EL2-related studies in irradiated and implanted GaAs

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Abstract
The midgap donor level EL2 is a very important defect because of the role it plays in the compensation of undoped semi-insulating GaAs. The knowledge of the exact EL2 structure becomes of even greater prime importance. We present here a review of the experimental results concerning artificial EL2 creation by electron and neutron irradiation and also ion implantation followed or not by annealing. These studies have greatly contributed in specifying the nature of EL2 namely a complex intrinsic defect with an arsenic antisite as a core (AsGa + X). We point out some new concepts such as hopping transitions due to inter-defect electron tunnelling which have been tentatively proposed to account for observations in implanted and neutron irradiated samples. We also discuss the main results of these artificial creation experiments as a function of the recent models proposed for EL2 up to the present day