Improvement of Quantum Efficiency in Transmission-Type Spin-Polarized Photocathode

Abstract

Abstract:We successfully developed a new transmission-type GaAs/GaAsP strained superlattice photocathode with an AlGaAs transparent inter-layer and Si 3 N 4 anti-reflection coating. The electrons emitted from this photocathode showed a high spin polarization of 90% with a quantum efficiency as high as 0.4%. In the application for spin-polarized low energy electron microscope, a high emission current of over 1 µA was observed at 3.6 mW pump laser power. Transmission electron microscopy observation revealed that there were a small disorder and some dislocations in the GaAs/GaAsP superlattice layers. The disordered superlattice layers result in a fluctuation of the superlattice band structure and the dislocations trap the photo-electrons during the diffusion to the surface. Both of the defects influenced the performance of spin-polarized photocathode.