P-I-N LIKE BEHAVIOR OF P-N-N+ DETECTORS UNDER HIGH FLUENCE NEUTRON-IRRADIATION()

Forward and reverse current-voltage (I-V) characteristics of non-irrad iated and irradiated p(+)-n-n(+) detectors, at neutron fluences (phi) up to 10(15)n/cm(2), were measured and the obtained data were analyzed . The I-f - V-f characteristics confirmed the existence of a critical fluence (phi(c) > 5 x 10(11)n/cm(2)), similar to those obtained by oth er types of measurement (DLTS, C-V). We found that at phi > phi(c) the rectification ratio is being reduced drastically, but a large reverse voltage could, nevertheless, be applied. The series resistivity (rho) , calculated from the I-f - V-f characteristics, for both non-irradiat ed (NI) and irradiated detectors, shows that for NI detectors the resi stivity is of the same order of magnitude like that of the silicon bul k (1200 Ohm cm). The resistivity (rho) for irradiated devices increase s (with increasing values of phi, of up to 10(15)n/cm(2)), up to about 4 x 10(3) Ohm cm. As a result of the increase of rho with phi, the p( +)-n-n(+) which is a wide diode, becomes a p(+)-v-n(+) device. This st udy explains the rather good charge collection efficiency in spite of strongly affected physical properties.