Defects in Irradiated Silicon. I. Electron Spin Resonance of the Si-ACenter

The Si-$A$ center is a major, radiation-damage defect produced in "pulled" silicon by a room temperature irradiation. As a result of studies described in this paper (I), and the following one (II), it is concluded that this center is a lattice vacancy with an oxygen atom impurity bridging two of the four broken bonds associated with the vacancy. Spin resonance and electrical activity arise from an electron trapped in the other two bonds. In this paper (I), the spin resonance studies are described. A molecular orbital treatment of the trapped electron wave-function satisfactorily accounts for the observed $g$ tensor, as well as the hyperfine interaction observed with neighboring 4.7% abundant ${\mathrm{Si}}^{29}$ nuclei. Study of the changes in the spectrum of a sample subjected to uniaxial stress are also described. Under stress, the amplitudes of the individual resonance components (which correspond to different orientations of the defect in the crystal) are observed to change. This results from (1) electronic redistribution of the trapped electrons among the defects, and (2) thermally activated reorientation of the defects themselves under the applied stress. These two effects are separated and a quantitative study of their magnitudes and signs, as well as their rates, is given. The results confirm many of the important microscopic features of the model.