Chlorine-mediated atomic layer deposition of HfO2 on graphene

Abstract

Although graphene and other 2D materials have been extensively studied with superlative electrical properties already reported, several processing constraints impede integration into advanced device structures. One such constraint is the chemical inertness of graphene, which has hindered the deposition of thin high-κ dielectrics, e.g., HfO₂ by processes such as the atomic layer deposition (ALD) technique. Through computational-guided experiments, we demonstrate that a partially defective chlorine adlayer on a graphene surface significantly improves the nucleation of HfO₂. The evolution of chlorinated graphene (CG) during the deposition of HfO₂via ALD was monitored with Raman spectroscopy and X-ray photoelectron spectroscopy (XPS), and modeled using first-principles calculations. Our calculations show that the enhancement of the ALD of HfO₂ is due to chlorine vacancies in the chlorine adlayer, which act as nucleation sites for HfO₂. Our experiment supports this observation; some thermally activated chlorine molecules partially desorbed from the graphene surface during the ALD process. This process enabled the deposition of a conformal 3.5 nm HfO₂ layer on graphene, which resulted in top-gated field-effect transistors (FETs) with no gate-leakage and hysteresis of less than 10 mV. Our work demonstrates a scalable and reliable approach for the integration of ultra-thin high-κ dielectrics onto graphene-based devices.