STUDY OF CURRENT-VOLTAGE CHARACTERISTICS OF IRRADIATED SILICON DETECTORS

Current-voltage (I-V) characteristics of non-irradiated and irradiated p+-n-n+ detectors, with neutron fluences (phi) up to 10(14) n/cm2 wer e measured and the obtained data were analyzed. The I(f)-V(f) characte ristics confirmed the existence of a critical fluence boundary (phi(b) > 5 x 10(11) n/cm2), similar to those found by other types of measure ment (DLTS, C-V). We found that at phi(b) the rectification ratio is r educed drastically, but a large reverse voltage can, nevertheless, be applied. The series resistivity (rho) calculated from the I(f)-V(f) ch aracteristics, for both non-irradiated (NI) and irradiated detectors, shows that for NI detectors the resistivity is of the order of that of the silicon bulk (1200 OMEGA cm). The resistivity (rho) for irradiate d devices increases (with increasing values of phi, of up to 10(14) n/ cm2), up to approximately 4 x 10(3) OMEGA cm. As a result of the incre ase of rho with phi, the p+-n-n+ becomes a p+-nu-n+ device. This study explains the rather good charge collection efficiency in spite of str ongly affected physical properties.