MAGNETIC-FIELD-INDUCED UNBINDING OF THE OFF-WELL-CENTER D- SINGLET-STATE IN GAAS AL0.3GA0.7AS MULTIPLE-QUANTUM WELLS/

Results of far-infrared Fourier-transform magnetotransmission from two GaAs/Al0.3Ga0.7As multiple quantum well samples delta-doped with Si-d onor on- and off-well centers are compared. In contrast to well-center D--ions, the off-well-center D-singlet binding energy decreases with increasing magnetic field between 5.5 and 15 T, as reflected by the de creasing strength of the D- singlet transition and a consequent increa se of the neutral donor 1s-2p(+) transition. This observation represen ts a verification of the predicted magnetic-field induced unbinding (m agnetic evaporation) of shallow impurity states for the off-well-cente r D--ion system.