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.