UC Riverside

Materials with Dirac-type electronic band structure have recently drawn much interest. These materials revealed unique electrical, thermal and optical properties, which can be potentially used in future high-speed electronics. In this dissertation research, I investigate on two different classes of Dirac materials: graphene and topological insulators of the bismuth telluride (Bi2Te3) family. The first part of the dissertation reports on fabrication of the suspended graphene structures using the selective dry and chemical etching and investigation of the low frequency1/f noise in graphene field-effect transistors under electron beam irradiation. Raman spectroscopy has been used for identification and quality control of the suspended and supported graphene. It also provided the quantitative assessment of the radiation induced defects. It was found that the suspended graphene layers had larger I(2D)/I(G) intensity ratio than that of the supported graphene. The latter was attributed to weaker impurity scattering from the substrate defects. The data for graphene device performance after exposure to different irradiation doses, which was obtained in this dissertation research, is important for graphene device fabrication and proposed applications in communications. The second part of the dissertation focuses on electrical and low-frequency noise characterization of the mechanically exfoliated films of bismuth selenide (Bi2Se3). This material belongs to the topological insulators, which are characterized by the presence of the Dirac-cone dispersion in their surface states. It was found that the field-effect devices with the channels made of topological insulator materials reveal 1/f noise below 10 kHz. The noise amplitudes scaled up with the channel resistance. The transport measurements revealed that the normalized resistance of the devices made from the exfoliated thin films of Bi2Se3 did not scale inversely with the film thickness. The latter indicates that the surface transport component was significant as compared to the bulk electron conduction. The scattering-protected surface states of topological insulator materials can lead to new methods of noise reduction. The obtained results are important for understanding the traps and carrier dynamics in topological insulators, and can potentially lead to ultra-low power and ultra-low noise electronics applications.