EPR line width and spin-relaxation rates of shallow and deep donors in isotopically controlled silicon

The results of a numerical calculation of the contribution of ligand superhyperfine interactions to the line width for the phosphorus donor electron in silicon are reported and show linear behavior at lower concentrations compared to deep centers. The linear dependence for the phosphorus center in silicon predicts an electron spin-relaxation time for isotopically purified Si28:P longer than expected on the basis of the common square-root law. The confrontation of line width in deep-level centers with shallow states confirms that the behavior depends on the distribution of spin density around the paramagnetic center.