Effect of thickness on the physical properties of ITO thin films

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 x 10(-4) and 4.75 x 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 rho has been studied as a function of thickness, ppo and temperature (T). The temperature was varied from room temperature (RT) to 450 degrees C and back to RT; a hysteresis effect nas observed in the rho vs. T curve. Also, a minimum in rho was observed, in all these samples, in the temperature range 260 to 280 degrees C. For these temperatures, we have studied the effect of annealing time on the electrical resistivity for samples having both textures. We noted that rho 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 mu(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.