Terahertz Characterization of Electrical Properties in Graphene Systems

Terahertz time-domain spectroscopy (THz-TDS) has emerged as a powerful non-contact technique for probing the electronic behaviour of graphene across frequencies from around 0.1 to 10 THz. By measuring the amplitude and phase of broadband THz pulses transmitted through or reflected from a graphene film, one can extract key parameters such as sheet conductivity, carrier density, carrier mobility and scattering time without the need for electrodes or lithographic contacts. In transmission geometry THz-TDS interrogates the intrinsic conductivity spectrum, while reflection geometry offers the flexibility to probe graphene on opaque or non-transparent substrates. Analysis of the frequency-dependent complex conductivity through Drude or Drude–Smith models reveals details of carrier scattering, backscattering from grain boundaries and the influence of substrate interactions. High-resolution spatial mapping with step sizes down to a few micrometres enables the visualisation of inhomogeneities, defects, grain orientations and non-linear field effects under strong THz excitation. Such capabilities are critical for quality control in wafer-scale production, optimisation of chemical vapour deposition parameters and integration of graphene films into next-generation high-speed electronics, sensors and telecommunication devices. The contactless nature, high throughput and sub-millimetre spatial resolution of THz-TDS position it as an indispensable tool for both fundamental studies of two-dimensional carrier dynamics and practical assessment of large-area graphene systems.

Research from Nature Portfolio

Recent studies have demonstrated the use of THz-TDS to map nanoscale carrier confinement in polycrystalline graphene grown on germanium. Frequency-resolved conductivity spectra fit to the Drude–Smith formalism reveal the role of small-angle grain boundaries in promoting backscattering, with direct comparison to Raman and transmission electron microscopy measurements. In reflection geometry, quantitative conductivity mapping has been validated across a range of substrates—including sapphire, silicon dioxide and germanium—without requiring a THz-transparent backing. These advances confirm that reflection-mode THz-TDS can deliver high-fidelity, contactless conductivity images and respond to gate-voltage modulation, opening pathways for in-line monitoring of large-area films. Furthermore, non-contact mobility mapping techniques have been developed that deconvolute carrier density and mobility over centimetre-scale areas, revealing that mobility variations often dominate inhomogeneities in conductance.

Terahertz Characterization of Electrical Properties in Graphene Systems publication trend

The graph below shows the total number of articles in terahertz characterization of electrical properties in graphene systems across all publications each year (not limited to Nature Index journals).

Technical terms

Terahertz time-domain spectroscopy (THz-TDS): A technique that measures the electric field of broadband THz pulses in time, enabling extraction of complex conductivity spectra.

Sheet conductivity: Electrical conductance per square unit area, a key descriptor of two-dimensional materials.

Carrier mobility: The ease with which charge carriers move under an applied electric field, reflecting scattering mechanisms.

Drude–Smith model: A phenomenological extension of the Drude model that accounts for carrier backscattering and localisation effects.

Reflection-mode spectroscopy: Measurement of THz pulses reflected from a sample, suitable for opaque substrates.

Transmission-mode spectroscopy: Measurement of THz pulses transmitted through a sample, requiring THz-transparent substrates.

Scattering time: Average time between collisions of charge carriers, influencing frequency-dependent conductivity.

References

1. Non-Linear Conductivity Response of Graphene on Thin-Film PET Characterized by Transmission and Reflection Air-Plasma THz-TDS. Sensors (2023).
2. Mapping nanoscale carrier confinement in polycrystalline graphene by terahertz spectroscopy. Scientific Reports (2024).
3. Robust mapping of electrical properties of graphene from terahertz time-domain spectroscopy with timing jitter correction.. Optics Express (2017).
4. Contactless graphene conductivity mapping on a wide range of substrates with terahertz time-domain reflection spectroscopy. Scientific Reports (2017).
5. Graphene mobility mapping. Scientific Reports (2015).
6. Quality assessment of terahertz time-domain spectroscopy transmission and reflection modes for graphene conductivity mapping.. Optics Express (2018).
7. Case studies of electrical characterisation of graphene by terahertz time-domain spectroscopy. 2D Materials (2021).