located similar to 0.35 eV below the conduction band edge of mu c-Si:H. A possible explanation for the observed localized state is that an oxidation produces weak bonds at the grain boundaries and/or amorphous silicon tissues. In mu c-3C-SiC:H film, an optical band-gap energy of similar to 2.2 eV was demonstrated assuming an indirect optical transition. The temperature coefficient of the optical band-gap energy was similar to 2.3 x 10(-4) eV K-1. The alpha(ex) spectrum of mu c-3C-SiC:H film is plateau-shaped and its magnitude is in accord with an increase in grain size.