Oscillations of magneto-donor binding energies are observed in photoluminescence spectra of modulation-doped GaAs/Ga0.67Al0.33As heterostructure. Both the experiment and the underlying theory provide direct evidence for an oscillatory screening of the Coulomb interaction by two-dimensional electron gas in the quantum Hall effect regime.

Interband photoluminescence (PL) is studied as a function of magnetic field in modulation-doped GaAs/Ga 0.67 Al 0.33 As heterostructures in the Quantum Hall regime. The oscillatory PL data exhibit free electron and donor (ground electric subband) to free hole transitions, as well as free and bound exciton (first excited subband) transitions. Pronounced intensity oscillations of all transitions are observed as the magnetic field varies between 0 and 12 T. In particular, we observe, for the first time, strong intensity oscillations of donor±hole and bound exciton transitions with exactly opposite phase from which we conclude that the observed bound excitons are bound to the donors at the GaAs/ Ga 0.67 Al 0.33 As interface. Similarly, the intensities of free electron±hole and free exciton transitions oscillate with exactly opposite phase. Various mechanisms of the intensity oscillations are discussed, taking into account the available parallel behaviour of the free and bound carrier excitations. We exclude an oscillatory screening by 2DEG to be the cause of the intensity oscillations. We conclude that the intensity transfer between the electron±hole and the free exciton transitions occurs when, as a function of magnetic field, the interband electron±hole energy becomes larger than the corresponding exciton energy, so that it is advantageous for the pair to form an excitonic state. A similar mechanism is responsible for the intensity transfer between the donor±hole and the bound exciton transitions.Magneto-donors (MD) in quantum wells were investigated by various authors with the use of optical methods [1]. Transport studies on heavily doped heterojunctions demonstrated a field-induced metal±nonmetal transition [2]. Magneto-donors in symmetric wells were described theoretically by Green and coworkers