Effect of oxygen partial pressure on the structural and optical properties of dc sputtered ITO thin films

Abstract

We present results on the effect of the partial pressure of oxygen (ppo) on the structural and optical properties of tin-doped indium oxide, In 2O 3:Sn (ITO), thin films deposited on glass substrates by reactive dc diode sputtering. The deposition rate decreases with increasing ppo. The ppo did not affect the chemical composition of the ITO films as inferred from X-ray photoemission spectroscopy (XPS). From X-ray diffraction, we find out that the samples have crystalline structure in the ppo range 2 × 10 −4 to 6 × 10 −4 mbar and are amorphous outside this range. These samples have a 〈1 0 0〉 preferred orientation for ppo between 2 × 10 −4 and 4.5 × 10 −4 mbar, but as the ppo increased beyond 4.7 × 10 −4 mbar, the 〈1 1 1〉 texture dominates. This change occurs for the same substrate temperature (about 130 °C). The grain size decreases as the ppo increases. Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) have been used to investigate the surface roughness and the morphology of these samples. The optical transmission is greater than 90% in the visible region and does depend on the ppo. The refractive index n values are found to be in the 1.68–1.86 range. The energy gap values are between 3.1 and 3.5 eV.