Researchers from AMO, Oxford Instruments, Cambridge University, RWTH Aachen University and the University of Wuppertal have demonstrated a new method to use plasma enhanced atomic layer deposition (PEALD) on graphene without introducing defects into the graphene itself.
Currently, the most advanced technique for depositing dielectrics on graphene is atomic layer deposition (ALD), which allows to precisely control the uniformity, the composition and the thickness of the film. The process typically used on graphene and other 2D materials is thermal water-based ALD, as it does not damage the graphene sheet. However, the lack of nucleation sites on graphene limits the quality of the dielectric film, and requires the deposition of a seed layer prior to ALD to achieve good results. Another approach is plasma enhanced atomic layer deposition (PEALD), which, when applied to growth on graphene, can introduce surface damage. This is what to team addressed in this recent work.
The trick, as was explained, is to use one monolayer of hexagonal boron nitride (hBN) – a two-dimensional insulator – as a protection layer on top of graphene. The monolayer hBN is thin enough to have a negligible effect on the quality of the dielectric, but thick enough to protect the graphene from the oxygen plasma used in PEALD Furthermore, the plasma creates nucleation sites on the hBN, which allow the fast growth of high-quality dielectric films.
The protective effect of the hBN monolayer was clearly revealed by Raman spectroscopy measurements performed before and after the deposition of the dielectric. “The Raman study is very important for the characterization of the graphene and for the optimization of the process”, says Dr. Bárbara Canto, first author of the study. “This can lead us to future graphene devices with higher quality dielectrics and an improved understanding of the effect of the different process steps on graphene”. Electrical characterization of field-effect devices fabricated on the hBN/graphene confirms that the graphene remains undamaged, and demonstrates the high quality of the dielectric.
Ravi Sundaram, Head of Strategic R&D Markets at Oxford Instruments UK, says “This work makes great progress on one of the key challenges in graphene (opto)electronic device manufacturing i.e, the deposition of high quality dielectrics. We are very pleased to have contributed to this multi-organization collaboration, to push the limits of low damage plasma enhanced ALD of dielectrics to enable the integration of these devices in practical applications”.