  The electron spin dynamics in multilayer GaAs/AlGaAs quantum wells,
containing high-mobility dense two-dimensional electron gases, have been
studied using time-resolved Kerr rotation and resonant spin amplification
techniques. The electron spin dynamics was regulated through the wave function
engineering and quantum confinement in multilayer quantum wells. We observed
the spin coherence with a remarkably long dephasing time T2* > 13 ns for the
structure doped beyond metal-insulator transition. Dyakonov-Perel spin
relaxation mechanism, as well as the inhomogeneity of electron g-factor, was
suggested as the major limiting factors for the spin coherence time. In the
metallic regime, we found that the electron-electron collisions become dominant
over microscopic scattering on the electron spin relaxation with the
Dyakonov-Perel mechanism. Furthermore, the data analysis indicated that in our
structure, due to the spin relaxation anisotropy, Dyakonov-Perel spin
relaxation mechanism is efficient for the spins oriented in-plane and
suppressed along the quantum well growth direction resulting in the enhancement
of T2*. Our findings, namely, long-lived spin coherence persisting up to about
room temperature, spin polarization decay time with and without a magnetic
field, the spin-orbit field, single electron relaxation time, transport
scattering time, and the electron-electron Coulomb scattering time highlight
the attractiveness of n-doped multilayer systems for spin devices.
