Study of Field Effect Transistors Based on Layered Semiconductors: Graphene and Beyond



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Graphene has attracted a lot of attention because of its extraordinary electronic, mechanical, optical, and thermal properties. The high carrier mobility in single-layer and multilayer graphene make them a suitable candidate for nanoelectronics applications. Chemical vapor deposition (CVD) is one of the most promising methods of synthesizing graphene on a large scale, and research on this field has been mainly focused on single-layer graphene. Here in this dissertation we focused on synthesis of multilayer graphene and developed a process of synthesizing multilayer graphene with AB-stacking via chemical vapor deposition. Field effect transistors (FET) were synthesized, and the weak electron-phonon coupling in graphene was investigated by a study of injected hot charge carriers in those devices in low temperature and applied magnetic field. The absence of an energy band gap in graphene hinders its potential for application in digital electronics. The following sections of the dissertation continued to shift the focus to other layered materials which could be complimentary to graphene. In chapter 5, we document our study of FETs based on CVD-grown single crystal MoS2. In contrast to graphene based devices, the FETs based on MoS2 exhibit high current modulation of ~ 108. The final sections of this dissertation focus on the search of new layered materials with a non-zero band energy band gap which could be complimentary to graphene. We successfully fabricated FETs based on mechanically exfoliated nano-crystals of tin disulfide, selenium doped tin disulfide, and beta-polymorphs of zirconium nitrogen halides. Tin disulfide-based devices demonstrate high current modulation. The current modulation was suppressed with selenium doping and the activation energy was found to be decreasing. In contrast to MoS2 and SnS2 based devices, a poor current modulation was observed in zirconium nitrogen halide (β-ZrNBr). Low temperature transport experiments suggest a variable range hopping (VRH) of charge carriers in β-ZrNBr. Mobility was observed to be reduced in SnS2 and β-ZrNBr based devices at low temperature, indicating a carrier transport dominated by charge-impurity scattering. There is a room for improvement of carrier mobility in both these materials by reducing the reducing the impurities.



Graphene, Semiconductors, Layered Structure, Field Effect Transistors, Chemical vapor depostion