Abstract
Carrier mobility and chemical doping level are essential figures of merit for graphene, and large-scale characterization of these properties and their uniformity is a prerequisite for commercialization of graphene for electronics and electrodes. However, existing mapping techniques cannot directly assess these vital parameters in a non-destructive way. By deconvoluting carrier mobility and density from non-contact terahertz spectroscopic measurements of conductance in graphene samples with terahertz-transparent backgates, we are able to present maps of the spatial variation of both quantities over large areas. The demonstrated non-contact approach provides a drastically more efficient alternative to measurements in contacted devices, with potential for aggressive scaling towards wafers/minute. The observed linear relation between conductance and carrier density in chemical vapour deposition graphene indicates dominance by charged scatterers. Unexpectedly, significant variations in mobility rather than doping are the cause of large conductance inhomogeneities, highlighting the importance of statistical approaches when assessing large-area graphene transport properties.
Highlights
Methods4000 fiber-coupled THz time-domain spectrometer relying on photoconductive switches for THz generation and detection, which is detailed elsewhere[21]
The THz response of the poly-crystalline Si (poly-Si)/Si3N4 stack is found to be negligible with a frequency-independent transmission of 100% ± 1% and a diminishing phase-shift of 2 °, which is attributed to slight differences in high resistivity Si substrate thickness between the positions of the reference and sample measurements
The 2-point contact DC sheet conductance of the poly-Si thin film was measured to be below σs,poly-Si = 0.1 mS, which is at the limit of sensitivity of the THz spectrometer
Summary
4000 fiber-coupled THz time-domain spectrometer relying on photoconductive switches for THz generation and detection, which is detailed elsewhere[21]. 0.6 mm at 0.5 THz and 0.3 mm at 0.9 THz21. By raster-scanning the graphene sample in steps of 0.2 mm in the THz focus, pulse waveforms are recorded in every pixel of a spatially resolved map with close to 7500 pixels covering the full extent of the 10 × 10 mm[2] graphene film. Through utilization of the electric field effect in graphene, THz maps are recorded at different carrier densities by applying voltages, Vg, in the range from 0 V to 40 V between poly-Si thin film and graphene film. The full acquisition time for each map is 16 minutes, and Vg is increased in discrete steps of 2 V between each map
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
