High-frequency photocathode based on CNT-yarn emitter and GaAs photoswitch

A high frequency photocathode based on a carbon nanotube (CNT)-yarn in series to a semi-insulating (s.i.) GaAs was fabricated and used for field electron emission in a diode configuration. This hybrid two-chip technology allows the separate optimization of the yarn emitter and the photoswitch. This concept can overcome the capacitance limitations of miniaturized high-frequency vacuum tubes. The used CNT yarn emitter with $20 \mu \mathrm {m}$ diameter had a threshold electric fields of $\sim 1.8\mathrm {V}/ \mu \mathrm {m}($ defined at 1mA/cm $^{\mathbf {2}}$textbf) with a stable field emitter current up to $400 \mu \mathrm {A}$. The high-voltage photomodulation was up to 100 MHz.