# Electronic and Transport Properties of Epitaxial Graphene on SiC and 3C-SiC/Si: A Review
## 1 Introduction  
The properties of graphene as well as other members of the two-dimensional (2D) class of materials differ fundamentally from those of typical electronic materials, which makes this class very attractive for future device applications [1]. A particular appealing property of graphene and other 2D materials is the possibility of dynamically tuning their electrical/electronic properties. Yet, no matter the application under consideration, which range from light detectors to signal modulators and switches, Hall standards, or chemical sensors, control of transport properties is paramount, and the achievement of the sought-after tunability is not always trivial. The very attractive physical nature of the class (i.e., the large surface to volume ratio [2]) is a double-edged sword as interfaces between the material and its surrounding environment, e.g., substrate, interfaces, adsorbents, and metallization, have a significant effect on conductivity [2; 3; 4; 5]. Graphene and 2D materials are made out of surfaces. The accurate control of surfaces and interfaces has historically always been a critical and challenging aspect of semiconductor technology [6; 7]. Hence, in order to harness the properties of graphene in electronics, a significant shift in the technological approach needs to be made. In this review, we explore recent advancements made in the charge transport research on epitaxial graphene (EG) synthesized on SiC and Si substrates as these are necessary ingredients for technological applications. Yet, the properties of EG on these substrates are very different. For EG on 6H-SiC(0001) (the so-called silicon-terminated surface, Si-face), silicon sublimation results in the formation of EG [8] and the properties are dominated by the 6\(\sqrt{3}\times\) 6\(\sqrt{3}\) rotated 30\({}^{\circ}\) reconstruction [9] of the SiC surface. The modification of this reconstruction at the interface after graphene synthesis, often termed the buffer layer, has a profound effect on EG conductivity. In addition,for two or more layers, this reconstruction naturally leads to Bernal stacking [10; 11]. For graphene on SiC(000\(\overline{1}\)) (aka the carbon-terminated, C-face), the surface reconstructs [9] as (\(1\times 1\)), which relaxes the stacking constraint and likely contributes to the observed rotational disorder of the layers [12] and weaker substrate interaction. Moreover, the enhanced Si sublimation rate at screw dislocations likely results in some non-uniformity of thickness [13]. The transport properties of these multilayer graphenes (sometimes termed multilayer epitaxial graphenes, MEG) are complex with at least three conduction channels present [14]. Yet, careful control of nucleation has resulted in one to two layers of EG on the C-face with more easily characterized properties [15]. For graphene on 3C-SiC films on Si surfaces, the synthesis route traditionally employs a modified sublimation approach [16; 17; 18; 19; 20] or, more recently, a precipitation method using a metal catalyst alloy with evidence pointing to an epitaxial ordering [21]. For the case of EG on 3C-SiC(100)/Si, no buffer layer is formed, but the current state-of-the-art results in interface oxidation/silicates, which contribute to the conductivity [21]. This is in contrast to EG on 3C-SiC(111)/Si, which does appear to form a buffer layer [17; 21] with similarity to that of the buffer layer formed on SiC(0001). However, silicates formation at the EG/3C-SiC interface competes to determine the conductivity. In the following sections, we begin with a discussion of some basic graphene properties, given in Section 2. The main transport measurements methods are discussed in Section 3. Section 4 provides a focus upon the properties of EG on the SiC and Si substrate components since these dominate the charge transport. Then, we discuss the impact of various situations that modify the conductivity of EG such as ambient adsorbents and metals contacts.