Large-area avalanche photodiodes for the detection of soft x rays.

The charge-collection efficiency of beveled-edge-type silicon avalanche photodiodes has been determined for soft x rays in the 50-300-eV range. An efficiency of greater than 80% is measured for energies below the Si L absorption edge. The measured efficiency is well described by a model that accounts for absorption in an oxide overlayer and recombination at the front surface of the diode. The avalanche photodiodes are shown to be significantly more sensitive compared with other detectors for pulsed sources such as a laser-produced plasma source. These results are also very encouraging for soft-xray/ extreme-UV applications involving synchrotron radiation.