Abstract
Polycrystalline ZnO thin films were prepared on silicon substrates using electrospray method with vertical setup. Water and ethanol were used as solvents for zinc acetate dehydrate and no postdeposition annealing was required for formation of ZnO. The influence of substrate temperature in the range of 150–250°C on surface morphology and roughness was studied by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and optical profilometry. An improvement of surface quality and smoothing of the films with temperature were obtained. X-ray diffraction measurements revealed that, at all investigated substrate temperatures, the films were polycrystalline with crystallites’ sizes decreasing with temperature. Besides, the preferred crystal orientation varies with the substrate temperature. The analysis of surface chemical composition and oxidation state was performed with X-ray photoelectron spectroscopy (XPS). It was shown that, at substrate temperature of 200°C, the deposited ZnO films were closest to the stoichiometric ones. In general, the films at 150°C were oxygen-deficient, while at other studied temperatures, the films had excess of oxygen more pronouncedly at 200°C. Spectral ellipsometric measurements confirmed that the structural disorder is the highest at 150°C and improves with temperature. Refractive indexes for films at 200°C and 250°C are almost the same, 1.97 and 1.93, respectively, at wavelength of 600 nm, while for the sample deposited at 150°C, the refractive index is substantially lower, 1.67. The optical band gap is slightly influenced by the substrate temperature: 3.27 eV at 150°C and 3.32 eV at 200°C.
Highlights
Due to its remarkable properties such as transparency in VIS and NIR spectral regions, low resistivity, biocompatibility, and long-term stability, ZnO gains increasing scientific interest
The influence of substrate temperature in the range of 150–250∘C on surface morphology and roughness was studied by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and optical profilometry
We study ZnO thin films prepared by electrospray method using zinc acetate dehydrate as precursor and water and ethanol as solvents
Summary
Due to its remarkable properties such as transparency in VIS and NIR spectral regions, low resistivity, biocompatibility, and long-term stability, ZnO gains increasing scientific interest. Thin ZnO films have been deposited using different vacuum-based techniques like RF sputtering [9], atomic layer deposition [10], plasma-enhanced chemical vapor deposition [11], pulsed laser deposition [4], and molecular beam epitaxy [12] These deposition methods require expensive facilities and precursors and sometimes impose restrictions on operation conditions (limiting coating area for instance). Mahmood et al [22] have studied the effect of substrate temperature in the range of 100–170∘C on morphological properties of deposited ZnO films and observed little influence. This could be expected because the decomposition temperature of Zn acetate is higher than 200∘C [16]. The tuning of films’ properties by changing the substrate temperature is demonstrated and discussed
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