| Summary: | 碩士 === 國立交通大學 === 應用化學系碩博士班 === 100 === In this study, the conduction mechanism of nitrogen-doped ultranano crystalline diamond films (N-doped UNCD) grown by microwave-assisted chemical vapor deposition (MPECVD) was investigated. From Raman spectroscopy analysis, the N-doped UNCD film shows significant D, G band and the 1150cm-1 characteristic peaks. From photoluminescence measurements we found no characteristic light emission of the nitrogen vacancy in the PL spectra of N-doped UNCD films. Therefore, the doped nitrogen atoms did not enter the grains, but only existed in the grain boundary. From the Hall measurement, the N-doped UNCD film was proven to be heavily doped n-type semiconductor with a carrier concentration as high as 1019 ~ 1020/cm3. Furthermore, we fabricated a field effect transistor (FET) structure on the N-doped UNCD film. From the transconductance measurements, we found that the electrical conductivity of N-doped UNCD film could not modulated by the gate bias. Such results are attributed to the high carrier concentration and the metallic conduction behavior of N-doped UNCD films. Finally, from the variable temperature electrical measurements, we conclude that the N-doped UNCD films exhibit thermionic conduction at a temperature above 220K. At a temperature below 220K, the hopping conduction is responsible for the carrier transport and it can be modeled with Mott `s hopping model where the free conducting electrons are provided from the grain boundaries C=N σ *, C=N π *and C-N σ * .
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