Direct comparison of time-resolved terahertz spectroscopy and Hall Van der Pauw methods for measurement of carrier conductivity and mobility in bulk semiconductors

Abstract

Charge carrier conductivity and mobility for various semiconductor wafers and crystals were measured by ultrafast above bandgap, optically excited Time-Resolved Terahertz Spectroscopy (TRTS) and Hall Van der Pauw contact methods to directly compare these approaches and validate the use of the non-contact optical approach for future materials and in-situ device analyses. Undoped and doped silicon (Si) wafers with resistances varying over six orders of magnitude were selected as model systems since contact Hall measurements are reliably made on this material. Conductivity and mobility obtained at room temperature by terahertz transmission and TRTS methods yields the sum of electron and hole mobility which agree very well with either directly measured or literature values for corresponding atomic and photo-doping densities. Careful evaluation of the optically-generated TRTS frequency-dependent conductivity also shows it is dominated by induced free-carrier absorption rather than small probe pulse phase shifts, which is commonly ascribed to changes in the complex conductivity from sample morphology and evaluation of carrier mobility by applying Drude scattering models. Thus, in this work, the real-valued, frequency-averaged conductivity was used to extract sample mobility without application of models. Examinations of germanium (Ge), gallium arsenide (GaAs), gallium phosphide (GaP) and zinc telluride (ZnTe) samples were also made to demonstrate the general applicability of the TRTS method, even for materials that do not reliably make good contacts (e.g., GaAs, GaP, ZnTe). For these cases, values for the sum of the electron and hole mobility also compare very favorably to measured or available published data.

Recent Progress in High‐Mobility Organic Transistors: A Reality Check

“…There are numerous other approaches that have been suggested for accurate mobility analysis. Using an alternative model, or a different measurement technique to avoid the OTFT contact resistance issues, is one approach; for example, scanning Kelvin probe microscopy, gated four point probe, gated van der Pauw method . These techniques are excellent for mobility verification or for further understanding of the underlying charge transport in OSCs.…”

Direct Heteroepitaxy of Orientation‐Patterned GaP on GaAs by Hydride Vapor Phase Epitaxy for Quasi‐Phase‐Matching Applications

“…Because the HVPE GaP reference layers were grown on semi‐insulating GaAs, the conductivity of the substrate is much lower than that of the grown layers. For such a situation, complex conductivity of the thin sample layer with thickness d s can be expressed aswhere n sub is the index of refraction of the substrate, Z 0 is the free space impedance (377 Ω), E sub ( ω ) and E s ( ω ) are the spectra of the complex electric field transmitted through the substrate and the substrate with the sample layer, respectively. The measurement of layer conductivity thus requires a separate measurement of the complex transmission spectra of the bare substrate and the substrate containing the HVPE GaP layer.…”

Z-scanning laser photoreflectance as a tool for characterization of electronic transport properties

“…The ratio ω 2 m /ω 2 m (Z) comes from the amplitude prefactor associated with the modulated pump beam, whereas the ratio ω 2 ac /ω 2 (Z) follows from the definite integrals of xexp{−x 2 } (= 1/2) proscribed in Eq. (7). However, from Eq.…”