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Variable Range Hopping and Thermal Activation Conduction of Y-doped ZnONanocrystalline Films

By T. T. Lin, S. L. Young, C. Y. Kung, H. Z. Chen, M. C. Kao, M. C. Chang and C. R. Ou


ZnO and Y-doped ZnO nanocrystalline films wereseparately fabricated on the glass substrates by sol-gelspin-coating method. X-ray diffraction patterns of the filmsshow the same wurtzite hexagonal structure and (002)preferential orientation. SEM images show that grain size andthickness of the nanocrystalline films decrease with increasingdoping concentration. The decrease of optical bandgap withthe increase of Y doping is deduced from the transmittancespectra. Temperature-dependent resistivity reveals asemiconductor transport behavior for all ZnO and Y-dopedZnO nanocrystalline films. The resulting conductivityoriginates from the combination of thermal activationconduction and Mott variable range hopping (VRH)conduction. In the high temperature range, thetemperature-dependent resistivity can be described by theArrhenius equation, σ(T)=σ0exp[-(Ea/kT)], which shows thethermal activation conduction. The activation energy Eaincreases from 0.47 meV for ZnO film to 0.83 meV forZn0.98Y0.02O film. On the contrary, in the low temperaturerange, the temperature-dependent resistivity can be fitted wellby the relationship, σ(T)=σh0exp[-(T0/T)1/4], which indicatesthe behavior of Mott VRH. The results demonstrate that thecrystallization and the corresponding carrier transportbehavior of the ZnO and Y-doped ZnO nanocrystalline filmsare affected by Y doping

Topics: ZnO nanocrystalline film, sol-gel spin-coating method, resistivity, variable range hopping, thermal activation conduction
Year: 2014
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