STUDIES OF FREQUENCY-DEPENDENT C-V CHARACTERISTICS OF NEUTRON-IRRADIATED P+-N SILICON DETECTORS

Frequency-dependent capacitance-voltage (C-V) characteristics of neutron irradiated high resistivity silicon p+-n detectors have been observed up to a fluence of 8.0x10(12) n/cm2. It has been found that frequency dependence of the deviation of the C-V characteristic (from its normal V-1/2 dependence), is strongly dependent on the ratio of the defect density and the effective doping density N(t)/N(d)'. As the defect density approaches the effective dopant density, or N(t)/N(d)' --> 1, the junction capacitance eventually assumes the value of the detector geometry capacitance at high frequencies (f greater-than-or-equal-to 10(5) Hz), independent of voltage. A two-trap-level model using the concept of quasi-fermi levels has been developed, which predicts both the effects of C-V frequency dependence and dopant compensation observed in this study.