The selective trapping of mobile group-V interstitials by impurities in electron-irradiated GaAs and GaP

Irradiation of GaAs or GaP by 2 MeV electrons at room temperature leads to the generation of group-V interstitials. These defects are immobile in n-type material but once the Fermi level is lowered to a critical position, corresponding to a threshold dose of irradiation, they diffuse through the crystal and may be trapped by isoelectronic boron Bsub(Ga), carbon acceptors C-sub(V) and boron impurity antisite defects Bsub(V) as monitored by the infrared vibrational absorption arising from these light atoms. Other defects, including [B-sub(V)-donor] pairs are also destroyed. The relative cross sections for these processes do not differ significantly and it is concluded that the interactions are dominated by elastic size effects rather than by a Coulombic field. The implication is that group-V interstitials are negatively charged in n-type material and neutral in high-resistivity irradiated samples. It is explained how the critical threshold dose for interstitial mobility may be used to explore the mechanism for production of other defects such as the Assub(Ga) antisite defect. (author)