Study of charge collection and noise in non-irradiated and irradiated silicon detectors

Charge collection and noise were studied in non-irradiated and irradiated silicon detectors as a function of temperature (T), shaping time (θ) and fluence (Φ), up to about 1.2 × 1014 protons cm−2, for minimum ionizing electrons yielded by a 106Ru source. The noise of irradiated detectors is found dominated for short shaping times (θ ≤ 50 ns) by a series noise component while for longer shaping time (θ ≥ 80 ns) a parallel noise component (correlated with the reverse current) prevails. For non-irradiated detectors, where the reverse current is three orders of magnitude smaller compared with irradiated detectors, the series noise dominates over the whole range of shaping times investigated (20–150 ns). A signal degradation is observed for irradiated detectors. However, the signal can be distinguished from noise, even after a fluence of about 1.2 × 1014 protons cm−2, at a temperature of 6°C and with a shaping time typical of LHC inter-bunch crossing time (20–30 ns). The measurement of the signal as a function of voltage shows that irradiated detectors depleted at 50% of the full depletion voltage can still provide a measurable signal-to-noise ratio.