This paper addresses the doping mechanism of amorphous semiconductors through the investigation of boron doped rf co-sputtered amorphous hydrogenated silicon. The activation energy and room temperature conductivity varied from 0.9 to 0.3 eV and from 10-12 to 10-4 Ohm-1 .cm-1, respectively, by ranging the boron concentration from 0 to 3 at.%. These ranges of electronic properties are of the same order of those reported for samples prepared by plasma enhanced chemical vapor deposition (PECVD). In spite of these similarities, there are some relevant differences. The doping effciency, at low boron concentrations, is much lower than that of PECVD samples. In addition, the creation of deep defects (dangling bonds) does not follow the square root power law dependence on the boron concentration as proposed by Street and observed in PECVD samples. These differences are associated with the density of defects, which is much higher in films prepared by sputtering. The increase in the deep defect density is more likely related to topological disorder, introduced by the presence of a high concentration of inactive impurities.