| Summary: | 碩士 === 國立交通大學 === 電子研究所 === 105 === The atomic thickness of 2D materials effectively mitigates the short channel effect, and opens up new possibilities to scale device and extend the Moore’s law. Among 2D materials, transition metal dichalcogenides-MoS2 has attracted many attentions as the channel material of the transistor and prompted new developments of numerous electric and optical devices. However, large contact resistance limited the MoS2 transistor performance. We synthesize monolayer MoS2 on sapphire substrate by chemical vapor deposition method, and then transfer MoS2 film to HfO2 dielectric substrate. We carefully engineer the interface between source/drain (S/D) metal and MoS2 to find stable methods for reducing contact resistance.
In this thesis, sulfur vacancies generated by H2 plasma treatment was found to result in band gap narrowing from optical analysis and VASP simulation. If only S/D region received the H2 plasma treatment, the band gap narrowing reduced the Schottky barrier between S/D metal and MoS2 and therefore reduced contact resistance. F- and Cl-based plasma treatment induced p-type doping in MoS2 transistors, and improved the p-type conduction of WSe2 transistors after the Cl2 plasma treatment.
A SiO2 capping layer was utilized to suppress the potential damage of the device fabrication process on monolayer MoS2. Furthermore, the SiO2 capping layer influences the contact between S/D metal and MoS2 due to charge transfer. Replacing S/D metal from Mo to Pd, which has a higher work function and less interaction with MoS2, shows reduced contact resistance. Although the Schottky barrier is higher, a large band bending can be achieved by applying gate voltage. We attributed this to the less interaction between Pd and MoS2.
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