Picosecond time evolution of free electron-hole pairs into excitons in GaAs quantum wells

We measure picosecond time resolved luminescence spectra in GaAs quantum wells using frequency upconversion luminescence spectroscopy. A careful line-shape analysis of the spectra is performed to separate the free exciton and free carrier related luminescence. From the time evolution of the free carrier luminescence, we deduce the characteristic time constant (${\mathrm{\tau }}_{\mathit{f}}$) for the bimolecular process of exciton formation by free electron-hole pairs. For an estimated initial carrier density of 4×${10}^{10}$ ${\mathrm{cm}}^{\mathrm{-}2}$, ${\mathrm{\tau }}_{\mathit{f}}$ is found to be 50 ps. © 1996 The American Physical Society.