Study of In2O3 and ZnO thin films for selective gas sensors applications: growth effect on the films structure factor in metal oxide thin films sensing applications

Abstract

The goal of this thesis is the study In2O3 and ZnO thin films for selective gas sensors applications with focus on growth effect on the films structure and surface topology as essential factor in metal oxide thin films. One of the main problems in the field of metal oxide thin film sensors is the impossibility to elaborate a unitary methodology for reproducibility of sensor response in correlation with the surface characteristics. For this, the systematic study of surface characteristics effects on metal oxide thin films sensing involved phenomena plays a major role. Using DC magnetron sputtering and pulsed laser deposition, nanostructured In2O3 and pure or doped ZnO thin films were grown and fully characterized. The study was focused on the morphology of the film and how this affects the photoreduction with UV light and the oxidation by oxidizing gas (ozone) exposure in order to optimize the film properties for gas sensing applications,. For this purpose, different series of samples were grown: In2O3 series by DC magnetron sputtering varying the following growth parameters: thickness, growth temperature and total pressure and oxygen:argon ratio during the deposition. Pure ZnO series by DC magnetron sputtering from metallic and ceramic targets varying the following growth parameters: thickness for different constant growth temperatures, temperature for constant thickness, total pressure and oxygen:argon ratio during the deposition. 2% Al doped ZnO by DC magnetron sputtering varying the following growth parameters: thickness and oxygen:argon ratio during growth. In doped ZnO thin films by DC magnetron sputtering varying the following growth parameters: thickness and oxygen:argon ratio during growth. Pure ZnO series by PLD varying the following growth parameters: thickness and substrate temperature with focus on very thin films (40nm and 100nm series at different growth temperatures). All films were fully characterized with respect to their structural and surface topology (for understating and optimization of the influences of the growth conditions on the surface properties), optical/electrical response (for understanding and optimization of the photoreduction and oxidation processes) and sensing behavior. Detailed surface characterization of each film surface was performed and results were collected for further correlation between surface properties and sensing response. Graphical correlations between surface parameters and sensor response ratios were done for each material studied.