Optical Transmission Spectroscopy of the 2D Electron Gas in GaAs in the Quantum Hall Regime.

Optical transmission spectroscopy of a 2D electron gas is shown to be a sensitive probe of the Fermi level and electronic density of states. Results are presented for inter-band transmission of modulation-doped GaAs multiple quantum wells in high magnetic fields. The appearance of new absorption transitions at even integral filing factors is the optical observation of quantum oscillations of the Fermi level of a two-dimensional electron gas. The broadening of the Landau level density of states is found to be 1.2 sqrt B meVT sup (-1/2) by fitting the Fermi level oscillations.