Preliminary radiation hardness tests of single photon Si detectors

Single photon Si detectors were fabricated by STMicroelectronics and fully characterized in standard operation conditions and after irradiations. Both single cells and arrays, of dimensions ranging from 5x5 up to 64x64, were electrically tested. The devices operation was studied as a function of the temperature from -25 degrees C to 65 degrees C varying the voltage over breakdown, from 5% up to 20% of the breakdown voltage before and after irradiation using both light ions, 10 MeV B ions to doses in the range 3x10(7)-5x10(10) cm(-2), and X-rays irradiations in the range 0.5-20 krad(Si). Optical characterization was performed using a laser at 659 nm and opportunely chosen filters to vary the optical power. A strong difference in the radiation damage effect is observed for the two different irradiation sources. Ion irradiation, or better implantation, produces a damage preferentially sitting in the active device region, hence even at the lowest irradiation dose the device functionality is compromised, while at the highest dose the device is completely blind. On the other hand, X-rays produce damage in a low concentration, in fact it does not significantly affect the device dark current, only an increase in the leakage current under breakdown is observed. Hence the device functionality is preserved to doses up to 20 Krad(Si).