Calculated Small Signal Characteristics for Iradiated PN Junctions

Numerical calculations have been used to study small signal trapping effects in neutron-irradiated pn junctions as a function of frequency. Good agreement has been obtained between the calculations and experimental data in n-type silicon using two acceptor centers to model the trapping centers produced by neutron irradiation. A single level donor center has been used for p-type material. These calculations indicate that complex changes in the carrier distributions within the device can be responsible for a rather simple change in the terminal capacitance and conductance. Although good agreement has been obtained between the calculated and experimental results, the calculations suggest that another deep acceptor level (consisting of about 10% of the total trap density) may be present in n-type material which provides a more gradual change in the terminal capacitance with frequency than that noted using the two acceptor centers.