Electrical resistivity and photoluminescence of zinc oxide films prepared by ultrasonic spray pyrolysis
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Date
2008-11-04
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Abstract
Zinc oxide (ZnO) thin films have been prepared by ultrasonic
Spray pyrolysis (USP) technique using zinc acetate dihydrate
dissolved in methanol, ethanol and deionized water. A number of techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared
(FTIR) spectroscopy, UV–visible, electrical resistivity, and
photoluminescence (PL) were used to characterize the obtained ZnO thin films. The evolution of the preferred crystalline orientations in the ZnO films was systematically investigated. The PL measurements indicated that the as-grown ZnO
thin films showed UV and green emission bands when they
were excited by a Hg arc lamp using 313 nm as the excitationbeen attributed to the compressive intrinsic stress present in
the films. It is confirmed that oxygen vacancy (VO) is the
most important factor that causes the broad visible emission.
Furthermore, the visible emission and electrical resistivity of
ZnO thin films are found to be a function of porosity. Also, it
has been interestingly found that the intensity of green emission at ~2.5 eV remarkably increased when the obtained ZnO
films were deposited at 320 °C. The reason might be the VO,
intrinsic stress, surface-to-volume ratio and porosity in the
sample increased at low substrate temperature. The resistivity
follows the same behavior as the intensity of the green emission. We propose a new luminescence mechanism based on
the recombination related to oxygen vacancies in Zn-rich or
stoichiometric conditions
source. A red-shift in the near band edge (NBE) has been observed with the increase in the substrate temperature and has