Doping efficiencies of gas-phase and ion-implantation doped a-Si:H

We compare the electronic properties of gas-phase and implantation doped a-Si:H films and analyze their properties within the framework of Street's auto-compensation model 1]. We find that this model can consistently explain the varying degrees of sensitivity with respect to doping for differently prepared a-Si:H materials. In agreement with sub-band-gap absorption data our analysis indicates that the density of native dangling bond defects is increased when the film thickness is decreased and when thin films are further subjected to ion bombardment. Considering the temperature dependence of conductivity, we find that the auto-compensation model can provide an explanation for the high-temperature kink in the conductivity of doped a-Si:H films but that it fails to account for the experimentally observed universality of the Meyer-Neldel-rule behaviour of the conductivity prefactor in differently prepared and doped a-Si:H films.