On the problem of the EL2 structure in semi-insulating GaAs: high-frequency ODEPR/ODENDOR measurements in W-band

Abstract For almost two decades the structure model of the EL2 defect in semi-insulating (SI) GaAs has been controversially discussed. Neither the isolated As Ga with T d symmetry, nor the As Ga –As i pair model nor any other As Ga -related defect model could be unambiguously established. The reason was that the analysis of previous optically detected electron nuclear double resonance (ODENDOR) and optically detected electron paramagnetic resonance (ODEPR) spectra measured at 24 GHz was difficult and not unambiguous because of forbidden transitions, pseudo-dipolar couplings and higher order effects. However, the ODEPR spectra of the EL2 defect measured in W-band (93 GHz) can be fitted by first order perturbation calculation of the spin Hamiltonian thus allowing a much simpler analysis compared to X- or K-band. From ODEPR measurements in different SI GaAs samples both in K- and W-band we show that the ODEPR spectra of the EL2 defect together with the K-band ODENDOR data are not consistent with the As Ga –As i pair model, but the highly symmetric isolated As Ga model has to be excluded as well. First ODENDOR measurements in W-band are also reported.