Abstract
The effects of a degenerate two-dimensional electron gas on the interband optical excitations, occurring in the active channel of Al0.32Ga 0.68As/In0.15Ga0.85As/GaAs high electron mobility transistor structures, were investigated by using phototransmittance spectroscopy. The ground state transition at room temperature exhibited a characteristic steplike line shape, which was considered to be an effect of the screening of excitons by the degenerate electron gas. A line shape fitting by using a first derivative of the absorption coefficient with respect to the electron sheet concentration ns, allowed an estimation of the latter quantity by phototransmittance. An observed temperature-sensitive excitonlike signal, associated with the second electron subband was attributed to the modulation of the many-body correlation-enhanced excitonic absorption, known as the Fermi-edge singularity.