Electron-paramagnetic-resonance study of metallic Si: P with iron

We have observed the electron paramagnetic resonance of iron (≈ 1 ppm) in metallic Si: P in the temperature range 1.4-77 K for electron concentrations $N_D=(3-100)\mathrm{}\times {10}^{18}$ ${\mathrm{cm}}^{-3\mathrm{}}$. The single observed line is a strongly coupled (bottlenecked) local-moment conduction-electron resonance, with the local-moment $g$ value ($g_d=2.000\mathrm{}$) different from the value (2.070) observed for ${\mathrm{Fe}}^0$ in semiconducting silicon. For electron concentrations below 2 × ${10}^{19}$ ${\mathrm{cm}}^{-3\mathrm{}}$, $g_d$ and the intrinsic local-moment relaxation rate ($\frac{1}{\gamma T_{\mathrm{dl}}}\approx 6$ G) do not depend on $N_D$. The spin-flip scattering cross section for conduction electrons on iron is not found to depend on $N_D$ but to increase with temperature with ${\sigma }_{\mathrm{sf}}=2\mathrm{}\times {10}^{-17\mathrm{}}$ ${\mathrm{cm}}^2$ at 77 K. Above 2 × ${10}^{19}$ ${\mathrm{cm}}^{-3\mathrm{}}$ the low-temperature broadening and $g$ shift decrease as $N_D$ increases until at ${10}^{20}$ ${\mathrm{cm}}^{-3\mathrm{}}$ no effect on the conduction-electron spin resonance is seen upon adding iron to the sample.