Influence of deposition conditions on long-range electronic disorder inn-type doped hydrogenated amorphous silicon

Measurements of the conductivity, thermopower, and infrared absorption for n-type doped hydrogenated amorphous silicon (a-Si:H) films grown under varying deposition conditions have been performed, in order to test the role that compositional fluctuations associated with the bonded hydrogen microstructure have on the long-range disorder present at the conduction-band edge. Films grown either with high deposition power or at low substrate temperature have a lower conductivity and more long-range disorder of the mobility edge, as measured by the difference in the activation energies of the conductivity and thermopower. The long-range disorder (measured by the activation energy difference) is larger for films with a larger fraction of Si=H₂ bonds, as inferred from the infrared absorption, indicating that the hydrogen bonding is related to long-range electronic disorder. Computer simulations have also been performed in order to test the proposal that long-range disorder is responsible for the difference in the conductivity and thermopower activation energies.