Charge and Energy Transfer in Different Types of Two-Dimensional Heterostructures

Abstract

In the last decade or so, layered materials have attracted significant attention due to their promise for tailoring electronic properties at an atomic level. Individually, these materials have exhibited strong attributes, relevant for both electronic and optoelectronic applications. However, the real world implementation of semiconducting materials is often derived from the junctions they form with other semiconductors. Thus, much of the interest in 2D materials arises from exploiting their ability to form low dimensional heterostructures. From a structural stand point, there are two ways these heterostructures can be formed, either vertically or laterally. The more common, vertical heterostructures, are intriguing due to their van der Waals adhesion, which eliminates many of the constraints attributed to lattice matching between materials. Lateral heterostructures, on the other hand, provide the unique opportunity to form in-plane junctions within a 2D sheet, creating novel 1D interfaces. To better understand these various heterostructures, this dissertation aims to explore photocarrier dynamics, using ultrafast laser spectroscopy techniques, in several types of structures yet to be extensively studied. First, charge and energy transfer mechanisms in vertical heterostructures formed between various transition metal dichalcogenide monolayers are studied, highlighting the addition of type-I band alignment to the discussion. Next, the extent to which materials can interact electronically through van der Waals adhesion is explored at the interface between amorphous and crystalline layers. From there, the focus shifts slightly to carrier dynamics across lateral junctions formed within monolayer sheets of transition metal dichalcogenides. This includes a discussion on lateral heterostructures, formed between different materials, as well as homostructures where an electronic junction can be induced in a single material. All of these studies will provide a unique overview on the possible directions and applications for which two dimensional materials can be facilitated. This dissertation includes previously published authored material.