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Spin-polarized electron photoemission has been studied for GaAs∕GaAs1−xPx strained superlattice cathodes grown by gas-source molecular beam epitaxy. The superlattice structural parameters are systematically varied to optimize the photoemission characteristics. The heavy-hole and light-hole transitions are reproducibly observed in quantum efficiency spectra, enabling direct measurement of the band energies and the energy splitting. Electron-spin polarization as high as 86% with over 1% quantum efficiency has been observed.

Photocathodes that provide high electron-spin polarization (ESP) and high quantum efficiency (QE) can significantly enhance the physics capabilities of electron accelerators. We report recordlevel QE from a high-polarization strained GaAs/GaAsP superlattice photocathode fabricated with a Distributed Bragg Reflector (DBR). The DBR photocathode technique enhances the absorption of incident laser light thereby enhancing QE, but as literature suggests, it is very challenging to optimize all of the parameters associated with the fabrication of complicated photocathode structures composed of many distinct layers. Past reports of DBR photocathodes describe high polarization but typically QE of only $1%, which is comparable to QE of high polarization photocathodes grown without a DBR structure. This work describes a strained GaAs/GaAsP superlattice DBR photocathode exhibiting a high polarization of 84% and significantly enhanced QE of 6.4%.

Strongly polarized photoluminescence and electroluminescence spectra have been obtained from strained GaxIn1−xP quantum wire heterostructures grown on (100) oriented, on-axis GaAs substrates by an in situ epitaxial technique. The phenomenon of strain-induced lateral layer ordering has been exploited in order to create lateral superlattices of GaxIn1−xP compositionally modulated in the [110] direction with a modulation period of 96 Å. The previous and subsequent growth of lattice-matched Ga0.51In0.49P ternary alloy epilayers results in the formation of compressively strained quantum wires. Transmission electron microscopy shows the wire cross sections to be ∼48×200 Å. These structures exhibit 77 K photoluminescence spectra at 1.79 eV that are strongly (96%) polarized parallel to the wires due to strain resulting from the lateral compositional modulation. The intensity of this emission depends critically on the polarization of the incident excitation. Electroluminescence spectra from multiple quantum wire light-emitting diodes display anisotropic polarization as well. The energies and optical anisotropies of these luminescence bands are consistent with a simple theoretical analysis.

Ga x In1−x As quantum wire heterostructures formed by straininduced laterallayer ordering