Spin lifetime measurements in MBE-grown GaAs epilayers

Electron spin relaxation times in excess of the localized limit have been measured in MBE n-GaAs layers, with the times depending on the doping concentration. We have optically oriented the electrons in the samples, and measured spin lifetimes via luminescence depolarization in a transverse magnetic field (Hanle effect). The lifetimes thus obtained were 14 and 26 ns for samples nominally doped at 1 X 10(15) and 3 X 10(15) cm(-3), respectively. The dominant dephasing mechanism, which is the hyperfine interaction of localized electrons with lattice nuclei, is discussed. Our results are presented in the context of our larger goal, which is to use resonance techniques for spin measurements and control. In this context, the Hanle spin lifetime measurement is a necessary step to be followed by optically detected magnetic resonance in a longitudinal magnetic field.