Abstract
Indium-tin-oxide (ITO) nanorods (NRs) and nanowhiskers (NWhs) were fabricated by an electron-beam glancing-angle deposition (GLAD) system. These nanomaterials are of interests as transparent conducting electrodes in various devices. Two terahertz (THz) time-domain spectrometers (TDS) with combined spectral coverage from 0.15 to 9.00 THz were used. These allow accurate determination of the optical and electrical properties of such ITO nanomaterials in the frequency range from 0.20 to 4.00 THz. Together with Fourier transform infrared spectroscopic (FTIR) measurements, we found that the THz and far-infrared transmittance of these nanomaterials can be as high as 70% up to 15 THz, as opposed to about 9% for sputtered ITO thin films. The complex conductivities of ITO NRs, NWhs as well films are well fitted by the Drude-Smith model. Taking into account that the volume filling factors of both type of nanomaterials are nearly same, mobilities, and DC conductivities of ITO NWhs are higher than those of NRs due to less severe carrier localization effects in the former. On the other hand, mobilities of sputtered ITO thin films are poorer than ITO nanomaterials because of larger concentration of dopant ions in films, which causes stronger carrier scattering. We note further that consideration of the extreme values of Re{σ} and Im{σ} as well the inflection points, which are functions of the carrier scattering time (τ) and the expectation value of cosine of the scattering angle (γ), provide additional criteria for accessing the accuracy of the extraction of electrical parameters of non-Drude-like materials using THz-TDS. Our studies so far indicate ITO NWhs with heights of ~1000 nm show outstanding transmittance and good electrical characteristics for applications such as transparent conducting electrodes of THz Devices.
Highlights
Indium-tin-oxide (ITO), one kind of heavily-doped transparent conductive oxides (TCOs), has been widely employed as transparent conducting electrode and direct-Ohmic contact layers in optoelectronic devices, due to its high transmittance and low resistivity in the visible [1,2,3,4,5]
For the frequency range below 0.50 THz and above 1.40 THz, we used data taken from the PC antenna and laser-induced gaseous plasma based systems, respectively
Combining the results of both type of experiments, we find that the transmittance of shorter and longer NRs are around 65% and 73%
Summary
Indium-tin-oxide (ITO), one kind of heavily-doped transparent conductive oxides (TCOs), has been widely employed as transparent conducting electrode and direct-Ohmic contact layers in optoelectronic devices, due to its high transmittance and low resistivity in the visible [1,2,3,4,5]. The ITO NWhs were found to exhibit superb terahertz (THz) transparency, mobility, and comparable conductivities to sputtered thin films [17]. ITO thin films were employed in optoelectronic devices for manipulation of the THz radiation [18,19,20,21]. ITO nanomaterials mentioned previously are interesting alternatives as transparent electrodes for THz devices. The conventional methods of characterizing electrical properties of materials can damage the morphology of nanomaterials because of the need of electrical contacts, or just provide information on the mobility and resistivity of an individual nanostructure [24,25,26]
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