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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-k 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 HfO2 via 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 ultrathin high-k dielectrics onto graphene-based devices. [ABSTRACT FROM AUTHOR]

Regardless of the application, MoS 2 requires encapsulation or passivation with a high-quality dielectric, whether as an integral aspect of the device (as with top-gated field-effect transistors (FETs)) or for protection from ambient conditions. However, the chemically inert surface of MoS 2 prevents uniform growth of a dielectric film using atomic layer deposition (ALD)-the most controlled synthesis technique. In this work, we show that a plasma-enhanced ALD (PEALD) process, compared to traditional thermal ALD, substantially improves nucleation on MoS 2 without hampering its electrical performance, and enables uniform growth of high-κ dielectrics to sub-5 nm thicknesses. Substrate-gated MoS 2 FETs were studied before/after ALD and PEALD of Al 2 O 3 and HfO 2 , indicating the impact of various growth conditions on MoS 2 properties, with PEALD of HfO 2 proving to be most favorable. Top-gated FETs with high-κ films as thin as ∼3.5 nm yielded robust performance with low leakage current and strong gate control. Mechanisms for the dramatic nucleation improvement and impact of PEALD on the MoS 2 crystal structure were explored by X-ray photoelectron spectroscopy (XPS). In addition to providing a detailed analysis of the benefits of PEALD versus ALD on MoS 2 , this work reveals a straightforward approach for realizing ultrathin films of device-quality high-κ dielectrics on 2D crystals without the use of additional nucleation layers or damage to the electrical performance.