Ohmic contact to monolayer semiconductors
Name
1227779042-MIT.pdf
Size
16.89 MB
Format
Adobe PDF
Checksum (MD5)
64975ffb911a53b99b11ba2d17485970
Author(s)
Shen, Pin-Chun.
Advisor(s)
Jing Kong.
Date Issued
2020
Publisher
Massachusetts Institute of Technology
Abstract
Scaling of silicon transistors is reaching its physical limits due to severe short channel effects, threatening to end Moore's law. Advanced beyond-silicon electronic technology requires discoveries of both new channel materials and ultralow-resistance contacts. The aim of this thesis is to develop an understanding of the science and engineering in applying synthetic monolayer semiconductors as the channel materials in field-effect transistors and in achieving excellent electrical contacts to these emerging materials. Monolayer semiconductors such as MoS₂,WS₂ and WSe₂ not only offer atomically thin thicknesses for device minimization, but also embrace desirable physical properties such as dandling-bond-free and atomically flat surface, sizable bandgap, and relatively heavier carrier effective mass to enhance transistor performance at the atomic limit.
We start by developing scalable methods for synthesizing high-quality monolayer MoS₂ that exhibits near intrinsic characteristics and moderate electron mobility at room temperature. These developments improve the fundamental transport property and reduce the unwanted impurity doping of the synthetic monolayer MoS₂ for electronic applications. Next, we further demonstrate a method to eliminate the detrimental defect states in monolayer MoS₂, which mitigates the defect-state induced Fermi-level pinning at the metal-MoS₂ interface. The monolayer MoS₂ transistors fabricated through this technique exhibit a lowered Schottky barrier and a reduced contact resistance at the metal-MoS₂ interface. This study provides an insight into the defect properties of MoS₂ that are fundamentally related to the device performance.
Finally, we provide a deeper understanding of the ohmic contact nature at metal-monolayer semiconductor interfaces and propose a new contact paradigm, gap-state saturation, to overcome the in-gap Fermi-level pinning and eventually eliminate the Schottky barrier. We experimentally apply this new ohmic contact technology to a variety of monolayer semiconductors and demonstrate high-performance monolayer semiconductor transistors. We have achieved record-low contact resistance approaching the quantum limit among all the metal-2D semiconductor interfaces. Our monolayer semiconductor transistors have also reached record-high ON-state current density among all the monolayer devices. We show that monolayer semiconductors can have a performance on par with the state-of-the-art silicon-based technology, reaching the goal of next-generation transistor technologies.
Description
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, September, 2020
Cataloged from student-submitted PDF of thesis.
Includes bibliographical references (pages 204-220).
Subjects
Electrical Engineering and Computer Science.
MIT Department
Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science
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