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Growth and Nb-doping of MoS2 towards novel 2D/3D heterojunction bipolar transistors

Lee, Edwin Wendell, II
http://rave.ohiolink.edu/etdc/view?acc_num=osu1480686917234143

Abstract Details

2016, Doctor of Philosophy, Ohio State University, Electrical and Computer Engineering.
Molybdenum disulfide (MoS2) is a member of a group of layered materials called transition metal dichalcogenides (TMDs) characterized by monolayers consisting of a transition metal atom (Mo or W for example) sandwiched between chalcogen atoms (S, Se, Te) on either side. The monolayers have no out-of-plane bonds and bulk TMDs consist of many monolayers stacked and held together weakly by van der Waals forces. Bulk MoS2 exhibits an indirect band gap of 1.2 eV, but monolayer films exhibit a direct gap of 1.8 eV. MoS2 has been studied for a wide range of applications, many by utilizing micromechanically exfoliated, micron-scale flakes to study its material properties. Study of these flakes points to scaling limitations, and many groups have explored large-area growth methods to produce high-quality, continuous films. This work aims to demonstrate traditional device engineering based on MoS2 including growth, doping, heterostructure study and device design. We demonstrate single crystal growth of MoS2 by depositing Mo on sapphire substrates and sulfurizing the samples in a chemical vapor transport process. The growth process is robust, and reasonably could be scaled up to wafer-scale processing. The films exhibited excellent structural qualities, and electrical measurements showed high space-charge mobility. The MoS2 films were also doped with Nb in order to achieve p-type mobility. Degenerate doping of the films was demonstrated and confirmed by low temperature Hall measurement, and film conductivity increased by four orders of magnitude over unintentionally doped films. The degenerately doped films were shown to exhibit a Hall mobility of approximately 10 cm2V-1s-1. Heterojunction diodes were formed between degenerately doped p-MoS2¬ and n-doped SiC and GaN by direct growth and film transfer, respectively, to form 2D/3D heterojunctions. Electrical measurements were utilized to extract the conduction band offsets in MoS2/SiC (¿EC = 1.6 eV) and MoS2/GaN (¿EC = 0.2 eV) junctions. Characterization of the heterostructures showed that traditional 3D semiconductor methods are sufficient to characterize the 2D materials despite the van der Waals gaps between each MoS2 monolayer. The MoS2/GaN heterojunction was used as the base/collector junction for a tunneling heterojunction bipolar transistor (THBT) for which the emitter was atomic layer deposited Al2O3. THBTs showed small common base gain corresponding with positive transconductance in the common emitter configuration. As such, the MoS2/GaN heterojunction shows significant promise for future HBT applications.
Siddharth Rajan (Advisor)
Aaron Arehart (Committee Member)
Roberto Myers (Committee Member)
142 p.
Engineering
MoS2; Molybdenum disulfide; Doping; 2D-3D; Heterojunction; heterojunction bipolar transistor; transition metal dichalcogenide; 2D materials;

Recommended Citations

Citations

  • Lee, II, E. W. (2016). Growth and Nb-doping of MoS2 towards novel 2D/3D heterojunction bipolar transistors [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1480686917234143

    APA Style (7th edition)

  • Lee, II, Edwin. Growth and Nb-doping of MoS2 towards novel 2D/3D heterojunction bipolar transistors. 2016. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1480686917234143.

    MLA Style (8th edition)

  • Lee, II, Edwin. "Growth and Nb-doping of MoS2 towards novel 2D/3D heterojunction bipolar transistors." Doctoral dissertation, Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1480686917234143

    Chicago Manual of Style (17th edition)

osu1480686917234143
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© 2016, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.