Spin coherence and formation dynamics of charged excitons in ${\mathrm{C}\mathrm{d}\mathrm{T}\mathrm{e}/\mathrm{C}\mathrm{d}}_{1-x-y}{\mathrm{Mg}}_x{\mathrm{Zn}}_y\mathrm{Te}$ quantum wells

We report on a study of the spin coherence and on the formation dynamics of charged excitons in a p-doped ${\mathrm{C}\mathrm{d}\mathrm{T}\mathrm{e}/\mathrm{C}\mathrm{d}}_{1-x-y}{\mathrm{Mg}}_x{\mathrm{Zn}}_y\mathrm{Te}$ quantum well by time-resolved photoluminescence under strictly resonant excitation of either the neutral or the charged exciton transition. The analysis of the decay of the charged exciton photoluminescence polarization and of the oscillation of this polarization when a transverse magnetic field is applied allows us to conclude that the formation of a charged exciton via an exciton state does not affect either the electron spin orientation or its coherence. The radiative lifetime of the charged exciton is directly measured and is found to be ∼60 ps. Its formation time is determined from the experiments via a detailed model and is found to be ∼65 ps. We also obtain information on the excitonic spin-flip time (12 ps) and the single-carrier spin-flip times within the exciton (electron, 60 ps and hole, 20 ps).