| Summary: | 碩士 === 國立交通大學 === 電子研究所 === 106 === Because of lack of dangling bonds at the contact interface, transition metal dichalcogenides (TMDs) encounter a significant challenge of reducing contact resistance. Heterophase edge-contacted structures, which form chemical bonds at the lateral interface, are promising solutions for the contact problem of TMD materials. Because of the similar ground-state energy of 2H and 1T’ phases of MoTe2, MoTe2 with a smaller phase transition barrier is considered as a highly potential candidate for realizing TMD devices with a heterophase contact. In this thesis, we successfully demonstrated heterophase edge-contacted MoTe2 back-gate transistors on a SiO2 substrate. We provided several methods for synthesizing 1T’-phase MoTe2 by sputtering amorphous MoTe2 films on the SiO2 substrate, such as control of synthesis temperature, atmosphere treatment, distilled water immersion, oxygen treatment and diluted HF treatment.
By using the diluted HF treatment method, 1T’-phase MoTe2 was selectively formed at designated source/drain region treated by diluted HF while 2H-phase MoTe2 was formed at the channel region without treatment. Palladium (Pd) and nickel (Ni) was deposited by electron beam evaporation as the contact metal. 1T’-MoTe2/ Pd interface is an ohmic-like contact because of their metallic properties. The major contact barrier that influences devices performance is the heterophase interface. To investigate the properties of heterophase interface of MoTe2, both the traditional metal top-contacted structure and heterophase edge-contacted structure were simulated by the density functional theory (DFT) using the Vienna Ab initio simulation package (VASP). Schottky barrier height was extracted by two improved layer-decomposed density of states methods. The in-plane averaged electric potential method was used to evaluate the tunnel barrier at the interface. The traditional metal top-contacted structures have large tunnel barriers at the interface. By contrast, the heterophase edge-contacted structure shows a lower tunnel barrier and a comparable Schottky barrier height. The results suggest that the reduction of tunnel barrier at the interface is the main advantage of using the heterophase edge-contacted structure.
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