Abstract
Indium doped zinc oxide [ZnO:In] thin films have been deposited at 430°C on soda-lime glass substrates by the chemical spray technique, starting from zinc acetate and indium acetate. Pulverization of the solution was done by ultrasonic excitation. The variations in the electrical, structural, optical, and morphological characteristics of ZnO:In thin films, as a function of both the water content in the starting solution and the substrate temperature, were studied. The electrical resistivity of ZnO:In thin films is not significantly affected with the increase in the water content, up to 200 mL/L; further increase in water content causes an increase in the resistivity of the films. All films show a polycrystalline character, fitting well with the hexagonal ZnO wurtzite-type structure. No preferential growth in samples deposited with the lowest water content was observed, whereas an increase in water content gave rise to a (002) growth. The surface morphology of the films shows a consistency with structure results, as non-geometrical shaped round grains were observed in the case of films deposited with the lowest water content, whereas hexagonal slices, with a wide size distribution were observed in the other cases. In addition, films deposited with the highest water content show a narrow size distribution.
Highlights
When water content increases to 100 mL/L, the corresponding spectrum of Zinc oxide (ZnO):In films shows the (002) intensity prevailing over all the rest
The variation in water content in the starting solution for the deposition of ZnO thin films leads to substantial modification in the surface morphology
Consistency in morphology changes is observed with the corresponding electrical results, as scattering of free carriers by grain boundaries is high in a film formed by hexagonal slice shaped grains, compared with an almost continuous growth occurring in films deposited with the lowest water content
Summary
According to the required application, the deposition of ZnO thin films can be done successfully by different physical techniques, as is the case of sputtering [4], reactive evaporation [5], pulsed laser deposition [6], and chemical techniques—sol-gel [7], chemical bath [8], chemical vapor deposition (CVD) [9], and chemical spray (CST) [10]. Among these deposition techniques, CST has been refined over the years for industrial applications due to the direct implementation of large area deposition using low cost equipment [11]. As a matter of fact, the ultrasonic atomization process generates smaller droplets than the conventional pneumatic process, which in turn yield films with a smoother surface and enhanced conductivity
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