Long Life High Brightness Photocathodes using III-Nitride Materials

High brightness photocathodes PCath) are needed for DOE facilities and laboratories employing electron accelerators used for Free Electron Lasers FEL), ultrafast electron microscopy, and diffraction. Typically alkali-antimonide cathodes, alkali-telluride, GaAs or metals are used; these semiconductor based PCaths have shown superior performances with respect to metals, however they are highly reactive and rapidly degrade even in isolated ultra-high vacuum UHV) enclosures over hours/days to at most months’ due to chemical poisoning or loss of alkali metals. The proposed non cesiated III-N based photocathodes will solve this continuing difficult chemical degradation of state-of-the-art photocathodes. The III-N photocathodes will be chemically stable, over extended times without exotic passivation in atmosphere and in vacuum while retaining higher quantum efficiency. This will be achieved by using the spontaneous stress-induced piezoelectric polarization field in the properly oriented nitrides and through band engineering and device designs. In Phase I project. the design for III-N based photocathodes to achieve negative electron affinity NEA) along with other properties of the photocathode will be demonstrated. The designed III-N based structure for photocathodes will also be grown and will be evaluated for proof of concept performance. The developing of photocathodes with longer life, higher quantum efficiency and low intrinsic emittance will allow future upgrades of the DOE facilities such as X-ray Free Electron Lasers XFELs) and ultra-fast electron diffraction UED). Improving these facilities will enable advancement in science studies of the dynamic evolution of chemical and physical processes with the resolution of a few femtoseconds 1 fs = 10-15 sec), and thus further unraveling the complex dynamics of the molecular structure of a single protein or virus. This project will have immense impact on scientific and technological understanding of materials.