Epitaxial graphene on siIicon carbide [electronic resource] : synthesis, structure and properties

The discovery of free-standing graphene in 2004 has attracted wide attention in both scientific community and industry because of its unusual electronic structure and properties. Due to the possible applications of graphene, many attempts to produce high-quality wafer-scale graphene films have been actively tried in the materials science and other scientific communities. Thermal decomposition of silicon carbide (SiC) is currently considered as one of the most promising routes toward the synthesis of well-controlled and characterized graphene films for electronic applications. This thesis focuses on the synthesis, structure and properties of epitaxial graphene on SiC. In the first chapter, I will investigate the structural properties of EG layers grown on the C-face of 4H-SiC in vacuum or Ar environments using synchrotron-based X-ray diffraction. The qualities and characteristics of layers will be also correlated with carrier mobilities obtained from Hall measurements. Since the Ar atmosphere produced higher quality graphene films on SiC than in vacuum, the inert-gas mediated thermal decomposition of SiC is regarded so far as the most effective method for the controlled EG growth. However, most studies have been done on the Si-face of SiC because of its slower reaction kinetics, which results in relatively uniform film thickness compared to the C-face. Nevertheless, there is significant interest in the C-face of SiC due to the superior electrical properties of EG grown on C-face SiC as compared to that grown on the Si-face. We find that Ar background pressure produces uniform graphene films on the C-face and the electronic properties (i.e. carrier mobility) of the films surpass that of vacuum-grown films due to larger crystalline domains formed in EG when the Ar pressure is above a certain threshold. In the second chapter, I will propose an alternative low-temperature, spatially controlled and scalable epitaxial graphene synthesis technique based on laser-induced surface decomposition of SiC. The high temperatures required in the conventional method are not compatible with large-scale device integration where different materials must be deposited and patterned prior to the formation of the semiconductor layer and limit the synthesis to single-crystal SiC substrates. Our technique is compatible with large-scale device integration. Furthermore, laser synthesis of graphene offers the advantage of combining synthesis and patterning in one step as the process can be designed to form graphene devices in predetermined locations on the substrate. In the last chapter, I will compare the structural properties of laser-synthesized EG on the Si-face and on the C-face of SiC. EG films on the C-face of 4H-SiC were successfully synthesized without the formation of carbon nanotubes by our laser technique, which are usually observed on the C-face upon vacuum high temperature anneals. The structural properties of these films were investigated by grazing incidence X-ray diffraction (GIXD) using synchrotron radiation and transmission electron microscopy. Since the graphene formation by UV laser irradiation is partially a photophysical process, I will illustrate the structural implications of the differences between the two formation processes.

Keywords: Materials Science and Engineering
Advisor: Salleo Alberto
Bao Zhenan advisor. Thesis advisor
Brongersma Mark L. advisor. Thesis advisor