"Through this thesis proposal, the author has demonstrated a variety of electronic and optoelectronic nanodevices including ultrascaled transistors, heterostructure diodes, chemical sensors, photodetectors and single-pixel infrared cameras using atomically thin two-dimensional (2D) materials such as graphene, molybdenum disulfide (MoS2) and black phosphorus (BP). As the scaling of the silicon-based transistor approaches its physical limit, exploratory research is needed to develop alternative channel materials for future sub-5 nm gate length devices. For such an ultrascaled electronic device, short channel effects would severely limit its performance and operation. In order to suppress the short channel effects at extreme scaling limits, the thickness of the channel material needs to be less than roughly one-third of the gate length in order to allow the gate to retain its effective electrostatic control of channel carrier concentration. However, for conventional bulk semiconductors such as silicon, germanium and gallium arsenide, the rough surface of the ultrathin body (a few atomic layers) would lead to severe surface scattering for carriers, resulting in severely degraded carrier mobility. In this regard, atomically thin 2D layered materials are excellent candidates for future ultimately scaled electronic and optoelectronic device applications. Compared with 3D bulk materials, 2D materials exhibit many exceptional properties. First, quantum confinement effect in the direction perpendicular to the 2D plane leads to many novel electronic and optical properties that are dramatically different from their bulk counterparts. Second, their surfaces are atomically smooth and free of dangling bonds and defect states, which lead to intrinsically low surface scattering and make it easy to integrate 2D films with photonic structures. It is also possible to construct heterostructures using different 2D materials without the conventional lattice mismatch issues. Third, despite being atomically thin nature, many 2D materials interact strongly with light and cover a very broad range of electromagnetic spectrum. Finally, these atomically thin 2D materials are immune to short channel effects owing to their small thickness. In this thesis, we will discuss the electronic and optoelectronic device applications using atomically thin 2D materials including graphene, MoS2 and BP. We mainly discuss the 2D BP which is the most stable and least reactive form of element phosphorus, and was discovered in bulk form 100 years ago. Unlike zero bandgap graphene, BP is a direct bandgap semiconductor with a thickness-dependent bandgap ranging from 0.3 eV (bulk) to 2.0 eV (monolayer). Few-layer BP flakes have been used as channel materials in field-effect transistors (FETs). Such BP FETs exhibit high on-off current ratios of 104 -105 . And, the room temperature field-effect mobility of BP FETs is up to 1000 cm2V-1 s -1 which is much higher than that of 2D MoS2 based FETs."--Pages ii-iii.
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