Exciton formation and hole-spin relaxation in intrinsic quantum wells

We have investigated the exciton spin dynamics in quantum wells. In nonresonant excitation conditions, the initial degree of circular polarization of the exciton luminescence is higher than the excitation light polarization. This demonstrates that excitons are formed from nongeminate electron-hole pairs. The understanding of the exciton formation process allows us to propose a method to measure directly the hole spin-relaxation time (${\mathrm{\tau }}_{\mathit{h}}$) in intrinsic quantum wells. We show how the analysis of the total photoluminescence intensity under circularly and linearly polarized excitation allows us to measure ${\mathrm{\tau }}_{\mathit{h}}$, independently of the other spin-flip processes.