In order to clarify the nature of the neutral Mn acceptor in this material, optical absorption and electron paramagnetic resonance experiments were carried out by monitoring conventional and thermally detected electron paramagnetic resonance in semi-insulating Mn-doped samples. In the case of thermal equilibrium at low temperatures, all of the Mn occurred in the charged acceptor state, MnGa2+(A-). By means of illumination with photon energies that were greater than 1.2eV, it could be partially converted into the neutral charge state. The resultant photo-stimulated electron paramagnetic resonance spectra revealed the characteristic features of a tetrahedrally distorted center with an integral spin. The resonance lines were detectable only at temperatures below 7K, and the line-width of about 50mT was attributed to unresolved Mn hyperfine splitting. The experimental data were explained in terms of MnGa3+ ions on strain-stabilized sites of tetragonal symmetry; due to strong Jahn-Teller coupling within the 5T2 ground state. Such a behavior was expected for a 3d4 defect, as observed for iso-electronic Cr2+ in GaAs and other tetrahedrally coordinated semiconductors. Analysis of the electron paramagnetic resonance spectra therefore confirmed that, in the present material, the neutral charge state of the Mn acceptor was MnGa3+(A0). This was different to its behavior in GaAs and InP.

J.Kreissl, W.Ulrici, M.El-Metoui, A.M.Vasson, A.Vasson, A.Gavaix: Physical Review B, 1996, 54[15], 10508-15