Electrical characteristics and charge collection efficiency of silicon detectors irradiated with very high neutron and proton fluences

Measurements performed on high resistivity silicon detectors irradiated with proton and neutron fluences, up to 3.5x10(14) p/cm(2) and 4.0x10(15) n/cm(2) respectively, are presented. The current-voltage (IV) and capacitance-voltage (CV) characteristics, as well as the charge collection efficiency (CCE) of the devices have been measured to carry out a complete detector performance analysis after irradiation. The IV, CV and CCE analyses show that the irradiated devices depart from the ideal p(+)n junction modelisation when the fluence (f) is of the order of 10(14) + 10(15) cm(-2). In this fluence range, it is impossible to fully deplete the irradiated device; the CV characteristics show evidence of full depletion voltages up to 10(3)-10(4) Volts; the IV and CCE(V) curves are found to be linear in this fluence range; reverse currents up to a few mA are measured. A well visible, although low, charge collection signal has been observed at 7 degrees C after exposure to the extreme irradiation fluence of 4.0x10(15) n/cm(2). This is probably due to a very narrow active region inside the semiconductor bulk, and corresponding approximately, to a 75% inefficiency in the detector performance.