Grand canonical equilibrium of two-dimensional electrons confined in asymmetric AlxGa1-xAs/GaAs heterostructures in a quantizing magnetic field

The energy of electronic states of a two-dimensional electron gas (2DEG) co nfined in a one-sided n-doped A1(x)Ga(1-x)As/GaAs asymmetric quantum well ( QW) in a perpendicular magnetic field B is studied using low-temperature ph otoluminescence experiments. The interband Landau-level energies show an os cillatory B dependence. This oscillatory behavior does not depend on QW wid th and is sensitive to the carrier concentration N-s of the 2DEG. These obs ervations disagree with what one would expect from many-body theory. A theo retical model is developed assuming that, under continuous illumination, th e 2DEG is in grand canonical equilibrium with the rest of the structure. Th en, N-s may change from that at B = 0 because of the B dependence of the de nsity of states. In these semi-equilibrium conditions, the Fermi level shou ld stay flat across the structure and should not depend on B. This study sh ows that, in asymmetric modulation doped quantum wells, the electronic tran sfer can be the main factor in the oscillatory behavior of interband transi tion energies as a function of B.