2D-Materials: Synthesis and Investigation of Electrical and Thermal Properties
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This dissertation presents a study of (1) the growth of in-plane MoS2-graphene heterostructure together with its electrical characterizations, (2) the power dissipation of the WSe2 FET as a representative of 2D-material FETs (Field effect transistors), and (3) thermal dissipation across monolayer CVD graphene, as a representative of 2D-materials, on different technologically-viable substrates. First, the in-plane MoS2-graphene heterostructure is grown by the CVD method for large-scale applications. Electrical characterizations and 1/f noise measurements of this heterostructure reveal an order of magnitude higher electron mobility and lower noise amplitude for this heterostructure compared to conventional metal-contact MoS2 devices. The KPFM (Kelvin Probe Force Microscop) study is performed to map the surface potential distribution across the MoS2-graphene interface and visualizes the reduction of the MoS2-graphene interface resistance at positive gate voltages. The DFT (Density Functional Theory) calculations demonstrate that the role of this interface resistance is less than 1% of the overall device resistance at gate voltages above 60 V. Similar failure modes and electrostatic breakdown fields for MoS2-graphene and MoS2-metal devices are also observed by electrostatic breakdown measurements. Second, the power dissipation of the WSe2 FET, as a representative of the 2D-materials, is investigated by the Raman thermometry method. The low-frequency E2g2 peak of WSe2 material is used to measure the temperature rise of the device versus different the applied electrical powers. The interface resistance measurement between WSe2 and SiO2/Si substrate reveals that their interface TBC (Thermal Boundary Conductance) is in the low range of the solid-solid interfaces, proving the importance of the interface resistances for thermal dissipation of 2D-FETs. Finally,to shed light on the role of the interface resistance of 2D-materials with different substrates, thermal dissipation of CVD graphene on different technologically-viable substrates is investigated. The interface resistances between graphene and different tested substrates reveal that the overall thermal dissipation performance on AlN is better than on diamond substrate, although the thermal conductance of the AlN is significantly lower than that diamond material. These results confirm that the thermal conductance of the substrate is not the only key factor which is important for thermal dissipation of the 2D-material devices and that the role of the boundary resistance between 2D-material and substrate is very crucial.