EFFECTS OF SUBMICRON CONFINEMENT ON SHALLOW DONORS IN GaAs-Ga//1// minus //xAl//xAs MULTIQUANTUM WELL STRUCTURES.

The nature of the free electronic states in GaAs-GaAlAs quantum well (QW) structures has been the subject of extensive investigation over the past few years and is by now relatively well understood. Previous measurements on Si impurities in QWs have been confined to photoluminescence and, more recently, Raman scattering. We report the results of far infrared (FIR) magnetotransmission measurements obtained with both Fourier transform and FIR laser spectrometers. All measurements reported were carried out in the Faraday geometry with the samples at 4. 2K. A number of MBE-grown multi-quantum-well (MQW) samples were investigated.