Dynamics of the creation of light-induced defects in amorphous silicon alloys

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Abstract
We have carried out both theoretical and experimental studies of the dynamics of creation of light-induced defects in amorphous silicon alloys. Calculations have been made based on a model which assumes that the light-induced defects are caused by the recombination of excess carriers. Different kinds of recombination processes that could initiate defect creation have been considered as well as the effect of the electronic nature of the new defects (donorlike or acceptorlike) and their energy location in the mobility gap. Measurements of photoconductivity have been made as a function of exposure time at different intensity and temperature. We find that the best fit to the experimental data is obtained if the defect-creating recombination event is between free electrons and holes trapped at special centers located about 120 meV above the valence-band edge. Analysis of the experimental data on the basis of our model also shows that new states are created in the upper half of the mobility gap, although the creation of states below midgap cannot be precluded.