Characterization of very large silicon avalanche photodiodes

In this paper, we discuss recent advances in the high gain, very large area silicon avalanche photodiode technology. Very large area APDs (square and octagonal design, up to 45 cm/sup 2/ area) have been built using the planar process. These APDs have been successfully operated as scintillation spectrometers. When cooled to -40 /spl deg/C, the energy resolution of 5.9 keV X-rays (/sup 55/Fe source) upon direct interaction with the 45 cm/sup 2/ APD was measured to be 2.4 keV (FWHM). The APD was coupled to a CsI(Tl) scintillator and irradiated with 662 keV gamma rays from /sup 137/Cs source and the energy resolution was measured to be /spl sim/10% (FWHM) at the temperature of -40 /spl deg/C. A rise time of < 2 ns was measured with the 40 cm/sup 2/ APD upon irradiation with 5.5 MeV alpha particles. A new packaging design has been developed to allow cooling of these large APDs to liquid nitrogen temperature. Evaluation of the 45 cm/sup 2/ APD has been conducted at LN/sub 2/ temperatures. Its gain was found to be as high as 10/sup 4/, while the noise was measured to be /spl sim/0.8 electrons (rms). Detection of low intensity optical signal (<8 photons/pulse) with the 45 cm/sup 2/ APD has also been accomplished.