Optical probe of the low doping regime in graphene: Comparison of Raman spectroscopy and transport measurements*

Identifying charge density fluctuations and impurities in graphene is vital for high-quality graphene-based devices. Here, we developed an optical probe to evaluate the doping level and charge fluctuation in the range from 10¹⁰ cm^-2 to 10¹² cm^-2 by using the Raman 2D peak. We compare charge density estimated from Raman measurements with electrical transport measurement, the benchmark method for evaluating charge density fluctuations and other scattering mechanism. At low doping level(< 10¹² cm^-2), the 2D Raman peak becomes asymmetric and can be fitted by two peaks, and the 2D peak-split(in cm^-1) correlates with charge density with high precision (2×10¹⁰ cm^-2 per 2D peak-split wavenumber). Our work provides a simple and non-invasive optical method to quantify the doping levels of graphene from 10¹⁰ cm^-2 to 10¹² cm^-2, two orders of magnitude higher precision than previously reported optical methods [1]. The 2D peak-split method provides a platform for evaluating the quality of graphene before building high-quality graphene devices.

Reference:
[1] Chen, Z., et. al., 2019. Monitoring the low doping regime in graphene using Raman 2D peak-splits: Comparison of gated Raman and transport measurements. arXiv preprint arXiv:1908.10961.