Photoemission characterization of N-polar III-Nitride photocathodes as bright electron beam source for accelerator applications

TL;DR

This paper introduces N-polar III-Nitride photocathodes with high brightness potential for accelerators, demonstrating stable operation and promising electron emission properties without cesium, suitable for RF gun applications.

Contribution

The study presents a novel N-polar III-Nitride photocathode design leveraging polarization fields for negative electron affinity, enabling stable high-brightness electron emission without cesium.

Findings

Quantum Efficiency of ~1x10^{-3} at 265 nm

Mean Transverse Energy of ~100 meV at 265 nm

Stable operation over 24 hours in ultra-high vacuum

Abstract

We report on the growth and characterization of a new class of photocathode structures for application as electron sources to produce high brightness electron beams for accelerator applications. The sources are realized using III-Nitride materials and are designed to leverage the strong polarization field characteristic of this class material while grown in their wurtzite crystal structure to produce a negative electron affinity condition without the use of Cs, possibly allowing these materials to be operated in RF gun. A Quantum Efficiency (QE) of about 1x10$^{-3}$ and a Mean Transverse Energy (MTE) of electron of about 100 meV are measured at the operating wavelength of 265 nm. In a vacuum level of 3x10$^{-10}$ Torr the QE does not decrease after more than 24 hours of continuous operation. The lowest MTE, about 50 meV, is measured at 300 nm where the measured QE is 1.5x10$^{-5}$. Surface characterizations reveal possible contribution to the MTE due to the surface morphology calling for more detailed studies.