Modelling of semiconductor diodes made of high defect concentration, irradiated, high resistivity and semi-insulating material: The capacitance–voltage characteristics

Full modelling is reported of the capacitance of a long PIN semiconductor diode with a high concentration of generation–recombination (g–r) centres and different concentrations of deep traps. There are considerable differences from the textbook results given for normal lifetime diodes which have low concentrations of g–r centres. For a low density of g–r centres, the capacitance is the usual value. That is it decreases as V−1/2 with increasing reverse bias while it increases rapidly with increasing forward bias. For high density of g–r centres and in reverse bias a departure from this voltage dependence is observed, while in forward bias a negative capacitance appears. This agrees with experiment. From these results we present a physical understanding of the processes involved. There are specific applications of these results to radiation damaged devices, lifetime killed diodes and devices made from high resistance and semi-insulating materials, especially in the interpretation of the C–V curves to evaluate the fixed space charge density.