pn-type substrate dependence of CsK2Sb photocathode performance

The CsK2Sb photocathode is capable of generating a high-intensity and low-emittance electron beam with visible laser light. In this study, we examined CsK2Sb photocathode evaporation on n- and p-type Si(100), GaAs(100), and Si(111) substrates, and compared their cathode performance. We found that the quantum efficiency of the p-type substrate was superior to that of the n-type substrate for the same substrate material and surface orientation. We show that this can be qualitatively analyzed by an energy-band model for the semiconductor(metal)-semiconductor junction between CsK2Sb and the substrate. We also evaporated the Cs3Sb cathode on n- and p-type Si(100) and GaAs(100) substrates, and confirmed that the cathode performance of all substrates was consistent with the model results. This finding indicates the possibility of improving the thin-film cathode performance by revisiting the semiconductor(metal)-semiconductor junction between the cathode and the substrate, which improves the understanding of high-performance photocathodes.