Charge collection inefficiency of p-in-n silicon microstrip detectors

Small area (1x1 cm(2)) microstrip detectors, made with p(+)-n diode structure on FZ silicon substrates with and without oxygen enrichment, have been irradiated with 24 GeV/c protons to fluences of 1.9, 2.9 and 5.1 10(14) cm(-2). Their charge collection properties have been studied with fast electrons from a Ru-106 radioactive source and using a wide bandwidth current amplifier. The results have been compared to a non-irradiated device. The integrated charge collected at different times (10, 25, 40 and 80 ns after the event) has been recorded in order to estimate the ballistic deficit as a function of the integration time. The charge deficit as compared to the pre-irradiation value has been measured for the various fluences at full depletion and for strong over-depletion of the irradiated detectors. A prediction for the charge deficit expected at fluences as high as 10(15) cm(-2) is presented. The charge collection data have been fitted with a method that takes into account the charge trapping and allows the estimate of the full depletion voltage of the irradiated detectors. This method is compared with the widely used capacitance-voltage (C-V) method.