Electrostatically Generated Air-Stable Negative Electron Affinity Silicon Photocathode

Negative electron affinity surfaces on semiconductors allow efficient electron emission while being illuminated by visible photons. However, generation of such surfaces requires an extremely unstable cesium-based coating and ultrahigh vacuum operation. Here, we have bypassed these stringent requirements by using a silicon/oxide/graphene heterostructure where silicon acts as the photoabsorber, while a bias voltage between graphene and silicon can electrostatically generate a tunable NEA surface with an emission current density of similar to 3.4 A/m(2) at an external quantum efficiency of similar to 0.1%. This silicon photocathode can operate at vacuum pressures as high as 1 mTorr and retain the emission characteristics. Through a theoretical device model validated with experimental results, we have presented a more comprehensive understanding of the emission characteristics that allows us to predict theoretical performance limits of the photocathode while showing a clear pathway toward achieving such limits experimentally.