Abstract

Results from avalanche photodiode arrays of the beveled edge type for use in PET systems are presented. Starting from a Si wafer, an avalanche photodiode was produced by deep Ga diffusion, followed by boron and phosphor diffusion. The detector exhibits low dark current and fast response, necessary for use in PET systems. The gain is determined by the external voltage, and values up to 200 are obtained without much excess noise. We measured the energy resolution of the detector coupled to a 3 by 3 by 30 mm 3 BGO scintillator as used in PET systems in response to a 22Na gamma ray source. The energy resolution at the 511 keV line was found comparable to photomultiplier tubes coupled to a scintillator of the same size. Calculation of the electric field and width of the depletion region was done to calculate the thickness of the undepleted front region and to optimize the quantum efficiency for detection of BGO light.