Band-structure modifications due to photogenerated carriers in a GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As heterostructure

We have investigated, by means of photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy, the carrier-induced band-structure modifications of a GaAs/${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As heterostructure containing a two-dimensional electron gas (2DEG). The PL spectra are dominated by an intense recombination line which originates from the 2DEG and which is blueshifted as a function of excitation density. In the PLE spectra, we observe excitonic transitions to unoccupied states of the 2DEG that are also slightly blueshifted. By comparison with self-consistent calculations of the subband structure of the electrons and holes, the origin of the observed transitions can be unambiguously determined. We developed a model in which the carrier-induced band-structure modifications can be calculated, taking into account the contribution of the photogenerated excess carriers. The dominant mechanism which causes the blueshift of the PL spectra is the change of the electrostatic potential due to the buildup of holes, separated in real space from the excess electrons in the 2DEG.