Electronic device fabrication and characterization based on two-dimensional materials

Two-dimensional (2D) materials have attracted extensive attention due to their unique and remarkable properties, such as the atomically thin body, pristine surface free of dangling bonds, tunable bandgap, and reasonably high mobility, which make 2D materials promising candidates for novel electronic and optoelectronic devices in low power, high performance and flexible applications. \n \nIn this thesis, the optical and electrical properties of MoS2/WS2 heterostructures grown by chemical vapor deposition (CVD) are studied. By using Raman spectra, photoluminescence (PL) spectra and atomic force microscopy (AFM), the vertical and lateral MoS2/WS2 structures are identified. The transistors and Hall-bar devices based on vertical monolayer-MoS2/monolayer-WS2 heterostructures are successfully fabricated. The devices show typical n-channel characteristics, indicating that MoS2 and WS2 are naturally n-type doped. Due to the type II band alignment and sharp interface, these vertical and lateral MoS2/WS2 heterostructures can potentially be used for tunneling field-effect transistors and high-speed photodetectors. \n \nIn addition, the crystal orientation and electronic transport in germanium selenide (GeSe) are also studied. The crystallographic direction of the GeSe is determined by angle-resolved polarized Raman measurement. The anisotropic electronic transport of the GeSe is measured by angle-resolved DC electrical conductance. The results indicate that GeSe has a prominent anisotropic electronic transport with maximum conductance likely along the armchair direction. The anisotropic conductance in GeSe may enable a new series of electronic and optoelectronic devices such as plasmonic devices with resonance frequency continuously tunable with light polarization direction, and high-efficiency thermoelectric devices. \n \nIn summary, the MoS2/WS2 heterostructures and anisotropic electronic transport in GeSe have been studied. The knowledge gained in these projects will be essential for designing and fabricating novel electronic devices based on these materials in the future.