Fast-timing silicon photodetectors

We are developing a detector module consisting of an array of Lutetium Orthosilicate (LSO) scintillation crystals coupled to a new type of silicon photodetector array specifically designed to provide the excellent energy and timing resolution needed for positron emission tomography. We have designed, fabricated and evaluated prototypical detector structures including single 2×2 mm² pixel test structures and eight-by-eight arrays of the 2×2 mm² pixels. Leakage current of ~1 pA per pixel and electronic noise of ~26 e ^- RMS were obtained with thermoelectric cooling. Quantum efficiency was 40% at 460 nm and 70% at 560 nm. Variation in photoresponse (±σ%) over the pixel active area was less than 0.3%. The coincidence resolving time with a LSO crystal was 16 ns. Energy resolutions of 6%, 10% and 13% FWHM for Cs-137 (662 keV) were obtained at the pixel level with 2×2×4 mm³ CsI(Tl), 2×2×10 mm³ BGO, and 2×2×10 mm³ LSO crystals, respectively