INTERBAND SPECTROSCOPY OF A QUASI-3-DIMENSIONAL ELECTRON-GAS IN WIDE PARABOLIC (AL,GA)AS QUANTUM-WELLS

The quasi-three-dimensional electron gas found in wide n-type paraboli c AlxGa1-xAs quantum wells has been studied through photoluminescence spectroscopy in perpendicular and in-plane magnetic fields. The conduc tion-band subband structure composed of several occupied closely space d levels (delta E approximate to 1 meV) can be clearly identified from the spectra, aided by the sharpening of the luminescence emission int o narrow peaks by Fermi-edge singularity effects (many-electron-one-ho le exciton). The luminescence behavior in magnetic fields shows clearl y the relative importance of the following energies in the problem: th e Fermi energy, the subband spacing, the cyclotron energy, and the Cou lomb perturbation by the photoholes. In the limit where the cyclotron energy dominates, an accurate measurement of the thickness of the elec tron slab is spectroscopically determined. A magnetic-field anomaly in the quantum limit near filling factor v=2/3 has been observed.