Theoretical study using density functional theory of defects in amorphous silicon dioxide

To identify the mechanisms responsible for the modifications of microelctronic devices characteristics, we used ab initio calculations (density functional theory) on clusters, modelling a-SiO2 structure. With this theoretical study we describe defect properties such as geometry and electronic structure. Considering E' centers, and especially E'gamma, both the precursor (the oxygen vacancy) and the defect (the positively charged oxygen vacancy) are well described by calculations. The levels introduced in the bandgap are consistent with the ability for the oxygen vacancy and E'gamma to trap charges. The method has been extended to phenomena which are not understood, such as charge compensation, by studying the effect of electron trapping on these structures. Charges trapped on levels introduced in the bandgap, lead to investigate stability and properties of other charged defects in a-SiO2 and especially the negatively charged oxygen vacancy. ta possible defect structure is proposed, which is consistent with the existing model of reversible charge compensation during annealing. (C) 1999 Published by Elsevier Science B.V. All rights reserved.