DEEP IMPURITY LEVELS OF COBALT IN SILICON

It has been believed until now that cobalt in silicon forms an acceptor level at around Ec–0.53 eV and a donor level at around Ev+0.35 eV. However, it is found that an acceptor level at Ec–(0.40±0.02)eV and a donor level at Ev+(0.23±0.01) eV are attributed to the amphoteric cobalt levels from the DLTS measurements for the samples diffused with cobalt deposited from the evaporation of a pure cobalt wire. The former levels (0.53 eV and 0.35 eV) are observed only for the samples prepared by the cobalt deposition from a tungsten filament wrapped with cobalt wire, and the tungsten contamination is regarded to be the cause of these levels. © 1990 The Japan Society of Applied Physics.