Dissertation Proposal Defense – Chris Perini
Prof. Eric Vogel, Advisor, MSE
Prof. Ilan Stern, GTRI
Prof. Faisal Alamgir, MSE
Prof. Mark Losego, MSE
Prof. Alan Doolittle, ECE
"The Role of Defects in Two Dimensional Vertical Heterostructures"
Two dimensional (2D) materials such as graphene, transition metal dichalchogenides (TMDs), and hexagonal Boron Nitride (hBN) have shown promise for novel device structures based on their unique materials properties. The step-like density of states, lack of interfacial dangling bonds, and thickness control via layer addition offer precise control of device characteristics that are tunable to the desired application. These properties are unique to 2D materials, and therefore 2D materials are a promising candidate for the next generation of devices. By stacking different 2D layers on top of one another, devices that exhibit fast turn on and large peak-to-valley ratios can be fabricated. Examples of these structures include the Symmetric Field Effect Transistor (SymFET) and Asymmetric Interlayer Tunneling Field Effect Transistor (ITFET). These devices are termed vertical heterostructures, due to the vertical stacking arrangement of dissimilar layers.
Although a number of studies have been performed to determine the type and nature of defects within individual 2D films, experimental studies on the role of defects in 2D vertical heterostructures remain unperformed. A deeper understanding of the effect defects have on 2D vertical heterostructures must be obtained in order for these devices to progress towards industrial application. Defects due to film synthesis, processing, radiation, and characterization will be studied. It has also been shown that different forms of irradiation alter the structure and properties of a single layer 2D material. For example, X-ray irradiation in atmosphere degrades the quality of graphene, increasing its resistance and threshold voltage. Because defect generation within single 2D layers due to irradiation is well understood, irradiation of 2D heterostructure devices can yield information on how radiation induced defects alter heterostructure device behavior.
Under this proposed effort, heterostructures involving graphene, hBN, TMDs, and high-k dielectrics will be fabricated, and the effect of defects on heterostructure device performance will be investigated. Once general defect behavior is understood, heterostructure devices will be exposed to ionizing radiation via X-rays, ions, and electrons, and will be exposed to ozone to provide a baseline for a reactive environment. The varying forms of radiation will incur defect states into the different layers of the heterostructure, changing the device’s properties. With general defect effects in 2D heterostructures understood, a better understanding of radiation induced defects can be obtained. Physical characterization including Raman spectroscopy, atomic force microscopy, and X-ray photoelectron spectroscopy, as well as electrical device characterization, will be used to investigate how radiation induces defects into a heterostructure, and how these defects impact device performance.