DEVELOPMENT OF ALKALI-BASED HIGH QUANTUM EFFICIENCY SEMICONDUCTORS FOR DISPENSER PHOTOCATHODES*

Photocathodes as electron beam sources are expected to meet the stringent requirements of high performance FELs but exhibit a lifetime-efficiency tradeoff. High quantum efficiency (QE) cathodes are typically semiconductors, well described by recently enhanced theory [1]. Cesium dispenser technology, proven to extend lifetime of Cs-W cathodes [2], is proposed to be extended to high QE via the development of semiconductor coatings which are suitable for rejuvenation. Rejuvenation occurs via controlled cesium diffusion through a sintered substrate to resupply the surface (as described by models of pore and surface diffusion). Compatible coatings must be thermally stable materials with a cesium-based surface layer. Following standard fabrication processes, we discuss alkali antimonides and alkali aurides as cesium dispenser photocathode coatings and analyze future prospects. We also describe improvements to experimental techniques.