Effects of Chlorine on Dopant Activation in a-Si:H

Abstract

AbstractThe incorporation of chlorine has a significant effect on the dark conductivity of doped and undoped hydrogenated amorphous silicon (a-Si:H). The dark conductivity of a-Si:H films deposited from dichlorosilane (SiCl2H2) and SiH4, and doped with diborane, increases by as much as a factor of 100 over the usual a-Si:H,B films deposited without SiCl2H2. The effect is observed at gas phase concentrations of diborane ranging from 0.006% to 0.5%, and for both DC and RF plasma depositions, although it is more noticeable for the DC discharge. An increase in dark conductivity is also observed in B doped a-Si,C:H films deposited with dichlorosilane, albeit coupled with a change in the Tauc gap. Chlorine reduces the conductivity of undoped and phosphorus doped a-Si:H films. Undoped a-Si:H films deposited from SiCl2H2 and SiH4 have a dark conductivity of ~1. 10-12 S.cm-1, which is an order of magnitude lower than films deposited from pure SiH4. We discuss several alternatives for the mechanism of chlorine enhanced or reduced dopant activation. We have made solar cells using chlorinated p-type a-SiC:H films as the p-layers.