We show that large piezoelectrically induced electric fields strongly modify the optical properties of [111] growth axis strained-layer superlattices with growth axis along [111]. These internal fields reduce the superlattice band gap, change optical matrix elements, and cause a spatial separation of photoexcited electrons and holes so as to screen the fields. Very large (${\mathrm{\chi }}^3$∼${10}^{\mathrm{-}1}$ esu) optical nonlinearities occur because of the free-carrier screening of the strain-generated internal electric fields.

• Received 8 December 1986

DOI:https://doi.org/10.1103/PhysRevLett.58.1264