Soft X-Ray silicon photodiodes with 100% quantum efficiency

Silicon p-n junction photodiodes (AXUV diodes) with nearly 100% quantum efficiency (QE) for soft X-ray photons (up to about 6 keV) were recently developed. This implies no recombination of photo-generated charge carriers in the front doped region and at the Si-SiO₂ interface. This work reports fabrication and testing of the AXUV diodes with 100% quantum efficiency for photons with energy up to 10 keV. Response of the new diodes was measured using electron-beam X-ray generators with copper and molybdenum anodes that, when filtered properly, provide K X rays at 8 and 17.5 keV respectively. AXUV photodiodes fabricated on high-resistivity silicon were found to exhibit gain in their response to these X rays. The X-ray signal was observed to increase, by up to a factor of 25, when the bias voltage was raised above the level required for full depletion of the silicon. A similar gain was found in the response to α particles when the diodes fabricated on high-resistivity silicon were operated in pulse mode. A diode fabricated from low resistivity silicon, with low leakage current, did not exhibit any gain in its X-ray response