Patent ID: 6903363

Claim:
A photocathode for emitting electrons in response to incident light, comprising: a semiconductor substrate of a first conductive type, said semiconductor substrate having a first surface and a second surface opposing the first surface; a first semiconductor layer of the first conductive type provided on the first surface of said semiconductor substrate; a second semiconductor layer of the first conductive type provided on said first semiconductor layer; a third semiconductor layer of a second conductive type provided on said second semiconductor layer, said third semiconductor layer having a shape such that a part in the surface of said second semiconductor layer is exposed; a surface electrode provided on said third semiconductor layer; an active layer, for reducing the work function of said second semiconductor layer, provided on the exposed part in the surface of said second semiconductor layer; and a backside electrode provided on the second surface of said semiconductor substrate, wherein a minimum interval 2L between parts of said third semiconductor layer, facing each other while sandwiching the exposed part in the surface of the second semiconductor layer, is 0.2 μm or more but 2 μm or less.