Abstract
We study the surface morphology of ZnO thin films deposited by nitrogen mediated crystallization method utilizing atomic force microscopy as a function of nitrogen flow rates. Initially, the surface morphology of ZnO thin film deposited without nitrogen exhibits a bumpy surface with spiky grains where the skewness and kurtosis values were found to be 0.48 and 4.80, respectively. By addition of small amount of nitrogen, the skewness and kurtosis values of the films significantly decrease associated with a flatter topography. Further increase in nitrogen flow rate to 16 sccm has roughened the surface shown mainly by the increase in kurtosis value to be 3.30. These results indicate that the addition of small amount of nitrogen during deposition process has enhanced the adatoms migration on the surface resulting in a superior film with a larger grain size. Two-dimensional power spectral density analysis reveals that all the films have self-affine fractal geometry with total fractal values in the range of 2.14 to above 3.00.
Highlights
ZnO thin film has drawn attention due to has many promising features such as a wide direct band gap energy (~ 3.3 eV) and high room temperature excitonic binding energy (60 meV) [1]
The surface morphology of ZnO thin film deposited without nitrogen exhibits more bumps with spiky surface where the skewness and kurtosis values were found to be 0.48 and 4.80, respectively
By addition small amount of nitrogen, skewness and kurtosis values of the films decrease to near Gaussian distribution indicating that the surface morphology has transformed from platykurtic to leptokurtic where the bumps decrease and the spiky surfaces become mild surfaces associated with a flatter topography
Summary
ZnO thin film has drawn attention due to has many promising features such as a wide direct band gap energy (~ 3.3 eV) and high room temperature excitonic binding energy (60 meV) [1]. ZnO exhibits disadvantages because its resistivity is higher than that of ITO and strongly depends on film thickness [3]. We have recently overcome the problems by inserting a very thin ZnO buffer layer deposited by nitrogen mediated crystallization (NMC) between ZnO:Al (AZO) and quartz glass substrate [4]. By inserting 10-nmthick NMC-ZnO buffer layer, AZO film with resistivity of 5×10-4 Ωcm with much lower thickness dependence can be obtained [5]. We study the morphological evolution utilizing power spectral density and scaled height distribution analysis
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