Stoichiometric and Non-stoichiometric Cesium Potassium Antimonide Photocathodes: Ab-initio Insights into its Properties for Photoemission

Abstract: Alkali-metal antimonides, especially cesium-potassium-antimonide (CsK2Sb), are strong candidates for next-generation photocathodes in linear accelerators due to their low work-function, fast response, high quantum yield, and ability to operate under visible light. In this study, first-principles methods are used to examine the structural, electronic, optical, and surface properties of CsK2Sb relevant to its photoemission performance. Our results for CsK2Sb show strong absorption in the visible range consistent with experimental observations. The computed work-functions for the stable surfaces are significantly lower than the commonly used metallic photocathodes. This material exhibits electron and hole mobilities of 111.86 cm2/Vs and 3.24 cm2/Vs, respectively. Since real materials inherently contain intrinsic defects, we analyze native point defects in CsK2Sb and identified Cs and K vacancies as most likely. These defects introduce mid-gap states, modify the absorption spectrum, and may significantly influence photoemission behavior. This work provides valuable insights into optimizing CsK2Sb for high-efficiency photocathode applications.