Performances of large area avalanche photodiodes at liquid nitrogen temperature

We report on the performance of the beveled-edge large area avalanche photodiodes (LAAPDs) operating at the near liquid nitrogen (LN/sub 2/) temperatures. The two-fold purpose of these studies was to determine the sensitivity that should be achievable with deeply cooled LAAPD in photon counting, and investigate different scintillators, as pure NaI crystal, at near LN/sub 2/ temperatures. The measurements were carried out with unpackaged 5 and 16 mm diameters LAAPD dies cooled in a modified cryostat used for Si(Li) X-ray detectors. Light from a green light emitting diode (LED) and 5.9 keV X-rays from a /sup 55/Fe source have been used to characterize performance of LAAPDs. Dark current below 1 pA has been measured for a 16 mm LAAPD at a gain of 5000. The ratios of the LAAPD gain for X-rays and light pulses, the excess noise factor and dark noise contribution of the LAAPD-preamplifier system were measured up to device gains of 4000. At a gain of 4000, pulse height spectra down to about 3 photon light pulses have been measured with a 5 mm LAAPD. The results of tests with a pure NaI crystal coupled to the LAAPD have been presented showing an energy resolution of 5.9 /spl plusmn/ 0.2% for 662 keV /spl gamma/-rays from a /sup 137/Cs source.