EFFECTS OF PRIOR HYDROGENATION ON THE STRUCTURE AND PROPERTIES OF THERMALLY NANOCRYSTALLIZED SILICON LAYERS

Nanocrystalline silicon layers have been obtained by thermal annealing of films sputtered in various hydrogen partial pressures. The as-depo sited and crystallized films were investigated by infrared, Raman, x-r ay diffraction, electron microscopy, and optical absorption techniques . The obtained data show evidence of a close correlation between the m icrostructure and properties of the processed material, and the hydrog en content in the as-grown deposit. The minimum stress deduced from Ra man was found to correspond to the widest band gap and to a maximum hy drogen content in the basic unannealed sample. Such a structure relaxa tion seems to originate from the so-called ''chemical annealing'' thou ght to be due to Si-H, species, as identified by infrared spectroscopy . The variation of the band gap has been interpreted in terms of the c hanges in the band tails associated with the disorder which would be i nduced by stress. Finally, the layers originally deposited with the hi ghest hydrogen pressure show a lowest stress-which does not correlate with the hydrogen content and the optical band gap-and some texturing. These features are likely related to the presence in these layers of a significant crystalline fraction already before annealing. (C) 1998 American Institute of Physics. [S0021-8979(98)00511-8].