Detection of soft x rays with NEA I I I–V photocathodes

We describe the experimental energy response of a negative electron affinity (NEA) III-V photocathode to x rays with energies from approximately 0.8 to approximately 3 keV. Energy resolutions, E/DeltaE, from approximately 1 to approximately 3 are obtained, together with approximately 100% quantum efficiency. Theoretical calculations based on an electron diffusion model are shown to be in good agreement with the experimental results. The use of NEA III-V photocathodes as efficient soft x-ray detectors with good energy and spatial resolution is discussed for imaging applications in x-ray astronomy.