Spin-polarized electron sources with GaAs–GaAsP superlattices for surface analyses

A spin-polarized electron source has been developed using the GaAs–GaAsP superlattice. Polarized electrons are obtainable by irradiating semiconductors of zincblende lattice structures such as GaAs with circularly polarized photons. In the case of GaAs, polarization is restricted to under 50% because of the degeneracy of the heavy-hole and light-hole states in the valence band. The degeneracy is removed in superlattices by their periodic potential and the heavy-hole state of GaAs wells is lifted in the GaAs–GaAsP superlattice. By exciting electrons only from the heavy-hole state of GaAs wells to the conduction band, polarized electron beams are obtained, and the degree of polarization is as high as 80%. This high polarization is obtained in a wide wavelength range from 810 to 830 nm that is easily realized by conventional semi-conductor laser diodes. A quantum efficiency of 0.3% and a polarization of 80% have been obtained. The developed source has potential applications in surface characterization and inverse photoemission spectroscopy.