Residual Metallic Contamination of Transferred Chemical Vapor Deposited Graphene

TL;DR

This study reveals that transferred chemical vapor deposited graphene contains residual metallic contaminants like copper and iron, which can affect its electronic properties and pose challenges for integration with silicon microelectronics.

Contribution

It provides detailed analysis of metallic contamination levels in transferred graphene and highlights the need for improved cleaning methods for electronic applications.

Findings

Residual metals exceed 10^13 atoms/cm^2 in transferred graphene.

Metal impurities are partly mobile upon thermal treatment.

Contaminants reduce silicon substrate charge carrier diffusion length.

Abstract

Integration of graphene with Si microelectronics is very appealing by offering potentially a broad range of new functionalities. New materials to be integrated with Si platform must conform to stringent purity standards. Here, we investigate graphene layers grown on copper foils by chemical vapor deposition and transferred to silicon wafers by wet etch and electrochemical delamination methods with respect to residual sub-monolayer metallic contaminations. Regardless of the transfer method and associated cleaning scheme, time-of-flight secondary ion mass spectrometry and total reflection x-ray fluorescence measurements indicate that the graphene sheets are contaminated with residual metals (copper, iron) with a concentration exceeding 10$^{13}$ atoms/cm$^{2}$. These metal impurities appear to be partly mobile upon thermal treatment as shown by depth profiling and reduction of the minority charge carrier diffusion length in the silicon substrate. As residual metallic impurities can significantly alter electronic and electrochemical properties of graphene and can severely impede the process of integration with silicon microelectronics these results reveal that further progress in synthesis, handling, and cleaning of graphene is required on the way to its advanced electronic and optoelectronic applications.