Performance of a large area avalanche photodiode

Avalanche photodiodes (APD) of beveled edge structure with large active areas (up to 200 mm/sup 2/) have been constructed and characterized for use in low-level light detection. These devices exhibit high gain (1000-2000), relatively low dark current ( approximately 200 nA), very low excess noise, and high detectivity. A resolution of 75 electrons RMS has been obtained for 5.9 keV X-rays in direct interaction with a 20 mm/sup 2/ APD. In scintillation detection resolutions of 6.05% (FWHM) with a CsI(TI) scintillator and 7.7% with NaI(Tl) were measured for the 662 keV line of /sup 137/Cs with a 200 mm/sup 2/ APD at 20 degrees C. With a BGO scintillator (bismuth germanate) a FWHM resolution of 11.2% for the 511 keV line of /sup 22/Na was obtained at 0 degrees C. The 200 mm/sup 2/ APDs exhibit rise times of 3 ns for an impulse input. These results illustrate the potential that APDs have as replacements for photomultiplier tubes and PIN diodes in scintillation detection.<
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