Investigations in cobalt doped silicon by DLTS and Mössbauer effect

We have investigated the system Co in Si by Möβbauer spectroscopy and DLTS. In p-type silicon no DLTS signal of cobalt species between Ev+ 0.1 eV and Ev+ 0.5 eV, neither of substitutional cobalt nor of Co-B pairs, is found giving evidence that many assignments in the literature of ionization energies to cobalt in solution are doubtful. If one lowers the diffusion temperature to 940 °C the main part of Co in Si remains in solution as substitutional cobalt and as a new species, tentatively attributed to a pair of cobalt with a shallow boron acceptor (sa). This new species even found in specimens with a boron concentration of Nsa= 2.8 1015cm-3anneals out below 110 °C.