Improved lifetime of a high spin polarization superlattice photocathode

TL;DR

This paper presents a novel activation method for GaAs-based photocathodes that significantly extends their operational lifetime while preserving high spin polarization and quantum efficiency, addressing a key challenge in electron beam sources.

Contribution

The study introduces a codeposition activation technique using Cs, Sb, and O2 that enhances photocathode lifetime without compromising performance, a novel approach compared to standard methods.

Findings

Achieved tenfold increase in photocathode lifetime.

Maintained 90% spin polarization with improved lifetime.

Demonstrated effectiveness on both bulk and superlattice GaAs samples.

Abstract

Negative Electron Affinity (NEA) activated surfaces are required to extract highly spin polarized electron beams from GaAs-based photocathodes, but they suffer extreme sensitivity to poor vacuum conditions that results in rapid degradation of quantum efficiency. We report on series of unconventional NEA activations on surfaces of bulk GaAs with Cs, Sb, and O2 using different methods of oxygen exposure for optimizing photocathode performance. One order of magnitude improvement in lifetime with respect to the standard Cs-O2 activation is achieved without significant loss on electron spin polarization and quantum efficiency by codepositing Cs, Sb, and O2. A strained GaAs/GaAsP superlattice sample activated with the codeposition method demonstrated similar enhancement in lifetime near the photoemission threshold while maintaining 90% spin polarization.