Evaluation of GaAsSb/AlGaAs strained superlattice photocathodes

GaAs-class strained superlattice (SSL) photocathodes can provide electron beams with electron spin polarization (ESP) exceeding the theoretical maximum 50% of bulk GaAs. In this paper, we describe the evaluation of a SSL structure composed of GaAsSb/AlGaAs and grown on a GaAs substrate. Theoretical analysis and numerical calculations show GaAsSb/AlGaAs SSL structures have the largest heavy-hole and light-hole energy splitting of all existing GaAs-class SSL structures, which should lead to the highest initial ESP. Five GaAsSb/AlGaAs SSL photocathode samples with different constituent species concentrations, number of layer pairs, and layer thicknesses were fabricated and evaluated. The highest ESP was ∼77% obtained from a photocathode based on the GaAsSb0.15/Al0.38GaAs (1.55/4.1 nm ×15 layer pairs) SSL structure.