Indium-tin-oxide (ITO) films are widely employed as transparent electrodes in the thin film silicon solar cell and light emitting diode. On the other hand, the GaAs and silicon photovoltaic solar cell employed ITO nanowhiskers as the conductive antireflective coating. In this work, we have used the transmission and reflection type terahertz-time domain spectroscopy (THz-TDS) to investigate the far-infrared optical and electrical properties of ITO thin films and nanowhiskers.
The ITO films we have investigated were prepared by the direct current reactive magnetron sputtering on fused silica substrates, and the ITO nanowhiskers were deposited onto the high resistivity silicon substrates by the glancing-angle electron-beam evaporation.
For different thicknesses of samples, the complex refractive indices and complex conductivities are determined experimentally by the THz-TDS measurement, and then the scattering times and the plasma frequencies are fitted by Drude-Smith model with the effective medium theory. The carrier concentrations and mobilities are also obtained from the fitted parameters. The mobilities of ITO thin films and ITO nanowhiskers are calculated to be 25.9~60.6 cm^2/Vs and 34.5~128.3 cm^2/Vs, respectively. The carrier concentrations are 〖~〖10〗^20 cm〗^(-3) in film samples and 〖~〖10〗^19 cm〗^(-3) in nanowhisker samples. The scattering times of ITO films are 12~26 fs, while that of the ITO nanowhiskers are 24.49~63.68 fs. In general, the conductivities of ITO thin films are better than ITO nanowhiskers, because the effect of higher carrier concentration for ITO thin films is stronger than the effect of lower electron mobility.

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