Nonlinear optical absorption in GaAs doping superlattices

The first direct nonlinear absorption measurements at energies below and above the band gap of GaAs doping superlattices are reported. Large period, lightly doped structures exhibit properties that are consistent with the Franz-Keldysh oscillations seen in bulk material. Very small period heavily doped structures show absorption features that reflect the quasi-two-dimensional nature of the conduction-band energy spectrum in such a system. The dependence on excitation of the nonlinear absorption in these systems is described.