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.

Articles you may be interested inDeep-level defects introduced by 1 MeV electron radiation in AlInGaP for multijunction space solar cells J. Appl. Phys. 98, 093701 (2005); 10.1063/1.2115095 Comparison between deep level defects in GaAs induced by gamma, 1 MeV electron, and neutron irradiation Isochronal annealing behavior of deep-level defects in 1 MeV electron irradiated vapor phase epitaxy GaAs was studied through deep level transient spectroscopy measurements. As the annealing temperature was increased, the activation energy of the ELZA trap remained at EC-O.823 eV, whereas the ELZ-B trap (EC-O.843 eV) transformed into a new trap, ELN-1 (Q-O.870 eV), and linally into another new trap, ELN-2 (E,-0.891 eV) before returning to the single EL2-A level at a 270 "C annealing temperature. The EL6 trap (Q-O.335 eV) varied similarly, transforming into EC-O.357 eV (Pl) before staying constant at E,-0.396 eV (ELN3) after a 270 "C! annealing temperature. The capture cross sections of EL2-B and EL6 increased by an order of magnitude during the annealing. These results suggest that the ELZB trap which was split from the EL2 center by the 1 MeV electrons could be related to EL6. Traps El and E2 remain at EC-O.032 eV and EC--O.129 eV, respectively, throughout the annealing, before annihilation at a 290 "C annealing temperature. This result indicates that the atomic structures of El and E2 defects could be related. The EL3 (EC-O.420 eV) is transformed into a new trap, ELN-4 (EC-O.456 eV), and then into &-OS0 eV (P2) during annealing. The free carrier concentration of the irradiated sample increases rapidly with annealing temperature and returns back to the starting free carrier concentration due to the rapid annealing rates of the electron induced defects. 2354

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The deep level transient spectroscopy technique has been used to study the EL2 defect in n-type semiconducting GaAs subjected to 1 MeV fast neutrons at room temperature. After neutron irradiation, the EL3 defect which is usually detected between 180 and 210 K disapperared and the EL2 defect measured between 280 and 320 K was found to remain single exponential (Ec−0.820 eV) despite the creation of a broad U band measured between 100 and 270 K. From this result, together with our earlier reports on the double exponential capacitance transient of the EL2 defect after 1 MeV electron irradiation [Lai, Nener, Faraone, Nassibian, and Hotchkis, J. Appl. Phys. 73, 640 (1993)] and the behavior of the electron irradiated EL2 defect upon isochronal annealing [Lai and Nener, J. Appl. Phys. 75, 2354 (1994)], we observe a difference in the behavior of the EL2 defect after neutron and electron irradiation. The results of the present study indicate that the EL2-B level reported in an earlier work is not due to any interaction of the stable EL2 (or EL2-A) level with either the U-band or EL6 defect. The EL2 defect is likely to be a complex defect which can manifest itself as a number of different defect levels depending on the particular details of the irradiation used. The U band is likely to be a cluster defect caused by the large number of atoms displaced from lattice sites by the fast neutrons, and is not likely to be due to any interaction mechanism between the EL2 and EL6 defects.

Deep level transient spectroscopy has been employed to determine the defect energy levels, capture cross sections, and trap densities in Si-doped vapor phase epitaxy GaAs both before and after irradiation by 1 MeV electrons at room temperature for electron fluence ranging from 1.1×1014 to 5.0×1015 e cm−2. The results indicate that the irradiated samples have an electron trap at Ec-0.334 eV(EL6) in addition to the two electron traps at Ec-0.815 eV(EL2) and Ec-0.420 eV(EL3) which are present in the nonirradiated sample. The density of the EL6 trap increases monotonically with irradiation fluence from 6.7×1013 to 24.4×1013 cm−3 as electron fluence is increased from 1.1×1014 to 3.1×1014 e cm−2. In contrast, both the EL2 and EL3 trap densities were found to be only moderately affected by electron irradiation with trap densities slightly greater than the nonirradiated sample. These results, along with the fact that the EL6 trap was not observed in the nonirradiated sample, strongly suggest that this trap is created by the electron irradiation. In addition to creating the EL6 trap, electron irradiation results in a nonexponential transient for the EL2 deep level at Ec-0.815 eV which can be resolved into the sum of two exponential transients arising from two closely spaced deep levels at Ec-0.815 eV and Ec-0.843 eV.