Defect-related absorption in hydrogenated silicon films

Recently introduced interference spectroscopy technique (IST) is used to investigate the absorption spectrum in the sub-gap energy range (0.6–1.7 eV) of hydrogenated silicon films prepared under a wide range of plasma conditions. The shape of the sub-gap absorption in several sets of samples, including amorphous, polymorphous (pm-Si:H) and microcrystalline films has been analyzed. In particular, for a series of polymorphous films deposited at 200 °C in the pressure range of 800–1800 mTorr a clear minimum of the sub-gap absorption is obtained at a pressure of 1400 mTorr. In the spectra of the best samples, a dip is observed in the conduction band tail in the region of 1.4–1.65 eV. The rise in absorption coefficient with the threshold around 1–1.1 eV in highly crystallized samples may be an indication of the crystallinity. Light-soaking effects on spectra and on the evolution of the dip at 1.5 eV are also studied in this work. The detailed analysis of results is presented.