Capacitance Recovery in Neutron-Irradiated Silicon Diodes by Majority and Minority Carrier Trapping

Majority and minority carrier trapping has been studied in neutron-irradiated silicon diodes by transient junction capacitance recovery as well as by capacitance-versus-frequency and pulsed field effect techniques. After exposure to damaging radiation, trapping results in a transient time dependence of depletion layer width which may determine the survivability of depletion layer devices in a radiation environment. Majority carrier traps have been found in n-type neutron-irradiated silicon at Ec -0.36 eV and in p-type silicon at Ev + 0.30 eV. The capture cross sections for both types of traps are of the order of 10-15 cm2. Following a burst of damaging radiation, traps with unequilibrated charge exist with concentration roughly an order of magnitude larger than observed in equilibrium. These unequilibrated states relax slowly via the majority carrier band but quite rapidly when minority carriers are deliberately injected. Capacitance-voltage characteristics of neutron-irradiated junctions recovered by minority carrier injection show that recovery occurs only within a diffusion length of the metallurgical junction. Capacitance and lifetime recovery effects can be qualitatively interpreted in terms of the Gossick model for the disordered region spacecharge layer modified to include minority, as well as majority, carrier trapping. Recovery in this model is attributed to a shrinking of the disordered region space-charge layer.