Indium Tin Oxide (ITO) thin films have attracted much attention in the recent years because of a large variety of technological applications in the field of optoelectronic (transparent electronics, heater window, gas sensors). Here, ITO thin films are deposited by Ion Beam Sputtering GLancing Angle Deposition (IBS GLAD). The morphology of single layers can be controlled by varying different growth parameters like the deposition angle or the nature and the energy of primary ion beam. This IBS GLAD deposition technique, promotes a very particular arrangement with strong in-plane biaxial texture and strong anisotropic porosity distribution (anisotropy of columnar percolation pathway). The general structure and the morphology of these complex systems were characterized by X-Ray diffraction, scanning electron microscopy (SEM and 3D FIB tomography). Advanced transmission electron microscopy (TEM) analyses including (S)TEM, HAADF, EDX spectrum imaging were performed to obtain further insights into these systems at the nanoscale.
This work is mainly focused on both experimental and theoretical descriptions of the optical and electric transport behaviour of these anisotropic and heterogeneous porous degenerate semiconductor media.
The optical properties were studied from visible to far infrared wavelength using generalized ellipsometry and spectrophotometry. For thin films grown at high deposition angles an extended Drude model is necessary to well describe the metallic behavior of thin films. Improvements made on optical modelling provided a better understanding of the nanostructure porosity profile and on the dopant distribution within the films.
The electrical properties were investigated by using Hall measurements at variable temperature (80-300K) to find out the shares in scattering mechanisms ascribable to in-grain (phonon, ionized impurities) and grain boundaries. Anisotropic Hall effect modelling has been used to extract the mobility temperature dependences in the two main orthogonal in plane directions. These two temperature mobility laws can exhibit drastically different signature of scattering ascribed not only to the porous anisotropic character of the layer but also to an anisotropic nature of the grain boundaries (defect, segregation).
Combining these advanced analyses, this work attempts to tackle the influence and the correlation of each parameters (anisotropic porosity, gradient profile, surface effect) in opto-electronic properties.