Determination of the FR3 acceptor level by direct excitation of the FR3 EPR in undoped semiinsulating GaAs.

A new photoexcitation band of the FR3 EPR signal in undoped semiinsulating GaAs has been discovered. It results from the excitation of an electron from the FR3 acceptor level to the conduction band. The spectral shape of the band has been measured by the initial slope technique. Its low energy threshold is at 1.44 eV from which we deduce an acceptor binding energy of (80 plus minus 10) meV. Nonmonotonic FR3 EPR transients are observed within this band. This unusual effect is, however, not related to the metastable properties of the AsGa/EL2 defect.