Probing charged impurities in suspended graphene using Raman spectroscopy

TL;DR

This study uses Raman spectroscopy to investigate charged impurities in suspended graphene, revealing that the 2D band intensity is highly sensitive to impurity levels, which impacts carrier mobility and device quality assessment.

Contribution

The paper demonstrates that the I2D/IG ratio is a more effective indicator of impurity levels in suspended graphene than the G band shift, advancing non-invasive quality assessment methods.

Findings

2D band intensity is sensitive to charged impurity concentration.

Suspended graphene shows a stronger I2D/IG ratio than non-suspended graphene.

The I2D/IG ratio is a better criterion for high-quality graphene selection.

Abstract

Charged impurity (CI) scattering is one of the dominant factors that affect the carrier mobility in graphene. In this paper, we use Raman spectroscopy to probe the charged impurities in suspended graphene. We find that the 2D band intensity is very sensitive to the CI concentration in graphene, while the G band intensity is not affected. The intensity ratio between the 2D and G bands, I2D/IG, of suspended graphene is much stronger compared to that of non-suspended graphene, due to the extremely weak CI scattering in the former. This finding is consistent with the ultra-high carrier mobility in suspended graphene observed in recent transport measurements. Our results also suggest that at low CI concentrations that are critical for device applications, the I2D/IG ratio is a better criterion in selecting high quality single layer graphene samples than is the G band blue shift.