Influence of oxygen/argon pressure ratio on the morphology, optical and electrical properties of ITO thin films deposited at room temperature

Abstract

Transparent conductive oxides (TCOs) such as indium tin oxide (ITO) thin films onto glass substrates are widely used as transparent and conductive electrodes for a variety of technological applications including flat panel displays, solar cells, smart windows, touch screens, etc. ITO films on glass and polycarbonate (PC) substrates were prepared at room temperature (RT) and at different P O 2 . The films were characterized in terms of the surface roughness ( δ), sheet resistance, the refractive index ( n) and extinction coefficient ( k). The free carrier density ( n c) and the carrier mobility ( μ) of the ITO (In 2O 3:Sn) films were measured and studied. The n c and μ values vary in different ratio of oxygen partial pressure ( P O 2 ) of ITO deposition. The observed changes in the ITO film resistivity are due to the combined effect of different parameter values for n c and μ. From AFM analysis and spectra calculations, the surface roughness values of the ITO films were studied and it was observed that the δ values were lower than 15 nm. The energy band gap E g ranges from 3.26 eV to 3.66 eV as determined from the absorption spectrum. It was observed an increase on the energy band gap as the P O 2 decrease in the range of 20–2% P O 2 . The Lorentz oscillator classical model has also been used to fit the ellipsometric spectra in order to obtain both refractive index n and extinction coefficient κ values.