Radiation Defects in Heavily Irradiated GaAs

Electrical properties and IR-absorption in GaAs irradiated at 80°C with various doses of 2.0 MeV electrons were investigated. Heavily irradiated specimens of n- and p-type GaAs are characterized by very low conductivity, carrier density and Hall mobility and large optical absorption in the interval of 0.5–1.5 eV. With increasing dose, the hole mobility, in contrast to electron mobility, decreases initially and passes through a minimum that is caused by recharging of Ev + (0.20 − 0.25) eV donor centres. The absorption spectra of n- and p-type irradiated crystals are identical. We observed structureless absorption and some absorption bands 0.96–0.98 eV being the dominant one. The temperature dependence of conductivity and thermostimulated current measurements indicate the presence of Ev + (0.45 ± 0.05) and Ev + (0.25 ± 0.05) eV centres which are very much like those introduced by heat treatment. It is found that upon annealing of heavily irradiated p-GaAs, the hole mobility exhibits very large reverse annealing at 100–200°C, caused by the creation during the annealing process of additional Ev + (0.20 − 0.25) eV centres. Results of isochronal annealing on carrier concentration in p-GaAs suggest that a large concentration of point defects agglomerate, forming the clusters whose annealing takes place at a temperature above 400°C.