An Air Stable, Electronically Tunable Negative Electron Affinity Silicon Photocathode

The application of negative electron affinity (NEA) photocathodes as high-frequency and high external quantum efficiency electron emission sources has gained attention due to their potential benefits in various fields, including but not limited to electronics, materials science, and microscopy. NEA photocathodes have been achieved by depositing a Cs/O surface layer on GaAs or other semiconductors [1], [2]. These devices have limited stability and require ultra-high vacuum, cluster tools for deposition and short lifetimes. To overcome these limitations, this work proposes the use of a silicon-insulator-graphene structure, Hot Electron Laser Assisted Cathode (HELAC), which is electronically tunable, air-stable, and can mimic a NEA surface under certain bias conditions. The devices explored here have exhibited an emission current of $\sim 20\mu \mathrm{A}$ under red light illumination, corresponding to a current density of 3.2 A/m2 and an external quantum efficiency (EQE) of 0.2%. In this paper, we have described the semiconductor device physics of this device and identified approaches to improve the photocathode performance.