ANNEALING-INDUCED EFFECTS ON THE STABILITY OF HYDROGENATED AMORPHOUS-SILICON

We performed isothermal annealing on a hydrogenated amorphous silicon (a-Si:H) sample deposited at low temperature in a glow discharge react or. In order to change the hydrogen bonding configuration without affe cting the silicon structure we choose a relatively low annealing tempe rature. We studied the dependence on the annealing time of the dark co nductivity, photoconductivity, light-induced degradation of the photoc onductivity, optical gap, vibrational spectra, and subgap defect densi ty. As the annealing time increased we found an increase in the dark c onductivity activation energy. This shift of the dark Fermi level towa rd the valence band was correlated with the growth of a peak in the de nsity of states below midgap. From the vibrational spectra we obtained the microstructure parameter, which is indicative of the amount of hy drogen bonded as polihydrides and/or to some sort of internal surface. We used the bond-breaking model to fit photoconductivity decay as a f unction of illumination time, and we found a correlation between the S taebler-Wronski susceptibility and the microstructure parameter. This would mean that the stability of the material concerning light-induced degradation is related to the way hydrogen is attached in the amorpho us network. (C) 1995 American Institute of Physics.