Optical anisotropy in GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As multiple quantum wells under thermally induced uniaxial strain

The effect of thermally induced in-plane uniaxial strain on the optical properties of a GaAs/${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As multiple quantum well (MQW) has been studied in detail. The strain was produced by bonding the MQW thin films to ${\mathrm{LiTaO}}_3$, a transparent substrate which possesses a direction-dependent thermal expansion coefficient. At temperatures different from the bonding temperature we have observed an anisotropy in the optical properties of the MQW due to the strain-induced lowering of its in-plane fourfold rotation symmetry. The anisotropic absorption and birefringence for light incident normal to such a MQW structure have been determined and compared to a theory involving the mixing of the valence subbands.