Comparison between deep level defects in GaAs induced by gamma, 1 MeV electron, and neutron irradiation

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Abstract
The deep level transient spectroscopy technique has been employed to follow closely the effect of 1–300 Mrad 60Co γ irradiation on the deep electron traps in undoped vapor-phase-epitaxy n-type GaAs. The 1 Mrad γ-irradiated Schottky device was identical to the as-grown or control device, with only two electron traps EL2 (Ec−0.820 eV) and EL3 (Ec−0.408 eV) detected. At a γ dose of 5 Mrad, two additional electron traps EL6 (Ec−0.336 eV) and E2 (Ec−0.128 eV) were observed. As the γ doses were increased to ≥10 Mrad, a third electron trap E1 (Ec−0.033 eV) was observed, and the single exponential EL2 capacitance transient became a double exponential, indicating two deep levels lying at Ec−0.820 eV (EL2/EL2-A) and Ec−0.843 eV (EL2-B). The trap concentration of EL2-A remained unchanged up to a γ dose of 50 Mrad before starting to increase slowly as the γ dose was increased to ≥100 Mrad. In contrast, the EL2-B trap concentration was found to increase by 32 times, reaching 2.6×1014 cm−3 at 300 Mrad from a low 8.0×1012 cm−3 at 10 Mrad when it was first observed, whereas for the 1 MeV electron irradiation with low electron fluence of 1014 e cm−2, the EL6, E2, E1, and the double exponential EL2 were detected at the same time. There was no sign of EL2-B, EL3, EL6, E2, or E1, but an additional broad U band was observed after irradiation with 1 MeV neutrons. The results of the γ and neutron irradiation suggest that the presence of the double exponential EL2 transients is not related to either EL6, E2, E1, or the U band, and is unlikely to be due AsGa→VGa+Asi but is probably caused by the AsGa complex defects involving an irradiation defect. The defect concentration of trap E1 increased strongly from 5.4×1013 cm−3 at 10 Mrad to 9.3×1014 cm−3 at 100 Mrad, and E2 increased from 2.1×1013 cm−3 at 5 Mrad to 6.7×1014 cm−3 at 100 Mrad.