Links between hydrogen bonding, residual stress, structural properties and metastability inhydrogenated nanostructured silicon thin films

Abstract

We present a systematic study of the local hydrogen bonding in hydrogenatedpolymorphous silicon thin films (pm-Si:H), a heterogeneous material deposited on the edgeof crystallinity, by means of Fourier transform infrared spectroscopy. A vibrational mode at is reported and attributed to hydrogen atoms bonded in hydrogen-rich regions present atthe interface between ordered regions and the amorphous matrix. This assignment is foundto be in good agreement with previous spectroscopic ellipsometry and Raman spectroscopystudies. Combined with stress measurements we draw a picture of the nanostructure ofpm-Si:H films, namely a two-domain material exhibiting: (i) large fluctuationsof H content, (ii) a high mass density and (iii) the coexistence of highly strainedcrystalline phases with a relaxed amorphous matrix. Unexplained optoelectronicproperties and metastability phenomena can also be accounted for by this picture.