Strain enhanced electron spin polarization observed in photoemision from InGaAs

Electron spin polarization in excess of 70 percent has been observed in photoemission from a 0.1 micron thick epitaxial layer of In(x)Ga(1-x)As with x (approx) 0.13 grown on a GaAs substrate. Under these conditions, the epitaxial layer is expected to be highly strained by the 0.9 percent 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 micron thickness, significantly larger than the critical thickness for pseudomorphic strain, show no polarization enhancement. These measurements represent the first observation of strain-enhanced electron spin polarization for photoemitted electrons.