Quenching of the exciton-spin relaxation via exchange interaction in $\mathrm{GaAs}/{\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ quantum wells

We studied the influence of the electron gas on the exciton spin relaxation in GaAs/AlGaAs quantum wells. We observed an increase of the continuous-wave degree of polarization and the exciton spin relaxation time with the electron density. These results are interpreted based on the quenching of the exciton bound state. As a consequence, the spin relaxation changes from one dominated by the long-range exciton exchange interaction for intrinsic excitonic transitions to one dominated by the hole spin relaxation when in the presence of the electron gas. The experimental results are in qualitative agreement with calculations of the exciton spin relaxation time in doped samples.