LOW DARK CURRENT PHOTOCATHODE

摘要

A photocathode having a low dark current comprises a first layer consisting of P+ type semiconductor material which is transparent to all wavelengths of the light to be detected, a second layer consisting of P+ type semiconductor in which the forbidden band is of sufficiently small width to convert the photons of the light to be detected into electron-hole pairs, at least one intercalary layer located within the second layer and consisting of P-type or N-type semiconductor material for creating a potential barrier with respect to the second layer, the thickness of said intercalary layer being of sufficiently low value to permit the passage of electrons by tunnel effect with high probability but of sufficiently high value to stop the greater part of a hole current, a metallic electrode for biasing the photocathode in order to accelerate the electrons of the electron-hole pairs created within the second layer by the light, a last layer for reducing the energy-gap potential with respect to the second layer in order to emit into the vacuum the electrons which have thus been accelerated.