Many‐Body Effects in the Electron–Hole Plasma Confined in GaAs–(GaAl) As Quantum Wells

Two‐beam transmission and photoluminescence spectra of GaAs–(GaAl)As multiple quantum wells are presented. The spectra are studied as a function of the electron–hole (c–h) pair density. At low and with increasing density a blue‐shift of the lowest exciton line is found. At densities above the Mott value, the band gap reduction depends on the width of the well and is much smaller than in a strictly two‐dimensional e–h plasma. Further, even in a relatively dense plasma the excitonic enhancement factor differs strongly from unity, though it depends only weakly on the energy.