Giant electropleochroism in GaAs-(Al,Ga)As heterostructures: The quantum-well Pockels effect

We report on the biaxial response of photoluminescence to electric fields in GaAs quantum-well structures. For fields along [001], emission due to nominally forbidden excitons exhibits substantial differences between [110] and [11¯0] polarizations. Transitions which are allowed within the envelope-function formalism show no noticeable anisotropy. In terms of symmetry, our observations relate to the linear electro-optic (Pockels) effect. The field dependence of the anisotropy is unusual in that it decreases with increasing field. Results can be qualitatively accounted for by perturbation analyses.