Absorption and emission in n type II–VI quantum wells

The evolution of the optical properties as a function of 2D electron concentration ne is studied using CdTe quantum wells. The trion absorption peak evolves to the Fermi edge singularity (FES) as the exciton peak progressively disappears. The splitting between these two peaks is linear in ne. This is explained in the framework of Hawrylakʹs theory of the many-body optical response of free carriers. The emission spectra show a transformation similar to that observed for gated electron gases and previously attributed to a metal–insulator transition. There is, however, a contradiction with the absorption results which can be explained in terms of a Fermi sea of electrons over the whole range of densities.