Variable sensitivity transmission mode negative electron affinity photocathode

Claim 1

A variable sensitivity negative electron affinity photocathode having means for varying the transmission mode photosensitivity to white or monochromatic light; said photocathode comprising: a photoemitter layer made of p-doped photoemissive single crystalline material from Group III-V including GaAs, GaInAs, InAsP, GaInAsP, or ternary or quaternary alloys with said photoemitter layer having an activation layer of cesium and oxygen on the order of monolayers of thickness on the output side thereof to provide a condition of negative electron affinity; a single crystal transparent window seed crystal substrate comprised of a conductor window acting as a field plate and made of low resistivity p- or n-doped material from Group III-V material including GaAlAs, GaP, GaInP, or GaAsP and a dielectric material insulator layer made of high resistivity material consisting of chromium or oxygen doped Group III-V material including GaAlAs, GaP, GaInP, or GaAsP wherein said insulator layer is contiguous with said photoemitter layer and with said conductor window to form a conductor-insulator combination in which the bandgap of said conductor window and insulator layer combination determined by the material composition of said seed crystal substrate is larger than the bandgap of said photoemitter layer and wherein said conductor window has an antireflection coating on the input side thereof to reduce the amount of reflected light from the photon receiving side of said photocathode; electrical contact rings applied to the outer peripheries of said conductor window and said photoemitter layer; and a bias supply connected across said electrical contact rings to modulate said transparent field plate conductor window by applying negative and positive voltage with respect to said photoemitter layer for creating field effect across said insulator layer and bending the bands up at the interface of said photoemitter layer and said conductor-insulator combination for lowering the backsurface recombination velocity and increase the photosensitivity of said photoemitter layer.