Magneto-Donors and Donor-Bound Excitons in GaAs/Ga0.67Al0.33As Heterostructures in the Quantum Hall Regime

Abstract

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

Current-induced spatial patterns of photoluminescence inAlxGa1−xAs/Novák1, Svoboda2, Kreuzer3 et al. 2001Phys. Rev. B2030View full textAdd to dashboardCite

“…1,2 Various aspects of the problem have their specific importance, both for its applicability as an experimental tool, such as the PL spectroscopy, 3,4 and for its potential physical significance, mostly through its connection to the QH effects. [5][6][7][8][9][10] However, until recently, 11 no attention has been paid to the question on a spatial distribution of the PL in the plane of the 2DEG. There are, still, various reasons to expect a spatial modulation of the PL: influence of the lateral confining potential, 12,13 near field and injection effects at the contact vicinity, 14 current filamentation due to a lateral density gradient [15][16][17] or a vertical field, 18,19 formation of percolating current channels, 20 and others.…”

Photoluminescence rings in a Corbino disk at quantizing magnetic fields

“…Various PL features have been identified typical for 2DEG in strong perpendicular magnetic fields. 1,2,3,4,5,6,7 However, little attention has been paid to the spatial distribution of the PL. This is a relevant problem especially in the case of a 2DEG carrying an unballanced external current in magnetic fields, when a self-induced spatial inhomogeneity may be expected.…”