Robust GaN-Based Photocathodes for High-Current RF Electron Injectors

Advanced electron injectors are based on photocathode electron guns. These guns can produces electron beams with short pulses and high brightness. High efficiency photo-injectors are the electron source of choice for future linear accelerators (linacs) and colliders, energy recovery linear accelerators (ERLs), fourth generation light sources, injectors for laser-driven plasma wake field accelerators, low-energy electron linacs for applied research, and high-power free electron lasers (FELs). Negative electron affinity semiconductor photocathodes, such as cesium-activated GaAs, can show relatively high quantum efficiency. However, these cathodes require very high vacuum environment for operation with reasonable lifetime which is generally incompatible with high intensity electron gun environment. Hence, there is an immediate need for the development of high QE photocathodes capable of robust operation at high emission currents. This program is directed toward the development of robust GaN-based photocathodes for operation in high-current electron injectors. The main goal is to optimize the electron source characteristics and lifetime for practical application in current and future DOE projects. In the phase I program, GaN-based photocathodes with novel structures were fabricated to demonstrate the remarkable efficiency and stability of these cathodes for electron emitter and UV imaging applications. Device modeling was also done to determine new cathode structures for the Phase II effort. Novel GaN-based photocathodes studied in Phase I will be further optimized by investigating parameters that can affect the reliability and lifetime of these cathodes for operation in high voltage electron guns. To speed up the development phase a new cathode activation and testing chamber will be added to the thin-film deposition system. However, the performance of the optimized cathodes will be evaluated in realistic gun environment by collaborators at Argonne National Lab and Cornell University facilities. Commercial Application and other Benefits: The high-performance UV photocathodes proposed in this work can provide a springboard to commercialization of two main products - an efficient electron emitter and a sensitive photodetector. These products have a great commercialization potential for many applications, including UV imaging, spectroscopy, maskless electron lithography and thin-film metrology.