EPR study of defects in neutron-irradiated silicon: Quenched-in alignment under〈110〉-uniaxial stress

The stress effect in an EPR study is first treated rigorously in terms of the piezospectroscopic tensor, taking account of the local symmetry of a defect. It is found that the degree of alignment ($\frac{n_{\perp }}{n_{\parallel }}$) provides incisive information on the structure of a defect; in general, a nonplanar vacancy cluster results in $\frac{n_{\perp }}{n_{\parallel }}<1.0\mathrm{}$ and a {110}-planar vacancy chain gives rise to $\frac{n_{\perp }}{n_{\parallel }}>1.0\mathrm{}$. We reanalyze the results on the $\mathrm{S}\mathrm{i}-P1\mathrm{}$ and $\mathrm{S}\mathrm{i}-P3\mathrm{}$ spectra. Based on the quenched-in alignment under uniaxial stress, we confirm the assignment on the $\mathrm{S}\mathrm{i}-P1\mathrm{}$ and the $\mathrm{S}\mathrm{i}-P3\mathrm{}$ spectra to a negative charge state of nonplanar pentavacancy cluster and to the neutral charge state (spin 1) of the {110}-planar tetravacancy chain, respectively. Tentative models of the $\mathrm{S}\mathrm{i}-A3\mathrm{}$ as a tetravacancy cluster and the $\mathrm{S}\mathrm{i}-A4\mathrm{}$ spectra as a {110}-planar trivacancy chain are discussed.