Atomic Layer Deposition of High-k Insulators on Epitaxial Graphene: A Review

Abstract

Due to its excellent physical properties and availability directly on a semiconductor substrate, epitaxial graphene (EG) grown on the (0001) face of hexagonal silicon carbide is a material of choice for advanced applications in electronics, metrology and sensing. The deposition of ultrathin high-k insulators on its surface is a key requirement for the fabrication of EG-based devices, and, in this context, atomic layer deposition (ALD) is the most suitable candidate to achieve uniform coating with nanometric thickness control. This paper presents an overview of the research on ALD of high-k insulators on EG, with a special emphasis on the role played by the peculiar electrical/structural properties of the EG/SiC (0001) interface in the nucleation step of the ALD process. The direct deposition of Al2O3 thin films on the pristine EG surface will be first discussed, demonstrating the critical role of monolayer EG uniformity to achieve a homogeneous Al2O3 coverage. Furthermore, the ALD of several high-k materials on EG coated with different seeding layers (oxidized metal films, directly deposited metal-oxides and self-assembled organic monolayers) or subjected to various prefunctionalization treatments (e.g., ozone or fluorine treatments) will be presented. The impact of the pretreatments and of thermal ALD growth on the defectivity and electrical properties (doping and carrier mobility) of the underlying EG will be discussed.

Electronic and Transport Properties of Epitaxial Graphene on SiC and 3C-SiC/Si: A Review

“…Fabrication of graphene FETs involves the challenges of selecting an appropriate gate insulator and controlling its thickness [150]. Generally, the oxides such as SiO 2 , HfO 2 , Al 2 O 3 , and Y 2 O 3 are used as the gate dielectrics, but these tend to become amorphous with scaling and interactions with the graphene can occur, which makes the high-quality defect-free interface formation difficult [150][151][152]. Hexagonal boron nitride (h-BN) forms a weak van der Waals interaction with the graphene (lattice mismatch only 2% [153]) and has been utilized as an ideal insulator for the graphene FET formation [151].…”

“…Generally, the oxides such as SiO 2 , HfO 2 , Al 2 O 3 , and Y 2 O 3 are used as the gate dielectrics, but these tend to become amorphous with scaling and interactions with the graphene can occur, which makes the high-quality defect-free interface formation difficult [150][151][152]. Hexagonal boron nitride (h-BN) forms a weak van der Waals interaction with the graphene (lattice mismatch only 2% [153]) and has been utilized as an ideal insulator for the graphene FET formation [151]. Due to the lower value of a dielectric constant (k~4), h-BN is usually combined with a high k-dielectric layer such as Y 2 O 3 formed via atomic layer deposition on h-BN [154].…”

Epitaxial Graphene on 4H-SiC (0001) as a Versatile Platform for Materials Growth: Mini-Review

“…In this context, the integration of epitaxial graphene with insulators can bring this material closer to real electronic applications. In a series of three papers [44,59,60], we presented and critically discussed the atomic layer deposition technique as a promising approach to grow high-quality Al 2 O 3 layers of different thicknesses. It was revealed that for a deposition temperature of 250 • C, the transition from island-based growth to layerby-layer growth mode occurs after 40 ALD cycles that correspond to ~2.4 nm (Figure 13).…”

Direct Atomic Layer Deposition of Ultrathin Aluminum Oxide on Monolayer MoS2 Exfoliated on Gold: The Role of the Substrate

“…Many of these approaches were inspired by ALD growth experiments performed on graphene. [13][14][15] As an example, Park et al [10] systematically investigated thermal ALD of Al 2 O 3 , using trimethyl-aluminum (TMA) as the Al precursor and water (H 2 O) as coreactant, on the surface of different TMDs, that is, MoS 2 , WS 2 , and WSe 2 multilayers. The deposition temperature (T dep ) and the TMA adsorption energy (E ads ) on the TMDs surface were demonstrated to play a crucial role on the uniformity of the deposited Al 2 O 3 (≈10 nm) films.…”