We have studied the Ec - 0.4 e V center in O-doped GaAs by a combination of temperature-dependent Hall-effect measurements, spark-source mass spectroscopy, and secondary-ion mass spectroscopy. The conclusion is that neither 0 nor any other impurity can account for the O.4-eV center; therefore, it is a pure defect.
Look, D. C.,
& Sizelove, J. R.
(1983). Defect Nature of the 0.4-Ev Center in O-Doped GaAs. Applied Physics Letters, 42 (9), 829-831.