Robust GaN-Based Photocathodes for High-Efficiency Polarized RF Electron Guns

Compared to DC electron guns, the significantly-higher field gradients that are possible with an radio frequency (RF) gun would allow short pulse generation, which would make an RF buncher unnecessary. This in turn would allow for a much simpler injector design in high-energy beam facilities, such as the International Linear Collider. However, activated GaAs-based photocathodes, used as the electron source in DC guns, cannot be operated with a long enough lifetime in the inadequate vacuum of an RF gun chamber. Therefore, this project will develop GaN-based photocathodes that can serve as robust polarized electron sources in RF guns. In addition to providing higher quantum efficiency, GaN¿s larger bandgap energy (3.4 eV) compared to GaAs (1.4 eV) makes the negative-electron-affinity surface much more suitable for the harsh vacuum environment encountered in RF guns. In Phase I, a baseline design will be determined by optimizing the growth and processing of the photocathodes, based on device modeling and performance characterization. The use of cesium-activated, strained (Al)GaN/(In)GaN structures, as well as Ce-free structures, will be investigated. Specific objectives include: (1) optimizing the polarized photocathode design, (2) optimizing photocathode growth and processing, and (3) characterizing the GaN-based polarized photocathode. Phase II will address the production of these photocathodes for different applications, including high-intensity electron sources and UV light detectors and imagers. Commercial Applications And Other Benefits as described by the Applicant: A robust, spin-polarized electron source, suitable for high-intensity RF guns, should have important scientific and industrial applications. In particular, the high-efficiency photocathodes would benefit Federal Government facilities that use electron colliders for conducting high-energy physics experiments. Such a device also would have applications in other fields such as magnetic materials research, surface science, and quantum computing