Effect of Hydrogen Dilution on Structure of a-Si:H Prepared by Substrate Impedance Tuning Technique

Abstract

The effect of hydrogen dilution of a source gas, SiH₄, on structural inhomogeneity has been studied for hydrogenated amorphous silicon films prepared under the mode involving a high deposition rate by the substrate impedance tuning technique. As the silane fraction decreases from 100% to 1% with hydrogen dilution, the SiH bonding configuration gradually changes into the dihydride (SiH₂) group; finally, the films become microcrystalline. On the other hand, the state density in the mid gap and the spin density, related to the structural disorder, have minima at silane fractions of 100% and 10%. These results seem to be consistent with a two-phase model suggested for high rate films, with an emphasis on a different medium range disorder between the films prepared at high and low deposition rates.