| 摘要 |
Photoemitters are used to convert received photons of light (or other electromagnetic radiation) into electrons, and it is common to employ an electron multiplier to amplify the low electron flux for use by an imaging or a counting system. Interest has been shown in semiconductor photoemitter and electron multiplier devices based on "mixtures" of the Group III and Group V elements gallium and arsenic or phosphorus, but these are not easy to use in a photoelectric tube. In transmissive mode these III-V materials have high sensitivity to infrared (IR), but have much poorer sensitivity to blue and ultraviolet. Now, it turns out that the III-IV materials are more blue-sensitive in reflective mode. Moreover, in this mode they are good as electron multipliers. The problem is to provide a device operating in this reflective mode with good imaging capability (the ejected electrons scatter). The present invention seeks to solve this by providing a III-V photoemitter structure where, though the photoemissive material is operating in blue-sensitive reflective mode, the device itself is operating in image-retaining transmissive mode. More specifically, the invention proposes that the III-V photoemitter layer (11) be in the form of an array of spaced III-V elements (13) the front faces of which are angled towards the gaps between the elements. Electrons (e-) ejected from the elements' front faces (by impacting photons or electrons) will, under the influence of an appropriate electrical field (E), be swept laterally towards and then through the spaces between the elements, so that though the III-V material is acting in reflective mode, and so has good blue sensitivity, the device itself is acting in transmissive mode, and so has good imaging properties. To form a photocathode/photomultiplier device a plurality of these individual III-V layers may be stacked one above the next, with the elements of each succeeding layer aligned with the gaps in the preceding layer, so that electrons ejected from each layer and passing through the gaps will impact the next adjacent layer without losing their image-defining spatial resolution. |
