Abstract
The transparent conductive oxides (TCOs, indium-tin oxide (ITO), aluminum-doped zinc oxide (AZO), aluminum and ytterbium-doped zinc oxide (AYZO)) thin films which exhibit outstanding properties such as high transparency in the visible region and good electrical conductivity are measured by terahertz time-domain spectroscopy (THz-TDS) based on photoconductive (PC) antenna and laser-induced air-plasma. The optical and electrical properties of these TCO thin films in the THz frequency range (0.1-2.4THz) are obtained. Broadband optical and electrical characteristics can be determined by combing the results from THz-TDS based on PC antenna and laser-induced air-plasma, respectively. The frequency-dependent complex refractive indices have been extracted from the TDS measurements. Complex conductivities of the TCO samples can then be determined. Together with Fourier transform infrared spectroscopic (FTIR) measurements, we’ve found that the THz and far-infrared transmittance of 100 nm-thick ITO, AZO, and AYZO thin films are ~21%, ~48%, and ~28%, respectively. By fitting complex conductivities of the TCOs with the Drude-Smith model, electrical properties such as DC mobility (μ), carrier concentration (Ne), and DC conductivity (σDC) are obtained. Here, μ and σDC for ITO thin films are 96-120cm2V-1s-1 and 1.18-1.65 ×103Ω-1cm-1, respectively. For AZO and AYZO thin films, these parameters are 7-84 cm2V-1s-1 and 0.41-1.06×103Ω-1cm-1 versus 26-85 cm2V-1s-1 and 0.91-1.12×103Ω-1cm-1, respectively. We have also examined structural and crystalline properties of samples by X-ray diffraction (XRD) measurements. From the XRD information, it can be concluded that motilities can be enhanced as increasing grain size, but reduced with overly high carrier concentration because of the smaller distance between impurity ions.