Spin orientation at semiconductor heterointerfaces

We demonstrate by Raman scattering that the spin splitting in the conduction band of a GaAs/ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Al}}_{\mathit{x}}$As asymmetric quantum well is anisotropic and inequivalent along the [11¯] and [11] directions. This agrees with the results of tight-binding calculations. The Rashba contribution to the spin orientation induced by the asymmetric potential is of comparable magnitude to the bulk inversion-asymmetry-induced term. Hence, we obtain quantitative information on the origin of the spin orientation at the GaAs/${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Al}}_{\mathit{x}}$As interface.