Electron-spin polarization in excess of 70% has been observed in photoemission from a 0.1-μm-thick epitaxial layer of ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As with x≊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.

• Received 26 February 1991

DOI:https://doi.org/10.1103/PhysRevLett.66.2376