Browsing by Author "Ueno, Keiji"

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Ambipolar MoTe2 Transistors and Their Applications in Logic Circuits
(2014-05-28)
Lin, Yen-Fu
;
Xu, Yong
;
Wang, Sheng-Tsung
;
Li, Song-Lin
;
Yamamoto, Mahito
We report ambipolar charge transport in a-molybdenum ditelluride (MoTe2) flakes, whereby the temperature dependence of the electrical characteristics was systematically analyzed. The ambipolarity of the charge transport originated from the formation of Schottky barriers at the metal/MoTe2 contacts. The Schottky barrier heights as well as the current on/off ratio could be modified by modulating the electrostatic fields of the back-gate voltage (V-bg) and drain-source voltage (V-ds). Using these ambipolar MoTe2 transistors we fabricated complementary inverters and amplifiers, demonstrating their feasibility for future digital and analog circuit applications.
Oxygen-Sensitive Layered MoTe2 Channels for Environmental Detection
(2019-12-18)
Yang, Shih-Hsien
;
Lin, Che-Yi
;
Chang, Yuan-Ming
;
Li, Mengjiao
;
Lee, Ko-Chun
The oxygen (O-2)-dependent resistance change of multilayered molybdenum ditelluride (MoTe2) channels was characterized. A variation of the channel resistance could reproducibly determine relative O-2 content (denoted as the O-2 index). We found that Joule heating in a layered MoTe2 field-effect transistor caused the O-2 index to decrease drastically from 100 to 12.1% in back gate modulation. Furthermore, Joule heating caused effective O-2 desorption from the MoTe2 surface and repeatable O-2 detection by multilayered MoTe2 channels was realized. This work not only explored the influence of O-2 on the electrical properties of multilayered MoTe2 channels but also revealed that MoTe2 channels are promising for sensing O-2 in an environmental condition.
Reversible and Precisely Controllable p/n-Type Doping of MoTe2 Transistors through Electrothermal Doping
(2018-03-27)
Chang, Yuan-Ming
;
Yang, Shih-Hsien
;
Lin, Che-Yi
;
Chen, Chang-Hung
;
Lien, Chen-Hsin
Precisely controllable and reversible p/n-type electronic doping of molybdenum ditelluride (MoTe2) transistors is achieved by electrothermal doping (E-doping) processes. E-doping includes electrothermal annealing induced by an electric field in a vacuum chamber, which results in electron (n-type) doping and exposure to air, which induces hole (p-type) doping. The doping arises from the interaction between oxygen molecules or water vapor and defects of tellurium at the MoTe2 surface, and allows the accurate manipulation of p/n-type electrical doping of MoTe2 transistors. Because no dopant or special gas is used in the E-doping processes of MoTe2, E-doping is a simple and efficient method. Moreover, through exact manipulation of p/n-type doping of MoTe2 transistors, quasi-complementary metal oxide semiconductor adaptive logic circuits, such as an inverter, not or gate, and not and gate, are successfully fabricated. The simple method, E-doping, adopted in obtaining p/n-type doping of MoTe2 transistors undoubtedly has provided an approach to create the electronic devices with desired performance.
Strong Enhancement of Raman Scattering from a Bulk-Inactive Vibrational Mode in Few-Layer MoTe2
(2014-04-01)
Yamamoto, Mahito
;
Wang, Sheng Tsung
;
Ni, Meiyan
;
Lin, Yen-Fu
;
Li, Song-Lin
Two-dimensional layered crystals could show phonon properties that are markedly distinct from those of their bulk counterparts, because of the loss of periodicities along the c-axis directions. Here we investigate the phonon properties of bulk and atomically thin alpha-MoTe2 using Raman spectroscopy. The Raman spectrum of alpha-MoTe2 shows a prominent peak of the in-plane E-2g(1) mode, with its frequency upshifting with decreasing thickness down to the atomic scale, similar to other dichalcogenides. Furthermore, we find large enhancement of the Raman scattering from the out-of-plane B-2g(1) mode in the atomically thin layers. The B-2g(1) models Raman inactive in the bulk, but is observed to become active in the few-layer films. The intensity ratio of the B-2g(1) to E-2g(1) peaks evolves significantly with decreasing thickness, in contrast with other dichalcogenides. Our observations point to strong effects of dimensionality on the phonon properties of MoTe2.