On the doping mechanism of boron-doped hydrogenated amorphous silicon deposited by rf-co-sputtering

The doping mechanism of boron-doped a-Si:H deposited by rf-co-sputtering was investigated and compared with results obtained by plasma enhanced chemical vapor deposition (PECVD). The activation energy and room temperature conductivity could be varied by approximately the same range as that reported for PECVD films. However, there are some relevant discrepancies between the results obtained by these two techniques. First, one needs a much larger amount of boron in the sputtered films, in comparison with PECVD ones, in order to get samples with almost the same activation energy. This implies that the doping efficiency is much lower in films prepared by sputtering. Second, the relation between the dangling bonds and the impurity concentration does not appear to follow the square root power law function as proposed by Street and observed in PECVD films indeed. These differences are likely to be related to the density of defects, which is much higher in films prepared by sputtering. The increase in the deep defect density is more likely to be related to topological disorder introduced by the presence of a large number of inactive impurities.