Strain enhanced electron spin polarization observed in photoemission from InGaAs

Electron spin polarization in excess of 70% has been observed in photoemission from a 0.1- mu m-thick epitaxial layer of In/sub x/Ga/sub 1-x/As, with x approximately=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, as confirmed by X-ray diffractometer measurements of the lattice parameter. 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. Measurements made on a control sample of 1.14- mu m thickness, significantly larger than the critical thickness for pseudomorphic strain, show no polarization enhancement.<>