ELECTRICAL CHARACTERISTICS AND CHARGE COLLECTION EFFICIENCY OF SILICON DETECTORS IRRADIATED WITH VERY HIGH NEUTRON AND PROTON FLUENCES

Measurements performed on high resistivity silicon detectors irradiate d with proton and neutron fluences, up to 3.5x10(14) p/cm(2) and 4.0x1 0(15) n/cm(2) respectively, are presented. The current-voltage (IV) an d capacitance-voltage (CV) characteristics, as well as the charge coll ection efficiency (CCE) of the devices have been measured to carry out a complete detector performance analysis after irradiation. The IV, C V and CCE analyses show that the irradiated devices depart from the id eal p(+)n junction modelisation when the fluence (f) is of the order o f 10(14) + 10(15) cm(-2). In this fluence range, it is impossible to f ully deplete the irradiated device; the CV characteristics show eviden ce 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 curren ts up to a few mA are measured. A well visible, although low, charge c ollection signal has been observed at 7 degrees C after exposure to th e 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 per formance.