Abstract: The electron source disclosed comprises a solid having a first semiconductor layer capable of releasing electrons under the effect of an electrical field, means to make at least one of its faces partially transparent to at least one part of the released electrons, and to enable this part of the electrons to be ejected from the solid, and a second unstable composite semiconductor layer having a structure having a negative differential resistance located between the first layer and its face which is at least partially transparent, in contact with the first layer. The electron source further includes means to form, with said first layer and the composite layer, an electrical resonant cavity.

Abstract: A photocathode having internal amplification includes a first electrode adapted for receiving a first voltage, and for transmitting received photons. An absorption layer is disposed adjacent the first electrode and comprises a P-type semiconductor material having a forbidden band of sufficiently small width to cause photons received through said first electrode to be converted into electron-hole pairs. At least one ionization-induced electron multiplication layer is disposed adjacent the absorption layer. Each such multiplication layer comprises two layers of N-type semiconductor material having respectively two different compositions at an interface therebetween. The two different compositions at the interface cause the multiplication layer, when biased, to accelerate the electrons received from the absorption layer to a degree greater than the acceleration provided to the holes received from the absorption layer.

Abstract: A photocathode having a low dark current comprises a first layer consisting of P.sup.+ type semiconductor material which is transparent to all wavelengths of the light to be detected, a second layer consisting of P.sup.