EFFECTS OF MICROSTRUCTURE ON TRANSPORT-PROPERTIES OF UNDOPED HYDROGENATED AMORPHOUS-SILICON FILMS

Electronic transport properties have been investigated in undoped hydrogenated amorphous silicon (a-Si:H) materials whose microstructure and void fraction are changed by deposition temperature (T(s)). The hydrogen content in these materials decreases from 15 to 5 at. % and the void fraction by 14% as T(s) is raised from 200 to 350-degrees-C. The photo and dark conductivities are measured from 40 to 190-degrees-C and extended state electron mobilities are derived from a self-consistent analysis. The room temperature mobilities are found to increase from 0.8 to 30 cm2/V s and become less temperature dependent as T(s) increases. These temperature activated mobilities explain the Meyer-Neldel rule [Z. Tech. Phys. 18, 588 (1937)] in a-Si:H materials whose dark conductivity activation energies are greater than 0.4 eV where it cannot be explained by the statistical shift of the Fermi level.