An optically detected electron-nuclear double resonance investigation was made of the so-called AsGa-X2 defect. The latter was an As antisite with a reduced hyperfine interaction, as compared with other As antisites such as EL2. It was produced in n-type material by 2MeV electron irradiation at 4.2K, followed by annealing to room temperature. Superhyperfine interactions, with the nearest As neighbor shell, were observed and were of the order of 240MHz. The first Ga, and the second As, shell exhibited superhyperfine interactions of about 54MHz (71Ga) and 52MHz, respectively. From these superhyperfine interactions, the electron paramagnetic resonance line-width was calculated. It was found, from a comparison of the measured and calculated electron paramagnetic resonance line-widths, that the first-neighbor shell consisted of only 3 nuclei. It was shown that the AsGa-X2 defect was still present after electron irradiation to high doses when the sample became semi-insulating. It was therefore possible to rule out a model which was based upon a distorted negatively charged isolated As antisite defect. The model proposed for the AsGa-X2 defect was an As-antisite plus As-vacancy complex, AsGa-VAs. Because AsGa-VAs could be produced only in n-type material, while the Ga vacancy, VGa, was produced in p-type and semi-insulating material, it was suggested that a form of Fermi level dependent bistability existed between these 2 intrinsic defects.

K.H.Wietzke, F.K.Koschnick, J.M.Spaeth: Materials Science Forum, 1995, 196-201, 1061-6