Self annealing effect on neutron irradiated silicon detectors by Hall effect analysis

High resistivity n-type silicon samples have been irradiated with -1 MeV neutrons at fluences between 10¹² and 1.4×10¹⁴ n/cm^-2. The radiation induced changes in the effective free carrier concentration have been analysed by Hall Effect measurement during a storage time of approximately seven months at room temperature. The Hall coefficient measured for the most irradiated samples, exposed to fluences higher than 4×10¹³ cm^-2 has switched from negative to positive values approximately 200 days after the irradiation. This experimental evidence explains the reverse annealing effect observed in neutron irradiated silicon detectors as being related to the creation of a deep acceptor level which causes the change in conductivity from n to p-type of the irradiated silicon bulk during self annealing. The behaviour of irradiated device has been analyzed with a model taking account of donor removal and acceptor creation. Results are in agreement with others obtained with different experimental techniques