Ultrabroadband terahertz conductivity of highly doped ZnO and ITO

Abstract

Abstract:The broadband complex conductivities of transparent conducting oxides (TCO), namely aluminum-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO) and tin-doped indium oxide (ITO), were investigated by terahertz time domain spectroscopy (THz-TDS) in the frequency range from 0.5 to 18 THz using air plasma techniques, supplemented by the photoconductive antenna (PCA) method. The complex conductivities were accurately calculated using a thin film extraction algorithm and analyzed in terms of the Drude conductivity model. All the measured TCOs have a scattering time below 15 fs. We find that a phonon response must be included in the description of the broadband properties of AZO and GZO for an accurate extraction of the scattering time in these materials, which is strongly influenced by the zinc oxide phonon resonance tail even in the low frequency part of the spectrum. The conductivity of AZO is found to be more thickness dependent than GZO and ITO, indicating high importance of the surface states for electron dynamics in AZO. Finally, we measure the transmittance of the TCO films from 10 to 200 THz with Fourier transform infrared spectroscopy (FTIR) measurements, thus closing the gap between THz-TDS measurements (0.5-18 THz) and ellipsometry measurements (200-1000 THz). ©2015 Optical Society of America

Robust and accurate terahertz time-domain spectroscopic ellipsometry

“…The results agree well with the transmission data from Yang et al [39,40] and the ellipsometry measurement by Yamashita et al [25], indicating excellent accuracy. To reveal the physical properties, the Drude model is fitted to the experimental data [40]. The fittings to the complex conductivity and the complex refractive index are shown as the solid curves in Fig.…”

“…[25,[39][40][41]. Although the properties of ITO can depend on the sample thickness and the fabrication techniques [39][40][41], the extracted model parameters in this work can still be found in a very reasonable range. The charge density of N c 1.312 × 10 20 ∕cm 3 highly agrees with the value of N c 1.33 × 10 20 ∕cm 3 in Ref.…”

THz characterization and demonstration of visible-transparent/terahertz-functional electromagnetic structures in ultra-conductive La-doped BaSnO3 Films

“…By virtue of being transparent at visible frequencies, these materials can be used to design structures whose optical response is encrypted at THz frequencies. On the other hand, spectroscopic characterization of these materials at terahertz frequencies reveals its high-frequency AC electronic transport properties, which enables greater understanding of carrier dynamics in these materials and thus, creates opportunities for developing devices that broaden the range of possible applications 8 – 10 .…”

Lossy Mode Resonance Sensors Fabricated by RF Magnetron Sputtering GZO Thin Film and D-Shaped Fibers

“…The evanescent field of a propagation wave in a D-shaped fiber is accessible through a removed part of the cladding. LMR is considered as the standing electromagnetic wave confined between the two surfaces of the waveguide [21]. For example, transparent conductive oxides (TCO) are good candidates for supporting LMR thanks to the combination of conductive and transparent properties in the visible/infrared region.…”