Distant iron-shallow-donor pairs in silicon detected by electron paramagnetic resonance

The electron-paramagnetic-resonance transitions of isolated neutral interstitial iron (Feᵢ⁰) in n-type silicon show a satellite structure, which is clearly detectable for donor concentrations (P or As, respectively) above 10¹⁵ cm^-3. The satellite structure reflects the hyperfine interaction with one shallow-donor nucleus and one iron nucleus in the case of doping with ⁵⁷Fe. The spectra are explained by the spin-spin interaction of one Feᵢ⁰ (spin SFe=1) and one shallow donor (spin SD=1/2). Neither line positions nor line shapes depend on the direction of the magnetic field with respect to the crystal axes. A random distribution of distant iron-donor pairs is suggested by the following facts. Both (SFe+SD) levels (high-field satellites) and (SFe-SD) levels (low-field satellites) are thermally populated. Asymmetric line shapes and dissimilar hyperfine components indicate a continuous distribution of spin-spin interaction parameters.