Stress induced exciton mixing in quantum wells

We present spectroscopic investigations of excitonic mixing in GaAs quantum wells due to in-plane uniaxial stress. Two unexpected anticrossings are se en in the photoreflectance spectra which cannot be explained by the effect of stress on the single particle states. The anticrossings can be ascribed to unusually strong Fano related interference between excitonic states insi de the QW. This presents a new type of signature for the strong valence ban d mixing which gives rise to the highly nonparabolic subband structure foun d in these systems. Photoluminescence spectra show clearly the non-linear s tress shift of the quantum well ground state exciton due to the competing e ffects of symmetry reduction and quantum confinement. The measurements are used to determine accurately the a and b deformation potentials of GaAs.