RADIATIVE RECOMBINATION IN MODULATION-DOPED GAAS ALGAAS HETEROSTRUCTURES IN THE PRESENCE OF AN ELECTRIC-FIELD

The radiative recombination processes involving two dimensional (2D) c arriers from the notch potential formed at the interface of modulation doped Ga-As/AlGaAs heterostructures have been studied by means of pho toluminescence (PL) and photoluminescence excitation spectroscopy in t he presence of an external electric field applied perpendicular to the layers via a gate electrode. Two PL bands related to the 2D electron gas are interpreted as the radiative recombination between 2D electron s and holes from the valence band (HB1) and from residual acceptors (H B2), respectively. The band bending in the active layer, which determi nes the energy positions of these H-bands, can be controlled by applyi ng an external electric field. However, also the separation between th e Fermi edge, E(F), and the second 2D electron subband is deliberately varied by applying an electric field. At a sufficiently small separat ion, an efficient scattering path near k = 0 is available for electron s at the Fermi energy. This can be observed in the PL spectra as a str iking enhancement of the many-body excitonic transition, usually refer red to as the Fermi edge singularity (FES). The enhancement of the FES is usually explained in terms of an efficient scattering for electron s at the Fermi edge via the nearly resonant adjacent subband. The effi ciency of this process is dependent on the separation between the Ferm i edge, E(F), and the next subband, which can be controlled via the ap plied field in our experiments.