High Polarization and High Peak Current Compositionally Graded AlGaAs/GaAs Superlattice Photocathodes for RF Gun Applications

Negative-electron-affinity (NEA) photocathodes, which produce polarized electrons, are a vital component of current electron accelerators. However, future systems, such as the International Linear Collider (ILC), will require significant upgrades to these photocathodes. For example, the polarized electron beam intensity will need to be at least 20 times greater than that produced by strained GaAs, which is used in the current generation of photocathodes. Additionally, the degree of electron polarization must be increased beyond the 75 percent currently attainable, the photocathodes must be more robust in an RF gun environment, and intrinsic material properties related to improving the surface charge limit must be addressed. This project will develop a new generation of robust photocathodes capable of yielding intense, highly polarized electron beams for use in advanced electron colliders. In Phase I, molecular beam epitaxy will be used to design and fabricate a strained superlattice structure with AlGaAs/GaAs. First, growth conditions will be optimized to achieve the desired alloy composition and interface quality. Then, photocathode structures will be fabricated, and their polarization and quantum efficiency will be measured. Commercial Applications and Other benefits as described by the awardee: A highly efficient polarized electron source for use in experimental research should find immediate application at the Stanford Linear Accelerator Center and other electron collider facilities. The devices also should have applications in other areas, including magnetic imaging research, surface analysis, Quantum computing and cryptography.