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

To identify the mechanisms responsible for the modifications of microelctro nic devices characteristics, we used ab initio calculations (density functi onal theory) on clusters, modelling a-SiO2 structure. With this theoretical study we describe defect properties such as geometry and electronic struct ure. Considering E' centers, and especially E'gamma, both the precursor (th e oxygen vacancy) and the defect (the positively charged oxygen vacancy) ar e well described by calculations. The levels introduced in the bandgap are consistent with the ability for the oxygen vacancy and E'gamma to trap char ges. The method has been extended to phenomena which are not understood, su ch as charge compensation, by studying the effect of electron trapping on t hese 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 st ructure is proposed, which is consistent with the existing model of reversi ble charge compensation during annealing. (C) 1999 Published by Elsevier Sc ience B.V. All rights reserved.