Energy Levels and Negative Photoconductivity in Cobalt-Doped Silicon

Some effects of cobalt doping on $n$-type silicon have been studied. Two deep acceptor levels have been found; the upper one 0.53 eV from the conduction band and the lower one 0.35 eV from the valence band. This double-acceptor behavior leads to extrinsic negative photoconductivity. The spectral response, frequency response, and temperature dependence of this negative photoconductivity are reported.