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 (H-3) beta-particles with high efficiency. In view of the very low energy of H-3 beta-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 surface dead layer of about 0.07 to 0.1 mu m and operated with low noise threshold (250-300 eV) for 2x2 mm(2) size. The H-3 beta-particle detection efficiency was measured to be approximately 50%. This is about the twice the detection efficiency achieved with standard APDs.