Aluminum oxide nucleation in the early stages of atomic layer deposition on epitaxial graphene

TL;DR

This study investigates the nucleation and growth of aluminum oxide on epitaxial graphene, revealing uniform nucleation sites and growth mechanisms that preserve graphene quality, with implications for device integration.

Contribution

It provides detailed insights into Al2O3 nucleation on epitaxial graphene, highlighting the role of the buffer layer and growth stages, which was previously not well understood.

Findings

Uniform nucleation sites due to buffer layer presence

Rapid formation of a continuous Al2O3 film after 40 ALD cycles

Minimal impact on graphene defects and doping during initial growth

Abstract

In this work, the nucleation and growth mechanism of aluminum oxide (Al2O3) in the early stages of the direct atomic layer deposition (ALD) on monolayer epitaxial graphene (EG) on silicon carbide (4H-SiC) has been investigated by atomic force microscopy (AFM) and Raman spectroscopy. Contrary to what is typically observed for other types of graphene, a large and uniform density of nucleation sites was observed in the case of EG and ascribed to the presence of the buffer layer at EG/SiC interface. The deposition process was characterized by Al2O3 island growth in the very early stages, followed by the formation of a continuous Al2O3 film (2.4 nm thick) after only 40 ALD cycles due to the islands coalescence, and subsequent layer-by-layer growth. Raman spectroscopy analyses showed low impact of the ALD process on the defects density and doping of EG. The EG strain was also almost unaffected by the deposition in the regime of island growth and coalescence, whereas a significant increase was observed after the formation of a compact Al2O3 film. The obtained results can have important implications for device applications of epitaxial graphene requiring the integration of ultra-thin high-k insulators.