Electrical properties of semi-insulating GaAS irradiated with neutrons

Conductivity, Hall mobility and magnetoresistance in semi-insulating (SI) GaAs samples irradiated with neutrons of various fluences ranging from 1/spl times/10/sup 17/ to 3/spl times/10/sup 19/ m/sup -2/ were measured and analysed in the temperature range 300-420 K. The magnetoresistance increases while the conductivity and the apparent Hall mobility decrease with increasing neutron fluence. The electron (n) to hole (p) concentration ratio resulting from the analysis of the room temperature parameters using a mixed conductivity model decreases with increasing neutron fluence as far as the ratio n/p exhibits values less than one at the highest fluences used. No remarkable differences were observed between activation energies for deep donors in samples with n/p>1 and that for deep acceptors in samples with n/p<1 deduced from the temperature dependences of the free charge carriers concentration. The role of thermal neutron shielding at irradiation, using a Cd-plate, is discussed.