MAGNETICALLY INDUCED BACK TRANSFER OF ELECTRONS CONFINED IN WELLS TO DONOR STATES IN N-TYPE MODULATION-DOPED GAAS ALAS QUANTUM-WELLS/

The photoluminescence spectra of n-type modulation doped GaAs/AlAs qua ntum wells with well width of 80 Angstrom exhibit a pronounced enhance ment of the photoluminescence intensity associated with electrons at t he Fermi energy. This enhancement is not observed in wider wells. The effect disappears when the temperature is raised above 70 K. The obser ved enhancement of the photoluminescence is attributed to the proximit y of the Fermi energy to the donors in the AlAs barriers. When the l=1 Landau levels are tuned above the donor states, there is strong indic ation that electrons are transferred from the GaAs wells to the AlAs b arriers.