Current-voltage characteristics of silicon PIN diodes irradiated in KAMINI nuclear reactor

The present study reports on the investigation of current-voltage (I-V) characteristics of commercial planar Si-PIN diodes, irradiated in a typical thermal nuclear reactor - KAMINI for neutron fluences ranging from 1×1014 to 1×1016 n/cm2. The I-V Characteristics of the virgin and neutron irradiated Si-PIN diodes are measured in ambient environment for the forward and reverse biased conditions. In the forward bias condition, one of the consequences of increasing the neutron irradiation fluence is the increase in knee voltage from ∼0.5 V for virgin diode to 37.4 V for neutron irradiated diode with fluence of 1×1016 n/cm2. Further analysis of forward characteristics, revealed increase in ideality factor from a typical value of ∼2 for virgin diode to an anomalous value of ∼496 for the highest irradiated diode specimen. This increase is attributed to the increasing neutron damage that the diodes undergo upon irradiation. Moreover, in the reverse biased condition, the reverse leakage current increased by four orders of magnitude from 10−9 to 10−5 ampere. A qualitative analysis of the forward and reverse I-V characteristics, showed that the diodes change from a rectifying to ohmic behaviour with increase in neutron fluence and this was inferred from the decrease in 'gap' between the forward and reverse currents in the low voltage regions. Quantitatively, the rectification ratio - ratio of the forward to reverse currents - was calculated to be 108 and 84 for the virgin and 1 × 1016 n/cm2 irradiated specimens, respectively. The damage constant evaluated from the reverse bias I-V measurements conditions was found to be 1.7683 × 10−18 A/cm.