Abstract
In this thesis, we firstly studied the non-Drude behavior of indium-tin-oxide (ITO) nanowhiskers (NWhs) and thin film by using the transmission-type THz-TDS (THz-TDTS) and reflection-type THz-TDRS (THz-TDRS). Their electrical properties, such as plasma frequencies, carrier scattering times, were found to be fitted well by the Drude-Smith model over 0.1~1.4 THz. The non-Drude behavior of complex conductivities in ITO NWhs can be attributed to carrier scattering from grain boundaries and impurity ions. On the other hand, in ITO thin films, non-Drude behavior observed is ascribed to scattering by impurity ions only. Under the condition of the same height, the mobility of NWhs (~125 cm2V-1s-1) is much larger than that of the ITO thin films (~27 cm2V-1s-1), which is due to the longer carrier scattering time of the NWhs. The DC conductivities (~250 -1cm-1) or real conductivities in the THz frequency region of ITO NWhs is, however, lower than those of the ITO thin films (~800 -1cm-1) but adequate for use as electrodes. Significantly, the transmittance of ITO NWhs ( 60~70 %) is much higher ( 13 times) than that of ITO thin films in the THz frequency range. The underneath basic physics is that the THz radiation can easily propagate through the air-space among NWhs. In order to realize the THz information in higher frequencies, two different types of THz -TDSbased on the photoconductive antenna, and laser-induced gaseous plasma, respectively, with combined spectral coverage from 0.15 to 9.00 THz were applied. These catalyze accurate determination of the optical and electrical properties of such ITO nanomaterials in the frequency range from 0.20 to 4.00 THz. When the volume filling factors of both type of nanomaterials, NWhs, and nanorods (NRs), are nearly same, mobilities and DC conductivities of ITO NWhs are higher than those of NRs due to less severe carrier localization effects on the NWhs. On the other hand, mobilities of sputtered ITO thin films are lower than ITO nanomaterials because of larger concentration of dopant ions in films, which causes stronger carrier scattering. To date, our study indicates that ITO NWhs at the height of ~1000 nm exhibit superb transmittance and adequate electrical characteristics for the applications of transparent conducting electrodes of THz Devices. Utilizing THz characteristics of ITO NWhs as transparent electrodes, we have also demonstrated two novel schemes of high-transmittance low-operative-voltage THz phase shifters by electrically tuning liquid crystals (LCs) cell. In place of traditional ITO thin film, NWhs with graded-refractive-index (GRIN) in the THz region act as transparent electrodes. Meanwhile, a new method of LCs alignment by using ITO NWhs is also presented. For two schemes with THz transmittance ~77%, phase shift of more than /2 at 1.0 THz is achieved in a ~513 m-thick cell with pretty low driving voltages, 17.68 and 2.83 V (rms), respectively. The ITO NWhs obliquely evaporated by electron-beam glancing-angle deposition can serve simultaneously as transparent electrodes and alignment layer for LC devices in the THz frequency range.