Spectroscopy of the Co-Te complex in GaAs

GaAs:Co samples have been obtained by diffusion in Te-doped samples. Isolated Co2 centres are observed in EPR, optical absorption and in photoluminescence studies. Other Co-related complexes are observed. The most important one is interpreted as a Co-Te first-neighbour complex. The luminescence and absorption of the complex are only slightly modified. In contrast, the EPR and photoluminescence excitation spectra are highly modified by the axial field: the acceptor level changes from EV+0.14 eV for isolated Co to EV+0.25 eV for the Co-Te complex.