A RAMAN-SCATTERING AND FAR-INFRARED MAGNETOABSORPTION STUDY OF DONORS IN A QUASI-2-DIMENSIONAL ELECTRON-GAS

We report Raman scattering and far-infrared magneto-absorption measurements of GaAs/AlGaAs quantum-well structures selectively doped with donors both in the wells and in the barriers. The resulting system, consisting of a small number of donors immersed in a degenerate electron gas, is studied through the intersubband transition spectra at two electron concentrations. An extra peak at the intersubband transition in the lower density sample is attributed to donors. Its energy relative to the free intersubband transition gives information on the form of screening in quasi-2D. At higher electron density this peak is not observed, however, a new, broad feature is measured. A tentative explanation for this scattering is suggested involving single particle scattering induced by the donors. Magneto-absorption, in contrast to Raman scattering, shows donor features in both samples. This is possibly explained by magnetic freezeout of the donors in the magnetic field. © 1990.