DEGENERATE ELECTRON-GAS EFFECTS IN THE MODULATION SPECTROSCOPY OF PSEUDOMORPHIC AL0.32GA0.68AS IN0.15GA0.85AS/GAAS HIGH-ELECTRON-MOBILITY TRANSISTOR STRUCTURES/

The effects of a degenerate two-dimensional electron gas on the interb and optical excitations, occurring in the active channel of Al0.32Ga0. 68As/In0.15Ga0.85As/GaAs high electron mobility transistor structures, were investigated by using phototransmittance spectroscopy. The groun d state transition at room temperature exhibited a characteristic step like line shape, which was considered to be an effect of the screening of excitons by the degenerate electron gas. A line shape fitting by u sing a first derivative of the absorption coefficient with respect to the electron sheet concentration n(s), allowed an estimation of the la tter quantity by phototransmittance. An observed temperature-sensitive excitonlike signal, associated with the second electron subband was a ttributed to the modulation of the many-body correlation-enhanced exci tonic absorption, known as the Fermi-edge singularity.