Anisotropies in Strain and Quantum E ciency of Strained GaAs grown on GaAsP ?

An anisotropy in the quantum e ciency (QE) has been observed in photoemission from strained GaAs photocathodes excited by linearly polarized light. The wavelength dependence of the anisotropy is closely correlated with that of the electron-spin polarization. Based on a theoretical analysis, we show that the QE anisotropy is caused by an inplane strain anisotropy arising from anisotropic strain relaxation. The QE anisotropy calculated from the in-plane strain anisotropy measured with X-ray di raction and the measured QE anisotropy are in good agreement. Submitted to Physical Review Letters Since the rst observation of electron-spin enhancement in photoemission from a strained InGaAs layer epitaxially grown on a GaAs substrate, [1] polarized electron photoemission ? This work was supported in part by the U. S. Department of Energy under contract numbers DE-AC03-76SF00515 (SLAC), and DE-AC02-76ER00881 (UW).