Ultra-fast gated p-silicon field emitter array photocathode

Field emitters are microfabricated sharp tip structures that facilitate the field emission process by concentrating the field at the tip. P- type Si based filed emitter arrays (FEAs) which, unlike metallic tips, exhibit a high photo- sensitivity saturation regime where the field emission current is limited due to carrier depletion and thus can be optically modulated. Optically modulating a gated p-Si FEA by ultra-short pulses can bypass the large gate-to-cathode capacitance in electrically gated cathodes thus potentially can generate ultra-short electron bunches as a cold cathode in Microwave Vacuum Electronics Devices (MVEDs) applications. We demonstrated optical-gating gated p-Si FEA photocathodes wirh a mode-locked laser having 110 fs rise time achieved a drift transit time spread (TTS) limited response of 40 ps rise/fall time. A proposed temporal model explianed the mechanisms of photoresponse for gatde p-Si FEA photocathodes. We envision proposed p-i-n based FEA photocathodes with backside irradiation enables near unity quantum efficiency TTS limited photoresponse. These findings are opening the way for a new generation of MVEDs.