Synergistic Influence of the Deposition Method, Postdeposition Annealing, and Textured Substrates on the Properties of ITO Thin Films

Indium tin oxide (ITO) thin films were sputtered on the plain and textured glass substrates using direct current (DC) and radio frequency (RF) magnetron sputtering and then subjected to annealing. The optical lithography process was adopted to give texture to the glass substrates with an array of microcuboids with ∼40 μm × ∼40 μm sides out of crosslinked negative photoresists SU-8 2000.5 and SU-8 2005 to obtain cuboid heights of ∼0.5 and ∼5 μm, respectively. The synergistic influences of the deposition technique, postdeposition annealing, and the use of textured substrates on the structural, optical, and electrical properties of the films were investigated using optical microscopy, scanning electron microscopy (SEM), optical profilometry, and X-ray diffraction (XRD) analyses. In addition to transmittance analysis using UV–vis spectroscopy, angle-dependent specular reflectance measurements and COMSOL simulations have been done to correlate the observed improved transmittance in ITO films grown on textured substrates. The ITO thin films deposited by DC and RF sputtering were polycrystalline with (222) and (400) orientations, respectively. The enhanced capability of accommodation of oxygen vacancies in (400)-oriented films led to better structural and electrical properties in RF-sputtered samples. Annealing has resulted in improved crystallinity and reduction in lattice distortion that account for a higher transmittance of ∼87.02% in the 350 nm to 1200 nm wavelength region and lowered electrical resistivity in both the annealed DC- and RF-sputtered samples. It is also observed that the transmittance improved due to the influence of underlying SU-8 periodical textures, with no undesired drastic changes to the electrical properties.