Local Photoresponses and Electrical Properties in Two-dimensional Chalcogenide Heterostructures

Abstract

The investigation of two dimensional materials has been one of the leading topics in nanomaterials research in the past decade after the discovery of the graphene in 2004. Wide range of applicability with selectable electronic and optoelectronic properties of two dimensional materials stimulate the research focus in the combination of these materials into heterostructures in two scientific point of views. First, atomically sharp interfaces between two dimensional layers of dissimilar materials give rise to a new types of quantum heterostructures with unexplored physics. Second, the atomic two dimensional heterostructure can serve as a thinnest device platform with high performance. This dissertation concerns both the synthetic integration of two dimensional materials into electronic and optoelectronic devices and the investigations on exotic optoelectronic properties of integrated heterostructures. First investigation is on the unique optical properties of two dimensional layered chalcogenide, Bi(Sb)2Te3. Specifically, photocurrent driven by hot carriers – a phenomenon called the photothermoelectric effect-arises at the heterointerface between few quintuple layers of Bi(Sb)2Te3 with monolayer step difference. The next part of the dissertation demonstrates that the interlayer coupling is influenced by rotational misfit between the transition metal dichalcogenide semiconductor MoS2/WS2 vertical heterostructure, which manifests tunable light emission and absorption. We also demonstrates the interlayer charge separation which is generated by low-energy photoexcitations is possible in MoS2/Bi2Te3. Finally, we integrated two dimensional transition metal dichalcogenide semiconductors(2H-MoTe2) and metals(1T’-MoTe2) for coplanar field effect transistor with the lowest contact-barrier. Metal-semiconductor interface by materials with the same chemical composition, so called seamless electrical contact, provide convincing way to lower contact resistance in electronic and optoelectronic devices. These studies show the promise of integrating two dimensional materials for applications in thinnest devices with unique electrical and optical properties.