Uniform Atomic Layer Deposition of Al₂O₃ on Graphene by Reversible Hydrogen Plasma Functionalization

Abstract

A novel method to form ultrathin, uniform Al2O3 layers on graphene using reversible hydrogen plasma functionalization followed by atomic layer deposition (ALD) is presented. ALD on pristine graphene is known to be a challenge due to the absence of dangling bonds, leading to nonuniform film coverage. We show that hydrogen plasma functionalization of graphene leads to uniform ALD of closed Al2O3 films down to 8 nm in thickness. Hall measurements and Raman spectroscopy reveal that the hydrogen plasma functionalization is reversible upon Al2O3 ALD and subsequent annealing at 400 °C and in this way does not deteriorate the graphene’s charge carrier mobility. This is in contrast with oxygen plasma functionalization, which can lead to a uniform 5 nm thick closed film, but which is not reversible and leads to a reduction of the charge carrier mobility. Density functional theory (DFT) calculations attribute the uniform growth on both H2 and O2 plasma functionalized graphene to the enhanced adsorption of trimethylaluminum (TMA) on these surfaces. A DFT analysis of the possible reaction pathways for TMA precursor adsorption on hydrogenated graphene predicts a binding mechanism that cleans off the hydrogen functionalities from the surface, which explains the observed reversibility of the hydrogen plasma functionalization upon Al2O3 ALD.

Atomic Layer Deposition for Graphene Device Integration

“…The difference in nucleation density can be explained by the larger amount of physisorbed H 2 O being present on the graphene at lower deposition temperatures. Adapted with permission . Copyright 2017, American Chemical Society.…”

“…H 2 O based ALD processes on HOPG and graphene result most of the time in the preferential growth of the material on the defects sites, grain boundaries and wrinkles present in the graphene, as illustrated in Figure for the deposition of Al 2 O 3 on CVD graphene . The preferential deposition on defect sites, grain boundaries and graphene wrinkles is a result of the lack of functionalized dangling bonds on the graphene basal plane.…”

“…Vervuurt et al developed a plasma functionalization method which avoids the use of a sacrificial graphene or GO layer altogether . In this case the graphene was functionalized by a H 2 plasma treatment.…”

“…The adsorption of TMA on hydrogenated graphene is accompanied by the release of H 2 from the graphene surface, restoring the graphene to its pristine sp 2 C state. Adapted with permission . Copyright 2017, American Chemical Society.…”

Impact of Post‐Lithography Polymer Residue on the Electrical Characteristics of MoS2 and WSe2 Field Effect Transistors

“…Plasma cleaning can also be challenging. For example, O 2 plasma is found to oxidize edges/defects on graphene and the top layer of WSe 2 , and is used in etching and p‐type doping of TMDs . H 2 plasma can lift graphene off SiO 2 , and Cl 2 plasma can cause a heavy p‐doping to graphene .…”