Terahertz wafer-scale mobility mapping of graphene on insulating substrates without a gate

Abstract

(2015). Terahertz wafer-scale mobility mapping of graphene on insulating substrates without a gate. Optics Express, 23(24) maps with a 400 µm step size. σ dc -and τ sc -maps are translated into µ drift and N s maps through Boltzmann transport theory for graphene charge carriers and these parameters are directly compared to van der Pauw device measurements on the same wafer. The technique is compatible with all substrate materials that exhibit a reasonably low absorption coefficient for terahertz radiation. This includes many materials used for transferring CVD graphene in production facilities as well as in envisioned products, such as polymer films, glass substrates, cloth, or paper substrates.

Atomic Layer Deposition Alumina‐Mediated Graphene Transfer for Reduced Process Contamination

“…The THz‐TDS sheet conductivity map of a transferred film shows a homogeneous conductive graphene layer underneath the ALD film, with an average sheet conductivity of 0.9 ± 0.3 mS. This conductivity and level of uniformity is comparable to the THz‐TDS results obtained from graphene films using alternative graphene transfer methods . In Figure b (i) we observe that the ALD‐coated graphene has a charge neutrality point close to 0 V. In comparison, two‐probe measurements on graphene transferred via conventional etching transfer (Figure b (ii)) show a charge neutrality point at 40 V ( n ≈ 3 × 10 12 cm 2 ), which is typical for chemical etching transfers and is indicative of heavy p‐doping .…”

Robust mapping of electrical properties of graphene from terahertz time-domain spectroscopy with timing jitter correction

“…This is usually done by only fitting to the real part of s σ [3,5,9]. Here, both real and imaginary parts of and to full fits to uncorrected data.…”

“…The non-contact approach is advantageous for in-line characterization and quality-control for industrial integration of graphene, especially when compared to standard field-effect measurements on graphene that require additional and intrusive fabrication steps for device processing. Non-gated rapid spatial mapping of the carrier drift mobility (µ drift ) and carrier density (N s ) of graphene by THz-TDS was recently reported [5], which presents a step forward compared to earlier reports that mainly gauges the conductivity [6,7] or extracts the mobility through back-gated THz-TDS measurements requiring special substrates [8,9].…”

Quality assessment of terahertz time-domain spectroscopy transmission and reflection modes for graphene conductivity mapping

“…THz-TDS has various practical advantages as compared to contact-based electrical measurements: no need for polymers/solvents that are known to adversely affect the electrical properties of graphene [23]), high throughput for large areas [24] and possibility of identifying imperfections (i.e. grain boundaries) on the microscale [25]. Although it is established that σ can be derived from THz-TDS measurements, with this study, we confirm for the first time the accuracy and reproducibility between different laboratories for spatial mapping of graphene conductivity, which is a necessary step towards establishing a robust and reliable metrology platform.…”