Characterization of deep levels and carrier compensation created by proton irradiation in undoped GaAs

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Abstract
Deep levels and carrier compensation created in undoped metal‐organic chemical‐vapor deposition grown GaAs by low fluence proton irradiation (1×108−1×1010 cm−2) are investigated by the deep level transient spectroscopy technique and capacitance‐voltage profiling. At least five main electron traps are observed after room‐temperature irradiation in addition to the EL2 present in the as‐grown material. Irradiation generates additional EL2, which annihilate at much lower temperatures than one would expect for isolated EL2. However, with further increase in irradiation fluence, the magnitude for this additional increment begin to decrease. The apparent decrease in the EL2 peak is accompanied by an increase of a broad peak in the deep level transient spectroscopic spectrum. This broad peak has a highly nonexponential capacitance transient and it is suggested to result from the interaction of the additional EL2 with EL6. One of the observed traps, with energy level, (Ec−0.40) eV, has not previously been reported in proton irradiated GaAs. The signature of this trap resembles that of EL5 and is quite stable at moderate annealing temperatures; annihilating completely only at a temperature of ∼600 °C. This level shows a saturation effect with increasing irradiation dose and we believe it is related to complex defect‐impurity formation. The temperature dependence of the carrier profiles reveals some complex behavior of carrier compensation, including acceptor‐ and donor‐like properties of the various traps.