Abstract
The effects of pre-hydrogenation on the variation in the optical bandgap E 0 in nanocrystallized silicon layers have been analysed in terms involving the relaxation of the structure after thermal annealing. This is suggested by the decrease in the internal stress Σ for increasingly higher hydrogen content in the precursor film, that is before annealing. The striking resemblance noticed between the evolution of Σ and that of the Urbach edge energy E u seems to suggest that, following the case of amorphous silicon, for example. E u would reflect the disorder in our mixed-phase material and then govern the observed variation in the bandgap. The close correlation found between the widening of E 0 and the increase in the hydrogen content in the basic hydrogenated amorphous silicon layer (a-Si:H), combined with the concomitant decrease in Σ or E u, has been interpreted on the basis of the beneficial role of hydride species, such as SiH2, in the relaxation of the structure during the thermal crystallization. These features are less evident for samples partially crystallized at the origin. The impact of the various degree of disorder on the extent of the temperature range of validity corresponding to each of the conduction mechanisms, the hopping and the thermally activated, has also been evidenced.