Development of polarized electron sources using AlGaAs-GaAs superlattice and using strained GaAs

Two types of polarized electron sources have been developed. First, an Al/sub 0.35/Ga/sub 0.65/As-GaAs superlattice grown by the MBE (molecular beam epitaxy) method was examined. The maximum polarization of 71.2+or-1.1(stat.) +or-6.1(sys.)% was obtained at a photon wavelength of 802 nm at room temperature. Second, a strained GaAs layer was grown on a GaP/sub 0.17/As/sub 0.83/ base layer by the MOCVD (metalorganic chemical vapor deposition) method: the maximum polarization of 85.0+or-1.1(stat.)+or-6.3(sys.)% was obtained at a photon wavelength of 860 nm at room temperature. It is concluded that the GaAs epilayer strained by the lattice-mismatch of the heterojunction and the AlGaAs-GaAs superlattice are potential candidates for the new photocathode of a polarized electron source, because they have much higher polarization than the GaAs photocathode and a reasonable quantum efficiency.<>