Variable-Range Hopping and Thermal Activation Conduction of Y-Doped ZnO Nanocrystalline Films

ZnO and Y-doped ZnO nanocrystalline films were separately fabricated on the glass substrates by sol-gel spin-coating method. X-ray diffraction patterns of the films show the same wurtzite hexagonal structure and (0 0 2) preferential orientation. Scanning electron microscope images show that grain si...

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Bibliographic Details
Published in:IEEE transactions on nanotechnology 2014-05, Vol.13 (3), p.425-430
Main Authors: Lin, T. T., Young, S. L., Kung, C. Y., Chen, H. Z., Kao, M. C., Chang, M. C., Ou, C. R.
Format: Article
Language:English
Subjects:
Activation
Conductivity
Doping
Electrical resistivity
Mathematical analysis
Nanocrystals
Resistivity
Scanning electron microscopy
Semiconductors
sol-gel spin-coating method
Temperature distribution
Temperature measurement
thermal activation conduction
variable-range hopping (VRH)
Zinc oxide
ZnO nanocrystalline films
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Summary:ZnO and Y-doped ZnO nanocrystalline films were separately fabricated on the glass substrates by sol-gel spin-coating method. X-ray diffraction patterns of the films show the same wurtzite hexagonal structure and (0 0 2) preferential orientation. Scanning electron microscope images show that grain size and thickness of the nanocrystalline films decrease with increasing doping concentration. The decrease of optical bandgap with the increase of Y doping is deduced from the transmittance spectra. Temperature-dependent resistivity reveals a semiconductor transport behavior for all ZnO and Y-doped ZnO nanocrystalline films. The resulting conductivity originates from the combination of thermal activation conduction and Mott variable-range hopping (VRH) conduction. In the high-temperature range, the temperature-dependent resistivity can be described by the Arrhenius equation, σ (T) = σ 0 exp[ -(E a /kT)], which shows the thermal activation conduction. The activation energy Ea increases from 0.47 meV for ZnO film to 0.83 meV for Zn 0.98 Y 0.02 O film. On the contrary, in the low-temperature range, the temperature-dependent resistivity can be fitted well by the relationship, σ(T) = σ h 0 exp[-(T 0 /T) 1/4 ], which indicates the behavior of Mott VRH. The results demonstrate that the crystallization and the corresponding carrier transport behavior of the ZnO and Y-doped ZnO nanocrystalline films are affected by Y doping.
ISSN:1536-125X
1941-0085
DOI:10.1109/TNANO.2013.2280648