Electron spin coherence in n-doped CdTe∕CdMgTe quantum wells

The spin coherence of a two-dimensional electron gas (2DEG) at different densities in $\mathrm{Cd}\mathrm{Te}∕{\mathrm{Cd}}_{0.85}{\mathrm{Mg}}_{0.15}\mathrm{Te}$ quantum wells has been examined by the time-resolved Kerr rotation technique using resonant excitation of either trions or excitons. The formation of negatively charged trions, either excited resonantly or via exciton states, causes strong spin polarization of the 2DEG. This effect leads to a long lasting exponential decay in the nanosecond regime. Spin dephasing times $T_2^{*}$ of the 2DEG measured as a function of electron density up to $2.4\times {10}^{11}{\mathrm{cm}}^{-2}$ show a nonmonotonic behavior with a maximum at $8\times {10}^{10}{\mathrm{cm}}^{-2}$ .