GaAs-AlxGa1−x As superlattices as sources of polarized photoelectons

We have measured the spin polarization of electrons optically pumped by polarized light and photoemitted from GaAs-AlxGa1−xAs superlattices with negative electron affinity. We find a maximum polarization of 49%, in contrast to the expectations related to polarized photoluminescence studies. Reasons for these findings based on the difference between photoemission from negative electron affinity sources and photoluminescence are discussed.