Degenerate electron gas effects in the modulation spectroscopy of pseudomorphic Al0.32Ga0.68As/In0.15Ga0.85As/GaAs high electron mobility transistor structures

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Abstract
The effects of a degenerate two‐dimensional electron gas on the interband 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 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.