Free carrier absorption in quantum well structures for polar optical phonon scattering

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Abstract
The free carrier absorption is calculated for quantum well structures fabricated from III-V semiconducting materials where polar optical phonon scattering is important. The free carrier absorption coefficient is found to be an oscillatory function of the photon frequency for the case where the free carriers are confined in a quasi-two-dimensional structure such as superlattice heterostructures or quantum wells. The absorption is found to depend upon the polarization of the electromagnetic radiation relative to the plane of the layer or quantum well and is enhanced by going to layers or quantum wells of decreasing thickness over its value in bulk III-V semiconducting materials. The oscillatory behavior of the absorption is explained in terms of phonon assisted transitions between the quantized subbands which arise from the confinement of the carriers in these quasi-two-dimensional structures.