In-plane birefringence of GaAs/AlAs multiple quantum wells

Confinement in semiconductor heterostructures induces optical anisotropy for light propagating perpendicular to the growth axis. By analyzing the intensity transmitted through crossed polarizers below the fundamental absorption edge, we have measured the wavelength-dependent linear birefringence of light propagating along the planes of wave guided GaAs/AlAs multiple quantum wells. This birefringence is dispersionless up to photon energies close to the ${\mathit{E}}_0$ gap where a resonance is observed, as expected. However, the birefringence in the dispersionless region is much larger than foreseen. We show that no isotropic point exists in the transparency region, thus preventing the separation of the birefringence from the optical gyration expected from symmetry grounds for light propagating with q parallel to a [100] direction. We analyze our results by evaluating the dielectric tensor components using two approaches, a two-dimensional critical point model with parabolic band approximation and a microscopic calculation using a tight-binding model for the energy bands of the multiple quantum well.