Charged and neutral exciton phase formation in the magnetically quantized two-dimensional electron gas

We report on a spectroscopic study of the lowest-energy electron-hole transitions of the two-dimensional electron gas (2DEG), with a density varied by photoexcitation in GaAs/(Formula presented)(Formula presented)As quantum wells and under a perpendicularly applied magnetic field B. The transition into the phase consisting of a charged exciton singlet ((Formula presented)) ground state and neutral exciton (X) excited state occurs at a filling factor ν=1. The relative intensities of the (Formula presented) and X transitions measured by photoluminescence excitation at T=2 K, as a function of ν≤1 and of B, are shown to depend on the relative area occupied by the magnetic-field-localized 2DEG and on the reduced orbit of the additional electron bound to (Formula presented).