Far-infrared magnetospectroscopy has been carried out on shallow donor impurities doped in the central region of GaAs quantum wells in $\mathrm{GaAs}-{\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ multiple-quantum-well structures. Quantum-well widths between 80 and 450 Å were investigated. Results are in very good agreement with recent effective-mass calculations for isolated impurities at the center of GaAs quantum wells.

• Received 3 December 1984

DOI:https://doi.org/10.1103/PhysRevLett.54.1283