Effects of defects and local thickness modulation on spin-polarization in photocathodes based on GaAs/GaAsP strained superlattices

摘要

The spin-polarization of electrons from the GaAs/GaAsP superlattice on a GaAs substrate (~90%) is higher than that from the same superlattice on a GaP substrate (~60%). Transmission electron microscopy and atomic force microscopy observations revealed that stacking faults were the main defects in the superlattice on the GaAs substrate, while local thickness modulation of the superlattice layers was prominent in the superlattice on the GaP substrate. According to the density of stacking faults and the areal ratio of the thickness modulation, it was concluded that the thickness modulation in the superlattice was the main reason for the spin-polarization reduction in the photocathode on the GaP substrate. Growth of a thin GaAs layer on a GaP substrate prior to superlattice growth eliminated the thickness modulation and the spin-polarization was recovered to 90%.