Free-carrier absorption in heavily doped quasi-two-dimensional semiconducting structures

Abstract

The quantum theory of free-carrier absorption in heavily doped semiconductors has been extended to treat the case where the electrons are confined in quasi-two-dimensional (2D) semiconducting structures such as n-type degenerate InSb films. It is assumed that the energy band of electrons in semiconductors is nonparabolic. The free-carrier absorption coefficient is shown to depend upon the polarization of the electromagnetic radiation relative to the direction normal to the quasi-2D structure, the film thickness, and the phonon frequency. When the dominant mechanism of the electron-phonon scattering is the deformation-potential coupling, some oscillations of the free-carrier absorption coefficient with the photon frequency or the film thickness can be observed in a small film thickness range d < 120 Angstrom. While the piezoelectric coupling is the dominant mechanism of the electron-phonon scattering, the oscillations of the free-carrier absorption coefficient with the phonon frequency or the film thickness can be observed in a larger film thickness range d < 1.5 x 10(3) Angstrom. Some oscillations of the free-carrier absorption coefficient with the phonon frequency or the film. thickness are different from those in nondegenerate semiconductors.