Abstract
Electron paramagnetic resonance (EPR) studies have been made of the stress-induced alignment and the subsequent recovery of the double donor (AA1 EPR center) that is formed in float-zone silicon following hydrogen implantation and annealing for ∼20 min at a temperature above ∼300 °C. The obtained data compare with those of the thermal double donor (NL8 EPR center). The activation energy for atomic reorientation of the (HDD+) AA1 defect is (2.3±0.1) eV. The reorientation rate is greater than that of the (TDD+) NL8 defect formed in Czochralski Si by a factor of 104. Both centers have C2v symmetry and piezospectroscopic measurements reveal a large compressional strain along their [001] (three-axis) direction. However, in contrast to the NL8, the core of the AA1 defect produces also large compressional strain along its one-axis parallel to [110] direction. These data demonstrate unambiguously that the two centers have different molecular structures, in spite of their similar EPR spectra and electrical properties. It is suggested that the two centers have similar core structures (a 〈001〉-oriented self-interstitials complexes), while the outer shell structure incorporates hydrogen or oxygen atoms, respectively.