Two-Dimensional Materials: Doping-Induced Variation, Heterojunction FETs and Hybrid Multilayers




Eshun, Kwesi P.

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As the size of Complementary Metal Oxide Semiconductor (CMOS) field effect transistor (FET) approaches its fundamental physical limit, two-dimensional (2D) layered structures, such as transitional metal dichalcogenides (TMDs), have been proposed as the alternative channel materials to extend the Moore’s law. In this thesis, we proposed and studied a new set of device structures based on 2D MoS2/WSe2 heterojunction in order to construct the smallest field effect transistor, whereas the switching is achieved via gated heterojunction. Following a step-by-step approach, we have studied the doping effect of different TMDs, formation of heterojunction between different TMDs and gated field effect transistor based on these 2D heterojunctions. During the study of Doping effect on 2D TMDs, we found that random dopant position led to large variation in electronic properties of 2D materials. Therefore, we focus on the study of 2D heterojunction FET instead of the pn-junction. We have studied the formation and transport properties of 2D heterojunctions, with a focus on MoS2/WSe2 heterojunction as it exhibits the best junction characteristics. We then used the MoS2/WSe2 heterojunctions as the channel materials to construct the smallest FET. Such 2D junction-based FETs exhibited very interesting and attractive device characteristics. This study has successfully demonstrated a new set of device structures and materials in order to achieve 2D FET for the extension of CMOS scaling. The results of this thesis may open a suit of new applications in future electronics.



Transition metal dichotcogenides, Heterjunction, Field effect transistor, Negative differential resistance, Monolayer, Bandstructure