Photo-response of a p-type Si field emitter

The high-frequency bunched-beam (pulsed beam train) generated directly from a cathode is strongly desired for a compact microwave vacuum tube with high efficiency. The emission current from a p-type semiconductor field emitter saturates in dark with increase of the gate voltage because of the supply limit of the minority carrier. When a p-type emitter is illuminated by light with photon energy larger than the band gap energy, the emission current is remarkably increased because of the additional supply of the photo-excited carriers. It suggests that the bunched beam could be obtained, when the p-type emitter is irradiated with a pulsed laser beam. The frequency of the bunched beam, however, is limited by the photo-response of the emitter. Therefore, we investigated the photo-response of a p-type Si field emitter under the irradiation of a pulsed laser beam.