Two-photon absorption in semiconducting quantum-well structures

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Abstract
A theoretical treatment of two-photon absorption is presented for quasi-one-dimensional (Q1D) and quasi-two-dimensional (Q2D) quantum-well structures. It is found that the absorption depends upon the polarization of the radiation field relative to the direction of confinement of the carriers. For radiation polarized perpendicular to the direction of confinement, the absorption is suppressed relative to its value in a bulk semiconductor with the suppression being greater for Q1D than for Q2D structures. When the radiation is polarized along the direction of confinement, the absorption coefficient is enhanced over its value in the bulk. The two-photon absorption in quantum-well systems is found to be a nonmonotonic function of the photon energy with new structure occurring whenever transitions can occur between new pairs of quantized subbands. The threshold for two-photon absorption is shifted towards higher photon energies by the confinement of the carriers.