Observation of strain-enhanced electron-spin polarization in photoemission from InGaAs

Electron-spin polarization in excess of 70% has been observed in photoemission from a 0.1-\ensuremath{\mu}m-thick epitaxial layer of ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As with x\ensuremath{\approxeq}0.13 grown on a GaAs substrate. Under these conditions, the epitaxial layer is expected to be highly strained by the 0.9% lattice mismatch. The electron polarization and the quantum efficiency have been measured as a function of the excitation photon energy from 1.25 to 2.0 eV. A significant enhancement of the electron polarization occurs in the vicinity of 1.33 eV where the expected strain-induced level splitting permits optical excitation of a single-band transition.