Development of Air Stable Silicon Photoemitter with Electronically Tunable Negative Electron Affinity

Negative electron affinity (NEA) cathodes are currently considered a potential high frequency photoemitter due to their relatively high external quantum efficiency and low mean transverse energies (MTE)1-3. GaAs surface treated with a Cs/O layer have been shown to simultaneously exhibit good external quantum efficiencies (EQE) of -10-
²
and reasonable MTEs, however, they face challenges in terms of stability and complexity in their manufacturing process. In this work, we have developed an electronically adjustable cathode called Hot Electron Laser-Assisted Cathode (HELAC) which mimics the negative electron affinity surfaces and is fabricated using a simple and ex-situ technique. Despite not being fully optimized, the proof-of-concept device has demonstrated great air stability with 90 uA of emission current, which is 14.4 A/m
²
in current density. Additionally, through control over the quality of the insulator and the tunneling mechanism, low-MTEs are expected to be possible. This work can give an idea of the possibilities and difficulties of designing new photocathodes with high quantum efficiency by using the negative electron affinity technique.