METASTABLE TRIPLET-STATE OF THE VACANCY-OXYGEN CENTER IN SILICON - AN AB-INITIO CLUSTER STUDY

An ab initio quantum chemical cluster study of the neutral vacancy-oxygen or (V-O)0 center in silicon, is presented, with emphasis on its metastable triplet state. We calculate a singlet-triplet splitting of 0.16 eV for (V-O)0. By calculation of the anisotropy of the nonradiative triplet life times we prove that the nonradiative decay occurs through combined spin-orbit and vibronic interaction. The observed C2upsilon off-center displacement is shown to be an effect of chemical bonding. Relaxation effects of nearest-neighbor Si and local vibrational modes are studied. As a check on the approach we study the effect of cluster size and compare our theoretical values for the hyperfine interactions with O-17 and the three nearest Si-29 neighbor shells to experiment.