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.
Highlights
Graphene, the two-dimensional (2D) sp2 allotropic form of carbon, has been the object of continuously increasing scientific and technological interest, starting from its first isolation in 2004 [1].Among the different types of graphene materials considered so far, the epitaxial graphene (EG) grown by controlled high temperature graphitization of the (0001) face of hexagonal silicon carbide (6Hor 4H-SiC) [2,3,4] is a material of choice for advanced applications in electronics [5,6], high precision metrology [7] and environmental sensing [8]
The features in the 1200–1500 cm−1 range were related to the interfacial buffer layer (BL), whereas no significant increase of the the intensity of the disorder-related D peak (1300 cm−1 ) was observed, indicating that no defects were introduced by the atomic layer deposition (ALD) process
In spite of the limited increase in the EG defectivity, a reduction of the electron mobility has been reported in most of the cases after ALD of high-k dielectrics seeded by an oxidized metal [34]
Summary
The two-dimensional (2D) sp allotropic form of carbon, has been the object of continuously increasing scientific and technological interest, starting from its first isolation in 2004 [1]. In the specific case of EG grown by thermal decomposition of SiC (0001), uniform ALD coverage has been observed on the monolayer (1 L) EG areas, whereas inhomogeneous growth has been found on the bilayer (2 L) of few layer regions [21] These ALD nucleation issues common to all the graphene materials are typically circumvent by adopting surface preparation protocols, consisting of chemical prefunctionalization of graphene surface to introduce reactive (sp3 ) sites, or by the predeposition of seed layers [22,23,24,25,26,27,28,29,30,31,32]. Growth in inert gas (Ar) distribution of the EG film was typically very inhomogeneous (composed of submicrometer 0 L, 1 L ambient at atmospheric pressure (approx. 900 mbar) allows it to greatly reduce the Si sublimation and 2 L patches) asthe shown by the atomic force and energy rate, raising
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