We report observations of three distinct conduction mechanisms in n-type doped mixed-phase amorphous/nanocrystalline silicon thin films over a range of nanocrystallite concentrations and temperatures. As the temperature is varied from 470 to 10 K, we observe activated conduction, multiphonon hopping (MPH), and Mott variable range hopping (VRH) as the nanocrystal content is increased. The transition from MPH to Mott-VRH hopping around 50 K is tentatively ascribed to the freeze out of the phonon modes.
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We gratefully acknowledge technical assistance from Zvie Razieli and discussions with Boris Shklovskii and David Emin. This work was partially supported by NSF grant DMR-0705675, the NINN Characterization Facility, the Nanofabrication Center, an Xcel Energy grant under RDF contract #RD3-25, NREL Sub-Contract XEA-9-99012-01, and the University of Minnesota. L.R.W. acknowledges support from a Doctoral Dissertation Fellowship provided by the University of Minnesota.