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Transport Phenomena of CVD Few-Layer MoS2 As-grown on an Al2O3 Substrate

Poehler, Scott A
http://orcid.org/0000-0001-6572-5342
http://rave.ohiolink.edu/etdc/view?acc_num=osu1440181154

Abstract Details

2015, Master of Science, Ohio State University, Electrical and Computer Engineering.
Fabricating devices with as-grown films is necessary for high volume production however challenges with adding functional gates to MoS2 films natively grown on Al2O3 have limited its usefulness for VLSI manufacturing. A more thorough understanding of this material configuration is required before we can develop effective surface treatment strategies prior to adding gate dielectrics. The scope of this study covers the transport phenomena of charge carriers in few layer MoS2 as-grown by CVD on Al2O3 substrate. We examine carrier transport mechanism dominance for temperatures ranging from 30 K to 310 K for AC conductance measurements and 5 K to 350 K for DC I-V measurements. Scaled AC conductance verses frequency indicating a one-to-one relationship between sDC and transition frequency ft, from 30 K to 90K is a signature of variable range hopping (VRH) transport as conductance becomes steadily independent of frequency with increased temperature. The scaling behavior with increasing temperature shows a saturation point indicating a shift from VRH transport. The fit of AC conductance to the universal power relation s = s0(1+f/ft)s supports the observed shift in transport mechanisms. Conductance becomes less sensitive to frequency beyond 90 K indicating dominance of band transport though there still exists a slight dispersion of carriers even at higher temperatures. The T-p relationship of conductance (Efros-Shklovskii (p=1/2) or Mott (p=1/3)) at low temperatures favors the Efros-Shklovskii model. Below the linear fit regions evidence shows resonant tunneling at localized states. Above these linear fit regions, the resistance curve derivative analysis of sDC from 100 K to 160 K is found to correspond to the shift from VRH to band transport. The mobility-temperature dependence calculated from measured DC current-voltage data using the Mott-Gurney law for space limited current correlates mobility measurements to the observed transition between transport mechanisms with a defining temperature point of about 160 K where the balance of transport mechanisms shift. We expected mobility to decrease at higher temperatures due to phonon scattering, but found that mobility only continued to increase. We determined that the modified Mott-Gurney-Hartke current model explained the experimental data better at the higher temperature indicating currents were more sensitive to the Frenkel effect and showing evidence of a high density of traps. In the transition from the hopping dominated transport at very low temperatures to the band transport at higher temperatures, the conductance continues to rise with temperature. The high density of traps increases the influence of impurity scattering, screening the effects of phonon scattering which explains the increasing mobility even at higher temperatures.
Wu Lu, PhD (Advisor)
Siddharth Rajan, PhD (Committee Member)
Marvin White, PhD (Committee Member)
67 p.
Electrical Engineering; Materials Science
MoS2, carrier transport mechanism, signature transport transition

Recommended Citations

Citations

  • Poehler, S. A. (2015). Transport Phenomena of CVD Few-Layer MoS2 As-grown on an Al2O3 Substrate [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1440181154

    APA Style (7th edition)

  • Poehler, Scott. Transport Phenomena of CVD Few-Layer MoS2 As-grown on an Al2O3 Substrate. 2015. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1440181154.

    MLA Style (8th edition)

  • Poehler, Scott. "Transport Phenomena of CVD Few-Layer MoS2 As-grown on an Al2O3 Substrate." Master's thesis, Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1440181154

    Chicago Manual of Style (17th edition)

osu1440181154
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This open access ETD is published by The Ohio State University and OhioLINK.