Hydrogen Balmer line broadening in Ar-N2-SiH4 DC glow discharge.
Résumé
Broadened hydrogen Balmer lines are observed in a DC glow discharge sustained in Ar-SiH4-
N2 gas mixture. This broadening is due to the Doppler frequency shift. H atoms translational
energy distribution is calculated in different positions between the two electrodes of the
discharge along the inter electrode axis and in different gas mixtures. Three main components
are observed at 0.6 (+/-0.5)eV, 12(+/-3)eV, 62(+/-6)eV and 1(+/-1)eV, 28(+/-6)eV and
105(+/-12)eV for Hα and Hβ, respectively. They correspond to hydrogen dissociation by
electron impact producing H(n=3, 4) atoms and to dissociative recombination of ion in the
cathode fall or to back-scattered fast H atoms on the cathode surface. The density ratio
nH2/nAr ranges from 44% to 13% or from 10% to 3% when a=nH/nH2=0.01 and 0.1,
respectively, in function of the gas mixture. So large hydrogen density could be due to
hydrogen desorption from the wall and cathodes and/or to the gas recirculation within the
reactor. A new low energy component is observed in Hα line profile, when silane and
nitrogen concentration decreases and increases, respectively. It could also be due to H atom
desorbing from the reactor wall or to NHx species dissociated by electron impact within the
reactor.
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