STUDY OF CHARGE COLLECTION AND NOISE IN NONIRRADIATED AND IRRADIATED SILICON DETECTORS

Charge collection and noise were studied in non-irradiated and irradia ted silicon detectors as a function of temperature (T), shaping time ( theta) and fluence (Phi), up to about 1.2 x 10(14) protons cm(-2), for minimum ionizing electrons yielded by a Ru-106 source. The noise of i rradiated detectors is found dominated for short shaping times (theta less than or equal to 50 ns) by a series noise component while for lon ger shaping time (theta > 80 ns) a parallel noise component (correlate d with the reverse current) prevails. For non-irradiated detectors, wh ere the reverse current is three orders of magnitude smaller compared with irradiated detectors, the series noise dominates over the whole r ange of shaping times investigated (20-150 ns). A signal degradation i s observed for irradiated detectors. However, the signal can be distin guished from noise, even after a fluence of about 1.2. x 10(14) proton s cm(-2), at a temperature of 6 degrees C and with a shaping time typi cal of LHC inter-bunch crossing time (20-30 ns). The measurement of th e signal as a function of voltage shows that irradiated detectors depl eted at 50% of the full depletion voltage can still provide a measurab le signal-to-noise ratio.