Microsecond spin-flip times inn−GaAsmeasured by time-resolved polarization of photoluminescence

We have observed microsecond spin-flip times in lightly doped $n-\mathrm{GaAs},$ by measuring the photoluminescence polarization in the time domain with pump and probe pulses. Times up to 1.4 μs have been measured. Our results as a function of magnetic field indicate three regions governing the spin relaxation: a low field region, where spin-flip times increase due to suppression of the nuclear hyperfine interaction for localized electrons, a medium field region where spin-flip times increase due to narrowing of the hyperfine relaxation for interacting electrons, and a high field region where spin-flip times begin to level off due to the increasing importance of spin-orbit relaxation mechanisms.