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Problem Addressed

For materials with excessively large resistance, traditional transport measurements fail because the current at reasonable voltages becomes too small to measure. By patterning hydrogenated amorphous silicon (a-Si:H) adjacent to a nanometer scale silicon metal-oxide semiconductor field-effect transistor (MOSFET), you are able to detect charging of the sample and measure extremely high resistances (~1017Ω) using moderate voltages (~1 V). This device geometry, in which the MOSFET sensor and sample can be gated independently, allows investigation of the field effect and dispersive transport. Additionally, these techniques allow measurement of the density of localized states near the Fermi energy.