The effects of radiation-induced displacement damage on impurity conduction in gallium arsenide

The effects of 60Co γ-ray and high-energy neutron displacement damage on impurity conduction in epitaxial gallium arsenide were investigated. The activation energy (ε2) associated with the transition regime of the impurity conduction process was found to increase by a factor of 5 as a result of 60Co γ irradiation, and only by a factor of 1.6 for a comparable neutron irradiation. In addition, the ratio of the Hall carrier density at low and high temperatures, (nH)4 K/(nH)300 K, decreased by a larger amount for 60Co γ irradiation than for neutron irradiation. The effects of neutron irradiation are explained in terms of increased compensation. For the case of 60Co γ irradiation, it is postulated that a new donor level is introduced which does not participate in the impurity conduction process. In addition, with respect to the impurity conduction process, it is found that ε2 is proportional to ε1 (the conduction-band activation energy) and varies inversely with neutral donor spacing in accord with the model proposed by Mikoshiba. Also ρ30, the hopping regime resistivity, is found to vary inversely with the square of the free-carrier concentration and exponentially with the quantity 0.6/ND1/3a.