Effect of thickness on the physical properties of ITO thin films

Abstract

We have studied the effect of thickness on the structural, optical and electrical properties of In₂O₃:Sn (ITO) thin films. Two series of ITO thin films have been deposited onto glass substrates by DC sputtering at two partial pressures of oxygen (ppo): 4 × 10⁻⁴ and 4.75 × 10⁻⁴ mbar. Each series consists of samples with thickness ranging from 306 nm to 1440 nm. We observed a change of texture with thickness; the thinner films grow with a 〈111〉 preferred orientation; however as the thickness increased, the preferred orientation becomes in the 〈100〉 direction. The lattice constant and the grain size have also been obtained from the X-ray spectra. The energy gap, E _g, has been obtained from the transmission curve; E _g is found to decrease with increasing thickness for both series. The electrical resistivity ρ has been studied as a function of thickness, ppo and temperature (T). The temperature was varied from room temperature (RT) to 450 °C and back to RT; a hysteresis effect was observed in the ρvs.T curve. Also, a minimum in ρ was observed, in all these samples, in the temperature range 260 to 280 °C. For these temperatures, we have studied the effect of annealing time on the electrical resistivity for samples having both textures. We noted that ρ increased with annealing time and reaches a saturation value equal to the RT temperature value. Hall effect experiments were done on all these samples. The concentration n and the mobility μ _H were obtained. These parameters are found to be sensitive to the thickness and the texture of these films. All these results will be correlated and discussed.