We show that the intensity-dependent below-band-gap refractive index of semiconductor superlattices behaves very differently from that prescribed by the band-gap scaling law for bulk semiconductors. Distinct new features in the frequency dependence of the nonlinear index (e.g., change of sign) are found and linked to specific superlattice band-structure parameters.

• Received 10 August 1992

DOI:https://doi.org/10.1103/PhysRevB.47.1620