Hydrogen-enhanced clusterization of carbon in crystalline silicon

The influence of hydrogen impurities on the formation of carbon nanoclusters in carbon-enriched (>1017 cm−3) float-zone (FZ) silicon has been studied by means of EPR along with uniaxial-stress experiments. Hydrogen was incorporated by proton implantation at room temperature. As object of research, we used EPR as a signal of the earlier not identified EPR defect with S=1/2 and a C2 symmetry of g-tensor (denoted as PK4), which was observed in fast neutrons irradiated silicon. We have found that hydrogen implantation in FZ silicon with elevated content of carbon upon subsequent annealing above ∼250 °C generate most prominent EPR signal of the defect. We have revealed reliably three sets of hyperfine (hf) satellites: (1) one equivalent Si atom with strong localization (∼42%) of the resonant wave function of tetragonal symmetry; (2) four equivalent Si atoms with ∼16% of the resonant wave function; (3) weak hfi, which can be caused by an isotope of 13C from four equivalent carbon atoms. Uniaxial stress experiments reveal very large value (∼2.8 eV) of the activation energy for atomic reorientation that, along with data of piezospectroscopic tensor, are in good agreement with the cluster nature of the defect. We suggest that the presence of hydrogen leads to a strongly coordinated formation of nanocluster, which include carbon and self-interstitial atoms. It is suggested that the electronic structure of this defect corresponds to the double donor in a positive charge state.