OPTICAL AND ELECTRICAL INVESTIGATION OF SUBBAND POPULATIONS, MOBILITIES AND FERMI LEVEL PINNING IN DELTA-DOPED QUANTUM-WELLS

Measurements are reported on the electrical and optical properties of a series of GaAs/Al0.33Ga0.67As quantum well structures in which a Si delta-doped plane has been placed at the centre of the well. By using a range of well widths for a given planar doping level, it has been possible to control the populations of the electron subbands, as evidenced by Hall, Shubnikov-de Haas, photoluminescence and photoluminescence excitation measurements. Combination of these techniques with the results of a self-consistent Poisson-Schrodinger model has enabled the bandgap renormalization to be determined as a function of electron density, and has also demonstrated that the Fermi energy is pinned at 190 meV above the GAMMA conduction band minimum at the delta-doped plane. There is, however, no evidence for a Fermi-edge singularity in the optical spectra of these layers. The transport and the quantum mobilities of the individual subbands have been measured at low temperature, and were found to be in the ratio of approximately 2:1.