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

Abstract

We report on terahertz characterization of La-doped BaSnO3 (BSO) thin-films. BSO is a transparent complex oxide material, which has attracted substantial interest due to its large electrical conductivity and wide bandgap. The complex refractive index of these films is extracted in the 0.3 to 1.5 THz frequency range, which shows a metal-like response across this broad frequency window. The large optical conductivity found in these films at terahertz wavelengths makes this material an interesting platform for developing electromagnetic structures having a strong response at terahertz wavelengths, i.e. terahertz-functional, while being transparent at visible and near-IR wavelengths. As an example of such application, we demonstrate a visible-transparent terahertz polarizer.

Wide Bandgap Perovskite Oxides with High Room‐Temperature Electron Mobility

“…BaSnO 3 has a wide indirect bandgap experimentally determined to be in the range of 2.9 eV -3.2 eV and a direct bandgap of ~ 3.6 eV, which makes it transparent in the optical wavelength regime. [76][77][78] Although calculations are shown to underestimate the bandgaps, Tran-Blaha modified Becke-Johnson (TB-mBJ) and Perdew-Burke-Ernzerhof density functionals are more accurate and predict an indirect band gap of 2.8 eV, which is in close agreement with the experimental values. 53,75,79,80 n-type BaSnO 3 on SrTiO 3 grown by hybrid molecular beam epitaxy (MBE) has a transmission of ~ 80%.…”

“…131 The optical transmission and room-temperature conductivity of BaSnO 3 are comparable to the value of transmission and room-temperature conductivity in ITO. 9,77 Theory predicts BaSnO 3 transmission in the visible range to be independent of doping. 81 SrSnO 3 , another candidate in the family of alkaline-earth stannates, has a wider indirect bandgap with experimental and theoretical values ranging between 4.0 eV -5.0 eV.…”

A review on thin films, conducting polymers as sensor devices

“…Zhu et al (2005) investigated the microstructural characteristics of Nb-doped SrTiO 3 thin films which were grown on SrTiO 3 substrate using laser molecular beam epitaxy [54]. Arezoomandan et al (2018) conducted terahertz characterization on La-doped BaSnO 3 (BSO) thin-films for developing electromagnetic structures [55].…”

Terahertz characterization of two-dimensional low-conductive layers enabled by metal gratings

“…Therefore, the sheet conductivity extracted from terahertz measurements would be a spatially averaged nanoscale conductivity and is minimally affected by microscale scattering phenomena that would play a role in direct current (DC) transport measurements wherein the carrier transport is typically probed over length scales that are three orders of magnitude larger (i.e., micrometers). These could include extended effects such as those arising from point defects or dislocations introduced in epitaxial layers during growth, or grain boundaries usually present in two-dimensional films [12][13][14] . As a result, charge transport characterization using terahertz spectroscopy can provide a more relevant estimate of such conductive layers' intrinsic carrier transport properties.…”