Electron-spin phase relaxation of phosphorus donors in nuclear-spin-enriched silicon

We report a pulsed electron paramagnetic resonance study of the phase relaxation of electron spins bound to phosphorus donors in isotopically purified Si-29 and natural abundance Si (Si-nat) single crystals measured at 8 K. The two-pulse echo decay curves for both samples show quadratic dependence on time, and the electron phase relaxation time T-M for Si-29 is about an order of magnitude shorter than that for Si-nat. The orientation dependence of T-M demonstrates that the phase relaxation is caused by spectral diffusion due to flip-flops of the host nuclear spins. The electron spin echo envelope modulation effects in Si-29 are analyzed in the frequency domain.