Optical pump-probe measurements of spin dynamics at temperatures down to $1.5\mathrm{K}$ are described for a series of (001)-oriented $\mathrm{Ga}\mathrm{As}∕\mathrm{Al}\mathrm{Ga}\mathrm{As}$ quantum well samples containing high mobility two-dimensional electron gases (2DEGs). For well widths ranging from $5\text{to}20\mathrm{nm}$ and 2DEG sheet densities from $1.75\times {10}^{11}\text{to}3.5\times {10}^{11}{\mathrm{cm}}^{-2}$, the evolution of a small injected spin population is found to be a damped oscillation rather than an exponential relaxation, consistent with the quasi-collision-free regime of the Dyakonov-Perel spin dynamics. A Monte Carlo simulation method is used to extract the spin-orbit-induced electron spin precession frequency $\mid \Omega \left(k_F\right)\mid$ and electron momentum scattering time $\tau _p{}^{*}$ at the Fermi wave vector. The spin decay time passes through a minimum at a temperature corresponding to the transition from collision-free to collision-dominated regimes and $\tau _p{}^{*}$ is found to be close to the ensemble momentum scattering time ${\tau }_p$ obtained from Hall measurements of electron mobility. The values of $\mid \Omega \left(k_F\right)\mid$ give the Dresselhaus or bulk inversion asymmetry (BIA) coefficient of spin-orbit interaction as a function of electron confinement energy in the quantum wells and show, qualitatively, the behavior expected from $k\bullet p$ theory.

• Received 24 July 2007

DOI:https://doi.org/10.1103/PhysRevB.76.195305