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 were measured and the obtained data were analyzed. The I(f)-V(f) characteristics confirmed the existence of a critical fluence boundary (phi(b) > 5 x 10(11) n/cm2), similar to those found by other types of measurement (DLTS, C-V). We found that at phi(b) the rectification ratio is reduced drastically, but a large reverse voltage can, nevertheless, be applied. The series resistivity (rho) calculated from the I(f)-V(f) characteristics, 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 irradiated 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 increase 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 strongly affected physical properties.