Excitons in two-dimensional electron gas

The near band edge absorption spectrum of a quantum well which contains an electron gas is studied. We show that electron-hole correlations play an important role in determining this spectrum. At zero magnetic field the spectrum evolves with increasing electron density from being dominated by neutral excitons at the very dilute limit to charged exciton and then into the Fermi edge singularity. At high magnetic fields the spectrum depends on the filling factor ν. Three regimes are well distinguished: ν < 1 where the spectrum consists of neutral and charged excitons, 1 < ν < 2 where the neutral exciton disappears, and ν > 2 where the electron-hole correlations do not play any important role and the spectrum is a simple band to band transition.