High efficiency detection of tritium using silicon avalanche photodiodes

This paper describes our recent work in developing low noise silicon avalanche photodiodes (APD) for detection of tritium (³ H) β-particles with high efficiency. In view of the very low energy of ³H β-particles (E_max=18 keV), research was carried out to produce APD structures with a very thin entrance window. This involved using low energy boron implantation into the APD front surface, followed by pulsed excimer laser annealing of the implanted face to form a p⁺ contact. The resulting devices had a surface dead layer of about 0.07 to 0.1 μm and operated with low noise threshold (250-300 eV) for 2×2 mm² size. The ³H β-particle detection efficiency was measured to be approximately 50%. This is about the twice the detection efficiency achieved with standard APDs