Effect of the Annealing Gas and RF Power Sputtering in the Electrical, Structural and Optical Properties of ITO Thin Films

In the paper we propose to investigate the effect of the annealing gas and RF power sputtering on the electrical, structural and optical properties of indium tin oxide thin films for solar cells applications. These thin films were prepared on lightly doped silicon wafer by RF sputtering in Ar environment at room temperature and with a pressure of 8·10 ^– 3 mbar. Process parameters such as RF power and post deposition annealing were varied in order to determine their dependence on electrical, structural and optical properties of ITO thin films. Layer morphology and thickness measurements (with cross section) were investigated by scanning electron microscopy, and atomic force microscopy was performed to determine the surface roughness. The dependence of the resistivity, mobility and carrier concentration of these films by varying RF power and thermal annealing were studied by Hall Effect measurement. Spectroscopic ellipsometry was also used to determine the refractive index, thickness, roughness, porosity and optical bandgap of the films. Thus, the optical transmittance in the visible region was found to be above 85 %, the low resistivity and high mobility were found 2.09 10 ^– 4 Ω·сm and 35.81 cm²/(V·s), respectively, for 200 nm thickness for the sample elaborated with a RF power of 150 W and an annealing at 400 °C for 10 min with rapid thermal annealing under N₂. The X-ray diffraction patterns of the thin films indicated a preferred orientation along the (222) plane, which provides a high degree of crystallinity for all N₂ annealed samples. The XPS was used to determine oxidation states and identify the elemental content in the films. Obtained results for the surface morphology, electrical and optical properties of the ITO thin film details will be presented.